fix: preserve API gateway path prefix in SSE client URL resolution#2243
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Varun6578 wants to merge 2 commits intomodelcontextprotocol:mainfrom
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fix: preserve API gateway path prefix in SSE client URL resolution#2243Varun6578 wants to merge 2 commits intomodelcontextprotocol:mainfrom
Varun6578 wants to merge 2 commits intomodelcontextprotocol:mainfrom
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Fixes modelcontextprotocol#795 When an MCP server sits behind a reverse proxy or API gateway that adds a path prefix, urljoin drops the prefix for absolute endpoint paths (starting with '/'). Add _resolve_endpoint_url() that detects gateway prefixes by finding where the endpoint's first path segment appears in the base URL path. Everything before that match is preserved as the prefix. Example: base_url: https://host/gateway/v1/sse endpoint: /v1/messages/?session_id=abc before: https://host/v1/messages/?session_id=abc (prefix lost) after: https://host/gateway/v1/messages/?session_id=abc Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Reported-by: lizzzcai <https://github.com/lizzzcai>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Fixes #795
When an MCP server sits behind a reverse proxy or API gateway that adds a path prefix (e.g.,
/gateway), the server's endpoint events contain paths without that prefix. The SSE client previously usedurljoin()which drops the base URL's path prefix for absolute paths (starting with/), causing incorrect routing through the gateway.Changes
src/mcp/client/sse.py:_resolve_endpoint_url()that detects and preserves reverse proxy/API gateway path prefixesurljoin(url, sse.data)with_resolve_endpoint_url(url, sse.data)on the endpoint event handlertests/shared/test_sse.py:_resolve_endpoint_url()covering:/org/team/v1/sse)How it works
The function detects gateway prefixes by finding where the endpoint's first path segment appears in the base URL path. Everything before that match is the prefix to preserve.