[Client] Check HTTP status codes in HttpTransport - #425
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HttpTransport::send() never looked at the HTTP status code of the response. A 404 JSON error body was parsed as a regular message, and non-JSON error bodies (e.g. text/plain) were dropped silently, leaving the caller waiting on the request timeout. Check the status code before dispatching the body: - 404 with a session id set means the session is gone: clear the local session id and throw SessionExpiredException so the application can re-initialize. - any other non-2xx status throws HttpTransportException carrying the status code and a snippet of the body. Also send the MCP-Protocol-Version header once the initialize handshake has negotiated a version, as the streamable HTTP spec requires. Tests cover the 404-with-session, 404-without-session, 500, 200 and header-present/absent cases with mocked HTTP clients.
ez-lbz
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CodeWithKyrian,
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chr-hertel and
soyuka
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August 16, 2026 15:05
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HttpTransport::send() never looked at the HTTP status code of the response. A 404 JSON error body was parsed as a regular message, and non-JSON error bodies (e.g. text/plain) were dropped silently, leaving the caller waiting on the request timeout.
This change checks the status code before dispatching the body:
SessionExpiredExceptionis thrown so the application can re-initialize.HttpTransportException(new, inMcp\Client\Exception) carrying the status code and a snippet of the body.It also sends the
MCP-Protocol-Versionheader on every POST once the initialize handshake has negotiated a version, as the streamable HTTP spec requires; before negotiation the header is omitted.Tests in
HttpTransportTestcover the 404-with-session, 404-without-session, 500 text/plain, 200 application/json and header-present/absent cases using mocked HTTP clients.