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fix(server): set Allow: POST on stateless legacy 405 responses - #3002
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felixweinberger merged 4 commits intoOct 23, 2026
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🦋 Changeset detectedLatest commit: d5f14f2 The changes in this PR will be included in the next version bump. This PR includes changesets to release 6 packages
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@modelcontextprotocol/client
@modelcontextprotocol/codemod
@modelcontextprotocol/core
@modelcontextprotocol/server
@modelcontextprotocol/server-legacy
@modelcontextprotocol/express
@modelcontextprotocol/fastify
@modelcontextprotocol/hono
@modelcontextprotocol/node
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Verified the fix: on main, a focused 405 test expects Allow: POST but receives null (2 failed). On this branch, the full server suite passes — 576 tests in 20.7s. The change adds the header in the non-POST branch at packages/server/src/server/createMcpHandler.ts:337-355, and the new assertions pin it at packages/server/test/server/legacyStatelessFallback.test.ts:90 and packages/server/test/server/createMcpHandler.test.ts:549. RFC 9110 compliance for the stateless fallback looks solid. |
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…nfo in result _meta, clientInfo optional (modelcontextprotocol#2513)
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createMcpHandler's legacy stateless fallback answered non-POST requests with 405 without an Allow header. RFC 9110 §15.5.6 requires Allow on 405, and WebStandardStreamableHTTPServerTransport.handleUnsupportedRequest already sets it. Stateless serving only accepts POST, so advertise that. Closes modelcontextprotocol#2970 Assisted-by: AI (Grok Bot)
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Moves the header into jsonRpcErrorResponse, so the 405 of legacy: 'reject' carries it too, and asserts it in the e2e requirement that runs on both postures.
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Motivation and Context
Fixes #2970.
createMcpHandler's legacy stateless fallback answers non-POSTrequests with405 Method not allowedbut omits theAllowheader. RFC 9110 §15.5.6 requiresAllowon 405 responses.WebStandardStreamableHTTPServerTransport.handleUnsupportedRequest()already setsAllow: GET, POST, DELETE; the stateless fallback only acceptsPOST, so it should advertiseAllow: POST.How Has This Been Tested?
legacyStatelessFallback.test.tsandcreateMcpHandler.test.tsto assertAllow: POST.mainand pass with this change.createMcpHandler+legacyStatelessFallbacksuites (61 tests).pnpm --filter @modelcontextprotocol/server typecheckandlintpassed.Breaking Changes
None. Adds a response header on an existing 405 path; status and JSON-RPC body are unchanged.
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AI assistance
This change was prepared with AI assistance (Grok Bot). I reviewed the diff, ran the tests above, and take responsibility for the content.