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feat: implement OPTIONS request support for Preflight checks in StreamableHTTP #1245

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feat: implement OPTIONS request support for Preflight checks in StreamableHTTP #1245

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TheRealSeber
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Motivation and Context

Fixes: (#1079)

How Has This Been Tested?

Locally

Breaking Changes

No

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

None

@TheRealSeber TheRealSeber requested review from a team and ihrpr August 7, 2025 02:35
@TheRealSeber TheRealSeber changed the title feat: implement OPTIONS request support for Preflight checks feat: implement OPTIONS request support for Preflight checks in StreamableHTTP Aug 7, 2025
domdomegg
domdomegg approved these changes Aug 9, 2025
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@domdomegg domdomegg left a comment

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LGTM. Would appreciate @ihrpr or @maxisbey sanity checking though

@Kludex
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Kludex commented Aug 9, 2025 •
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This shouldn't go in like this.

Similar to #1201.

felixweinberger
felixweinberger requested changes Sep 22, 2025
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@felixweinberger felixweinberger left a comment •
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Requesting changes as this seems too permissive - needs some alignment on what the right approach is to handle this.

@felixweinberger felixweinberger added needs more eyes Needs alignment among maintainers whether this is something we want to add needs maintainer action Potentially serious issue - needs proactive fix and maintainer attention enhancement New feature or request labels Sep 22, 2025
@felixweinberger felixweinberger mentioned this pull request Sep 22, 2025
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@felixweinberger felixweinberger modified the milestones: middle, Middleware Sep 23, 2025
@felixweinberger
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Taking a step back, what's the actual motivation for this support? I'm not sure OPTIONS should be supported on StreamableHTTP.

@felixweinberger felixweinberger added needs confirmation Needs confirmation that the PR is actually required or needed. needs SEP Major changes to structs and features generally require a SEP to be approved. and removed needs maintainer action Potentially serious issue - needs proactive fix and maintainer attention needs confirmation Needs confirmation that the PR is actually required or needed. needs more eyes Needs alignment among maintainers whether this is something we want to add labels Sep 30, 2025
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Discussed this internally, this would need a SEP as the spec doesn't currently contain any specification for OPTIONS support, we only specify POST and GET on the streamable HTTP transport: https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http

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@felixweinberger felixweinberger felixweinberger requested changes

@domdomegg domdomegg domdomegg approved these changes

@ihrpr ihrpr Awaiting requested review from ihrpr

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enhancement New feature or request needs SEP Major changes to structs and features generally require a SEP to be approved.
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4 participants
@TheRealSeber @Kludex @felixweinberger @domdomegg