#20314

Committed 11 Jun 2026 05:34PM UTC coverage: 88.883% (+0.002%) from 88.881%

Build # #20314

Build Type

push

github

Committed by

web-flow

Commit Message

Upgrade to Netty 4.2.15

Netty 4.2 has the thread classes interact in a new way, so they've
deprecated the Netty 4.1 threading APIs. While we want to use Netty 4.2,
not all build systems compiling gRPC may have upgraded to 4.2 yet, so
let's not begin using Netty 4.2 APIs yet.

Coverage Stats

36508 of 41074 relevant lines covered (88.88%)

0.89 hits per line

Source File
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84.36

/../netty/src/main/java/io/grpc/netty/Utils.java

/*
 * Copyright 2014 The gRPC 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 io.grpc.netty;

import static com.google.common.base.Preconditions.checkState;
import static io.grpc.internal.GrpcUtil.CONTENT_TYPE_KEY;
import static io.grpc.internal.TransportFrameUtil.toHttp2Headers;
import static io.grpc.internal.TransportFrameUtil.toRawSerializedHeaders;
import static io.netty.channel.ChannelOption.SO_LINGER;
import static io.netty.channel.ChannelOption.SO_TIMEOUT;
import static io.netty.util.CharsetUtil.UTF_8;
import static java.nio.charset.StandardCharsets.US_ASCII;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.CheckReturnValue;
import io.grpc.InternalChannelz;
import io.grpc.InternalMetadata;
import io.grpc.Metadata;
import io.grpc.Status;
import io.grpc.internal.GrpcUtil;
import io.grpc.internal.SharedResourceHolder.Resource;
import io.grpc.internal.TransportTracer;
import io.grpc.netty.GrpcHttp2HeadersUtils.GrpcHttp2InboundHeaders;
import io.grpc.netty.NettySocketSupport.NativeSocketOptions;
import io.netty.buffer.ByteBufAllocator;
import io.netty.buffer.PooledByteBufAllocator;
import io.netty.buffer.UnpooledByteBufAllocator;
import io.netty.channel.Channel;
import io.netty.channel.ChannelConfig;
import io.netty.channel.ChannelFactory;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.ReflectiveChannelFactory;
import io.netty.channel.ServerChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.DecoderException;
import io.netty.handler.codec.http2.Http2Connection;
import io.netty.handler.codec.http2.Http2Exception;
import io.netty.handler.codec.http2.Http2FlowController;
import io.netty.handler.codec.http2.Http2Headers;
import io.netty.handler.codec.http2.Http2Stream;
import io.netty.util.AsciiString;
import io.netty.util.NettyRuntime;
import io.netty.util.concurrent.DefaultThreadFactory;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.UnresolvedAddressException;
import java.util.Locale;
import java.util.Map;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Nullable;
import javax.net.ssl.SSLException;

/**
 * Common utility methods.
 */
class Utils {
  private static final Logger logger = Logger.getLogger(Utils.class.getName());

  public static final AsciiString STATUS_OK = AsciiString.of("200");
  public static final AsciiString HTTP_METHOD = AsciiString.of(GrpcUtil.HTTP_METHOD);
  public static final AsciiString HTTP_GET_METHOD = AsciiString.of("GET");
  public static final AsciiString HTTPS = AsciiString.of("https");
  public static final AsciiString HTTP = AsciiString.of("http");
  public static final AsciiString CONTENT_TYPE_HEADER = AsciiString.of(CONTENT_TYPE_KEY.name());
  public static final AsciiString CONTENT_TYPE_GRPC = AsciiString.of(GrpcUtil.CONTENT_TYPE_GRPC);
  public static final AsciiString TE_HEADER = AsciiString.of(GrpcUtil.TE_HEADER.name());
  public static final AsciiString TE_TRAILERS = AsciiString.of(GrpcUtil.TE_TRAILERS);
  public static final AsciiString USER_AGENT = AsciiString.of(GrpcUtil.USER_AGENT_KEY.name());
  public static final Resource<EventLoopGroup> NIO_BOSS_EVENT_LOOP_GROUP
      = new DefaultEventLoopGroupResource(1, "grpc-nio-boss-ELG", EventLoopGroupType.NIO);
  public static final Resource<EventLoopGroup> NIO_WORKER_EVENT_LOOP_GROUP
      = new DefaultEventLoopGroupResource(0, "grpc-nio-worker-ELG", EventLoopGroupType.NIO);
  private static final int HEADER_ENTRY_OVERHEAD = 32;
  private static final byte[] binaryHeaderSuffixBytes =
      Metadata.BINARY_HEADER_SUFFIX.getBytes(US_ASCII);
  public static final Resource<EventLoopGroup> DEFAULT_BOSS_EVENT_LOOP_GROUP;
  public static final Resource<EventLoopGroup> DEFAULT_WORKER_EVENT_LOOP_GROUP;

  // This class is initialized on first use, thus provides delayed allocator creation.
  private static final class ByteBufAllocatorPreferDirectHolder {
    private static final ByteBufAllocator allocator = createByteBufAllocator(true);
  }

  // This class is initialized on first use, thus provides delayed allocator creation.
  private static final class ByteBufAllocatorPreferHeapHolder {
    private static final ByteBufAllocator allocator = createByteBufAllocator(false);
  }

  public static final ChannelFactory<? extends ServerChannel> DEFAULT_SERVER_CHANNEL_FACTORY;
  public static final Class<? extends Channel> DEFAULT_CLIENT_CHANNEL_TYPE;
  public static final Class<? extends Channel> EPOLL_DOMAIN_CLIENT_CHANNEL_TYPE;

  @Nullable
  private static final Constructor<? extends EventLoopGroup> EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR;

  static {
    // Decide default channel types and EventLoopGroup based on Epoll availability
    if (isEpollAvailable()) {
      DEFAULT_CLIENT_CHANNEL_TYPE = epollChannelType();
      EPOLL_DOMAIN_CLIENT_CHANNEL_TYPE = epollDomainSocketChannelType();
      DEFAULT_SERVER_CHANNEL_FACTORY = new ReflectiveChannelFactory<>(epollServerChannelType());
      EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR = epollEventLoopGroupConstructor();
      DEFAULT_BOSS_EVENT_LOOP_GROUP = new DefaultEventLoopGroupResource(
          1, "grpc-default-boss-ELG", EventLoopGroupType.EPOLL);
      DEFAULT_WORKER_EVENT_LOOP_GROUP = new DefaultEventLoopGroupResource(
          0, "grpc-default-worker-ELG", EventLoopGroupType.EPOLL);
    } else {
      logger.log(Level.FINE, "Epoll is not available, using Nio.", getEpollUnavailabilityCause());
      DEFAULT_SERVER_CHANNEL_FACTORY = nioServerChannelFactory();
      DEFAULT_CLIENT_CHANNEL_TYPE = NioSocketChannel.class;
      EPOLL_DOMAIN_CLIENT_CHANNEL_TYPE = null;
      DEFAULT_BOSS_EVENT_LOOP_GROUP = NIO_BOSS_EVENT_LOOP_GROUP;
      DEFAULT_WORKER_EVENT_LOOP_GROUP = NIO_WORKER_EVENT_LOOP_GROUP;
      EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR = null;
    }
  }

  public static ByteBufAllocator getByteBufAllocator(boolean forceHeapBuffer) {
    if (Boolean.parseBoolean(
            System.getProperty("io.grpc.netty.useCustomAllocator", "true"))) {

      String allocType = System.getProperty("io.netty.allocator.type", "pooled");
      if (allocType.toLowerCase(Locale.ROOT).equals("unpooled")) {
        logger.log(Level.FINE, "Using unpooled allocator");
        return UnpooledByteBufAllocator.DEFAULT;
      }

      boolean defaultPreferDirect = PooledByteBufAllocator.defaultPreferDirect();
      logger.log(
          Level.FINE,
          "Using custom allocator: forceHeapBuffer={0}, defaultPreferDirect={1}",
          new Object[] { forceHeapBuffer, defaultPreferDirect });
      if (forceHeapBuffer || !defaultPreferDirect) {
        return ByteBufAllocatorPreferHeapHolder.allocator;
      } else {
        return ByteBufAllocatorPreferDirectHolder.allocator;
      }
    } else {
      logger.log(Level.FINE, "Using default allocator");
      return ByteBufAllocator.DEFAULT;
    }
  }

  private static ByteBufAllocator createByteBufAllocator(boolean preferDirect) {
    int maxOrder;
    logger.log(Level.FINE, "Creating allocator, preferDirect=" + preferDirect);
    if (System.getProperty("io.netty.allocator.maxOrder") == null) {
      // See the implementation of PooledByteBufAllocator.  DEFAULT_MAX_ORDER in there is
      // 11, which makes chunk size to be 8192 << 11 = 16 MiB.  We want the chunk size to be
      // 2MiB, thus reducing the maxOrder to 8.
      maxOrder = 8;
      logger.log(Level.FINE, "Forcing maxOrder=" + maxOrder);
    } else {
      maxOrder = PooledByteBufAllocator.defaultMaxOrder();
      logger.log(Level.FINE, "Using default maxOrder=" + maxOrder);
    }
    return new PooledByteBufAllocator(
        preferDirect,
        PooledByteBufAllocator.defaultNumHeapArena(),
        // Assuming neither gRPC nor netty are using allocator.directBuffer() to request
        // specifically for direct buffers, which is true as I just checked, setting arenas to 0
        // will make sure no direct buffer is ever created.
        preferDirect ? PooledByteBufAllocator.defaultNumDirectArena() : 0,
        PooledByteBufAllocator.defaultPageSize(),
        maxOrder,
        PooledByteBufAllocator.defaultSmallCacheSize(),
        PooledByteBufAllocator.defaultNormalCacheSize(),
        PooledByteBufAllocator.defaultUseCacheForAllThreads());
  }

  public static Metadata convertHeaders(Http2Headers http2Headers) {
    if (http2Headers instanceof GrpcHttp2InboundHeaders) {
      GrpcHttp2InboundHeaders h = (GrpcHttp2InboundHeaders) http2Headers;
      return InternalMetadata.newMetadata(h.numHeaders(), h.namesAndValues());
    }
    return InternalMetadata.newMetadata(convertHeadersToArray(http2Headers));
  }

  public static int getH2HeadersSize(Http2Headers http2Headers) {
    if (http2Headers instanceof GrpcHttp2InboundHeaders) {
      GrpcHttp2InboundHeaders h = (GrpcHttp2InboundHeaders) http2Headers;
      int size = 0;
      for (int i = 0; i < h.numHeaders(); i++) {
        size += h.namesAndValues()[2 * i].length;
        size +=
            maybeAddBinaryHeaderOverhead(h.namesAndValues()[2 * i], h.namesAndValues()[2 * i + 1]);
        size += HEADER_ENTRY_OVERHEAD;
      }
      return size;
    }

    // the binary header is not decoded yet, no need to add overhead.
    int size = 0;
    for (Map.Entry<CharSequence, CharSequence> entry : http2Headers) {
      size += entry.getKey().length();
      size += entry.getValue().length();
      size += HEADER_ENTRY_OVERHEAD;
    }
    return size;
  }

  private static int maybeAddBinaryHeaderOverhead(byte[] name, byte[] value) {
    if (endsWith(name, binaryHeaderSuffixBytes)) {
      return value.length * 4 / 3;
    }
    return value.length;
  }

  private static boolean endsWith(byte[] bytes, byte[] suffix) {
    if (bytes == null || suffix == null || bytes.length < suffix.length) {
      return false;
    }

    for (int i = 0; i < suffix.length; i++) {
      if (bytes[bytes.length - suffix.length + i] != suffix[i]) {
        return false;
      }
    }

    return true;
  }

  public static boolean shouldRejectOnMetadataSizeSoftLimitExceeded(
      int h2HeadersSize, int softLimitHeaderListSize, int maxHeaderListSize) {
    if (h2HeadersSize < softLimitHeaderListSize) {
      return false;
    }
    double failProbability =
        (double) (h2HeadersSize - softLimitHeaderListSize) / (double) (maxHeaderListSize
            - softLimitHeaderListSize);
    return Math.random() < failProbability;
  }

  @CheckReturnValue
  private static byte[][] convertHeadersToArray(Http2Headers http2Headers) {
    // The Netty AsciiString class is really just a wrapper around a byte[] and supports
    // arbitrary binary data, not just ASCII.
    byte[][] headerValues = new byte[http2Headers.size() * 2][];
    int i = 0;
    for (Map.Entry<CharSequence, CharSequence> entry : http2Headers) {
      headerValues[i++] = bytes(entry.getKey());
      headerValues[i++] = bytes(entry.getValue());
    }
    return toRawSerializedHeaders(headerValues);
  }

  private static byte[] bytes(CharSequence seq) {
    if (seq instanceof AsciiString) {
      // Fast path - sometimes copy.
      AsciiString str = (AsciiString) seq;
      return str.isEntireArrayUsed() ? str.array() : str.toByteArray();
    }
    // Slow path - copy.
    return seq.toString().getBytes(UTF_8);
  }

  public static Http2Headers convertClientHeaders(Metadata headers,
      AsciiString scheme,
      AsciiString defaultPath,
      AsciiString authority,
      AsciiString method,
      AsciiString userAgent) {
    Preconditions.checkNotNull(defaultPath, "defaultPath");
    Preconditions.checkNotNull(authority, "authority");
    Preconditions.checkNotNull(method, "method");

    // Discard any application supplied duplicates of the reserved headers
    headers.discardAll(CONTENT_TYPE_KEY);
    headers.discardAll(GrpcUtil.TE_HEADER);
    headers.discardAll(GrpcUtil.USER_AGENT_KEY);

    return GrpcHttp2OutboundHeaders.clientRequestHeaders(
        toHttp2Headers(headers),
        authority,
        defaultPath,
        method,
        scheme,
        userAgent);
  }

  public static Http2Headers convertServerHeaders(Metadata headers) {
    // Discard any application supplied duplicates of the reserved headers
    headers.discardAll(CONTENT_TYPE_KEY);
    headers.discardAll(GrpcUtil.TE_HEADER);
    headers.discardAll(GrpcUtil.USER_AGENT_KEY);

    return GrpcHttp2OutboundHeaders.serverResponseHeaders(toHttp2Headers(headers));
  }

  public static Metadata convertTrailers(Http2Headers http2Headers) {
    if (http2Headers instanceof GrpcHttp2InboundHeaders) {
      GrpcHttp2InboundHeaders h = (GrpcHttp2InboundHeaders) http2Headers;
      return InternalMetadata.newMetadata(h.numHeaders(), h.namesAndValues());
    }
    return InternalMetadata.newMetadata(convertHeadersToArray(http2Headers));
  }

  public static Http2Headers convertTrailers(Metadata trailers, boolean headersSent) {
    if (!headersSent) {
      return convertServerHeaders(trailers);
    }
    return GrpcHttp2OutboundHeaders.serverResponseTrailers(toHttp2Headers(trailers));
  }

  public static Status statusFromThrowable(Throwable t) {
    Status s = Status.fromThrowable(t);
    if (s.getCode() != Status.Code.UNKNOWN) {
      return s;
    }
    if (t instanceof ClosedChannelException) {
      if (t.getCause() != null) {
        // If the remote closes the connection while the event loop is processing, then a write or
        // flush can be the first operation to notice the closure. Those exceptions are a
        // ClosedChannelException, with a cause that provides more information, which is exactly
        // what we'd hope for.
        return Status.UNAVAILABLE.withDescription("channel closed").withCause(t);
      }
      // ClosedChannelException is used for all operations after the Netty channel is closed. But it
      // doesn't have the original closure information. Proper error processing requires remembering
      // the error that occurred before this one and using it instead.
      //
      // Netty uses an exception that has no stack trace, while we would never hope to show this to
      // users, if it happens having the extra information may provide a small hint of where to
      // look.
      ClosedChannelException extraT = new ClosedChannelException();
      extraT.initCause(t);
      return Status.UNKNOWN.withDescription("channel closed").withCause(extraT);
    }
    if (t instanceof DecoderException && t.getCause() instanceof SSLException) {
      return Status.UNAVAILABLE.withDescription("ssl exception").withCause(t);
    }
    if (t instanceof IOException) {
      return Status.UNAVAILABLE.withDescription("io exception").withCause(t);
    }
    if (t instanceof UnresolvedAddressException) {
      return Status.UNAVAILABLE.withDescription("unresolved address").withCause(t);
    }
    if (t instanceof Http2Exception) {
      return Status.INTERNAL.withDescription("http2 exception").withCause(t);
    }
    return s;
  }

  @VisibleForTesting
  static boolean isEpollAvailable() {
    try {
      return (boolean) (Boolean)
          Class
              .forName("io.netty.channel.epoll.Epoll")
              .getDeclaredMethod("isAvailable")
              .invoke(null);
    } catch (ClassNotFoundException e) {
      // this is normal if netty-epoll runtime dependency doesn't exist.
      return false;
    } catch (Exception e) {
      throw new RuntimeException("Exception while checking Epoll availability", e);
    }
  }

  private static Throwable getEpollUnavailabilityCause() {
    try {
      return (Throwable)
          Class
              .forName("io.netty.channel.epoll.Epoll")
              .getDeclaredMethod("unavailabilityCause")
              .invoke(null);
    } catch (Exception e) {
      return e;
    }
  }

  // Must call when epoll is available
  private static Class<? extends Channel> epollChannelType() {
    try {
      Class<? extends Channel> channelType = Class
          .forName("io.netty.channel.epoll.EpollSocketChannel").asSubclass(Channel.class);
      return channelType;
    } catch (ClassNotFoundException e) {
      throw new RuntimeException("Cannot load EpollSocketChannel", e);
    }
  }

  // Must call when epoll is available
  private static Class<? extends Channel> epollDomainSocketChannelType() {
    try {
      Class<? extends Channel> channelType = Class
          .forName("io.netty.channel.epoll.EpollDomainSocketChannel").asSubclass(Channel.class);
      return channelType;
    } catch (ClassNotFoundException e) {
      throw new RuntimeException("Cannot load EpollDomainSocketChannel", e);
    }
  }

  // Must call when epoll is available
  private static Constructor<? extends EventLoopGroup> epollEventLoopGroupConstructor() {
    try {
      return Class
          .forName("io.netty.channel.epoll.EpollEventLoopGroup").asSubclass(EventLoopGroup.class)
          .getConstructor(Integer.TYPE, ThreadFactory.class);
    } catch (ClassNotFoundException e) {
      throw new RuntimeException("Cannot load EpollEventLoopGroup", e);
    } catch (NoSuchMethodException e) {
      throw new RuntimeException("EpollEventLoopGroup constructor not found", e);
    }
  }

  // Must call when epoll is available
  private static Class<? extends ServerChannel> epollServerChannelType() {
    try {
      Class<? extends ServerChannel> serverSocketChannel =
          Class
              .forName("io.netty.channel.epoll.EpollServerSocketChannel")
              .asSubclass(ServerChannel.class);
      return serverSocketChannel;
    } catch (ClassNotFoundException e) {
      throw new RuntimeException("Cannot load EpollServerSocketChannel", e);
    }
  }

  private static EventLoopGroup createEpollEventLoopGroup(
      int parallelism,
      ThreadFactory threadFactory) {
    checkState(EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR != null, "Epoll is not available");

    try {
      return EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR
          .newInstance(parallelism, threadFactory);
    } catch (Exception e) {
      throw new RuntimeException("Cannot create Epoll EventLoopGroup", e);
    }
  }

  private static ChannelFactory<ServerChannel> nioServerChannelFactory() {
    return new ChannelFactory<ServerChannel>() {
      @Override
      public ServerChannel newChannel() {
        return new NioServerSocketChannel();
      }
    };
  }

  /**
   * Returns TCP_USER_TIMEOUT channel option for Epoll channel if Epoll is available, otherwise
   * null.
   */
  @Nullable
  static ChannelOption<Integer> maybeGetTcpUserTimeoutOption() {
    return getEpollChannelOption("TCP_USER_TIMEOUT");
  }

  @Nullable
  @SuppressWarnings("unchecked")
  private static <T> ChannelOption<T> getEpollChannelOption(String optionName) {
    if (isEpollAvailable()) {
      try {
        return
            (ChannelOption<T>) Class.forName("io.netty.channel.epoll.EpollChannelOption")
                .getField(optionName)
                .get(null);
      } catch (Exception e) {
        throw new RuntimeException("ChannelOption(" + optionName + ") is not available", e);
      }
    }
    return null;
  }

  private static final class DefaultEventLoopGroupResource implements Resource<EventLoopGroup> {
    private final String name;
    private final int numEventLoops;
    private final EventLoopGroupType eventLoopGroupType;

    DefaultEventLoopGroupResource(
        int numEventLoops, String name, EventLoopGroupType eventLoopGroupType) {
      this.name = name;
      // See the implementation of MultithreadEventLoopGroup.  DEFAULT_EVENT_LOOP_THREADS there
      // defaults to NettyRuntime.availableProcessors() * 2.  We don't think we need that many
      // threads.  The overhead of a thread includes file descriptors and at least one chunk
      // allocation from PooledByteBufAllocator.  Here we reduce the default number of threads by
      // half.
      if (numEventLoops == 0 && System.getProperty("io.netty.eventLoopThreads") == null) {
        this.numEventLoops = NettyRuntime.availableProcessors();
      } else {
        this.numEventLoops = numEventLoops;
      }
      this.eventLoopGroupType = eventLoopGroupType;
    }

    @Override
    public EventLoopGroup create() {
      // Use Netty's DefaultThreadFactory in order to get the benefit of FastThreadLocal.
      ThreadFactory threadFactory = new DefaultThreadFactory(name, /* daemon= */ true);
      switch (eventLoopGroupType) {
        case NIO:
          @SuppressWarnings("deprecation") // Wait a bit before migrating to the Netty 4.2 API
          EventLoopGroup group =
              new io.netty.channel.nio.NioEventLoopGroup(numEventLoops, threadFactory);
          return group;
        case EPOLL:
          return createEpollEventLoopGroup(numEventLoops, threadFactory);
        default:
          throw new AssertionError("Unknown/Unsupported EventLoopGroupType: " + eventLoopGroupType);
      }
    }

    @Override
    public void close(EventLoopGroup instance) {
      instance.shutdownGracefully(0, 0, TimeUnit.SECONDS);
    }

    @Override
    public String toString() {
      return name;
    }
  }

  static final class FlowControlReader implements TransportTracer.FlowControlReader {
    private final Http2Stream connectionStream;
    private final Http2FlowController local;
    private final Http2FlowController remote;

    FlowControlReader(Http2Connection connection) {
      // 'local' in Netty is the _controller_ that controls inbound data. 'local' in Channelz is
      // the _present window_ provided by the remote that allows data to be sent. They are
      // opposites.
      local = connection.remote().flowController();
      remote = connection.local().flowController();
      connectionStream = connection.connectionStream();
    }

    @Override
    public TransportTracer.FlowControlWindows read() {
      return new TransportTracer.FlowControlWindows(
          local.windowSize(connectionStream),
          remote.windowSize(connectionStream));
    }
  }

  static InternalChannelz.SocketOptions getSocketOptions(Channel channel) {
    ChannelConfig config = channel.config();
    InternalChannelz.SocketOptions.Builder b = new InternalChannelz.SocketOptions.Builder();

    // The API allows returning null but not sure if it can happen in practice.
    // Let's be paranoid and do null checking just in case.
    Integer lingerSeconds = config.getOption(SO_LINGER);
    if (lingerSeconds != null) {
      b.setSocketOptionLingerSeconds(lingerSeconds);
    }

    Integer timeoutMillis = config.getOption(SO_TIMEOUT);
    if (timeoutMillis != null) {
      // in java, SO_TIMEOUT only applies to receiving
      b.setSocketOptionTimeoutMillis(timeoutMillis);
    }

    for (Map.Entry<ChannelOption<?>, Object> opt : config.getOptions().entrySet()) {
      ChannelOption<?> key = opt.getKey();
      // Constants are pooled, so there should only be one instance of each constant
      if (key.equals(SO_LINGER) || key.equals(SO_TIMEOUT)) {
        continue;
      }
      Object value = opt.getValue();
      // zpencer: Can a netty option be null?
      b.addOption(key.name(), String.valueOf(value));
    }

    NativeSocketOptions nativeOptions
        = NettySocketSupport.getNativeSocketOptions(channel);
    if (nativeOptions != null) {
      b.setTcpInfo(nativeOptions.tcpInfo); // may be null
      for (Map.Entry<String, String> entry : nativeOptions.otherInfo.entrySet()) {
        b.addOption(entry.getKey(), entry.getValue());
      }
    }
    return b.build();
  }

  private enum EventLoopGroupType {
    NIO,
    EPOLL
  }

  private Utils() {
    // Prevents instantiation
  }
}

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