25902955617

Committed 14 May 2026 01:11PM UTC coverage: 82.2% (+2.0%) from 80.18%

Build # 25902955617

Build Type

push

github

Committed by

web-flow

Commit Message

Fix message block corruption on filestore cipher conversion with cache clear (#8166)

This ensures that using an old `mb.bek` doesn't corrupt the block by
maintaining an old offset from before the cache clear.

Coverage Stats

76650 of 93248 relevant lines covered (82.2%)

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Source File
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89.9

/server/leafnode.go

// Copyright 2019-2026 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package server

import (
        "bufio"
        "bytes"
        "crypto/tls"
        "encoding/base64"
        "encoding/json"
        "fmt"
        "io"
        "math/rand"
        "net"
        "net/http"
        "net/url"
        "os"
        "path"
        "regexp"
        "runtime"
        "strconv"
        "strings"
        "sync"
        "sync/atomic"
        "time"

        "github.com/klauspost/compress/s2"
        "github.com/nats-io/jwt/v2"
        "github.com/nats-io/nkeys"
        "github.com/nats-io/nuid"
)

const (
        // Warning when user configures leafnode TLS insecure
        leafnodeTLSInsecureWarning = "TLS certificate chain and hostname of solicited leafnodes will not be verified. DO NOT USE IN PRODUCTION!"

        // When a loop is detected, delay the reconnect of solicited connection.
        leafNodeReconnectDelayAfterLoopDetected = 30 * time.Second

        // When a server receives a message causing a permission violation, the
        // connection is closed and it won't attempt to reconnect for that long.
        leafNodeReconnectAfterPermViolation = 30 * time.Second

        // When we have the same cluster name as the hub.
        leafNodeReconnectDelayAfterClusterNameSame = 30 * time.Second

        // Prefix for loop detection subject
        leafNodeLoopDetectionSubjectPrefix = "$LDS."

        // Path added to URL to indicate to WS server that the connection is a
        // LEAF connection as opposed to a CLIENT.
        leafNodeWSPath = "/leafnode"

        // When a soliciting leafnode is rejected because it does not meet the
        // configured minimum version, delay the next reconnect attempt by this long.
        leafNodeMinVersionReconnectDelay = 5 * time.Second
)

type leaf struct {
        // We have any auth stuff here for solicited connections.
        remote *leafNodeCfg
        // isSpoke tells us what role we are playing.
        // Used when we receive a connection but otherside tells us they are a hub.
        isSpoke bool
        // remoteCluster is when we are a hub but the spoke leafnode is part of a cluster.
        remoteCluster string
        // remoteServer holds onto the remote server's name or ID.
        remoteServer string
        // domain name of remote server
        remoteDomain string
        // account name of remote server
        remoteAccName string
        // Whether or not we want to propagate east-west interest from other LNs.
        isolated bool
        // Used to suppress sub and unsub interest. Same as routes but our audience
        // here is tied to this leaf node. This will hold all subscriptions except this
        // leaf nodes. This represents all the interest we want to send to the other side.
        smap map[string]int32
        // This map will contain all the subscriptions that have been added to the smap
        // during initLeafNodeSmapAndSendSubs. It is short lived and is there to avoid
        // race between processing of a sub where sub is added to account sublist but
        // updateSmap has not be called on that "thread", while in the LN readloop,
        // when processing CONNECT, initLeafNodeSmapAndSendSubs is invoked and add
        // this subscription to smap. When processing of the sub then calls updateSmap,
        // we would add it a second time in the smap causing later unsub to suppress the LS-.
        tsub  map[*subscription]struct{}
        tsubt *time.Timer
        // Selected compression mode, which may be different from the server configured mode.
        compression string
        // This is for GW map replies.
        gwSub *subscription
}

// Used for remote (solicited) leafnodes.
type leafNodeCfg struct {
        sync.RWMutex
        *RemoteLeafOpts
        urls           []*url.URL
        curURL         *url.URL
        tlsName        string
        username       string
        password       string
        perms          *Permissions
        connDelay      time.Duration // Delay before a connect, could be used while detecting loop condition, etc..
        jsMigrateTimer *time.Timer
        quitCh         chan struct{}
        removed        bool
        connInProgress bool
}

// Check to see if this is a solicited leafnode. We do special processing for solicited.
func (c *client) isSolicitedLeafNode() bool {
        return c.kind == LEAF && c.leaf != nil && c.leaf.remote != nil
}

// Returns true if this is a solicited leafnode and is not configured to be treated as a hub or a receiving
// connection leafnode where the otherside has declared itself to be the hub.
func (c *client) isSpokeLeafNode() bool {
        return c.kind == LEAF && c.leaf != nil && c.leaf.isSpoke
}

func (c *client) isHubLeafNode() bool {
        return c.kind == LEAF && c.leaf != nil && !c.leaf.isSpoke
}

func (c *client) isIsolatedLeafNode() bool {
        // TODO(nat): In future we may want to pass in and consider an isolation
        // group name here, which the hub and/or leaf could provide, so that we
        // can isolate away certain LNs but not others on an opt-in basis. For
        // now we will just isolate all LN interest until then.
        return c.kind == LEAF && c.leaf != nil && c.leaf.isolated
}

// This will spin up go routines to solicit the remote leaf node connections.
func (s *Server) solicitLeafNodeRemotes(remotes []*RemoteLeafOpts) {
        sysAccName := _EMPTY_
        sAcc := s.SystemAccount()
        if sAcc != nil {
                sysAccName = sAcc.Name
        }
        addRemote := func(r *RemoteLeafOpts, isSysAccRemote bool) *leafNodeCfg {
                s.mu.Lock()
                remote := newLeafNodeCfg(r)
                creds := remote.Credentials
                accName := remote.LocalAccount
                if s.leafRemoteCfgs == nil {
                        s.leafRemoteCfgs = make(map[*leafNodeCfg]struct{})
                }
                s.leafRemoteCfgs[remote] = struct{}{}
                // Print notice if
                if isSysAccRemote {
                        if len(remote.DenyExports) > 0 {
                                s.Noticef("Remote for System Account uses restricted export permissions")
                        }
                        if len(remote.DenyImports) > 0 {
                                s.Noticef("Remote for System Account uses restricted import permissions")
                        }
                }
                s.mu.Unlock()
                if creds != _EMPTY_ {
                        contents, err := os.ReadFile(creds)
                        defer wipeSlice(contents)
                        if err != nil {
                                s.Errorf("Error reading LeafNode Remote Credentials file %q: %v", creds, err)
                        } else if items := credsRe.FindAllSubmatch(contents, -1); len(items) < 2 {
                                s.Errorf("LeafNode Remote Credentials file %q malformed", creds)
                        } else if _, err := nkeys.FromSeed(items[1][1]); err != nil {
                                s.Errorf("LeafNode Remote Credentials file %q has malformed seed", creds)
                        } else if uc, err := jwt.DecodeUserClaims(string(items[0][1])); err != nil {
                                s.Errorf("LeafNode Remote Credentials file %q has malformed user jwt", creds)
                        } else if isSysAccRemote {
                                if !uc.Permissions.Pub.Empty() || !uc.Permissions.Sub.Empty() || uc.Permissions.Resp != nil {
                                        s.Noticef("LeafNode Remote for System Account uses credentials file %q with restricted permissions", creds)
                                }
                        } else {
                                if !uc.Permissions.Pub.Empty() || !uc.Permissions.Sub.Empty() || uc.Permissions.Resp != nil {
                                        s.Noticef("LeafNode Remote for Account %s uses credentials file %q with restricted permissions", accName, creds)
                                }
                        }
                }
                return remote
        }
        for _, r := range remotes {
                // We need to call this, even if the leaf is disabled. This is so that
                // the number of internal configuration matches the options' remote leaf
                // configuration required for configuration reload.
                remote := addRemote(r, r.LocalAccount == sysAccName)
                if !r.Disabled {
                        s.connectToRemoteLeafNodeAsynchronously(remote, true)
                }
        }
}

// Ensure that leafnode is properly configured.
func validateLeafNode(o *Options) error {
        if err := validateLeafNodeAuthOptions(o); err != nil {
                return err
        }

        if len(o.LeafNode.Remotes) > 0 {
                names := make(map[string]struct{})
                // Check for duplicate remotes, also, users can bind to any local account,
                // if its empty we will assume the $G account.
                for _, r := range o.LeafNode.Remotes {
                        if r.LocalAccount == _EMPTY_ {
                                r.LocalAccount = globalAccountName
                        }
                        rn := r.name()
                        if _, dup := names[rn]; dup {
                                return fmt.Errorf("duplicate remote %s", r.safeName())
                        }
                        names[rn] = struct{}{}
                }
        }

        // In local config mode, check that leafnode configuration refers to accounts that exist.
        if len(o.TrustedOperators) == 0 {
                accNames := map[string]struct{}{}
                for _, a := range o.Accounts {
                        accNames[a.Name] = struct{}{}
                }
                // global account is always created
                accNames[DEFAULT_GLOBAL_ACCOUNT] = struct{}{}
                // in the context of leaf nodes, empty account means global account
                accNames[_EMPTY_] = struct{}{}
                // system account either exists or, if not disabled, will be created
                if o.SystemAccount == _EMPTY_ && !o.NoSystemAccount {
                        accNames[DEFAULT_SYSTEM_ACCOUNT] = struct{}{}
                }
                checkAccountExists := func(accName string, cfgType string) error {
                        if _, ok := accNames[accName]; !ok {
                                return fmt.Errorf("cannot find local account %q specified in leafnode %s", accName, cfgType)
                        }
                        return nil
                }
                if err := checkAccountExists(o.LeafNode.Account, "authorization"); err != nil {
                        return err
                }
                for _, lu := range o.LeafNode.Users {
                        if lu.Account == nil { // means global account
                                continue
                        }
                        if err := checkAccountExists(lu.Account.Name, "authorization"); err != nil {
                                return err
                        }
                }
                for _, r := range o.LeafNode.Remotes {
                        if err := checkAccountExists(r.LocalAccount, "remote"); err != nil {
                                return err
                        }
                }
        } else {
                if len(o.LeafNode.Users) != 0 {
                        return fmt.Errorf("operator mode does not allow specifying users in leafnode config")
                }
                for _, r := range o.LeafNode.Remotes {
                        if !nkeys.IsValidPublicAccountKey(r.LocalAccount) {
                                return fmt.Errorf(
                                        "operator mode requires account nkeys in remotes. " +
                                                "Please add an `account` key to each remote in your `leafnodes` section, to assign it to an account. " +
                                                "Each account value should be a 56 character public key, starting with the letter 'A'")
                        }
                }
                if o.LeafNode.Port != 0 && o.LeafNode.Account != "" && !nkeys.IsValidPublicAccountKey(o.LeafNode.Account) {
                        return fmt.Errorf("operator mode and non account nkeys are incompatible")
                }
        }

        // Validate compression settings
        if o.LeafNode.Compression.Mode != _EMPTY_ {
                if err := validateAndNormalizeCompressionOption(&o.LeafNode.Compression, CompressionS2Auto); err != nil {
                        return err
                }
        }

        // If a remote has a websocket scheme, all need to have it.
        for _, rcfg := range o.LeafNode.Remotes {
                // Validate proxy configuration
                if _, err := validateLeafNodeProxyOptions(rcfg); err != nil {
                        return err
                }

                if len(rcfg.URLs) >= 2 {
                        firstIsWS, ok := isWSURL(rcfg.URLs[0]), true
                        for i := 1; i < len(rcfg.URLs); i++ {
                                u := rcfg.URLs[i]
                                if isWS := isWSURL(u); isWS && !firstIsWS || !isWS && firstIsWS {
                                        ok = false
                                        break
                                }
                        }
                        if !ok {
                                return fmt.Errorf("remote leaf node configuration cannot have a mix of websocket and non-websocket urls: %q", redactURLList(rcfg.URLs))
                        }
                }
                if !wsAllowedFIPS() {
                        for _, u := range rcfg.URLs {
                                if isWSURL(u) {
                                        return fmt.Errorf("remote leaf node URL %q cannot be used in FIPS-140 mode when built with this Go version, use Go 1.26 or later", redactURLString(u.String()))
                                }
                        }
                }
                // Validate compression settings
                if rcfg.Compression.Mode != _EMPTY_ {
                        if err := validateAndNormalizeCompressionOption(&rcfg.Compression, CompressionS2Auto); err != nil {
                                return err
                        }
                }
        }

        if o.LeafNode.Port == 0 {
                return nil
        }

        // If MinVersion is defined, check that it is valid.
        if mv := o.LeafNode.MinVersion; mv != _EMPTY_ {
                if err := checkLeafMinVersionConfig(mv); err != nil {
                        return err
                }
        }

        // The checks below will be done only when detecting that we are configured
        // with gateways. So if an option validation needs to be done regardless,
        // it MUST be done before this point!

        if o.Gateway.Name == _EMPTY_ && o.Gateway.Port == 0 {
                return nil
        }
        // If we are here we have both leaf nodes and gateways defined, make sure there
        // is a system account defined.
        if o.SystemAccount == _EMPTY_ {
                return fmt.Errorf("leaf nodes and gateways (both being defined) require a system account to also be configured")
        }
        if err := validatePinnedCerts(o.LeafNode.TLSPinnedCerts); err != nil {
                return fmt.Errorf("leafnode: %v", err)
        }
        return nil
}

func checkLeafMinVersionConfig(mv string) error {
        if ok, err := versionAtLeastCheckError(mv, 2, 8, 0); !ok || err != nil {
                if err != nil {
                        return fmt.Errorf("invalid leafnode's minimum version: %v", err)
                } else {
                        return fmt.Errorf("the minimum version should be at least 2.8.0")
                }
        }
        return nil
}

// Used to validate user names in LeafNode configuration.
// - rejects mix of single and multiple users.
// - rejects duplicate user names.
func validateLeafNodeAuthOptions(o *Options) error {
        if len(o.LeafNode.Users) == 0 {
                return nil
        }
        if o.LeafNode.Username != _EMPTY_ {
                return fmt.Errorf("can not have a single user/pass and a users array")
        }
        if o.LeafNode.Nkey != _EMPTY_ {
                return fmt.Errorf("can not have a single nkey and a users array")
        }
        users := map[string]struct{}{}
        for _, u := range o.LeafNode.Users {
                if _, exists := users[u.Username]; exists {
                        return fmt.Errorf("duplicate user %q detected in leafnode authorization", u.Username)
                }
                users[u.Username] = struct{}{}
        }
        return nil
}

func validateLeafNodeProxyOptions(remote *RemoteLeafOpts) ([]string, error) {
        var warnings []string

        if remote.Proxy.URL == _EMPTY_ {
                return warnings, nil
        }

        proxyURL, err := url.Parse(remote.Proxy.URL)
        if err != nil {
                return warnings, fmt.Errorf("invalid proxy URL: %v", err)
        }

        if proxyURL.Scheme != "http" && proxyURL.Scheme != "https" {
                return warnings, fmt.Errorf("proxy URL scheme must be http or https, got: %s", proxyURL.Scheme)
        }

        if proxyURL.Host == _EMPTY_ {
                return warnings, fmt.Errorf("proxy URL must specify a host")
        }

        if remote.Proxy.Timeout < 0 {
                return warnings, fmt.Errorf("proxy timeout must be >= 0")
        }

        if (remote.Proxy.Username == _EMPTY_) != (remote.Proxy.Password == _EMPTY_) {
                return warnings, fmt.Errorf("proxy username and password must both be specified or both be empty")
        }

        if len(remote.URLs) > 0 {
                hasWebSocketURL := false
                hasNonWebSocketURL := false

                for _, remoteURL := range remote.URLs {
                        if remoteURL.Scheme == wsSchemePrefix || remoteURL.Scheme == wsSchemePrefixTLS {
                                hasWebSocketURL = true
                                if (remoteURL.Scheme == wsSchemePrefixTLS) &&
                                        remote.TLSConfig == nil && !remote.TLS {
                                        return warnings, fmt.Errorf("proxy is configured but remote URL %s requires TLS and no TLS configuration is provided. When using proxy with TLS endpoints, ensure TLS is properly configured for the leafnode remote", remoteURL.String())
                                }
                        } else {
                                hasNonWebSocketURL = true
                        }
                }

                if !hasWebSocketURL {
                        warnings = append(warnings, "proxy configuration will be ignored: proxy settings only apply to WebSocket connections (ws:// or wss://), but all configured URLs use TCP connections (nats://)")
                } else if hasNonWebSocketURL {
                        warnings = append(warnings, "proxy configuration will only be used for WebSocket URLs: proxy settings do not apply to TCP connections (nats://)")
                }
        }

        return warnings, nil
}

// Wait for the configured reconnect interval before attempting to connect
// again to the remote leafnode.
func (s *Server) reConnectToRemoteLeafNode(remote *leafNodeCfg) {
        clearInProgress := true
        defer func() {
                s.grWG.Done()
                if clearInProgress {
                        remote.setConnectInProgress(false)
                }
        }()
        delay := s.getOpts().LeafNode.ReconnectInterval
        select {
        case <-time.After(delay):
        case <-remote.quitCh:
                return
        case <-s.quitCh:
                return
        }
        clearInProgress = !connectToRemoteLeafNode(s, remote, false)
}

// Creates a leafNodeCfg object that wraps the RemoteLeafOpts.
func newLeafNodeCfg(remote *RemoteLeafOpts) *leafNodeCfg {
        cfg := &leafNodeCfg{
                RemoteLeafOpts: remote,
                urls:           make([]*url.URL, 0, len(remote.URLs)),
                quitCh:         make(chan struct{}, 1),
        }
        if len(remote.DenyExports) > 0 || len(remote.DenyImports) > 0 {
                perms := &Permissions{}
                if len(remote.DenyExports) > 0 {
                        perms.Publish = &SubjectPermission{Deny: remote.DenyExports}
                }
                if len(remote.DenyImports) > 0 {
                        perms.Subscribe = &SubjectPermission{Deny: remote.DenyImports}
                }
                cfg.perms = perms
        }
        // Start with the one that is configured. We will add to this
        // array when receiving async leafnode INFOs.
        cfg.urls = append(cfg.urls, cfg.URLs...)
        // If allowed to randomize, do it on our copy of URLs
        if !remote.NoRandomize {
                rand.Shuffle(len(cfg.urls), func(i, j int) {
                        cfg.urls[i], cfg.urls[j] = cfg.urls[j], cfg.urls[i]
                })
        }
        // If we are TLS make sure we save off a proper servername if possible.
        // Do same for user/password since we may need them to connect to
        // a bare URL that we get from INFO protocol.
        for _, u := range cfg.urls {
                cfg.saveTLSHostname(u)
                cfg.saveUserPassword(u)
                // If the url(s) have the "wss://" scheme, and we don't have a TLS
                // config, mark that we should be using TLS anyway.
                if !cfg.TLS && isWSSURL(u) {
                        cfg.TLS = true
                }
        }
        return cfg
}

// Notifies the quit channel without blocking.
// No lock is needed to invoke this function.
func (cfg *leafNodeCfg) notifyQuitChannel() {
        select {
        case cfg.quitCh <- struct{}{}:
        default:
        }
}

// Sets the connect-in-progress status for this remote leaf configuration.
func (cfg *leafNodeCfg) setConnectInProgress(inProgress bool) {
        cfg.Lock()
        defer cfg.Unlock()
        // In both cases we want to drain the "quit" channel.
        select {
        case <-cfg.quitCh:
        default:
        }
        cfg.connInProgress = inProgress
}

// Returns `true` if this remote is in the middle of a connect, `false` otherwise.
func (cfg *leafNodeCfg) isConnectInProgress() bool {
        cfg.RLock()
        defer cfg.RUnlock()
        return cfg.connInProgress
}

// Mark that this remote is being removed from the configuration.
func (cfg *leafNodeCfg) markAsRemoved() {
        cfg.Lock()
        defer cfg.Unlock()
        // This function should be invoked only once, but protect.
        if cfg.removed {
                return
        }
        cfg.removed = true
        cfg.notifyQuitChannel()
}

// Returns false if it has been disabled or removed.
func (cfg *leafNodeCfg) stillValid() bool {
        cfg.RLock()
        defer cfg.RUnlock()
        return !cfg.Disabled && !cfg.removed
}

// Will pick an URL from the list of available URLs.
func (cfg *leafNodeCfg) pickNextURL() *url.URL {
        cfg.Lock()
        defer cfg.Unlock()
        // If the current URL is the first in the list and we have more than
        // one URL, then move that one to end of the list.
        if cfg.curURL != nil && len(cfg.urls) > 1 && urlsAreEqual(cfg.curURL, cfg.urls[0]) {
                first := cfg.urls[0]
                copy(cfg.urls, cfg.urls[1:])
                cfg.urls[len(cfg.urls)-1] = first
        }
        cfg.curURL = cfg.urls[0]
        return cfg.curURL
}

// Returns the current URL
func (cfg *leafNodeCfg) getCurrentURL() *url.URL {
        cfg.RLock()
        defer cfg.RUnlock()
        return cfg.curURL
}

// Returns how long the server should wait before attempting
// to solicit a remote leafnode connection.
func (cfg *leafNodeCfg) getConnectDelay() time.Duration {
        cfg.RLock()
        delay := cfg.connDelay
        cfg.RUnlock()
        return delay
}

// Sets the connect delay.
func (cfg *leafNodeCfg) setConnectDelay(delay time.Duration) {
        cfg.Lock()
        cfg.connDelay = delay
        cfg.Unlock()
}

// Ensure that non-exported options (used in tests) have
// been properly set.
func (s *Server) setLeafNodeNonExportedOptions() {
        opts := s.getOpts()
        s.leafNodeOpts.dialTimeout = opts.LeafNode.dialTimeout
        if s.leafNodeOpts.dialTimeout == 0 {
                // Use same timeouts as routes for now.
                s.leafNodeOpts.dialTimeout = DEFAULT_ROUTE_DIAL
        }
        s.leafNodeOpts.resolver = opts.LeafNode.resolver
        if s.leafNodeOpts.resolver == nil {
                s.leafNodeOpts.resolver = net.DefaultResolver
        }
}

const sharedSysAccDelay = 250 * time.Millisecond

// establishHTTPProxyTunnel establishes an HTTP CONNECT tunnel through a proxy server
func establishHTTPProxyTunnel(proxyURL, targetHost string, timeout time.Duration, username, password string) (net.Conn, error) {
        proxyAddr, err := url.Parse(proxyURL)
        if err != nil {
                // This should not happen since proxy URL is validated during configuration parsing
                return nil, fmt.Errorf("unexpected proxy URL parse error (URL was pre-validated): %v", err)
        }

        // Connect to the proxy server
        conn, err := natsDialTimeout("tcp", proxyAddr.Host, timeout)
        if err != nil {
                return nil, fmt.Errorf("failed to connect to proxy: %v", err)
        }

        // Set deadline for the entire proxy handshake
        if err := conn.SetDeadline(time.Now().Add(timeout)); err != nil {
                conn.Close()
                return nil, fmt.Errorf("failed to set deadline: %v", err)
        }

        req := &http.Request{
                Method: http.MethodConnect,
                URL:    &url.URL{Opaque: targetHost}, // Opaque is required for CONNECT
                Host:   targetHost,
                Header: make(http.Header),
        }

        // Add proxy authentication if provided
        if username != "" && password != "" {
                req.Header.Set("Proxy-Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(username+":"+password)))
        }

        if err := req.Write(conn); err != nil {
                conn.Close()
                return nil, fmt.Errorf("failed to write CONNECT request: %v", err)
        }

        resp, err := http.ReadResponse(bufio.NewReader(conn), req)
        if err != nil {
                conn.Close()
                return nil, fmt.Errorf("failed to read proxy response: %v", err)
        }

        if resp.StatusCode != http.StatusOK {
                resp.Body.Close()
                conn.Close()
                return nil, fmt.Errorf("proxy CONNECT failed: %s", resp.Status)
        }

        // Close the response body
        resp.Body.Close()

        // Clear the deadline now that we've finished the proxy handshake
        if err := conn.SetDeadline(time.Time{}); err != nil {
                conn.Close()
                return nil, fmt.Errorf("failed to clear deadline: %v", err)
        }

        return conn, nil
}

// Connect to a remote leaf node asynchronously (that is, this function will do
// the connect in a go routine).
func (s *Server) connectToRemoteLeafNodeAsynchronously(remote *leafNodeCfg, firstConnect bool) {
        remote.setConnectInProgress(true)
        s.startGoRoutine(func() {
                defer s.grWG.Done()
                if !connectToRemoteLeafNode(s, remote, firstConnect) {
                        remote.setConnectInProgress(false)
                }
        })
}

// Connect to a remote leaf node. Should only be invoked from
// `s.connectToRemoteLeafNodeAsynchronously()` or `s.reConnectToRemoteLeafNode()`.
// Returns `true` if this function invoked `s.createLeafNode()`, false otherwise.
func connectToRemoteLeafNode(s *Server, remote *leafNodeCfg, firstConnect bool) bool {

        if remote == nil || len(remote.URLs) == 0 {
                s.Debugf("Empty remote leafnode definition, nothing to connect")
                return false
        }

        opts := s.getOpts()
        reconnectDelay := opts.LeafNode.ReconnectInterval
        s.mu.RLock()
        dialTimeout := s.leafNodeOpts.dialTimeout
        resolver := s.leafNodeOpts.resolver
        var isSysAcc bool
        if s.eventsEnabled() {
                isSysAcc = remote.LocalAccount == s.sys.account.Name
        }
        jetstreamMigrateDelay := remote.JetStreamClusterMigrateDelay
        s.mu.RUnlock()

        // If we are sharing a system account and we are not standalone delay to gather some info prior.
        if firstConnect && isSysAcc && !s.standAloneMode() {
                s.Debugf("Will delay first leafnode connect to shared system account due to clustering")
                remote.setConnectDelay(sharedSysAccDelay)
        }

        if connDelay := remote.getConnectDelay(); connDelay > 0 {
                select {
                case <-time.After(connDelay):
                case <-remote.quitCh:
                        return false
                case <-s.quitCh:
                        return false
                }
                remote.setConnectDelay(0)
        }

        var conn net.Conn

        const connErrFmt = "Error trying to connect as leafnode to remote server %q (attempt %v): %v"

        // Capture proxy configuration once before the loop with proper locking
        remote.RLock()
        proxyURL := remote.Proxy.URL
        proxyUsername := remote.Proxy.Username
        proxyPassword := remote.Proxy.Password
        proxyTimeout := remote.Proxy.Timeout
        remote.RUnlock()

        // Set default proxy timeout if not specified
        if proxyTimeout == 0 {
                proxyTimeout = dialTimeout
        }

        attempts := 0

        // In case the migrate timer was created but not canceled, do it when
        // this function exits. Note that the timer would not be created if
        // `jetstreamMigrateDelay == 0`.
        if jetstreamMigrateDelay > 0 {
                defer remote.cancelMigrateTimer()
        }

        for s.isRunning() && remote.stillValid() {
                rURL := remote.pickNextURL()
                url, err := s.getRandomIP(resolver, rURL.Host, nil)
                if err == nil {
                        var ipStr string
                        if url != rURL.Host {
                                ipStr = fmt.Sprintf(" (%s)", url)
                        }
                        // Some test may want to disable remotes from connecting
                        if s.isLeafConnectDisabled() {
                                s.Debugf("Will not attempt to connect to remote server on %q%s, leafnodes currently disabled", rURL.Host, ipStr)
                                err = ErrLeafNodeDisabled
                        } else {
                                s.Debugf("Trying to connect as leafnode to remote server on %q%s", rURL.Host, ipStr)

                                // Check if proxy is configured
                                if proxyURL != _EMPTY_ {
                                        targetHost := rURL.Host
                                        // If URL doesn't include port, add the default port for the scheme
                                        if rURL.Port() == _EMPTY_ {
                                                defaultPort := "80"
                                                if rURL.Scheme == wsSchemePrefixTLS {
                                                        defaultPort = "443"
                                                }
                                                targetHost = net.JoinHostPort(rURL.Hostname(), defaultPort)
                                        }

                                        conn, err = establishHTTPProxyTunnel(proxyURL, targetHost, proxyTimeout, proxyUsername, proxyPassword)
                                } else {
                                        // Direct connection
                                        conn, err = natsDialTimeout("tcp", url, dialTimeout)
                                }
                        }
                }
                if err != nil {
                        jitter := time.Duration(rand.Int63n(int64(reconnectDelay)))
                        delay := reconnectDelay + jitter
                        attempts++
                        if s.shouldReportConnectErr(firstConnect, attempts) {
                                s.Errorf(connErrFmt, rURL.Host, attempts, err)
                        } else {
                                s.Debugf(connErrFmt, rURL.Host, attempts, err)
                        }
                        remote.Lock()
                        // if we are using a delay to start migrating assets, kick off a migrate timer.
                        if remote.jsMigrateTimer == nil && jetstreamMigrateDelay > 0 {
                                remote.jsMigrateTimer = time.AfterFunc(jetstreamMigrateDelay, func() {
                                        s.checkJetStreamMigrate(remote)
                                })
                        }
                        remote.Unlock()
                        select {
                        case <-s.quitCh:
                                return false
                        case <-remote.quitCh:
                                return false
                        case <-time.After(delay):
                                // Check if we should migrate any JetStream assets immediately while this remote is down.
                                // This will be used if JetStreamClusterMigrateDelay was not set
                                if jetstreamMigrateDelay == 0 {
                                        s.checkJetStreamMigrate(remote)
                                }
                                continue
                        }
                }
                remote.cancelMigrateTimer()
                // We can check here, but really we will have to check again when the server
                // is about to add to the `s.leafs` map later in the process.
                if !remote.stillValid() {
                        conn.Close()
                        return false
                }

                // We have a connection here to a remote server.
                // Go ahead and create our leaf node and return.
                s.createLeafNode(conn, rURL, remote, nil)

                // Clear any observer states if we had them.
                s.clearObserverState(remote)

                return true
        }

        return false
}

func (cfg *leafNodeCfg) cancelMigrateTimer() {
        cfg.Lock()
        stopAndClearTimer(&cfg.jsMigrateTimer)
        cfg.Unlock()
}

// This will clear any observer state such that stream or consumer assets on this server can become leaders again.
func (s *Server) clearObserverState(remote *leafNodeCfg) {
        s.mu.RLock()
        accName := remote.LocalAccount
        s.mu.RUnlock()

        acc, err := s.LookupAccount(accName)
        if err != nil {
                s.Warnf("Error looking up account [%s] checking for JetStream clear observer state on a leafnode", accName)
                return
        }

        acc.jscmMu.Lock()
        defer acc.jscmMu.Unlock()

        // Walk all streams looking for any clustered stream, skip otherwise.
        for _, mset := range acc.streams() {
                node := mset.raftNode()
                if node == nil {
                        // Not R>1
                        continue
                }
                // Check consumers
                for _, o := range mset.getConsumers() {
                        if n := o.raftNode(); n != nil {
                                // Ensure we can become a leader again.
                                n.SetObserver(false)
                        }
                }
                // Ensure we can not become a leader again.
                node.SetObserver(false)
        }
}

// Check to see if we should migrate any assets from this account.
func (s *Server) checkJetStreamMigrate(remote *leafNodeCfg) {
        s.mu.RLock()
        accName, shouldMigrate := remote.LocalAccount, remote.JetStreamClusterMigrate
        s.mu.RUnlock()

        if !shouldMigrate {
                return
        }

        acc, err := s.LookupAccount(accName)
        if err != nil {
                s.Warnf("Error looking up account [%s] checking for JetStream migration on a leafnode", accName)
                return
        }

        acc.jscmMu.Lock()
        defer acc.jscmMu.Unlock()

        // Walk all streams looking for any clustered stream, skip otherwise.
        // If we are the leader force stepdown.
        for _, mset := range acc.streams() {
                node := mset.raftNode()
                if node == nil {
                        // Not R>1
                        continue
                }
                // Collect any consumers
                for _, o := range mset.getConsumers() {
                        if n := o.raftNode(); n != nil {
                                n.StepDown()
                                // Ensure we can not become a leader while in this state.
                                n.SetObserver(true)
                        }
                }
                // Stepdown if this stream was leader.
                node.StepDown()
                // Ensure we can not become a leader while in this state.
                node.SetObserver(true)
        }
}

// Helper for checking.
func (s *Server) isLeafConnectDisabled() bool {
        s.mu.RLock()
        defer s.mu.RUnlock()
        return s.leafDisableConnect
}

// Save off the tlsName for when we use TLS and mix hostnames and IPs. IPs usually
// come from the server we connect to.
//
// We used to save the name only if there was a TLSConfig or scheme equal to "tls".
// However, this was causing failures for users that did not set the scheme (and
// their remote connections did not have a tls{} block).
// We now save the host name regardless in case the remote returns an INFO indicating
// that TLS is required.
//
// Lock held on entry.
func (cfg *leafNodeCfg) saveTLSHostname(u *url.URL) {
        if cfg.tlsName == _EMPTY_ && net.ParseIP(u.Hostname()) == nil {
                cfg.tlsName = u.Hostname()
        }
}

// Save off the username/password for when we connect using a bare URL
// that we get from the INFO protocol.
//
// Lock held on entry.
func (cfg *leafNodeCfg) saveUserPassword(u *url.URL) {
        if cfg.username == _EMPTY_ && u.User != nil {
                cfg.username = u.User.Username()
                cfg.password, _ = u.User.Password()
        }
}

// This starts the leafnode accept loop in a go routine, unless it
// is detected that the server has already been shutdown.
func (s *Server) startLeafNodeAcceptLoop() {
        // Snapshot server options.
        opts := s.getOpts()

        port := opts.LeafNode.Port
        if port == -1 {
                port = 0
        }

        if s.isShuttingDown() {
                return
        }

        s.mu.Lock()
        hp := net.JoinHostPort(opts.LeafNode.Host, strconv.Itoa(port))
        l, e := natsListen("tcp", hp)
        s.leafNodeListenerErr = e
        if e != nil {
                s.mu.Unlock()
                s.Fatalf("Error listening on leafnode port: %d - %v", opts.LeafNode.Port, e)
                return
        }

        s.Noticef("Listening for leafnode connections on %s",
                net.JoinHostPort(opts.LeafNode.Host, strconv.Itoa(l.Addr().(*net.TCPAddr).Port)))

        tlsRequired := opts.LeafNode.TLSConfig != nil
        tlsVerify := tlsRequired && opts.LeafNode.TLSConfig.ClientAuth == tls.RequireAndVerifyClientCert
        // Do not set compression in this Info object, it would possibly cause
        // issues when sending asynchronous INFO to the remote.
        info := Info{
                ID:            s.info.ID,
                Name:          s.info.Name,
                Version:       s.info.Version,
                GitCommit:     gitCommit,
                GoVersion:     runtime.Version(),
                AuthRequired:  true,
                TLSRequired:   tlsRequired,
                TLSVerify:     tlsVerify,
                MaxPayload:    s.info.MaxPayload, // TODO(dlc) - Allow override?
                Headers:       s.supportsHeaders(),
                JetStream:     opts.JetStream,
                Domain:        opts.JetStreamDomain,
                Proto:         s.getServerProto(),
                InfoOnConnect: true,
                JSApiLevel:    JSApiLevel,
        }
        // If we have selected a random port...
        if port == 0 {
                // Write resolved port back to options.
                opts.LeafNode.Port = l.Addr().(*net.TCPAddr).Port
        }

        s.leafNodeInfo = info
        // Possibly override Host/Port and set IP based on Cluster.Advertise
        if err := s.setLeafNodeInfoHostPortAndIP(); err != nil {
                s.Fatalf("Error setting leafnode INFO with LeafNode.Advertise value of %s, err=%v", opts.LeafNode.Advertise, err)
                l.Close()
                s.mu.Unlock()
                return
        }
        s.leafURLsMap[s.leafNodeInfo.IP]++
        s.generateLeafNodeInfoJSON()

        // Setup state that can enable shutdown
        s.leafNodeListener = l

        // As of now, a server that does not have remotes configured would
        // never solicit a connection, so we should not have to warn if
        // InsecureSkipVerify is set in main LeafNodes config (since
        // this TLS setting matters only when soliciting a connection).
        // Still, warn if insecure is set in any of LeafNode block.
        // We need to check remotes, even if tls is not required on accept.
        warn := tlsRequired && opts.LeafNode.TLSConfig.InsecureSkipVerify
        if !warn {
                for _, r := range opts.LeafNode.Remotes {
                        if r.TLSConfig != nil && r.TLSConfig.InsecureSkipVerify {
                                warn = true
                                break
                        }
                }
        }
        if warn {
                s.Warnf(leafnodeTLSInsecureWarning)
        }
        go s.acceptConnections(l, "Leafnode", func(conn net.Conn) { s.createLeafNode(conn, nil, nil, nil) }, nil)
        s.mu.Unlock()
}

// RegEx to match a creds file with user JWT and Seed.
var credsRe = regexp.MustCompile(`\s*(?:(?:[-]{3,}.*[-]{3,}\r?\n)([\w\-.=]+)(?:\r?\n[-]{3,}.*[-]{3,}(\r?\n|\z)))`)

// clusterName is provided as argument to avoid lock ordering issues with the locked client c
// Lock should be held entering here.
func (c *client) sendLeafConnect(clusterName string, headers bool) error {
        // We support basic user/pass and operator based user JWT with signatures.
        cinfo := leafConnectInfo{
                Version:       VERSION,
                ID:            c.srv.info.ID,
                Domain:        c.srv.info.Domain,
                Name:          c.srv.info.Name,
                Hub:           c.leaf.remote.Hub,
                Cluster:       clusterName,
                Headers:       headers,
                JetStream:     c.acc.jetStreamConfigured(),
                DenyPub:       c.leaf.remote.DenyImports,
                Compression:   c.leaf.compression,
                RemoteAccount: c.acc.GetName(),
                Proto:         c.srv.getServerProto(),
                Isolate:       c.leaf.remote.RequestIsolation,
        }

        // If a signature callback is specified, this takes precedence over anything else.
        if cb := c.leaf.remote.SignatureCB; cb != nil {
                nonce := c.nonce
                c.mu.Unlock()
                jwt, sigraw, err := cb(nonce)
                c.mu.Lock()
                if err == nil && c.isClosed() {
                        err = ErrConnectionClosed
                }
                if err != nil {
                        c.Errorf("Error signing the nonce: %v", err)
                        return err
                }
                sig := base64.RawURLEncoding.EncodeToString(sigraw)
                cinfo.JWT, cinfo.Sig = jwt, sig

        } else if creds := c.leaf.remote.Credentials; creds != _EMPTY_ {
                // Check for credentials first, that will take precedence..
                c.Debugf("Authenticating with credentials file %q", c.leaf.remote.Credentials)
                contents, err := os.ReadFile(creds)
                if err != nil {
                        c.Errorf("%v", err)
                        return err
                }
                defer wipeSlice(contents)
                items := credsRe.FindAllSubmatch(contents, -1)
                if len(items) < 2 {
                        c.Errorf("Credentials file malformed")
                        return err
                }
                // First result should be the user JWT.
                // We copy here so that the file containing the seed will be wiped appropriately.
                raw := items[0][1]
                tmp := make([]byte, len(raw))
                copy(tmp, raw)
                // Seed is second item.
                kp, err := nkeys.FromSeed(items[1][1])
                if err != nil {
                        c.Errorf("Credentials file has malformed seed")
                        return err
                }
                // Wipe our key on exit.
                defer kp.Wipe()

                sigraw, _ := kp.Sign(c.nonce)
                sig := base64.RawURLEncoding.EncodeToString(sigraw)
                cinfo.JWT = bytesToString(tmp)
                cinfo.Sig = sig
        } else if nkey := c.leaf.remote.Nkey; nkey != _EMPTY_ {
                kp, err := nkeys.FromSeed([]byte(nkey))
                if err != nil {
                        c.Errorf("Remote nkey has malformed seed")
                        return err
                }
                // Wipe our key on exit.
                defer kp.Wipe()
                sigraw, _ := kp.Sign(c.nonce)
                sig := base64.RawURLEncoding.EncodeToString(sigraw)
                pkey, _ := kp.PublicKey()
                cinfo.Nkey = pkey
                cinfo.Sig = sig
        }
        // In addition, and this is to allow auth callout, set user/password or
        // token if applicable.
        if userInfo := c.leaf.remote.curURL.User; userInfo != nil {
                cinfo.User = userInfo.Username()
                var ok bool
                cinfo.Pass, ok = userInfo.Password()
                // For backward compatibility, if only username is provided, set both
                // Token and User, not just Token.
                if !ok {
                        cinfo.Token = cinfo.User
                }
        } else if c.leaf.remote.username != _EMPTY_ {
                cinfo.User = c.leaf.remote.username
                cinfo.Pass = c.leaf.remote.password
                // For backward compatibility, if only username is provided, set both
                // Token and User, not just Token.
                if cinfo.Pass == _EMPTY_ {
                        cinfo.Token = cinfo.User
                }
        }
        b, err := json.Marshal(cinfo)
        if err != nil {
                c.Errorf("Error marshaling CONNECT to remote leafnode: %v\n", err)
                return err
        }
        // Although this call is made before the writeLoop is created,
        // we don't really need to send in place. The protocol will be
        // sent out by the writeLoop.
        c.enqueueProto([]byte(fmt.Sprintf(ConProto, b)))
        return nil
}

// Makes a deep copy of the LeafNode Info structure.
// The server lock is held on entry.
func (s *Server) copyLeafNodeInfo() *Info {
        clone := s.leafNodeInfo
        // Copy the array of urls.
        if len(s.leafNodeInfo.LeafNodeURLs) > 0 {
                clone.LeafNodeURLs = append([]string(nil), s.leafNodeInfo.LeafNodeURLs...)
        }
        return &clone
}

// Adds a LeafNode URL that we get when a route connects to the Info structure.
// Regenerates the JSON byte array so that it can be sent to LeafNode connections.
// Returns a boolean indicating if the URL was added or not.
// Server lock is held on entry
func (s *Server) addLeafNodeURL(urlStr string) bool {
        if s.leafURLsMap.addUrl(urlStr) {
                s.generateLeafNodeInfoJSON()
                return true
        }
        return false
}

// Removes a LeafNode URL of the route that is disconnecting from the Info structure.
// Regenerates the JSON byte array so that it can be sent to LeafNode connections.
// Returns a boolean indicating if the URL was removed or not.
// Server lock is held on entry.
func (s *Server) removeLeafNodeURL(urlStr string) bool {
        // Don't need to do this if we are removing the route connection because
        // we are shuting down...
        if s.isShuttingDown() {
                return false
        }
        if s.leafURLsMap.removeUrl(urlStr) {
                s.generateLeafNodeInfoJSON()
                return true
        }
        return false
}

// Server lock is held on entry
func (s *Server) generateLeafNodeInfoJSON() {
        s.leafNodeInfo.Cluster = s.cachedClusterName()
        s.leafNodeInfo.LeafNodeURLs = s.leafURLsMap.getAsStringSlice()
        s.leafNodeInfo.WSConnectURLs = s.websocket.connectURLsMap.getAsStringSlice()
        s.leafNodeInfoJSON = generateInfoJSON(&s.leafNodeInfo)
}

// Sends an async INFO protocol so that the connected servers can update
// their list of LeafNode urls.
func (s *Server) sendAsyncLeafNodeInfo() {
        for _, c := range s.leafs {
                c.mu.Lock()
                c.enqueueProto(s.leafNodeInfoJSON)
                c.mu.Unlock()
        }
}

// Called when an inbound leafnode connection is accepted or we create one for a solicited leafnode.
func (s *Server) createLeafNode(conn net.Conn, rURL *url.URL, remote *leafNodeCfg, ws *websocket) *client {
        // Snapshot server options.
        opts := s.getOpts()

        maxPay := int32(opts.MaxPayload)
        maxSubs := int32(opts.MaxSubs)
        // For system, maxSubs of 0 means unlimited, so re-adjust here.
        if maxSubs == 0 {
                maxSubs = -1
        }
        now := time.Now().UTC()

        c := &client{srv: s, nc: conn, kind: LEAF, opts: defaultOpts, mpay: maxPay, msubs: maxSubs, start: now, last: now}
        // Do not update the smap here, we need to do it in initLeafNodeSmapAndSendSubs
        c.leaf = &leaf{}

        // If the leafnode subject interest should be isolated, flag it here.
        s.optsMu.RLock()
        if c.leaf.isolated = s.opts.LeafNode.IsolateLeafnodeInterest; !c.leaf.isolated && remote != nil {
                c.leaf.isolated = remote.LocalIsolation
        }
        s.optsMu.RUnlock()

        // For accepted LN connections, ws will be != nil if it was accepted
        // through the Websocket port.
        c.ws = ws

        // For remote, check if the scheme starts with "ws", if so, we will initiate
        // a remote Leaf Node connection as a websocket connection.
        if remote != nil && rURL != nil && isWSURL(rURL) {
                remote.RLock()
                c.ws = &websocket{compress: remote.Websocket.Compression, maskwrite: !remote.Websocket.NoMasking}
                remote.RUnlock()
        }

        // Determines if we are soliciting the connection or not.
        var solicited bool
        var acc *Account
        var remoteSuffix string
        if remote != nil {
                // For now, if lookup fails, we will constantly try
                // to recreate this LN connection.
                lacc := remote.LocalAccount
                var err error
                acc, err = s.LookupAccount(lacc)
                if err != nil {
                        // An account not existing is something that can happen with nats/http account resolver and the account
                        // has not yet been pushed, or the request failed for other reasons.
                        // remote needs to be set or retry won't happen
                        c.leaf.remote = remote
                        c.closeConnection(MissingAccount)
                        s.Errorf("Unable to lookup account %s for solicited leafnode connection: %v", lacc, err)
                        return nil
                }
                remoteSuffix = fmt.Sprintf(" for account: %s", acc.traceLabel())
        }

        c.mu.Lock()
        c.initClient()
        c.Noticef("Leafnode connection created%s %s", remoteSuffix, c.opts.Name)

        var (
                tlsFirst         bool
                tlsFirstFallback time.Duration
                infoTimeout      time.Duration
        )
        if remote != nil {
                solicited = true
                remote.Lock()
                c.leaf.remote = remote
                c.setPermissions(remote.perms)
                if !c.leaf.remote.Hub {
                        c.leaf.isSpoke = true
                }
                tlsFirst = remote.TLSHandshakeFirst
                infoTimeout = remote.FirstInfoTimeout
                remote.Unlock()
                c.acc = acc
        } else {
                c.flags.set(expectConnect)
                if ws != nil {
                        c.Debugf("Leafnode compression=%v", c.ws.compress)
                }
                tlsFirst = opts.LeafNode.TLSHandshakeFirst
                if f := opts.LeafNode.TLSHandshakeFirstFallback; f > 0 {
                        tlsFirstFallback = f
                }
        }
        c.mu.Unlock()

        var nonce [nonceLen]byte
        var info *Info

        // Grab this before the client lock below.
        if !solicited {
                // Grab server variables
                s.mu.Lock()
                info = s.copyLeafNodeInfo()
                // For tests that want to simulate old servers, do not set the compression
                // on the INFO protocol if configured with CompressionNotSupported.
                if cm := opts.LeafNode.Compression.Mode; cm != CompressionNotSupported {
                        info.Compression = cm
                }
                // We always send a nonce for LEAF connections. Do not change that without
                // taking into account presence of proxy trusted keys.
                s.generateNonce(nonce[:])
                s.mu.Unlock()
        }

        // Grab lock
        c.mu.Lock()

        var preBuf []byte
        if solicited {
                // For websocket connection, we need to send an HTTP request,
                // and get the response before starting the readLoop to get
                // the INFO, etc..
                if c.isWebsocket() {
                        var err error
                        var closeReason ClosedState

                        preBuf, closeReason, err = c.leafNodeSolicitWSConnection(opts, rURL, remote)
                        if err != nil {
                                c.Errorf("Error soliciting websocket connection: %v", err)
                                c.mu.Unlock()
                                if closeReason != 0 {
                                        c.closeConnection(closeReason)
                                }
                                return nil
                        }
                } else {
                        // If configured to do TLS handshake first
                        if tlsFirst {
                                if _, err := c.leafClientHandshakeIfNeeded(remote, opts); err != nil {
                                        c.mu.Unlock()
                                        return nil
                                }
                        }
                        // We need to wait for the info, but not for too long.
                        c.nc.SetReadDeadline(time.Now().Add(infoTimeout))
                }

                // We will process the INFO from the readloop and finish by
                // sending the CONNECT and finish registration later.
        } else {
                // Send our info to the other side.
                // Remember the nonce we sent here for signatures, etc.
                c.nonce = make([]byte, nonceLen)
                copy(c.nonce, nonce[:])
                info.Nonce = bytesToString(c.nonce)
                info.CID = c.cid
                proto := generateInfoJSON(info)

                var pre []byte
                // We need first to check for "TLS First" fallback delay.
                if tlsFirstFallback > 0 {
                        // We wait and see if we are getting any data. Since we did not send
                        // the INFO protocol yet, only clients that use TLS first should be
                        // sending data (the TLS handshake). We don't really check the content:
                        // if it is a rogue agent and not an actual client performing the
                        // TLS handshake, the error will be detected when performing the
                        // handshake on our side.
                        pre = make([]byte, 4)
                        c.nc.SetReadDeadline(time.Now().Add(tlsFirstFallback))
                        n, _ := io.ReadFull(c.nc, pre[:])
                        c.nc.SetReadDeadline(time.Time{})
                        // If we get any data (regardless of possible timeout), we will proceed
                        // with the TLS handshake.
                        if n > 0 {
                                pre = pre[:n]
                        } else {
                                // We did not get anything so we will send the INFO protocol.
                                pre = nil
                                // Set the boolean to false for the rest of the function.
                                tlsFirst = false
                        }
                }

                if !tlsFirst {
                        // We have to send from this go routine because we may
                        // have to block for TLS handshake before we start our
                        // writeLoop go routine. The other side needs to receive
                        // this before it can initiate the TLS handshake..
                        c.sendProtoNow(proto)

                        // The above call could have marked the connection as closed (due to TCP error).
                        if c.isClosed() {
                                c.mu.Unlock()
                                c.closeConnection(WriteError)
                                return nil
                        }
                }

                // Check to see if we need to spin up TLS.
                if !c.isWebsocket() && info.TLSRequired {
                        // If we have a prebuffer create a multi-reader.
                        if len(pre) > 0 {
                                c.nc = &tlsMixConn{c.nc, bytes.NewBuffer(pre)}
                        }
                        // Perform server-side TLS handshake.
                        if err := c.doTLSServerHandshake(tlsHandshakeLeaf, opts.LeafNode.TLSConfig, opts.LeafNode.TLSTimeout, opts.LeafNode.TLSPinnedCerts); err != nil {
                                c.mu.Unlock()
                                return nil
                        }
                }

                // If the user wants the TLS handshake to occur first, now that it is
                // done, send the INFO protocol.
                if tlsFirst {
                        c.flags.set(didTLSFirst)
                        c.sendProtoNow(proto)
                        if c.isClosed() {
                                c.mu.Unlock()
                                c.closeConnection(WriteError)
                                return nil
                        }
                }

                // Leaf nodes will always require a CONNECT to let us know
                // when we are properly bound to an account.
                //
                // If compression is configured, we can't set the authTimer here because
                // it would cause the parser to fail any incoming protocol that is not a
                // CONNECT (and we need to exchange INFO protocols for compression
                // negotiation). So instead, use the ping timer until we are done with
                // negotiation and can set the auth timer.
                timeout := secondsToDuration(opts.LeafNode.AuthTimeout)
                if needsCompression(opts.LeafNode.Compression.Mode) {
                        c.ping.tmr = time.AfterFunc(timeout, func() {
                                c.authTimeout()
                        })
                } else {
                        c.setAuthTimer(timeout)
                }
        }

        // Keep track in case server is shutdown before we can successfully register.
        if !s.addToTempClients(c.cid, c) {
                c.mu.Unlock()
                c.setNoReconnect()
                c.closeConnection(ServerShutdown)
                return nil
        }

        // Spin up the read loop.
        s.startGoRoutine(func() { c.readLoop(preBuf) })

        // We will spin the write loop for solicited connections only
        // when processing the INFO and after switching to TLS if needed.
        if !solicited {
                s.startGoRoutine(func() { c.writeLoop() })
        }

        c.mu.Unlock()

        return c
}

// Will perform the client-side TLS handshake if needed. Assumes that this
// is called by the solicit side (remote will be non nil). Returns `true`
// if TLS is required, `false` otherwise.
// Lock held on entry.
func (c *client) leafClientHandshakeIfNeeded(remote *leafNodeCfg, opts *Options) (bool, error) {
        // Check if TLS is required and gather TLS config variables.
        tlsRequired, tlsConfig, tlsName, tlsTimeout := c.leafNodeGetTLSConfigForSolicit(remote)
        if !tlsRequired {
                return false, nil
        }

        // If TLS required, peform handshake.
        // Get the URL that was used to connect to the remote server.
        rURL := remote.getCurrentURL()

        // Perform the client-side TLS handshake.
        if resetTLSName, err := c.doTLSClientHandshake(tlsHandshakeLeaf, rURL, tlsConfig, tlsName, tlsTimeout, opts.LeafNode.TLSPinnedCerts); err != nil {
                // Check if we need to reset the remote's TLS name.
                if resetTLSName {
                        remote.Lock()
                        remote.tlsName = _EMPTY_
                        remote.Unlock()
                }
                return false, err
        }
        return true, nil
}

func (c *client) processLeafnodeInfo(info *Info) {
        c.mu.Lock()
        if c.leaf == nil || c.isClosed() {
                c.mu.Unlock()
                return
        }
        s := c.srv
        opts := s.getOpts()
        remote := c.leaf.remote
        didSolicit := remote != nil
        firstINFO := !c.flags.isSet(infoReceived)

        // In case of websocket, the TLS handshake has been already done.
        // So check only for non websocket connections and for configurations
        // where the TLS Handshake was not done first.
        if didSolicit && !c.flags.isSet(handshakeComplete) && !c.isWebsocket() && !remote.TLSHandshakeFirst {
                // If the server requires TLS, we need to set this in the remote
                // otherwise if there is no TLS configuration block for the remote,
                // the solicit side will not attempt to perform the TLS handshake.
                if firstINFO && info.TLSRequired {
                        // Check for TLS/proxy configuration mismatch
                        if remote.Proxy.URL != _EMPTY_ && !remote.TLS && remote.TLSConfig == nil {
                                c.mu.Unlock()
                                c.Errorf("TLS configuration mismatch: Hub requires TLS but leafnode remote is not configured for TLS. When using a proxy, ensure TLS leafnode configuration matches the Hub requirements.")
                                c.closeConnection(TLSHandshakeError)
                                return
                        }
                        remote.TLS = true
                }
                if _, err := c.leafClientHandshakeIfNeeded(remote, opts); err != nil {
                        c.mu.Unlock()
                        return
                }
        }

        // Check for compression, unless already done.
        if firstINFO && !c.flags.isSet(compressionNegotiated) {
                // A solicited leafnode connection must first receive a leafnode INFO.
                // Classify wrong-port connections before any leaf-specific negotiation.
                if didSolicit && (info.CID == 0 || info.LeafNodeURLs == nil) {
                        c.mu.Unlock()
                        c.Errorf(ErrConnectedToWrongPort.Error())
                        c.closeConnection(WrongPort)
                        return
                }

                // Prevent from getting back here.
                c.flags.set(compressionNegotiated)

                var co *CompressionOpts
                if !didSolicit {
                        co = &opts.LeafNode.Compression
                } else {
                        co = &remote.Compression
                }
                if needsCompression(co.Mode) {
                        // Release client lock since following function will need server lock.
                        c.mu.Unlock()
                        compress, err := s.negotiateLeafCompression(c, didSolicit, info.Compression, co)
                        if err != nil {
                                c.sendErrAndErr(err.Error())
                                c.closeConnection(ProtocolViolation)
                                return
                        }
                        if compress {
                                // Done for now, will get back another INFO protocol...
                                return
                        }
                        // No compression because one side does not want/can't, so proceed.
                        c.mu.Lock()
                        // Check that the connection did not close if the lock was released.
                        if c.isClosed() {
                                c.mu.Unlock()
                                return
                        }
                } else {
                        // Coming from an old server, the Compression field would be the empty
                        // string. For servers that are configured with CompressionNotSupported,
                        // this makes them behave as old servers.
                        if info.Compression == _EMPTY_ || co.Mode == CompressionNotSupported {
                                c.leaf.compression = CompressionNotSupported
                        } else {
                                c.leaf.compression = CompressionOff
                        }
                }
                // Accepting side does not normally process an INFO protocol during
                // initial connection handshake. So we keep it consistent by returning
                // if we are not soliciting.
                if !didSolicit {
                        // If we had created the ping timer instead of the auth timer, we will
                        // clear the ping timer and set the auth timer now that the compression
                        // negotiation is done.
                        if info.Compression != _EMPTY_ && c.ping.tmr != nil {
                                clearTimer(&c.ping.tmr)
                                c.setAuthTimer(secondsToDuration(opts.LeafNode.AuthTimeout))
                        }
                        c.mu.Unlock()
                        return
                }
                // Fall through and process the INFO protocol as usual.
        }

        // Note: For now, only the initial INFO has a nonce. We
        // will probably do auto key rotation at some point.
        if firstINFO {
                // Mark that the INFO protocol has been received.
                c.flags.set(infoReceived)
                // Prevent connecting to non leafnode port. Need to do this only for
                // the first INFO, not for async INFO updates...
                //
                // Content of INFO sent by the server when accepting a tcp connection.
                // -------------------------------------------------------------------
                // Listen Port Of | CID | ClientConnectURLs | LeafNodeURLs | Gateway |
                // -------------------------------------------------------------------
                //      CLIENT    |  X* |        X**        |              |         |
                //      ROUTE     |     |        X**        |      X***    |         |
                //     GATEWAY    |     |                   |              |    X    |
                //     LEAFNODE   |  X  |                   |       X      |         |
                // -------------------------------------------------------------------
                // *   Not on older servers.
                // **  Not if "no advertise" is enabled.
                // *** Not if leafnode's "no advertise" is enabled.
                //
                // Reject a cluster that contains spaces.
                if info.Cluster != _EMPTY_ && strings.Contains(info.Cluster, " ") {
                        c.mu.Unlock()
                        c.sendErrAndErr(ErrClusterNameHasSpaces.Error())
                        c.closeConnection(ProtocolViolation)
                        return
                }
                // For solicited outbound leaf connections, capture the remote's nonce.
                // For inbound leaf connections, keep using the server-issued nonce that
                // was sent in our initial INFO and must be signed in CONNECT.
                if didSolicit {
                        c.nonce = []byte(info.Nonce)
                }
                if info.TLSRequired && didSolicit {
                        remote.TLS = true
                }
                supportsHeaders := c.srv.supportsHeaders()
                c.headers = supportsHeaders && info.Headers

                // Remember the remote server.
                // Pre 2.2.0 servers are not sending their server name.
                // In that case, use info.ID, which, for those servers, matches
                // the content of the field `Name` in the leafnode CONNECT protocol.
                if info.Name == _EMPTY_ {
                        c.leaf.remoteServer = info.ID
                } else {
                        c.leaf.remoteServer = info.Name
                }
                c.leaf.remoteDomain = info.Domain
                c.leaf.remoteCluster = info.Cluster
                // We send the protocol version in the INFO protocol.
                // Keep track of it, so we know if this connection supports message
                // tracing for instance.
                c.opts.Protocol = info.Proto
        }

        // For both initial INFO and async INFO protocols, Possibly
        // update our list of remote leafnode URLs we can connect to,
        // unless we are instructed not to.
        if didSolicit && !remote.IgnoreDiscoveredServers &&
                (len(info.LeafNodeURLs) > 0 || len(info.WSConnectURLs) > 0) {
                // Consider the incoming array as the most up-to-date
                // representation of the remote cluster's list of URLs.
                c.updateLeafNodeURLs(info)
        }

        // Only solicited leafnode connections trust permission updates from INFO.
        if didSolicit && (info.Import != nil || info.Export != nil) {
                perms := &Permissions{
                        Publish:   info.Export,
                        Subscribe: info.Import,
                }
                // Check if we have local deny clauses that we need to merge.
                if remote := c.leaf.remote; remote != nil {
                        if len(remote.DenyExports) > 0 {
                                if perms.Publish == nil {
                                        perms.Publish = &SubjectPermission{}
                                }
                                perms.Publish.Deny = append(perms.Publish.Deny, remote.DenyExports...)
                        }
                        if len(remote.DenyImports) > 0 {
                                if perms.Subscribe == nil {
                                        perms.Subscribe = &SubjectPermission{}
                                }
                                perms.Subscribe.Deny = append(perms.Subscribe.Deny, remote.DenyImports...)
                        }
                }
                c.setPermissions(perms)
        }

        var resumeConnect bool

        // If this is a remote connection and this is the first INFO protocol,
        // then we need to finish the connect process by sending CONNECT, etc..
        if firstINFO && didSolicit {
                // Clear deadline that was set in createLeafNode while waiting for the INFO.
                c.nc.SetDeadline(time.Time{})
                resumeConnect = true
        } else if !firstINFO && didSolicit {
                c.leaf.remoteAccName = info.RemoteAccount
        }

        // Check if we have the remote account information and if so make sure it's stored.
        if info.RemoteAccount != _EMPTY_ {
                if c.acc == nil {
                        c.mu.Unlock()
                        c.sendErr("Authorization Violation")
                        c.closeConnection(ProtocolViolation)
                        return
                }
                s.leafRemoteAccounts.Store(c.acc.Name, info.RemoteAccount)
        }
        c.mu.Unlock()

        finishConnect := info.ConnectInfo
        if resumeConnect && s != nil {
                s.leafNodeResumeConnectProcess(c)
                if !info.InfoOnConnect {
                        finishConnect = true
                }
        }
        if finishConnect {
                s.leafNodeFinishConnectProcess(c)
        }

        // Check to see if we need to kick any internal source or mirror consumers.
        // This will be a no-op if JetStream not enabled for this server or if the bound account
        // does not have jetstream.
        s.checkInternalSyncConsumers(c.acc)
}

func (s *Server) negotiateLeafCompression(c *client, didSolicit bool, infoCompression string, co *CompressionOpts) (bool, error) {
        // Negotiate the appropriate compression mode (or no compression)
        cm, err := selectCompressionMode(co.Mode, infoCompression)
        if err != nil {
                return false, err
        }
        c.mu.Lock()
        // For "auto" mode, set the initial compression mode based on RTT
        if cm == CompressionS2Auto {
                if c.rttStart.IsZero() {
                        c.rtt = computeRTT(c.start)
                }
                cm = selectS2AutoModeBasedOnRTT(c.rtt, co.RTTThresholds)
        }
        // Keep track of the negotiated compression mode.
        c.leaf.compression = cm
        cid := c.cid
        var nonce string
        if !didSolicit {
                nonce = bytesToString(c.nonce)
        }
        c.mu.Unlock()

        if !needsCompression(cm) {
                return false, nil
        }

        // If we end-up doing compression...

        // Generate an INFO with the chosen compression mode.
        s.mu.Lock()
        info := s.copyLeafNodeInfo()
        info.Compression, info.CID, info.Nonce = compressionModeForInfoProtocol(co, cm), cid, nonce
        infoProto := generateInfoJSON(info)
        s.mu.Unlock()

        // If we solicited, then send this INFO protocol BEFORE switching
        // to compression writer. However, if we did not, we send it after.
        c.mu.Lock()
        if didSolicit {
                c.enqueueProto(infoProto)
                // Make sure it is completely flushed (the pending bytes goes to
                // 0) before proceeding.
                for c.out.pb > 0 && !c.isClosed() {
                        c.flushOutbound()
                }
        }
        // This is to notify the readLoop that it should switch to a
        // (de)compression reader.
        c.in.flags.set(switchToCompression)
        // Create the compress writer before queueing the INFO protocol for
        // a route that did not solicit. It will make sure that that proto
        // is sent with compression on.
        c.out.cw = s2.NewWriter(nil, s2WriterOptions(cm)...)
        if !didSolicit {
                c.enqueueProto(infoProto)
        }
        c.mu.Unlock()
        return true, nil
}

// When getting a leaf node INFO protocol, use the provided
// array of urls to update the list of possible endpoints.
func (c *client) updateLeafNodeURLs(info *Info) {
        cfg := c.leaf.remote
        cfg.Lock()
        defer cfg.Unlock()

        // We have ensured that if a remote has a WS scheme, then all are.
        // So check if first is WS, then add WS URLs, otherwise, add non WS ones.
        if len(cfg.URLs) > 0 && isWSURL(cfg.URLs[0]) {
                // It does not really matter if we use "ws://" or "wss://" here since
                // we will have already marked that the remote should use TLS anyway.
                // But use proper scheme for log statements, etc...
                proto := wsSchemePrefix
                if cfg.TLS {
                        proto = wsSchemePrefixTLS
                }
                c.doUpdateLNURLs(cfg, proto, info.WSConnectURLs)
                return
        }
        c.doUpdateLNURLs(cfg, "nats-leaf", info.LeafNodeURLs)
}

func (c *client) doUpdateLNURLs(cfg *leafNodeCfg, scheme string, URLs []string) {
        cfg.urls = make([]*url.URL, 0, 1+len(URLs))
        // Add the ones we receive in the protocol
        for _, surl := range URLs {
                url, err := url.Parse(fmt.Sprintf("%s://%s", scheme, surl))
                if err != nil {
                        // As per below, the URLs we receive should not have contained URL info, so this should be safe to log.
                        c.Errorf("Error parsing url %q: %v", surl, err)
                        continue
                }
                // Do not add if it's the same as what we already have configured.
                var dup bool
                for _, u := range cfg.URLs {
                        // URLs that we receive never have user info, but the
                        // ones that were configured may have. Simply compare
                        // host and port to decide if they are equal or not.
                        if url.Host == u.Host && url.Port() == u.Port() {
                                dup = true
                                break
                        }
                }
                if !dup {
                        cfg.urls = append(cfg.urls, url)
                        cfg.saveTLSHostname(url)
                }
        }
        // Add the configured one
        cfg.urls = append(cfg.urls, cfg.URLs...)
}

// Similar to setInfoHostPortAndGenerateJSON, but for leafNodeInfo.
func (s *Server) setLeafNodeInfoHostPortAndIP() error {
        opts := s.getOpts()
        if opts.LeafNode.Advertise != _EMPTY_ {
                advHost, advPort, err := parseHostPort(opts.LeafNode.Advertise, opts.LeafNode.Port)
                if err != nil {
                        return err
                }
                s.leafNodeInfo.Host = advHost
                s.leafNodeInfo.Port = advPort
        } else {
                s.leafNodeInfo.Host = opts.LeafNode.Host
                s.leafNodeInfo.Port = opts.LeafNode.Port
                // If the host is "0.0.0.0" or "::" we need to resolve to a public IP.
                // This will return at most 1 IP.
                hostIsIPAny, ips, err := s.getNonLocalIPsIfHostIsIPAny(s.leafNodeInfo.Host, false)
                if err != nil {
                        return err
                }
                if hostIsIPAny {
                        if len(ips) == 0 {
                                s.Errorf("Could not find any non-local IP for leafnode's listen specification %q",
                                        s.leafNodeInfo.Host)
                        } else {
                                // Take the first from the list...
                                s.leafNodeInfo.Host = ips[0]
                        }
                }
        }
        // Use just host:port for the IP
        s.leafNodeInfo.IP = net.JoinHostPort(s.leafNodeInfo.Host, strconv.Itoa(s.leafNodeInfo.Port))
        if opts.LeafNode.Advertise != _EMPTY_ {
                s.Noticef("Advertise address for leafnode is set to %s", s.leafNodeInfo.IP)
        }
        return nil
}

// Add the connection to the map of leaf nodes.
// If `checkForDup` is true (invoked when a leafnode is accepted), then we check
// if a connection already exists for the same server name and account.
// That can happen when the remote is attempting to reconnect while the accepting
// side did not detect the connection as broken yet.
// But it can also happen when there is a misconfiguration and the remote is
// creating two (or more) connections that bind to the same account on the accept
// side.
// When a duplicate is found, the new connection is accepted and the old is closed
// (this solves the stale connection situation). An error is returned to help the
// remote detect the misconfiguration when the duplicate is the result of that
// misconfiguration.
func (s *Server) addLeafNodeConnection(c *client, srvName, clusterName string, checkForDup bool) bool {
        var accName string
        c.mu.Lock()
        cid := c.cid
        acc := c.acc
        if acc != nil {
                accName = acc.Name
        }
        myRemoteDomain := c.leaf.remoteDomain
        mySrvName := c.leaf.remoteServer
        remoteAccName := c.leaf.remoteAccName
        myClustName := c.leaf.remoteCluster
        remote := c.leaf.remote
        solicited := remote != nil
        c.mu.Unlock()

        var old *client
        s.mu.Lock()
        // We check for empty because in some test we may send empty CONNECT{}
        if checkForDup && srvName != _EMPTY_ {
                for _, ol := range s.leafs {
                        ol.mu.Lock()
                        // We care here only about non solicited Leafnode. This function
                        // is more about replacing stale connections than detecting loops.
                        // We have code for the loop detection elsewhere, which also delays
                        // attempt to reconnect.
                        if !ol.isSolicitedLeafNode() && ol.leaf.remoteServer == srvName &&
                                ol.leaf.remoteCluster == clusterName && ol.acc.Name == accName &&
                                remoteAccName != _EMPTY_ && ol.leaf.remoteAccName == remoteAccName {
                                old = ol
                        }
                        ol.mu.Unlock()
                        if old != nil {
                                break
                        }
                }
        }
        // Now that we are under the server lock and before adding it to the map,
        // for a solicited leaf, we need to make sure that it has not been removed
        // from the config or disabled.
        if solicited {
                // If no longer valid, do not add to the server map. The connection
                // should have been marked so that it can't reconnect. When the caller
                // calls closeConnection(), cleanup (including clearing the connect-
                // in-progress flag) will occur at the appropriate time.
                if !remote.stillValid() {
                        // Prevent reconnect in case it was not yet done.
                        c.setNoReconnect()
                        s.mu.Unlock()
                        s.removeFromTempClients(cid)
                        return false
                }
                remote.setConnectInProgress(false)
        }
        // Store new connection in the map
        s.leafs[cid] = c
        s.mu.Unlock()
        s.removeFromTempClients(cid)

        // If applicable, evict the old one.
        if old != nil {
                old.sendErrAndErr(DuplicateRemoteLeafnodeConnection.String())
                old.closeConnection(DuplicateRemoteLeafnodeConnection)
                c.Warnf("Replacing connection from same server")
        }

        srvDecorated := func() string {
                if myClustName == _EMPTY_ {
                        return mySrvName
                }
                return fmt.Sprintf("%s/%s", mySrvName, myClustName)
        }

        opts := s.getOpts()
        sysAcc := s.SystemAccount()
        js := s.getJetStream()
        var meta *raft
        if js != nil {
                if mg := js.getMetaGroup(); mg != nil {
                        meta = mg.(*raft)
                }
        }
        blockMappingOutgoing := false
        // Deny (non domain) JetStream API traffic unless system account is shared
        // and domain names are identical and extending is not disabled

        // Check if backwards compatibility has been enabled and needs to be acted on
        forceSysAccDeny := false
        if len(opts.JsAccDefaultDomain) > 0 {
                if acc == sysAcc {
                        for _, d := range opts.JsAccDefaultDomain {
                                if d == _EMPTY_ {
                                        // Extending JetStream via leaf node is mutually exclusive with a domain mapping to the empty/default domain.
                                        // As soon as one mapping to "" is found, disable the ability to extend JS via a leaf node.
                                        c.Noticef("Not extending remote JetStream domain %q due to presence of empty default domain", myRemoteDomain)
                                        forceSysAccDeny = true
                                        break
                                }
                        }
                } else if domain, ok := opts.JsAccDefaultDomain[accName]; ok && domain == _EMPTY_ {
                        // for backwards compatibility with old setups that do not have a domain name set
                        c.Debugf("Skipping deny %q for account %q due to default domain", jsAllAPI, accName)
                        return true
                }
        }

        // If the server has JS disabled, it may still be part of a JetStream that could be extended.
        // This is either signaled by js being disabled and a domain set,
        // or in cases where no domain name exists, an extension hint is set.
        // However, this is only relevant in mixed setups.
        //
        // If the system account connects but default domains are present, JetStream can't be extended.
        if opts.JetStreamDomain != myRemoteDomain || (!opts.JetStream && (opts.JetStreamDomain == _EMPTY_ && opts.JetStreamExtHint != jsWillExtend)) ||
                sysAcc == nil || acc == nil || forceSysAccDeny {
                // If domain names mismatch always deny. This applies to system accounts as well as non system accounts.
                // Not having a system account, account or JetStream disabled is considered a mismatch as well.
                if acc != nil && acc == sysAcc {
                        c.Noticef("System account connected from %s", srvDecorated())
                        c.Noticef("JetStream not extended, domains differ")
                        c.mergeDenyPermissionsLocked(both, denyAllJs)
                        // When a remote with a system account is present in a server, unless otherwise disabled, the server will be
                        // started in observer mode. Now that it is clear that this not used, turn the observer mode off.
                        if solicited && meta != nil && meta.IsObserver() {
                                meta.setObserver(false, extNotExtended)
                                c.Debugf("Turning JetStream metadata controller Observer Mode off")
                                // Take note that the domain was not extended to avoid this state from startup.
                                writePeerState(js.config.StoreDir, meta.currentPeerState())
                                // Meta controller can't be leader yet.
                                // Yet it is possible that due to observer mode every server already stopped campaigning.
                                // Therefore this server needs to be kicked into campaigning gear explicitly.
                                meta.Campaign()
                        }
                } else {
                        c.Noticef("JetStream using domains: local %q, remote %q", opts.JetStreamDomain, myRemoteDomain)
                        c.mergeDenyPermissionsLocked(both, denyAllClientJs)
                }
                blockMappingOutgoing = true
        } else if acc == sysAcc {
                // system account and same domain
                s.sys.client.Noticef("Extending JetStream domain %q as System Account connected from server %s",
                        myRemoteDomain, srvDecorated())
                // In an extension use case, pin leadership to server remotes connect to.
                // Therefore, server with a remote that are not already in observer mode, need to be put into it.
                if solicited && meta != nil && !meta.IsObserver() {
                        meta.setObserver(true, extExtended)
                        c.Debugf("Turning JetStream metadata controller Observer Mode on - System Account Connected")
                        // Take note that the domain was not extended to avoid this state next startup.
                        writePeerState(js.config.StoreDir, meta.currentPeerState())
                        // If this server is the leader already, step down so a new leader can be elected (that is not an observer)
                        meta.StepDown()
                }
        } else {
                // This deny is needed in all cases (system account shared or not)
                // If the system account is shared, jsAllAPI traffic will go through the system account.
                // So in order to prevent duplicate delivery (from system and actual account) suppress it on the account.
                // If the system account is NOT shared, jsAllAPI traffic has no business
                c.Debugf("Adding deny %+v for account %q", denyAllClientJs, accName)
                c.mergeDenyPermissionsLocked(both, denyAllClientJs)
        }
        // If we have a specified JetStream domain we will want to add a mapping to
        // allow access cross domain for each non-system account.
        if opts.JetStreamDomain != _EMPTY_ && opts.JetStream && acc != nil && acc != sysAcc {
                for src, dest := range generateJSMappingTable(opts.JetStreamDomain) {
                        if err := acc.AddMapping(src, dest); err != nil {
                                c.Debugf("Error adding JetStream domain mapping: %s", err.Error())
                        } else {
                                c.Debugf("Adding JetStream Domain Mapping %q -> %s to account %q", src, dest, accName)
                        }
                }
                if blockMappingOutgoing {
                        src := fmt.Sprintf(jsDomainAPI, opts.JetStreamDomain)
                        // make sure that messages intended for this domain, do not leave the cluster via this leaf node connection
                        // This is a guard against a miss-config with two identical domain names and will only cover some forms
                        // of this issue, not all of them.
                        // This guards against a hub and a spoke having the same domain name.
                        // But not two spokes having the same one and the request coming from the hub.
                        c.mergeDenyPermissionsLocked(pub, []string{src})
                        c.Debugf("Adding deny %q for outgoing messages to account %q", src, accName)
                }
        }
        return true
}

func (s *Server) removeLeafNodeConnection(c *client) {
        s.mu.Lock()
        c.mu.Lock()
        cid := c.cid
        if c.leaf != nil {
                if c.leaf.tsubt != nil {
                        c.leaf.tsubt.Stop()
                        c.leaf.tsubt = nil
                }
                if c.leaf.gwSub != nil {
                        s.gwLeafSubs.Remove(c.leaf.gwSub)
                        // We need to set this to nil for GC to release the connection
                        c.leaf.gwSub = nil
                }
                if remote := c.leaf.remote; remote != nil {
                        // If "noReconnect" is true, then we won't attempt to reconnect, so
                        // we will clear the "connect-in-progress" flag. However, if we can
                        // reconnect, then we should set "connect-in-progress" to true while
                        // we are under the server/client lock. The go routine that performs
                        // the reconnect will be started later and there would be a gap with
                        // the wrong flag value otherwise.
                        remote.setConnectInProgress(!c.flags.isSet(noReconnect))
                }
        }
        proxyKey := c.proxyKey
        c.mu.Unlock()
        delete(s.leafs, cid)
        if proxyKey != _EMPTY_ {
                s.removeProxiedConn(proxyKey, cid)
        }
        s.mu.Unlock()
        s.removeFromTempClients(cid)
}

// Connect information for solicited leafnodes.
type leafConnectInfo struct {
        Version   string   `json:"version,omitempty"`
        Nkey      string   `json:"nkey,omitempty"`
        JWT       string   `json:"jwt,omitempty"`
        Sig       string   `json:"sig,omitempty"`
        User      string   `json:"user,omitempty"`
        Pass      string   `json:"pass,omitempty"`
        Token     string   `json:"auth_token,omitempty"`
        ID        string   `json:"server_id,omitempty"`
        Domain    string   `json:"domain,omitempty"`
        Name      string   `json:"name,omitempty"`
        Hub       bool     `json:"is_hub,omitempty"`
        Cluster   string   `json:"cluster,omitempty"`
        Headers   bool     `json:"headers,omitempty"`
        JetStream bool     `json:"jetstream,omitempty"`
        DenyPub   []string `json:"deny_pub,omitempty"`
        Isolate   bool     `json:"isolate,omitempty"`

        // There was an existing field called:
        // >> Comp bool `json:"compression,omitempty"`
        // that has never been used. With support for compression, we now need
        // a field that is a string. So we use a different json tag:
        Compression string `json:"compress_mode,omitempty"`

        // Just used to detect wrong connection attempts.
        Gateway string `json:"gateway,omitempty"`

        // Tells the accept side which account the remote is binding to.
        RemoteAccount string `json:"remote_account,omitempty"`

        // The accept side of a LEAF connection, unlike ROUTER and GATEWAY, receives
        // only the CONNECT protocol, and no INFO. So we need to send the protocol
        // version as part of the CONNECT. It will indicate if a connection supports
        // some features, such as message tracing.
        // We use `protocol` as the JSON tag, so this is automatically unmarshal'ed
        // in the low level process CONNECT.
        Proto int `json:"protocol,omitempty"`
}

// processLeafNodeConnect will process the inbound connect args.
// Once we are here we are bound to an account, so can send any interest that
// we would have to the other side.
func (c *client) processLeafNodeConnect(s *Server, arg []byte, lang string) error {
        // Way to detect clients that incorrectly connect to the route listen
        // port. Client provided "lang" in the CONNECT protocol while LEAFNODEs don't.
        if lang != _EMPTY_ {
                c.sendErrAndErr(ErrClientConnectedToLeafNodePort.Error())
                c.closeConnection(WrongPort)
                return ErrClientConnectedToLeafNodePort
        }

        // Unmarshal as a leaf node connect protocol
        proto := &leafConnectInfo{}
        if err := json.Unmarshal(arg, proto); err != nil {
                return err
        }

        // Reject a cluster that contains spaces.
        if proto.Cluster != _EMPTY_ && strings.Contains(proto.Cluster, " ") {
                c.sendErrAndErr(ErrClusterNameHasSpaces.Error())
                c.closeConnection(ProtocolViolation)
                return ErrClusterNameHasSpaces
        }

        // Check for cluster name collisions.
        if cn := s.cachedClusterName(); cn != _EMPTY_ && proto.Cluster != _EMPTY_ && proto.Cluster == cn {
                c.sendErrAndErr(ErrLeafNodeHasSameClusterName.Error())
                c.closeConnection(ClusterNamesIdentical)
                return ErrLeafNodeHasSameClusterName
        }

        // Reject if this has Gateway which means that it would be from a gateway
        // connection that incorrectly connects to the leafnode port.
        if proto.Gateway != _EMPTY_ {
                errTxt := fmt.Sprintf("Rejecting connection from gateway %q on the leafnode port", proto.Gateway)
                c.Errorf(errTxt)
                c.sendErr(errTxt)
                c.closeConnection(WrongGateway)
                return ErrWrongGateway
        }

        if mv := s.getOpts().LeafNode.MinVersion; mv != _EMPTY_ {
                major, minor, update, _ := versionComponents(mv)
                if !versionAtLeast(proto.Version, major, minor, update) {
                        // Send back an INFO so recent remote servers process the rejection
                        // cleanly, then close immediately. The soliciting side applies the
                        // reconnect delay when it processes the error.
                        s.sendPermsAndAccountInfo(c)
                        c.sendErrAndErr(fmt.Sprintf("%s %q", ErrLeafNodeMinVersionRejected, mv))
                        c.closeConnection(MinimumVersionRequired)
                        return ErrMinimumVersionRequired
                }
        }

        // Check if this server supports headers.
        supportHeaders := c.srv.supportsHeaders()

        c.mu.Lock()
        // Leaf Nodes do not do echo or verbose or pedantic.
        c.opts.Verbose = false
        c.opts.Echo = false
        c.opts.Pedantic = false
        // This inbound connection will be marked as supporting headers if this server
        // support headers and the remote has sent in the CONNECT protocol that it does
        // support headers too.
        c.headers = supportHeaders && proto.Headers
        // If the compression level is still not set, set it based on what has been
        // given to us in the CONNECT protocol.
        if c.leaf.compression == _EMPTY_ {
                // But if proto.Compression is _EMPTY_, set it to CompressionNotSupported
                if proto.Compression == _EMPTY_ {
                        c.leaf.compression = CompressionNotSupported
                } else {
                        c.leaf.compression = proto.Compression
                }
        }

        // Remember the remote server.
        c.leaf.remoteServer = proto.Name
        // Remember the remote account name
        c.leaf.remoteAccName = proto.RemoteAccount
        // Remember if the leafnode requested isolation.
        c.leaf.isolated = c.leaf.isolated || proto.Isolate

        // If the other side has declared itself a hub, so we will take on the spoke role.
        if proto.Hub {
                c.leaf.isSpoke = true
        }

        // The soliciting side is part of a cluster.
        if proto.Cluster != _EMPTY_ {
                c.leaf.remoteCluster = proto.Cluster
        }

        c.leaf.remoteDomain = proto.Domain

        // When a leaf solicits a connection to a hub, the perms that it will use on the soliciting leafnode's
        // behalf are correct for them, but inside the hub need to be reversed since data is flowing in the opposite direction.
        if !c.isSolicitedLeafNode() && c.perms != nil {
                sp, pp := c.perms.sub, c.perms.pub
                c.perms.sub, c.perms.pub = pp, sp
                if c.opts.Import != nil {
                        c.darray = c.opts.Import.Deny
                } else {
                        c.darray = nil
                }
        }

        // Set the Ping timer
        c.setFirstPingTimer()

        // If we received pub deny permissions from the other end, merge with existing ones.
        c.mergeDenyPermissions(pub, proto.DenyPub)

        acc := c.acc
        c.mu.Unlock()

        // If the account is not set (e.g. connection was closed due to auth
        // timeout while still being processed), bail out to avoid a panic.
        if acc == nil {
                c.closeConnection(MissingAccount)
                return ErrMissingAccount
        }

        // Register the cluster, even if empty, as long as we are acting as a hub.
        if !proto.Hub {
                acc.registerLeafNodeCluster(proto.Cluster)
        }

        // Add in the leafnode here since we passed through auth at this point.
        s.addLeafNodeConnection(c, proto.Name, proto.Cluster, true)

        // If we have permissions bound to this leafnode we need to send then back to the
        // origin server for local enforcement.
        s.sendPermsAndAccountInfo(c)

        // Create and initialize the smap since we know our bound account now.
        // This will send all registered subs too.
        s.initLeafNodeSmapAndSendSubs(c)

        // Announce the account connect event for a leaf node.
        // This will be a no-op as needed.
        s.sendLeafNodeConnect(c.acc)

        // Check to see if we need to kick any internal source or mirror consumers.
        // This will be a no-op if JetStream not enabled for this server or if the bound account
        // does not have jetstream.
        s.checkInternalSyncConsumers(acc)

        return nil
}

// checkInternalSyncConsumers
func (s *Server) checkInternalSyncConsumers(acc *Account) {
        // Grab our js
        js := s.getJetStream()

        // Only applicable if we have JS and the leafnode has JS as well.
        // We check for remote JS outside.
        if !js.isEnabled() || acc == nil {
                return
        }

        // We will check all streams in our local account. They must be a leader and
        // be sourcing or mirroring. We will check the external config on the stream itself
        // if this is cross domain, or if the remote domain is empty, meaning we might be
        // extending the system across this leafnode connection and hence we would be extending
        // our own domain.
        jsa := js.lookupAccount(acc)
        if jsa == nil {
                return
        }

        var streams []*stream
        jsa.mu.RLock()
        for _, mset := range jsa.streams {
                mset.cfgMu.RLock()
                // We need to have a mirror or source defined.
                // We do not want to force another lock here to look for leader status,
                // so collect and after we release jsa will make sure.
                if mset.cfg.Mirror != nil || len(mset.cfg.Sources) > 0 {
                        streams = append(streams, mset)
                }
                mset.cfgMu.RUnlock()
        }
        jsa.mu.RUnlock()

        // Now loop through all candidates and check if we are the leader and have NOT
        // created the sync up consumer.
        for _, mset := range streams {
                mset.retryDisconnectedSyncConsumers()
        }
}

// Returns the remote cluster name. This is set only once so does not require a lock.
func (c *client) remoteCluster() string {
        if c.leaf == nil {
                return _EMPTY_
        }
        return c.leaf.remoteCluster
}

// Sends back an info block to the soliciting leafnode to let it know about
// its permission settings for local enforcement.
func (s *Server) sendPermsAndAccountInfo(c *client) {
        // Copy
        s.mu.Lock()
        info := s.copyLeafNodeInfo()
        s.mu.Unlock()
        c.mu.Lock()
        info.CID = c.cid
        info.Import = c.opts.Import
        info.Export = c.opts.Export
        info.RemoteAccount = c.acc.Name
        // s.SystemAccount() uses an atomic operation and does not get the server lock, so this is safe.
        info.IsSystemAccount = c.acc == s.SystemAccount()
        info.ConnectInfo = true
        c.enqueueProto(generateInfoJSON(info))
        c.mu.Unlock()
}

// Snapshot the current subscriptions from the sublist into our smap which
// we will keep updated from now on.
// Also send the registered subscriptions.
func (s *Server) initLeafNodeSmapAndSendSubs(c *client) {
        acc := c.acc
        if acc == nil {
                c.Debugf("Leafnode does not have an account bound")
                return
        }
        // Collect all account subs here.
        _subs := [1024]*subscription{}
        subs := _subs[:0]
        ims := []string{}

        // Hold the client lock otherwise there can be a race and miss some subs.
        c.mu.Lock()
        defer c.mu.Unlock()

        acc.mu.RLock()
        accName := acc.Name
        accNTag := acc.nameTag

        // To make printing look better when no friendly name present.
        if accNTag != _EMPTY_ {
                accNTag = "/" + accNTag
        }

        // If we are solicited we only send interest for local clients.
        if c.isSpokeLeafNode() {
                acc.sl.localSubs(&subs, true)
        } else {
                acc.sl.All(&subs)
        }

        // Check if we have an existing service import reply.
        siReply := copyBytes(acc.siReply)

        // Since leaf nodes only send on interest, if the bound
        // account has import services we need to send those over.
        for isubj := range acc.imports.services {
                if c.isSpokeLeafNode() && !c.canSubscribe(isubj) {
                        c.Debugf("Not permitted to import service %q on behalf of %s%s", isubj, accName, accNTag)
                        continue
                }
                ims = append(ims, isubj)
        }
        // Likewise for mappings.
        for _, m := range acc.mappings {
                if c.isSpokeLeafNode() && !c.canSubscribe(m.src) {
                        c.Debugf("Not permitted to import mapping %q on behalf of %s%s", m.src, accName, accNTag)
                        continue
                }
                ims = append(ims, m.src)
        }

        // Create a unique subject that will be used for loop detection.
        lds := acc.lds
        acc.mu.RUnlock()

        // Check if we have to create the LDS.
        if lds == _EMPTY_ {
                lds = leafNodeLoopDetectionSubjectPrefix + nuid.Next()
                acc.mu.Lock()
                acc.lds = lds
                acc.mu.Unlock()
        }

        // Now check for gateway interest. Leafnodes will put this into
        // the proper mode to propagate, but they are not held in the account.
        gwsa := [16]*client{}
        gws := gwsa[:0]
        s.getOutboundGatewayConnections(&gws)
        for _, cgw := range gws {
                cgw.mu.Lock()
                gw := cgw.gw
                cgw.mu.Unlock()
                if gw != nil {
                        if ei, _ := gw.outsim.Load(accName); ei != nil {
                                if e := ei.(*outsie); e != nil && e.sl != nil {
                                        e.sl.All(&subs)
                                }
                        }
                }
        }

        applyGlobalRouting := s.gateway.enabled
        if c.isSpokeLeafNode() {
                // Add a fake subscription for this solicited leafnode connection
                // so that we can send back directly for mapped GW replies.
                // We need to keep track of this subscription so it can be removed
                // when the connection is closed so that the GC can release it.
                c.leaf.gwSub = &subscription{client: c, subject: []byte(gwReplyPrefix + ">")}
                c.srv.gwLeafSubs.Insert(c.leaf.gwSub)
        }

        // Now walk the results and add them to our smap
        rc := c.leaf.remoteCluster
        c.leaf.smap = make(map[string]int32)
        for _, sub := range subs {
                // Check perms regardless of role.
                if c.perms != nil && !c.canSubscribe(string(sub.subject)) {
                        c.Debugf("Not permitted to subscribe to %q on behalf of %s%s", sub.subject, accName, accNTag)
                        continue
                }
                // Don't advertise interest from leafnodes to other isolated leafnodes.
                if sub.client.kind == LEAF && c.isIsolatedLeafNode() {
                        continue
                }
                // We ignore ourselves here.
                // Also don't add the subscription if it has a origin cluster and the
                // cluster name matches the one of the client we are sending to.
                if c != sub.client && (sub.origin == nil || (bytesToString(sub.origin) != rc)) {
                        count := int32(1)
                        if len(sub.queue) > 0 && sub.qw > 0 {
                                count = sub.qw
                        }
                        c.leaf.smap[keyFromSub(sub)] += count
                        if c.leaf.tsub == nil {
                                c.leaf.tsub = make(map[*subscription]struct{})
                        }
                        c.leaf.tsub[sub] = struct{}{}
                }
        }
        // FIXME(dlc) - We need to update appropriately on an account claims update.
        for _, isubj := range ims {
                c.leaf.smap[isubj]++
        }
        // If we have gateways enabled we need to make sure the other side sends us responses
        // that have been augmented from the original subscription.
        // TODO(dlc) - Should we lock this down more?
        if applyGlobalRouting {
                c.leaf.smap[oldGWReplyPrefix+"*.>"]++
                c.leaf.smap[gwReplyPrefix+">"]++
        }
        // Detect loops by subscribing to a specific subject and checking
        // if this sub is coming back to us.
        c.leaf.smap[lds]++

        // Check if we need to add an existing siReply to our map.
        // This will be a prefix so add on the wildcard.
        if siReply != nil {
                wcsub := append(siReply, '>')
                c.leaf.smap[string(wcsub)]++
        }
        // Queue all protocols. There is no max pending limit for LN connection,
        // so we don't need chunking. The writes will happen from the writeLoop.
        var b bytes.Buffer
        for key, n := range c.leaf.smap {
                c.writeLeafSub(&b, key, n)
        }
        if b.Len() > 0 {
                c.enqueueProto(b.Bytes())
        }
        if c.leaf.tsub != nil {
                // Clear the tsub map after 5 seconds.
                c.leaf.tsubt = time.AfterFunc(5*time.Second, func() {
                        c.mu.Lock()
                        if c.leaf != nil {
                                c.leaf.tsub = nil
                                c.leaf.tsubt = nil
                        }
                        c.mu.Unlock()
                })
        }
}

// updateInterestForAccountOnGateway called from gateway code when processing RS+ and RS-.
func (s *Server) updateInterestForAccountOnGateway(accName string, sub *subscription, delta int32) {
        // Since we're in the gateway's readLoop, and we would otherwise block, don't allow fetching.
        acc, err := s.lookupOrFetchAccount(accName, false)
        if acc == nil || err != nil {
                s.Debugf("No or bad account for %q, failed to update interest from gateway", accName)
                return
        }
        acc.updateLeafNodes(sub, delta)
}

// updateLeafNodesEx will make sure to update the account smap for the subscription.
// Will also forward to all leaf nodes as needed.
// If `hubOnly` is true, then will update only leaf nodes that connect to this server
// (that is, for which this server acts as a hub to them).
func (acc *Account) updateLeafNodesEx(sub *subscription, delta int32, hubOnly bool) {
        if acc == nil || sub == nil {
                return
        }

        // We will do checks for no leafnodes and same cluster here inline and under the
        // general account read lock.
        // If we feel we need to update the leafnodes we will do that out of line to avoid
        // blocking routes or GWs.

        acc.mu.RLock()
        // First check if we even have leafnodes here.
        if acc.nleafs == 0 {
                acc.mu.RUnlock()
                return
        }

        // Is this a loop detection subject.
        isLDS := bytes.HasPrefix(sub.subject, []byte(leafNodeLoopDetectionSubjectPrefix))

        // Capture the cluster even if its empty.
        var cluster string
        if sub.origin != nil {
                cluster = bytesToString(sub.origin)
        }

        // If we have an isolated cluster we can return early, as long as it is not a loop detection subject.
        // Empty clusters will return false for the check.
        if !isLDS && acc.isLeafNodeClusterIsolated(cluster) {
                acc.mu.RUnlock()
                return
        }

        // We can release the general account lock.
        acc.mu.RUnlock()

        // We can hold the list lock here to avoid having to copy a large slice.
        acc.lmu.RLock()
        defer acc.lmu.RUnlock()

        // Do this once.
        subject := string(sub.subject)

        // Walk the connected leafnodes from a random starting point to avoid
        // concurrent callers all contending over leafs in the same order.
        nleafs := len(acc.lleafs)
        start := 0
        if nleafs > 1 {
                start = rand.Intn(nleafs)
        }
        for i := 0; i < nleafs; i++ {
                ln := acc.lleafs[(start+i)%nleafs]
                if ln == sub.client {
                        continue
                }
                ln.mu.RLock()
                // Don't advertise interest from leafnodes to other isolated leafnodes.
                if sub.client.kind == LEAF && ln.isIsolatedLeafNode() {
                        ln.mu.RUnlock()
                        continue
                }
                // If `hubOnly` is true, it means that we want to update only leafnodes
                // that connect to this server (so isHubLeafNode() would return `true`).
                if hubOnly && !ln.isHubLeafNode() {
                        ln.mu.RUnlock()
                        continue
                }
                // Check to make sure this sub does not have an origin cluster that matches the leafnode.
                // If skipped, make sure that we still let go the "$LDS." subscription that allows
                // the detection of loops as long as different cluster.
                clusterDifferent := cluster != ln.remoteCluster()
                update := (isLDS && clusterDifferent) ||
                        ((cluster == _EMPTY_ || clusterDifferent) && (delta <= 0 || ln.canSubscribeInternal(subject)))
                ln.mu.RUnlock()
                if update {
                        ln.mu.Lock()
                        // The leaf role, isolation mode, and remote cluster are stable
                        // for the connection. Recheck canSubscribe here since permissions
                        // can change, and to initializes mperms for wildcard subscriptions
                        // that collide with deny rules.
                        if isLDS || delta <= 0 || ln.canSubscribe(subject) {
                                ln.updateSmap(sub, delta, isLDS)
                        }
                        ln.mu.Unlock()
                }
        }
}

// updateLeafNodes will make sure to update the account smap for the subscription.
// Will also forward to all leaf nodes as needed.
func (acc *Account) updateLeafNodes(sub *subscription, delta int32) {
        acc.updateLeafNodesEx(sub, delta, false)
}

// This will make an update to our internal smap and determine if we should send out
// an interest update to the remote side.
// Lock should be held.
func (c *client) updateSmap(sub *subscription, delta int32, isLDS bool) {
        if c.leaf.smap == nil {
                return
        }

        // If we are solicited make sure this is a local client or a non-solicited leaf node
        skind := sub.client.kind
        updateClient := skind == CLIENT || skind == SYSTEM || skind == JETSTREAM || skind == ACCOUNT
        if !isLDS && c.isSpokeLeafNode() && !(updateClient || (skind == LEAF && !sub.client.isSpokeLeafNode())) {
                return
        }

        // For additions, check if that sub has just been processed during initLeafNodeSmapAndSendSubs
        if delta > 0 && c.leaf.tsub != nil {
                if _, present := c.leaf.tsub[sub]; present {
                        delete(c.leaf.tsub, sub)
                        if len(c.leaf.tsub) == 0 {
                                c.leaf.tsub = nil
                                c.leaf.tsubt.Stop()
                                c.leaf.tsubt = nil
                        }
                        return
                }
        }

        key := keyFromSub(sub)
        n, ok := c.leaf.smap[key]
        if delta < 0 && !ok {
                return
        }

        // We will update if its a queue, if count is zero (or negative), or we were 0 and are N > 0.
        update := sub.queue != nil || (n <= 0 && n+delta > 0) || (n > 0 && n+delta <= 0)
        n += delta
        if n > 0 {
                c.leaf.smap[key] = n
        } else {
                delete(c.leaf.smap, key)
        }
        if update {
                c.sendLeafNodeSubUpdate(key, n)
        }
}

// Used to force add subjects to the subject map.
func (c *client) forceAddToSmap(subj string) {
        c.mu.Lock()
        defer c.mu.Unlock()

        if c.leaf.smap == nil {
                return
        }
        n := c.leaf.smap[subj]
        if n != 0 {
                return
        }
        // Place into the map since it was not there.
        c.leaf.smap[subj] = 1
        c.sendLeafNodeSubUpdate(subj, 1)
}

// Used to force remove a subject from the subject map.
func (c *client) forceRemoveFromSmap(subj string) {
        c.mu.Lock()
        defer c.mu.Unlock()

        if c.leaf.smap == nil {
                return
        }
        n := c.leaf.smap[subj]
        if n == 0 {
                return
        }
        n--
        if n == 0 {
                // Remove is now zero
                delete(c.leaf.smap, subj)
                c.sendLeafNodeSubUpdate(subj, 0)
        } else {
                c.leaf.smap[subj] = n
        }
}

// Send the subscription interest change to the other side.
// Lock should be held.
func (c *client) sendLeafNodeSubUpdate(key string, n int32) {
        // If we are a spoke, we need to check if we are allowed to send this subscription over to the hub.
        if c.isSpokeLeafNode() {
                checkPerms := true
                if len(key) > 0 && (key[0] == '$' || key[0] == '_') {
                        if strings.HasPrefix(key, leafNodeLoopDetectionSubjectPrefix) ||
                                strings.HasPrefix(key, oldGWReplyPrefix) ||
                                strings.HasPrefix(key, gwReplyPrefix) {
                                checkPerms = false
                        }
                }
                if checkPerms {
                        var subject string
                        if sep := strings.IndexByte(key, ' '); sep != -1 {
                                subject = key[:sep]
                        } else {
                                subject = key
                        }
                        if !c.canSubscribe(subject) {
                                return
                        }
                }
        }
        // If we are here we can send over to the other side.
        _b := [64]byte{}
        b := bytes.NewBuffer(_b[:0])
        c.writeLeafSub(b, key, n)
        c.enqueueProto(b.Bytes())
}

// Helper function to build the key.
func keyFromSub(sub *subscription) string {
        var sb strings.Builder
        sb.Grow(len(sub.subject) + len(sub.queue) + 1)
        sb.Write(sub.subject)
        if sub.queue != nil {
                // Just make the key subject spc group, e.g. 'foo bar'
                sb.WriteByte(' ')
                sb.Write(sub.queue)
        }
        return sb.String()
}

const (
        keyRoutedSub         = "R"
        keyRoutedSubByte     = 'R'
        keyRoutedLeafSub     = "L"
        keyRoutedLeafSubByte = 'L'
)

// Helper function to build the key that prevents collisions between normal
// routed subscriptions and routed subscriptions on behalf of a leafnode.
// Keys will look like this:
// "R foo"          -> plain routed sub on "foo"
// "R foo bar"      -> queue routed sub on "foo", queue "bar"
// "L foo bar"      -> plain routed leaf sub on "foo", leaf "bar"
// "L foo bar baz"  -> queue routed sub on "foo", queue "bar", leaf "baz"
func keyFromSubWithOrigin(sub *subscription) string {
        var sb strings.Builder
        sb.Grow(2 + len(sub.origin) + 1 + len(sub.subject) + 1 + len(sub.queue))
        leaf := len(sub.origin) > 0
        if leaf {
                sb.WriteByte(keyRoutedLeafSubByte)
        } else {
                sb.WriteByte(keyRoutedSubByte)
        }
        sb.WriteByte(' ')
        sb.Write(sub.subject)
        if sub.queue != nil {
                sb.WriteByte(' ')
                sb.Write(sub.queue)
        }
        if leaf {
                sb.WriteByte(' ')
                sb.Write(sub.origin)
        }
        return sb.String()
}

// Lock should be held.
func (c *client) writeLeafSub(w *bytes.Buffer, key string, n int32) {
        if key == _EMPTY_ {
                return
        }
        if n > 0 {
                w.WriteString("LS+ " + key)
                // Check for queue semantics, if found write n.
                if strings.Contains(key, " ") {
                        w.WriteString(" ")
                        var b [12]byte
                        var i = len(b)
                        for l := n; l > 0; l /= 10 {
                                i--
                                b[i] = digits[l%10]
                        }
                        w.Write(b[i:])
                        if c.trace {
                                arg := fmt.Sprintf("%s %d", key, n)
                                c.traceOutOp("LS+", []byte(arg))
                        }
                } else if c.trace {
                        c.traceOutOp("LS+", []byte(key))
                }
        } else {
                w.WriteString("LS- " + key)
                if c.trace {
                        c.traceOutOp("LS-", []byte(key))
                }
        }
        w.WriteString(CR_LF)
}

// processLeafSub will process an inbound sub request for the remote leaf node.
func (c *client) processLeafSub(argo []byte) (err error) {
        // Indicate activity.
        c.in.subs++

        srv := c.srv
        if srv == nil {
                return nil
        }

        // Copy so we do not reference a potentially large buffer
        arg := make([]byte, len(argo))
        copy(arg, argo)

        args := splitArg(arg)
        sub := &subscription{client: c}

        delta := int32(1)
        switch len(args) {
        case 1:
                sub.queue = nil
        case 3:
                sub.queue = args[1]
                sub.qw = int32(parseSize(args[2]))
                // TODO: (ik) We should have a non empty queue name and a queue
                // weight >= 1. For 2.11, we may want to return an error if that
                // is not the case, but for now just overwrite `delta` if queue
                // weight is greater than 1 (it is possible after a reconnect/
                // server restart to receive a queue weight > 1 for a new sub).
                if sub.qw > 1 {
                        delta = sub.qw
                }
        default:
                return fmt.Errorf("processLeafSub Parse Error: '%s'", arg)
        }
        sub.subject = args[0]

        c.mu.Lock()
        if c.isClosed() {
                c.mu.Unlock()
                return nil
        }

        acc := c.acc
        // Guard against LS+ arriving before CONNECT has been processed, which
        // can happen when compression is enabled.
        if acc == nil {
                c.mu.Unlock()
                c.sendErr("Authorization Violation")
                c.closeConnection(ProtocolViolation)
                return nil
        }
        // Check if we have a loop.
        ldsPrefix := bytes.HasPrefix(sub.subject, []byte(leafNodeLoopDetectionSubjectPrefix))

        if ldsPrefix && bytesToString(sub.subject) == acc.getLDSubject() {
                c.mu.Unlock()
                c.handleLeafNodeLoop(true)
                return nil
        }

        // Check permissions if applicable. (but exclude the $LDS, $GR and _GR_)
        checkPerms := true
        if sub.subject[0] == '$' || sub.subject[0] == '_' {
                if ldsPrefix ||
                        bytes.HasPrefix(sub.subject, []byte(oldGWReplyPrefix)) ||
                        bytes.HasPrefix(sub.subject, []byte(gwReplyPrefix)) {
                        checkPerms = false
                }
        }

        // If we are a hub check that we can publish to this subject.
        if checkPerms {
                subj := string(sub.subject)
                if subjectIsLiteral(subj) && !c.pubAllowedFullCheck(subj, true, true) {
                        c.mu.Unlock()
                        c.leafSubPermViolation(sub.subject)
                        c.Debugf(fmt.Sprintf("Permissions Violation for Subscription to %q", sub.subject))
                        return nil
                }
        }

        // Check if we have a maximum on the number of subscriptions.
        if c.subsAtLimit() {
                c.mu.Unlock()
                c.maxSubsExceeded()
                return nil
        }

        // If we have an origin cluster associated mark that in the sub.
        if rc := c.remoteCluster(); rc != _EMPTY_ {
                sub.origin = []byte(rc)
        }

        // Like Routes, we store local subs by account and subject and optionally queue name.
        // If we have a queue it will have a trailing weight which we do not want.
        if sub.queue != nil {
                sub.sid = arg[:len(arg)-len(args[2])-1]
        } else {
                sub.sid = arg
        }
        key := bytesToString(sub.sid)
        osub := c.subs[key]
        if osub == nil {
                c.subs[key] = sub
                // Now place into the account sl.
                if err := acc.sl.Insert(sub); err != nil {
                        delete(c.subs, key)
                        c.mu.Unlock()
                        c.Errorf("Could not insert subscription: %v", err)
                        c.sendErr("Invalid Subscription")
                        return nil
                }
        } else if sub.queue != nil {
                // For a queue we need to update the weight.
                delta = sub.qw - atomic.LoadInt32(&osub.qw)
                atomic.StoreInt32(&osub.qw, sub.qw)
                acc.sl.UpdateRemoteQSub(osub)
        }
        spoke := c.isSpokeLeafNode()
        c.mu.Unlock()

        // Only add in shadow subs if a new sub or qsub.
        if osub == nil {
                if err := c.addShadowSubscriptions(acc, sub); err != nil {
                        c.Errorf(err.Error())
                }
        }

        // If we are not solicited, treat leaf node subscriptions similar to a
        // client subscription, meaning we forward them to routes, gateways and
        // other leaf nodes as needed.
        if !spoke {
                // If we are routing add to the route map for the associated account.
                srv.updateRouteSubscriptionMap(acc, sub, delta)
                if srv.gateway.enabled {
                        srv.gatewayUpdateSubInterest(acc.Name, sub, delta)
                }
        }
        // Now check on leafnode updates for other leaf nodes. We understand solicited
        // and non-solicited state in this call so we will do the right thing.
        acc.updateLeafNodes(sub, delta)

        return nil
}

// If the leafnode is a solicited, set the connect delay based on default
// or private option (for tests). Sends the error to the other side, log and
// close the connection.
func (c *client) handleLeafNodeLoop(sendErr bool) {
        accName, delay := c.setLeafConnectDelayIfSoliciting(leafNodeReconnectDelayAfterLoopDetected)
        errTxt := fmt.Sprintf("Loop detected for leafnode account=%q. Delaying attempt to reconnect for %v", accName, delay)
        if sendErr {
                c.sendErr(errTxt)
        }

        c.Errorf(errTxt)
        // If we are here with "sendErr" false, it means that this is the server
        // that received the error. The other side will have closed the connection,
        // but does not hurt to close here too.
        c.closeConnection(ProtocolViolation)
}

// processLeafUnsub will process an inbound unsub request for the remote leaf node.
func (c *client) processLeafUnsub(arg []byte) error {
        // Indicate any activity, so pub and sub or unsubs.
        c.in.subs++

        srv := c.srv

        c.mu.Lock()
        if c.isClosed() {
                c.mu.Unlock()
                return nil
        }

        acc := c.acc
        // Guard against LS- arriving before CONNECT has been processed.
        if acc == nil {
                c.mu.Unlock()
                c.sendErr("Authorization Violation")
                c.closeConnection(ProtocolViolation)
                return nil
        }

        spoke := c.isSpokeLeafNode()
        // We store local subs by account and subject and optionally queue name.
        // LS- will have the arg exactly as the key.
        sub, ok := c.subs[string(arg)]
        if !ok {
                // If not found, don't try to update routes/gws/leaf nodes.
                c.mu.Unlock()
                return nil
        }
        delta := int32(1)
        if len(sub.queue) > 0 {
                delta = sub.qw
        }
        c.mu.Unlock()

        c.unsubscribe(acc, sub, true, true)
        if !spoke {
                // If we are routing subtract from the route map for the associated account.
                srv.updateRouteSubscriptionMap(acc, sub, -delta)
                // Gateways
                if srv.gateway.enabled {
                        srv.gatewayUpdateSubInterest(acc.Name, sub, -delta)
                }
        }
        // Now check on leafnode updates for other leaf nodes.
        acc.updateLeafNodes(sub, -delta)
        return nil
}

func (c *client) processLeafHeaderMsgArgs(arg []byte) error {
        // Unroll splitArgs to avoid runtime/heap issues
        args := c.argsa[:0]
        start := -1
        for i, b := range arg {
                switch b {
                case ' ', '\t', '\r', '\n':
                        if start >= 0 {
                                args = append(args, arg[start:i])
                                start = -1
                        }
                default:
                        if start < 0 {
                                start = i
                        }
                }
        }
        if start >= 0 {
                args = append(args, arg[start:])
        }

        c.pa.arg = arg
        switch len(args) {
        case 0, 1, 2:
                return fmt.Errorf("processLeafHeaderMsgArgs Parse Error: '%s'", args)
        case 3:
                c.pa.reply = nil
                c.pa.queues = nil
                c.pa.hdb = args[1]
                c.pa.hdr = parseSize(args[1])
                c.pa.szb = args[2]
                c.pa.size = parseSize(args[2])
        case 4:
                c.pa.reply = args[1]
                c.pa.queues = nil
                c.pa.hdb = args[2]
                c.pa.hdr = parseSize(args[2])
                c.pa.szb = args[3]
                c.pa.size = parseSize(args[3])
        default:
                // args[1] is our reply indicator. Should be + or | normally.
                if len(args[1]) != 1 {
                        return fmt.Errorf("processLeafHeaderMsgArgs Bad or Missing Reply Indicator: '%s'", args[1])
                }
                switch args[1][0] {
                case '+':
                        c.pa.reply = args[2]
                case '|':
                        c.pa.reply = nil
                default:
                        return fmt.Errorf("processLeafHeaderMsgArgs Bad or Missing Reply Indicator: '%s'", args[1])
                }
                // Grab header size.
                c.pa.hdb = args[len(args)-2]
                c.pa.hdr = parseSize(c.pa.hdb)

                // Grab size.
                c.pa.szb = args[len(args)-1]
                c.pa.size = parseSize(c.pa.szb)

                // Grab queue names.
                if c.pa.reply != nil {
                        c.pa.queues = args[3 : len(args)-2]
                } else {
                        c.pa.queues = args[2 : len(args)-2]
                }
        }
        if c.pa.hdr < 0 {
                return fmt.Errorf("processLeafHeaderMsgArgs Bad or Missing Header Size: '%s'", arg)
        }
        if c.pa.size < 0 {
                return fmt.Errorf("processLeafHeaderMsgArgs Bad or Missing Size: '%s'", args)
        }
        if c.pa.hdr > c.pa.size {
                return fmt.Errorf("processLeafHeaderMsgArgs Header Size larger then TotalSize: '%s'", arg)
        }
        maxPayload := atomic.LoadInt32(&c.mpay)
        if maxPayload != jwt.NoLimit && int64(c.pa.size) > int64(maxPayload) {
                c.maxPayloadViolation(c.pa.size, maxPayload)
                return ErrMaxPayload
        }

        // Common ones processed after check for arg length
        c.pa.subject = args[0]

        return nil
}

func (c *client) processLeafMsgArgs(arg []byte) error {
        // Unroll splitArgs to avoid runtime/heap issues
        args := c.argsa[:0]
        start := -1
        for i, b := range arg {
                switch b {
                case ' ', '\t', '\r', '\n':
                        if start >= 0 {
                                args = append(args, arg[start:i])
                                start = -1
                        }
                default:
                        if start < 0 {
                                start = i
                        }
                }
        }
        if start >= 0 {
                args = append(args, arg[start:])
        }

        c.pa.arg = arg
        switch len(args) {
        case 0, 1:
                return fmt.Errorf("processLeafMsgArgs Parse Error: '%s'", args)
        case 2:
                c.pa.reply = nil
                c.pa.queues = nil
                c.pa.szb = args[1]
                c.pa.size = parseSize(args[1])
        case 3:
                c.pa.reply = args[1]
                c.pa.queues = nil
                c.pa.szb = args[2]
                c.pa.size = parseSize(args[2])
        default:
                // args[1] is our reply indicator. Should be + or | normally.
                if len(args[1]) != 1 {
                        return fmt.Errorf("processLeafMsgArgs Bad or Missing Reply Indicator: '%s'", args[1])
                }
                switch args[1][0] {
                case '+':
                        c.pa.reply = args[2]
                case '|':
                        c.pa.reply = nil
                default:
                        return fmt.Errorf("processLeafMsgArgs Bad or Missing Reply Indicator: '%s'", args[1])
                }
                // Grab size.
                c.pa.szb = args[len(args)-1]
                c.pa.size = parseSize(c.pa.szb)

                // Grab queue names.
                if c.pa.reply != nil {
                        c.pa.queues = args[3 : len(args)-1]
                } else {
                        c.pa.queues = args[2 : len(args)-1]
                }
        }
        if c.pa.size < 0 {
                return fmt.Errorf("processLeafMsgArgs Bad or Missing Size: '%s'", args)
        }
        maxPayload := atomic.LoadInt32(&c.mpay)
        if maxPayload != jwt.NoLimit && int64(c.pa.size) > int64(maxPayload) {
                c.maxPayloadViolation(c.pa.size, maxPayload)
                return ErrMaxPayload
        }

        // Common ones processed after check for arg length
        c.pa.subject = args[0]

        return nil
}

// processInboundLeafMsg is called to process an inbound msg from a leaf node.
func (c *client) processInboundLeafMsg(msg []byte) {
        // Update statistics
        // The msg includes the CR_LF, so pull back out for accounting.
        c.in.msgs++
        c.in.bytes += int32(len(msg) - LEN_CR_LF)

        srv, acc, subject := c.srv, c.acc, string(c.pa.subject)

        // Mostly under testing scenarios.
        if srv == nil || acc == nil {
                return
        }

        // Check that leaf messages respect the subject permissions.
        if c.perms != nil && !c.leafMsgAllowed() {
                c.leafPubPermViolation(c.pa.subject)
                return
        }

        // Match the subscriptions. We will use our own L1 map if
        // it's still valid, avoiding contention on the shared sublist.
        var r *SublistResult
        var ok bool

        genid := atomic.LoadUint64(&c.acc.sl.genid)
        if genid == c.in.genid && c.in.results != nil {
                r, ok = c.in.results[subject]
        } else {
                // Reset our L1 completely.
                c.in.results = make(map[string]*SublistResult)
                c.in.genid = genid
        }

        // Go back to the sublist data structure.
        if !ok {
                r = c.acc.sl.Match(subject)
                // Prune the results cache. Keeps us from unbounded growth. Random delete.
                if len(c.in.results) >= maxResultCacheSize {
                        n := 0
                        for subj := range c.in.results {
                                delete(c.in.results, subj)
                                if n++; n > pruneSize {
                                        break
                                }
                        }
                }
                // Then add the new cache entry.
                c.in.results[subject] = r
        }

        // Collect queue names if needed.
        var qnames [][]byte

        // Check for no interest, short circuit if so.
        // This is the fanout scale.
        if len(r.psubs)+len(r.qsubs) > 0 {
                flag := pmrNoFlag
                // If we have queue subs in this cluster, then if we run in gateway
                // mode and the remote gateways have queue subs, then we need to
                // collect the queue groups this message was sent to so that we
                // exclude them when sending to gateways.
                if len(r.qsubs) > 0 && c.srv.gateway.enabled &&
                        atomic.LoadInt64(&c.srv.gateway.totalQSubs) > 0 {
                        flag |= pmrCollectQueueNames
                }
                // If this is a mapped subject that means the mapped interest
                // is what got us here, but this might not have a queue designation
                // If that is the case, make sure we ignore to process local queue subscribers.
                if len(c.pa.mapped) > 0 && len(c.pa.queues) == 0 {
                        flag |= pmrIgnoreEmptyQueueFilter
                }
                _, qnames = c.processMsgResults(acc, r, msg, nil, c.pa.subject, c.pa.reply, flag)
        }

        // Now deal with gateways
        if c.srv.gateway.enabled {
                c.sendMsgToGateways(acc, msg, c.pa.subject, c.pa.reply, qnames, true)
        }
}

// Checks whether the inbound leaf message is allowed by the
// connection's permissions. On the hub side this enforces what
// the remote leaf may publish. On the spoke side this enforces
// import restrictions such as deny_imports.
func (c *client) leafMsgAllowed() bool {
        wireSubject := c.pa.subject
        if len(c.pa.mapped) > 0 {
                // Mappings rewrite c.pa.subject to the internal
                // destination. For leaf ACLs, need to check
                // the original wire subject from the remote side.
                wireSubject = c.pa.mapped
        }
        // Strip any gateway routing prefix for the permission check.
        subjectToCheck, isGW := getGWRoutedSubjectOrSelf(wireSubject)

        // Service-import replies (_R_), JS ack subjects ($JS.ACK.)
        // are internal routing subjects forwarded via LS+ without
        // permission checks.
        if isServiceReply(subjectToCheck) || isJSAckSubject(subjectToCheck) {
                return true
        }

        c.mu.RLock()
        if c.isSpokeLeafNode() {
                // Gateway routed replies are forwarded without
                // permission checks.
                if isGW || c.leafReceiveAllowed(subjectToCheck) {
                        c.mu.RUnlock()
                        return true
                }
        } else if c.leafSendAllowed(subjectToCheck) {
                c.mu.RUnlock()
                return true
        }

        // If allow_responses is not configured, or there is no tracked reply for
        // this subject, the answer is "denied" and we can return it while still
        // holding only the read lock.
        replySubject := bytesToString(wireSubject)
        if c.perms == nil || c.perms.resp == nil || c.replies[replySubject] == nil {
                c.mu.RUnlock()
                return false
        }
        c.mu.RUnlock()

        // Check tracked reply permissions (allow_responses).
        // Use the pre-strip subject since deliverMsg tracks
        // replies under the original form, which includes
        // the GW routing prefix for routed requests.
        c.mu.Lock()
        defer c.mu.Unlock()
        return c.responseAllowed(replySubject)
}

// Returns true if the leaf side ACLs allow importing this subject,
// based on the permissions received over INFO and any local deny_imports.
// At least a read lock must be held.
func (c *client) leafReceiveAllowed(subject []byte) bool {
        return c.canSubscribeInternal(bytesToString(subject))
}

// Returns true if the hub side ACLs allow the remote leaf to send
// this subject.
// At least a read lock must be held.
func (c *client) leafSendAllowed(bsubject []byte) bool {
        // Use the original export ACL captured for this accepted leaf.
        // The live perms also contain additional JetStream denies used by
        // the normal forwarding path, and applying them here would reject
        // legitimate inbound JS API requests.
        subject := bytesToString(bsubject)
        perms := c.opts.Export
        if perms == nil || (perms.Allow == nil && perms.Deny == nil) {
                return true
        }

        allowed := true
        if perms.Allow != nil && !strings.HasPrefix(subject, mqttPrefix) {
                allowed = false
                for _, allowSubj := range perms.Allow {
                        if matchLiteral(subject, allowSubj) {
                                allowed = true
                                break
                        }
                }
        }

        if allowed && len(perms.Deny) > 0 {
                for _, denySubj := range perms.Deny {
                        if matchLiteral(subject, denySubj) {
                                allowed = false
                                break
                        }
                }
        }
        return allowed
}

// Handles a subscription permission violation.
// See leafPermViolation() for details.
func (c *client) leafSubPermViolation(subj []byte) {
        c.leafPermViolation(false, subj)
}

// Handles a publish permission violation.
// See leafPermViolation() for details.
func (c *client) leafPubPermViolation(subj []byte) {
        c.leafPermViolation(true, subj)
}

// Common function to process publish or subscribe leafnode permission violation.
// Sends the permission violation error to the remote, logs it and closes the connection.
// If this is from a server soliciting, the reconnection will be delayed.
func (c *client) leafPermViolation(pub bool, subj []byte) {
        if c.isSpokeLeafNode() {
                // For spokes these are no-ops since the hub server told us our permissions.
                // We just need to not send these over to the other side since we will get cutoff.
                return
        }
        // FIXME(dlc) ?
        c.setLeafConnectDelayIfSoliciting(leafNodeReconnectAfterPermViolation)
        var action string
        if pub {
                c.sendErr(fmt.Sprintf("Permissions Violation for Publish to %q", subj))
                action = "Publish"
        } else {
                c.sendErr(fmt.Sprintf("Permissions Violation for Subscription to %q", subj))
                action = "Subscription"
        }
        c.Errorf("%s Violation on %q - Check other side configuration", action, subj)
        // TODO: add a new close reason that is more appropriate?
        c.closeConnection(ProtocolViolation)
}

// Invoked from generic processErr() for LEAF connections.
func (c *client) leafProcessErr(errStr string) {
        // Check if we got a cluster name collision.
        if strings.Contains(errStr, ErrLeafNodeHasSameClusterName.Error()) {
                _, delay := c.setLeafConnectDelayIfSoliciting(leafNodeReconnectDelayAfterClusterNameSame)
                c.Errorf("Leafnode connection dropped with same cluster name error. Delaying attempt to reconnect for %v", delay)
                return
        }
        if strings.Contains(errStr, ErrLeafNodeMinVersionRejected.Error()) {
                _, delay := c.setLeafConnectDelayIfSoliciting(leafNodeMinVersionReconnectDelay)
                c.Errorf("Leafnode connection dropped due to minimum version requirement. Delaying attempt to reconnect for %v", delay)
                return
        }

        // We will look for Loop detected error coming from the other side.
        // If we solicit, set the connect delay.
        if !strings.Contains(errStr, "Loop detected") {
                return
        }
        c.handleLeafNodeLoop(false)
}

// If this leaf connection solicits, sets the connect delay to the given value,
// or the one from the server option's LeafNode.connDelay if one is set (for tests).
// Returns the connection's account name and delay.
func (c *client) setLeafConnectDelayIfSoliciting(delay time.Duration) (string, time.Duration) {
        c.mu.Lock()
        if c.isSolicitedLeafNode() {
                if s := c.srv; s != nil {
                        if srvdelay := s.getOpts().LeafNode.connDelay; srvdelay != 0 {
                                delay = srvdelay
                        }
                }
                c.leaf.remote.setConnectDelay(delay)
        }
        var accName string
        if c.acc != nil {
                accName = c.acc.Name
        }
        c.mu.Unlock()
        return accName, delay
}

// For the given remote Leafnode configuration, this function returns
// if TLS is required, and if so, will return a clone of the TLS Config
// (since some fields will be changed during handshake), the TLS server
// name that is remembered, and the TLS timeout.
func (c *client) leafNodeGetTLSConfigForSolicit(remote *leafNodeCfg) (bool, *tls.Config, string, float64) {
        var (
                tlsConfig  *tls.Config
                tlsName    string
                tlsTimeout float64
        )

        remote.RLock()
        defer remote.RUnlock()

        tlsRequired := remote.TLS || remote.TLSConfig != nil
        if tlsRequired {
                if remote.TLSConfig != nil {
                        tlsConfig = remote.TLSConfig.Clone()
                } else {
                        tlsConfig = &tls.Config{MinVersion: tls.VersionTLS12}
                }
                tlsName = remote.tlsName
                tlsTimeout = remote.TLSTimeout
                if tlsTimeout == 0 {
                        tlsTimeout = float64(TLS_TIMEOUT / time.Second)
                }
        }

        return tlsRequired, tlsConfig, tlsName, tlsTimeout
}

// Initiates the LeafNode Websocket connection by:
// - doing the TLS handshake if needed
// - sending the HTTP request
// - waiting for the HTTP response
//
// Since some bufio reader is used to consume the HTTP response, this function
// returns the slice of buffered bytes (if any) so that the readLoop that will
// be started after that consume those first before reading from the socket.
// The boolean
//
// Lock held on entry.
func (c *client) leafNodeSolicitWSConnection(opts *Options, rURL *url.URL, remote *leafNodeCfg) ([]byte, ClosedState, error) {
        remote.RLock()
        compress := remote.Websocket.Compression
        // By default the server will mask outbound frames, but it can be disabled with this option.
        noMasking := remote.Websocket.NoMasking
        infoTimeout := remote.FirstInfoTimeout
        remote.RUnlock()
        // Will do the client-side TLS handshake if needed.
        tlsRequired, err := c.leafClientHandshakeIfNeeded(remote, opts)
        if err != nil {
                // 0 will indicate that the connection was already closed
                return nil, 0, err
        }

        // For http request, we need the passed URL to contain either http or https scheme.
        scheme := "http"
        if tlsRequired {
                scheme = "https"
        }
        // We will use the `/leafnode` path to tell the accepting WS server that it should
        // create a LEAF connection, not a CLIENT.
        // In case we use the user's URL path in the future, make sure we append the user's
        // path to our `/leafnode` path.
        lpath := leafNodeWSPath
        if curPath := rURL.EscapedPath(); curPath != _EMPTY_ {
                if curPath[0] == '/' {
                        curPath = curPath[1:]
                }
                lpath = path.Join(curPath, lpath)
        } else {
                lpath = lpath[1:]
        }
        ustr := fmt.Sprintf("%s://%s/%s", scheme, rURL.Host, lpath)
        u, _ := url.Parse(ustr)
        req := &http.Request{
                Method:     "GET",
                URL:        u,
                Proto:      "HTTP/1.1",
                ProtoMajor: 1,
                ProtoMinor: 1,
                Header:     make(http.Header),
                Host:       u.Host,
        }
        wsKey, err := wsMakeChallengeKey()
        if err != nil {
                return nil, WriteError, err
        }

        req.Header["Upgrade"] = []string{"websocket"}
        req.Header["Connection"] = []string{"Upgrade"}
        req.Header["Sec-WebSocket-Key"] = []string{wsKey}
        req.Header["Sec-WebSocket-Version"] = []string{"13"}
        if compress {
                req.Header.Add("Sec-WebSocket-Extensions", wsPMCReqHeaderValue)
        }
        if noMasking {
                req.Header.Add(wsNoMaskingHeader, wsNoMaskingValue)
        }
        c.nc.SetDeadline(time.Now().Add(infoTimeout))
        if err := req.Write(c.nc); err != nil {
                return nil, WriteError, err
        }

        var resp *http.Response

        br := bufio.NewReaderSize(c.nc, MAX_CONTROL_LINE_SIZE)
        resp, err = http.ReadResponse(br, req)
        if err == nil &&
                (resp.StatusCode != 101 ||
                        !strings.EqualFold(resp.Header.Get("Upgrade"), "websocket") ||
                        !strings.EqualFold(resp.Header.Get("Connection"), "upgrade") ||
                        resp.Header.Get("Sec-Websocket-Accept") != wsAcceptKey(wsKey)) {

                err = fmt.Errorf("invalid websocket connection")
        }
        // Check compression extension...
        if err == nil && c.ws.compress {
                // Check that not only permessage-deflate extension is present, but that
                // we also have server and client no context take over.
                srvCompress, noCtxTakeover := wsPMCExtensionSupport(resp.Header, false)

                // If server does not support compression, then simply disable it in our side.
                if !srvCompress {
                        c.ws.compress = false
                } else if !noCtxTakeover {
                        err = fmt.Errorf("compression negotiation error")
                }
        }
        // Same for no masking...
        if err == nil && noMasking {
                // Check if server accepts no masking
                if resp.Header.Get(wsNoMaskingHeader) != wsNoMaskingValue {
                        // Nope, need to mask our writes as any client would do.
                        c.ws.maskwrite = true
                }
        }
        if resp != nil {
                resp.Body.Close()
        }
        if err != nil {
                return nil, ReadError, err
        }
        c.Debugf("Leafnode compression=%v masking=%v", c.ws.compress, c.ws.maskwrite)

        var preBuf []byte
        // We have to slurp whatever is in the bufio reader and pass that to the readloop.
        if n := br.Buffered(); n != 0 {
                preBuf, _ = br.Peek(n)
        }
        return preBuf, 0, nil
}

const connectProcessTimeout = 2 * time.Second

// This is invoked for remote LEAF remote connections after processing the INFO
// protocol.
func (s *Server) leafNodeResumeConnectProcess(c *client) {
        clusterName := s.ClusterName()

        c.mu.Lock()
        if c.isClosed() {
                c.mu.Unlock()
                return
        }
        if err := c.sendLeafConnect(clusterName, c.headers); err != nil {
                c.mu.Unlock()
                c.closeConnection(WriteError)
                return
        }

        // Spin up the write loop.
        s.startGoRoutine(func() { c.writeLoop() })

        // timeout leafNodeFinishConnectProcess
        c.ping.tmr = time.AfterFunc(connectProcessTimeout, func() {
                c.mu.Lock()
                // check if leafNodeFinishConnectProcess was called and prevent later leafNodeFinishConnectProcess
                if !c.flags.setIfNotSet(connectProcessFinished) {
                        c.mu.Unlock()
                        return
                }
                clearTimer(&c.ping.tmr)
                closed := c.isClosed()
                c.mu.Unlock()
                if !closed {
                        c.sendErrAndDebug("Stale Leaf Node Connection - Closing")
                        c.closeConnection(StaleConnection)
                }
        })
        c.mu.Unlock()
        c.Debugf("Remote leafnode connect msg sent")
}

// This is invoked for remote LEAF connections after processing the INFO
// protocol and leafNodeResumeConnectProcess.
// This will send LS+ the CONNECT protocol and register the leaf node.
func (s *Server) leafNodeFinishConnectProcess(c *client) {
        c.mu.Lock()
        if !c.flags.setIfNotSet(connectProcessFinished) {
                c.mu.Unlock()
                return
        }
        if c.isClosed() {
                c.mu.Unlock()
                s.removeLeafNodeConnection(c)
                return
        }
        remote := c.leaf.remote
        if remote == nil || c.acc == nil {
                c.mu.Unlock()
                c.sendErr("Authorization Violation")
                c.closeConnection(ProtocolViolation)
                return
        }
        // Check if we will need to send the system connect event.
        remote.RLock()
        sendSysConnectEvent := remote.Hub
        remote.RUnlock()

        // Capture account before releasing lock
        acc := c.acc
        // cancel connectProcessTimeout
        clearTimer(&c.ping.tmr)
        c.mu.Unlock()

        // Make sure we register with the account here.
        if err := c.registerWithAccount(acc); err != nil {
                if err == ErrTooManyAccountConnections {
                        c.maxAccountConnExceeded()
                        return
                } else if err == ErrLeafNodeLoop {
                        c.handleLeafNodeLoop(true)
                        return
                }
                c.Errorf("Registering leaf with account %s resulted in error: %v", acc.Name, err)
                c.closeConnection(ProtocolViolation)
                return
        }
        if !s.addLeafNodeConnection(c, _EMPTY_, _EMPTY_, false) {
                // Was not added, could be because the remote configuration has been removed.
                c.closeConnection(ClientClosed)
                return
        }
        s.initLeafNodeSmapAndSendSubs(c)
        if sendSysConnectEvent {
                s.sendLeafNodeConnect(acc)
        }
        s.accountConnectEvent(c)

        // The above functions are not running under the client lock, so it is
        // possible that between the time we have started the read/write loops
        // and now, that the connection was closed. This would leave the closed
        // LN connection possibly registered with the account and/or the server's
        // leafs map. So check if connection is closed, and if so, manually cleanup.
        c.mu.Lock()
        closed := c.isClosed()
        if !closed {
                c.setFirstPingTimer()
        }
        c.mu.Unlock()
        if closed {
                s.removeLeafNodeConnection(c)
                if prev := acc.removeClient(c); prev == 1 {
                        s.decActiveAccounts()
                }
        }
}

nats-io / nats-server / 25902955617

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