Dispose the POST response in SseClientSessionTransport to stop leaking a connection per message - #1841
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SendMessageAsync sends every message with HttpCompletionOption.ResponseHeadersRead (via McpHttpClient) but never disposed the returned HttpResponseMessage on the success path, so the underlying connection was never returned to the pool. Each JSON-RPC POST therefore opened and stranded a new connection, which was only reclaimed by GC or an idle timeout. Disposing the response returns the connection to the pool deterministically; subsequent POSTs reuse a single connection. Fixes modelcontextprotocol#1840 Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #1840
What
One-word change in
SseClientSessionTransport.SendMessageAsync: theHttpResponseMessagereturned for each POSTed JSON-RPC message is now wrapped in
using.Why
McpHttpClient.SendAsyncsends every request withHttpCompletionOption.ResponseHeadersRead,so the underlying connection stays checked out until the response is consumed or disposed.
The POST path never did either on the success path (a
202 Acceptedwhose body is unused),so every sent message stranded one ESTABLISHED connection — never returned to the pool,
never reused, reclaimed only by GC or an idle timeout. Measurements and the full analysis
are in #1840 (per client: 1 live SSE connection + one stranded connection per POST —
initialize,notifications/initialized,tools/list).The surrounding code already does this correctly: the SSE GET response is wrapped in
using var responsein the same file, and the failure path reads the body before throwing.Only the success path was missing the dispose.
Notes
usingscope unwinds.ModelContextProtocol.Corebuilds cleanly with the change.🤖 Generated with Claude Code