fix: preserve HTTP status code in streamable HTTP client error messages#2173
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giulio-leone wants to merge 1 commit intomodelcontextprotocol:mainfrom
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When the streamable HTTP transport receives a 4xx/5xx response it currently reports a generic 'Server returned an error response' message, discarding the actual HTTP status code and any response body. This makes it very hard to debug upstream issues (e.g. 401 vs 403 vs 502). Include the HTTP status code and up to 200 chars of the response body in the error message so callers get actionable diagnostics. Fixes modelcontextprotocol#2110 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Problem
When the streamable HTTP transport receives a 4xx/5xx response, it currently reports a generic
Server returned an error responsemessage, discarding the actual HTTP status code and any response body. This makes it very hard to debug upstream issues (e.g., distinguishing a 401 Unauthorized from a 403 Forbidden or a 502 Bad Gateway).Fixes #2110
Solution
Include the HTTP status code and up to 200 characters of the response body in the error message so callers get actionable diagnostics.
Before
After
Changes
src/mcp/client/streamable_http.py: Read and include the HTTP status code and (truncated) response body in the error message returned viaErrorData.Testing