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fix(mcp): comply with spec on protocol version negotiation #8

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fix(mcp): comply with spec on protocol version negotiation #8

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13 changes: 3 additions & 10 deletions src/mcp/mcp_server.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -145,17 +145,10 @@ json McpServer::handleInitialize(const json& msg)
{
json id = msg.value("id", json(nullptr));

// Validate client protocol version for compatibility
// Per MCP spec: always respond with the version we support; the client
// decides whether to continue or disconnect. Strict equality on the
// client's requested version was wrong and breaks newer clients.
static constexpr const char* kSupportedProtocolVersion = "2025-03-26";
json params = msg.value("params", json::object());
if (params.contains("protocolVersion")) {
std::string clientVersion = params["protocolVersion"].get<std::string>();
if (clientVersion != kSupportedProtocolVersion) {
return makeError(id, -32602,
"Unsupported protocol version: " + clientVersion +
" (server supports " + kSupportedProtocolVersion + ")");
}
}

json result;
result["protocolVersion"] = kSupportedProtocolVersion;
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