Move markInitialized/reconnect after status code check in Streamable HTTP transport#851
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rameshreddy-adutla wants to merge 1 commit intomodelcontextprotocol:mainfrom
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…HTTP transport When the server returns a non-2xx status code (e.g. 405 Method Not Allowed), markInitialized() and reconnect() were called before the status code was checked. This caused an unnecessary GET request, which is problematic when using transport fallback (Streamable HTTP -> SSE) as it creates duplicate SSE sessions on the server. Move markInitialized() and reconnect() inside the 2xx success branch so they are only called when the server actually accepted the connection. Fixes modelcontextprotocol#773 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Move
markInitialized()andreconnect()inside the 2xx success branch inHttpClientStreamableHttpTransport#sendMessageso they are only called when the server actually accepted the connection.Problem
When connecting to an MCP server that doesn't support Streamable HTTP transport (returns 405 Method Not Allowed), the transport still calls
markInitialized()andreconnect()before checking the status code. This triggers an unnecessary GET request, causing duplicate SSE sessions when using transport fallback (Streamable HTTP → SSE).The root cause is in the
flatMapchain at line ~480:markInitialized()andreconnect()execute unconditionally before the status code is evaluated on the next line.Fix
Move the
markInitialized()/reconnect()block inside theif (statusCode >= 200 && statusCode < 300)branch. This ensures:Testing
All 98 Streamable HTTP transport tests pass. The 1 pre-existing failure (
startContainer) is a Docker/Testcontainers infrastructure issue unrelated to this change.Fixes #773