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Title: fix: propagate HTTP errors from transports instead of silently logging by MaxwellCalkin · Pull Request #2249 · modelcontextprotocol/python-sdk · GitHub

Open Graph Title: fix: propagate HTTP errors from transports instead of silently logging by MaxwellCalkin · Pull Request #2249 · modelcontextprotocol/python-sdk

X Title: fix: propagate HTTP errors from transports instead of silently logging by MaxwellCalkin · Pull Request #2249 · modelcontextprotocol/python-sdk

Description: Note: This PR was authored by Claude (AI), operated by @MaxwellCalkin. Summary Fixes #2110 When an MCP server returns non-2xx HTTP status codes (401/403/404/5xx), the Streamable HTTP and SSE transports silently log the error but don't propagate it to the caller. The caller hangs indefinitely waiting for a response on the read stream. Changes New HttpError exception class (src/mcp/shared/exceptions.py): Preserves the original HTTP status code is_auth_error property to distinguish 401/403 from other failures Optional body field for response body context Exported from the top-level mcp package Streamable HTTP transport (src/mcp/client/streamable_http.py): _handle_post_request: 401/403 responses now raise HttpError (in addition to sending a JSONRPCError for request messages), so the caller gets an exception instead of hanging _handle_post_request: Generic 4xx/5xx responses also raise HttpError instead of silently returning _handle_post_request: HTTP 404 error message now includes "(HTTP 404)" and data={"http_status": 404} to preserve HTTP-level context _handle_post_request: All error responses include data={"http_status": } in the JSONRPCError post_writer: handle_request_async now wraps calls in try/except and forwards exceptions through read_stream_writer.send(exc) so callers don't hang post_writer: Outer exception handler also forwards errors through the read stream SSE transport (src/mcp/client/sse.py): post_writer: 401/403 responses detected before raise_for_status() and forwarded as HttpError through the read stream post_writer: httpx.HTTPStatusError from raise_for_status() converted to HttpError and forwarded through the read stream post_writer: Generic exceptions forwarded through the read stream instead of being silently logged Before # Caller hangs forever waiting for a response that will never come async with streamable_http_client("https://example.com/mcp") as (read, write): await write.send(SessionMessage(request)) response = await read.receive() # blocks indefinitely on 401/403/5xx After # Caller receives an HttpError exception through the read stream async with streamable_http_client("https://example.com/mcp") as (read, write): await write.send(SessionMessage(request)) response = await read.receive() # receives HttpError or JSONRPCError with http_status # Or catch it directly from mcp.shared.exceptions import HttpError try: ... except HttpError as e: if e.is_auth_error: print(f"Auth failed: {e.status_code}") Test plan Verify existing tests pass (no behavioral change for 2xx responses) Verify 401/403 responses raise HttpError with is_auth_error == True Verify 404 responses include HTTP status in error data Verify 5xx responses raise HttpError and don't cause caller to hang Verify HttpError is importable from mcp top-level package

Open Graph Description: Note: This PR was authored by Claude (AI), operated by @MaxwellCalkin. Summary Fixes #2110 When an MCP server returns non-2xx HTTP status codes (401/403/404/5xx), the Streamable HTTP and SSE transp...

X Description: Note: This PR was authored by Claude (AI), operated by @MaxwellCalkin. Summary Fixes #2110 When an MCP server returns non-2xx HTTP status codes (401/403/404/5xx), the Streamable HTTP and SSE transp...

Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/pull/2249

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