fix: reject unsupported MCP protocol version headers#958
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Fixes #957.
This keeps
initializeon the existing negotiation path. At that point the client can still be advertising its newest supported protocol version, so rejecting the header before negotiation would break the current fallback behavior.For later Streamable HTTP requests, the servlet now rejects a non-empty
MCP-Protocol-Versionvalue unless it is one of the server supported versions. That covers POST requests on an established session as well as GET and DELETE session operations.I added an integration test that initializes a session, sends
notifications/initialized, then verifies thattools/listreturns 400 for both an unsupported version and a malformed version.Tested with:
./mvnw.cmd -pl mcp-test -am -Dtest=HttpClientStreamableHttpVersionNegotiationIntegrationTests -Dsurefire.failIfNoSpecifiedTests=false test