Fix MCP Streamable HTTP transport compliance#6610
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IMax153 merged 4 commits intoJul 25, 2026
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🦋 Changeset detectedLatest commit: 34ddf6f The changes in this PR will be included in the next version bump. This PR includes changesets to release 28 packages
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📝 WalkthroughWalkthroughMcpServer now centralizes protocol sessions and versions, validates HTTP methods and protocol headers, returns 202 for accepted empty responses, and expands lifecycle and transport tests with reusable HTTP harnesses. ChangesMCP HTTP transport and lifecycle
Estimated code review effort: 4 (Complex) | ~45 minutes Suggested labels: Sequence Diagram(s)sequenceDiagram
participant Client
participant HttpRouter
participant McpServer
participant McpProtocolState
Client->>HttpRouter: Send MCP HTTP request
HttpRouter->>McpServer: Route POST request
McpServer->>McpProtocolState: Validate version and read session
McpProtocolState-->>McpServer: Return negotiated state
McpServer-->>Client: Return 200, 202, or 400 response
HttpRouter-->>Client: Return 405 for unsupported method
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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@packages/effect/src/unstable/ai/McpServer.ts`:
- Around line 442-448: Update the HTTP request lookup in the shown dispatch
callback to use Context.getOrUndefined with the current fiber context, matching
clientMiddleware’s existing behavior. Preserve the isHttp guard and subsequent
undefined check so callbacks without HttpServerRequest degrade gracefully
instead of throwing.
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Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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.changeset/calm-servers-share.mdpackages/effect/src/unstable/ai/McpServer.tspackages/effect/test/unstable/ai/McpServer.test.ts
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@ebramanti - I took the opportunity while reviewing your PR to fix a bunch of issues we had with MCP server initialization, and add a targeted test suite for lifecycle tests. A member of our community is interested in working with me on the more global MCP server refactor, which you can follow along with / chat with us about here. |
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Type
Description
Updates
McpServer.layerHttpto comply with the MCP Streamable HTTP transport specification.405 Method Not AllowedwithAllow: POSTfor unsupported GET, HEAD, PUT, PATCH, and DELETE requests at the MCP endpoint.202 Acceptedresponse for accepted JSON-RPC notifications and responses while preserving normal200JSON-RPC request responses.MCP-Protocol-Versionheaders before dispatch and returns an empty400 Bad Requestresponse for unsupported versions.MCP-Protocol-Versionresponse header after initialization.Related
Summary by CodeRabbit
New Features
404 Not Found.202 Accepted, including the negotiated protocol/version headers.Bug Fixes
405 Method Not Allowedand advertiseallow: POST.MCP-Protocol-Versionvalues are rejected with400 Bad Request.Documentation
layerHttptransport docs to reflect the new status-code and header rules.Tests