mcp: reject discover when transport lacks version - #1108
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piyushbag wants to merge 2 commits into
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Use the session transport-filtered supportedVersions in ServerSession.handle so stateful Streamable HTTP servers return UnsupportedProtocolVersionError instead of a DiscoverResult that omits the probed protocol version.
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| if validatedMeta.usesNewProtocol { | ||
| requested := validatedMeta.initializeParams.ProtocolVersion | ||
| ss.mu.Lock() | ||
| versions := ss.supportedVersions | ||
| ss.mu.Unlock() |
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rejecting calls to server/discover when stateless=false, will make the ss.supportedVersions useless.
We decided to implement it in this way to allow a more meaningful response in case of new server but on stateful mode.
If we want to change this implementation, it would be easier to change the code in streamable, removing the guard for server discover
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Problem
On a stateful Streamable HTTP server,
ServerSession.handlegates new-protocol requests against the globalsupportedProtocolVersionslist. The transport-filtered list (viafilterSupportedVersions/SupportsProtocolVersion) can omit2026-07-28, yetserver/discoverstill returned HTTP 200 with aDiscoverResultthat excluded the probed version instead ofUnsupportedProtocolVersionError.Approach
Align the version gate in
handlewith the session's transport-filteredsupportedVersions, matching whatserver/discoveradvertises. Rename and update the stateful regression test to expect HTTP 400 withCodeUnsupportedProtocolVersion.Test plan
go test ./...go test -race ./...TestStreamableStateful_DiscoverRejectsUnsupportedVersionFixes #1025