René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"HTTP transport swallows non-2xx status codes causing client to hang","articleBody":"## Summary\n\nWhen an MCP server returns non-2xx HTTP status codes (401/403/404/5xx), the Streamable HTTP and SSE transports do not reliably propagate the error to the caller. In the Streamable HTTP transport, `post_writer` catches exceptions and logs them, but the caller blocks indefinitely waiting for a response on the read stream. HTTP 404 responses are also converted to `JSONRPCError(code=32600)`, losing the original HTTP status information.\n\n## Expected Behavior\n\n- Non-2xx HTTP responses should be surfaced as exceptions to the caller, not silently logged\n- The original HTTP status code should be preserved and accessible\n- Auth-related errors (401/403) should be distinguishable from other failures\n\n## Current Behavior\n\n- `post_writer` in Streamable HTTP transport catches and logs errors without forwarding them through the read stream\n- Callers hang indefinitely waiting for a response\n- HTTP 404 is converted to `JSONRPCError(code=32600)`, destroying HTTP-level context\n\n## Affected Code\n\n- `src/mcp/client/streamable_http.py` (post_writer)\n- `src/mcp/client/sse.py` (sse_reader)\n\n## Related\n\n- #1742 — broader typed error classes design","author":{"url":"https://github.com/maxisbey","@type":"Person","name":"maxisbey"},"datePublished":"2026-02-19T20:29:41.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/2110/python-sdk/issues/2110"}