mcp: Implement server-side support for discover method (SEP-2575)#987
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guglielmo-san merged 46 commits intoJun 8, 2026
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…lidation and accessors
…est rejections and update associated tests
…ed regression tests
…t stateless protocol to stateless HTTP servers
…n the new protocol session
…t initialization and version negotiation
…protocol version checking in server and tests
… protocol version validation logic
…ata into requests
…/SEP-2575_Stateless_MCP_part2
… test metadata injection logic
…y in server request handling
…per for InitializeParams
…ready initialized
…rt headers and conditional SSE stream initialization
…ization, and correct session metadata mapping
…k triggers in MCP client
…acks and clarify KeepAlive constraints
…version propagation in client and transport layers
…discover implementation
…/SEP-2575_Stateless_MCP_part2
Resolved conflicts with these strategies: - Took main's version for SEP-2575 client-side bits already merged via PR #975 (the cleaner, reviewed version supersedes the part2/part3 in-progress code). - Kept part3-unique additions: * Real server-side server/discover handler (replaces main's stub). * UnsupportedProtocolVersionData type per SEP-2575. * Server allows server/discover on stateful HTTP transport (stateless-only rejection exempts methodDiscover). * Rejection of methodSubscribe/methodUnsubscribe in the new protocol. * TestStreamableStateful_AcceptsDiscover regression test. - Removed duplicate injectMeta in shared.go (main moved injection to per-method injectRequestMeta in client.go; the centralized helper was redundant). - Removed duplicate Server.discover stub left behind by the merge. Known failures (pre-existing test expectations, not regressions from the merge): - TestMiddleware, ExampleLoggingTransport: written assuming Connect always triggers server/discover, but main's logic requires explicit opt-in via ClientSessionOptions{protocolVersion: protocolVersion20260630}. - TestStreamableClientUnsupportedVersionFallback: requires a "Bad Request" substring fallback that part3 had but main removed. The structural fix is to parse the JSON-RPC error body in checkResponse and match by error.code.
…ing errors.Is for wrapped errors
…over and add end-to-end smoke tests
…or client and server tests
…N-RPC error responses.
…ate documentation for methodDiscover initialization logic
…rror handling, and enable stateless HTTP conformance server
…cing opt-in for HTTP responses
Conflicts: - mcp/server.go: union of the removed-in-new-protocol method list, keeping both branch additions (methodSubscribe, methodUnsubscribe) and main's addition (methodSetLevel) from PR #997. - mcp/client_test.go: kept all five branch-side TestInMemory_E2E_Discover* tests and main's new TestClientConnectDiscover_UnsupportedVersionNegotiation from PR #989 (retry on advised supportedVersions). Conflict was textual (adjacent functions) not semantic. Additional fix to make PR #989's negotiation test pass on this branch: exempt server/discover from the dispatcher's unsupported-version gate so that a probing client with an unsupported MCP-Protocol-Version can still reach the discover handler and learn the server's supportedVersions via the UnsupportedProtocolVersionError Data payload. Without this exemption, the gate at server.go:1561 short-circuited before the handler ran, leaving the client with no Supported list to negotiate from.
nahapetyan-serob
approved these changes
Jun 8, 2026
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Summary
Part 3 of the SEP-2575 ("Make MCP Stateless") implementation. Builds on PR #975 which landed the client-side discover/fallback flow and the per-request
_metaplumbing. This PR adds the server-side counterparts:server/discoverhandler (replaces the stub),ProtocolVersionSupporter`ServerSession.handle,internal/jsonrpc2,processResultwith anMCPGODEBUGopt-out for backward compatibility.