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A request without MCP-Protocol-Version is treated as 2025-03-26, so servePOST accepted its JSON-RPC batch even when ServerOptions.SupportedProtocolVersions excluded every version before 2025-06-18, while the same batch with an explicit 2025-03-26 header was rejected as an unsupported version. Reject such batches with 400. Servers that still support 2025-03-26 or earlier keep accepting them. Fixes modelcontextprotocol#1513 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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This PR has been closed automatically. This repo only keeps pull requests open when they come from a maintainer, or from a contributor a maintainer has assigned to the linked issue, and you aren't currently assigned to #1513. You're welcome to keep pushing commits here (just avoid force-pushing, since GitHub can't reopen a rewritten branch), but that on its own won't get the PR reviewed or the issue assigned. There's no need to open a new PR either way. Maintainers: reopen, remove |
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Fixes #1513
A Streamable HTTP request without
MCP-Protocol-Versionis treated as 2025-03-26, so its JSON-RPC batch was accepted even whenServerOptions.SupportedProtocolVersionsexcluded every version before 2025-06-18. The same batch with an explicitMCP-Protocol-Version: 2025-03-26header is rejected as an unsupported version.servePOSTnow rejects such a batch with 400 when the server supports no version before 2025-06-18. Servers that still support 2025-03-26 or earlier, including the default configuration, keep accepting batches, and single messages without the header are unaffected.Covered by the new table test
TestStreamableServerBatchWithoutVersionHeader(stateful and stateless);gofmt,go vet,staticcheckandgo test -race ./...pass.I used Claude Code to help investigate this and write the patch; I reviewed the change and can explain it.
🤖 Generated with Claude Code