stacklok / toolhive / 30026855331

69%

Build Type

push

github

Committed by web-flow

Commit Message

Route server-to-client MCP messages per session (#5934)

The streamable HTTP proxy returned 405 on GET and dropped every
container->client message, so server-initiated MCP flows (progress,
resources/updated, */list_changed) never reached clients over the modern
transport. This adds a standalone GET SSE stream and routes each
server->client message to the correct session, or securely refuses it —
no cross-session leakage over the shared-backend multiplexing proxy.

- Per-session GET SSE stream registry (keyed by Mcp-Session-Id, one
  stream per session, evict-and-replace; data channel never closed, per
  stream stop signal — no send-on-closed panic).
- Routing: */list_changed -> every session once; progress -> the
  originating request's POST SSE stream (progressToken rewritten to a
  proxy-minted unique token); resources/updated -> only subscribed
  sessions (ref-counted upstream subscribe/unsubscribe, recorded only on
  upstream success); logging + server-initiated requests
  (sampling/elicitation) securely dropped (unattributable over a shared
  backend; requests get -32601 so the backend unblocks).
- Per-URI keyed mutex orders concurrent same-URI subscribe/unsubscribe;
  GET streams torn down on DELETE and by the reaper.

Reviewed-by: amirejaz. Conformant with MCP 2025-11-25 and forward-compatible
with 2026-07-28 (progress already matches the Modern model; server-initiated
requests become moot under MRTR). Sampling/elicitation + per-session logging
require per-session backends (vMCP) — tracked as follow-ups.

Closes #5744

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WG3mSjVGWNc8nfgbkdd79

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649 of 832 new or added lines in 6 files covered. (78.0%)

27 existing lines in 8 files now uncovered.

77753 of 112351 relevant lines covered (69.21%)

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