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mcp: fix potential nil-pointer dereference on message send - #1115
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nahapetyan-serob
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Jul 27, 2026
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gwyszynski-sa
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Aug 13, 2026
setMCPHeaders resolved Mcp-Protocol-Version from the request context before c.initializedResult. modelcontextprotocol#1107 established the opposite order and said so in its description; the code it replaced also consulted the context last. The two branches were transposed by the switch-to-if rewrite in modelcontextprotocol#1115, whose subject was an unrelated nil-pointer check. The context branch serves the pre-negotiation server/discover probe, which sets its own value in Client.Connect. Once a version has been negotiated it is the authoritative one for that connection, so initializedResult should win. _meta.protocolVersion from the outgoing message stays on top, so modelcontextprotocol#1109 stays fixed. The existing table built its request with http.NewRequest, so protocolVersionFromContext returned "" in every case and the two orderings were indistinguishable, which is why the transposition went unnoticed. Adds a ctxVersion dimension and three cases pinning the precedence. Fixes modelcontextprotocol#1162
guglielmo-san
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Aug 18, 2026
…1163) setMCPHeaders resolved Mcp-Protocol-Version from the request context before c.initializedResult. #1107 established the opposite order and said so in its description; the code it replaced also consulted the context last. The two branches were transposed by the switch-to-if rewrite in #1115, whose subject was an unrelated nil-pointer check. The context branch serves the pre-negotiation server/discover probe, which sets its own value in Client.Connect. Once a version has been negotiated it is the authoritative one for that connection, so initializedResult should win. _meta.protocolVersion from the outgoing message stays on top, so #1109 stays fixed. The existing table built its request with http.NewRequest, so protocolVersionFromContext returned "" in every case and the two orderings were indistinguishable, which is why the transposition went unnoticed. Adds a ctxVersion dimension and three cases pinning the precedence. Fixes #1162 Co-authored-by: Guglielmo Colombo <guglielmoc@google.com>
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