add compatibility language to version header requirement #668
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halter73
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Jun 6, 2025
9 tasks
felixweinberger
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Jun 9, 2025
…ader When the MCP-Protocol-Version header is not present in requests, the server now assumes protocol version "2025-03-26" instead of returning an error. This maintains backwards compatibility with older clients that don't send the version header. The server still validates and returns 400 Bad Request for invalid or unsupported protocol versions when the header is explicitly provided. This change addresses the backwards compatibility requirement from modelcontextprotocol/modelcontextprotocol#668 - Modified _validate_protocol_version to assume "2025-03-26" when header is missing - Updated tests to verify backwards compatibility behavior - Added new test specifically for backwards compatibility scenario
felixweinberger
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Jun 9, 2025
…ader When the MCP-Protocol-Version header is not present in requests, the server now assumes protocol version "2025-03-26" instead of returning an error. This maintains backwards compatibility with older clients that don't send the version header. The server still validates and returns 400 Bad Request for invalid or unsupported protocol versions when the header is explicitly provided. This change addresses the backwards compatibility requirement from modelcontextprotocol/modelcontextprotocol#668 - Modified _validate_protocol_version to assume "2025-03-26" when header is missing - Updated tests to verify backwards compatibility behavior - Added new test specifically for backwards compatibility scenario
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felixweinberger
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Jun 11, 2025
…ader When the MCP-Protocol-Version header is not present in requests, the server now assumes protocol version "2025-03-26" instead of returning an error. This maintains backwards compatibility with older clients that don't send the version header. The server still validates and returns 400 Bad Request for invalid or unsupported protocol versions when the header is explicitly provided. This change addresses the backwards compatibility requirement from modelcontextprotocol/modelcontextprotocol#668 - Modified _validate_protocol_version to assume "2025-03-26" when header is missing - Updated tests to verify backwards compatibility behavior - Added new test specifically for backwards compatibility scenario
felixweinberger
added a commit
to modelcontextprotocol/python-sdk
that referenced
this pull request
Jun 12, 2025
…ader When the MCP-Protocol-Version header is not present in requests, the server now assumes protocol version "2025-03-26" instead of returning an error. This maintains backwards compatibility with older clients that don't send the version header. The server still validates and returns 400 Bad Request for invalid or unsupported protocol versions when the header is explicitly provided. This change addresses the backwards compatibility requirement from modelcontextprotocol/modelcontextprotocol#668 - Modified _validate_protocol_version to assume "2025-03-26" when header is missing - Updated tests to verify backwards compatibility behavior - Added new test specifically for backwards compatibility scenario
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The original definition for the new version header requirement (#548, #658) breaks backward compatibility by requiring servers to reject requests from old clients. Here we add a compatibility condition that lets servers assume protocol version
03-26-2025if the header is missing and the server has no other information about what protocol version the client is using.