Improved Trio support by agronholm · Pull Request #946 · modelcontextprotocol/python-sdk · GitHub

Removed the asyncio-only parametrization of the anyio_backend except for test_ws, as websockets doesn't support Trio yet
Try to close async generators explicitly where possible
Changed nesting order for more predictable closing of async resources
Refactored __aenter__ and __aexit__ in some cases to exit the task group if there's a problem during initialization
Fixed test failures in client/test_auth.py where an async fixture was used in sync tests
Fixed subtle bug in SimpleEventStore where retrieving the stream ID was timing-dependent
Added typing-extensions to dependencies, as the code already imported it unconditionally

Motivation and Context

This was requested at https://github.com/anthropics/oss-collab/issues/60.

How Has This Been Tested?

No.

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

* Removed the asyncio-only parametrization of the anyio_backend except for test_ws, as `websockets` doesn't support Trio yet * Try to close async generators explicitly where possible * Changed nesting order for more predictable closing of async resources * Refactored `__aenter__` and `__aexit__` in some cases to exit the task group if there's a problem during initialization * Fixed test failures in client/test_auth.py where an async fixture was used in sync tests * Fixed subtle bug in `SimpleEventStore` where retrieving the stream ID was timing-dependent

Can we solve those? Why this doesn't happen on asyncio?

Trio considers implicit async generator finalization a bad practice and emits a warning. Pytest turns this into an unraisable exception warning.

The only way to fix this is to fix the problem in httpcore.

How would the fix in httpcore look like?

Ah, this is not resource warning anyway, I'm okay with it. I read it wrongly.

The httpcore PR is ready, just waiting for review.

EDIT: the PR has been accepted, waiting for merge.

The httpx PR: encode/httpx#3593

Everything seems to fall into place now. With all my local changes applied, the test suite runs flawlessly on Trio.

Great work!

The httpx PR is now passing all tests with 100% coverage. Waiting for a review and merging.

…c library on the test server

I found another issue in the test suite where I got a RuntimeError: Task got bad yield: <class 'trio._core._traps.CancelShieldedCheckpoint'>. This turned out to be caused by multiprocess forking the process for running a test server, where the sniffio contextvar was inherited from the parent. I fixed that by using spawning instead of forking.

The only things standing in the way of this passing are:

tests: use inline_snapshot.Is on parametrized test #945

a new httpx-sse release v0.4.1 has been released now

getting Ensure that all async generators are explicitly closed encode/httpcore#1019 merged and a new release cut

getting Ensured explicit closing of async generators encode/httpx#3593 merged and a new release cut

Hi both, thank you for working on this!

Just catching up here on the current state, looks like we're still waiting on these items to be able to land this PR?

httpx-sse dependency seems resolved
#945 from @Kludex
encode/httpcore#1019 from @agronholm (looks approved?)
encode/httpx#3593 possibly waiting for review from @Kludex?
Probably a rebase pending the above?

Let me know if I can help with any of these!

Marking this as "pending dependency changes" for now - looks like encode/httpx#3593 may have been closed while encode/httpcore#1019 is still pending?

Keen to support where needed to get this improvement landed! I've commented on encode/httpcore#1019 to see if there's anything else needed as it looks approved and able to merge?

Marking this as "pending dependency changes" for now - looks like encode/httpx#3593 may have been closed while encode/httpcore#1019 is still pending?

Keen to support where needed to get this improvement landed! I've commented on encode/httpcore#1019 to see if there's anything else needed as it looks approved and able to merge?

httpcore is abandonware now that httpx 1.0 is under development. I don't expect to ever see another release of httpcore.

Marking this as "pending dependency changes" for now - looks like encode/httpx#3593 may have been closed while encode/httpcore#1019 is still pending?
Keen to support where needed to get this improvement landed! I've commented on encode/httpcore#1019 to see if there's anything else needed as it looks approved and able to merge?

httpcore is abandonware now that httpx 1.0 is under development. I don't expect to ever see another release of httpcore.

Gotcha, thanks for the response! Looking at the discussion here https://github.com/anthropics/oss-collab/issues/60 it sounds like we'd need to update this repo to httpx 1.0 whenever it lands to be able to ship this change?

That seems like it might require some bigger changes / refactors to the SDK, tentatively earmarking that for v2 for now as it seems like it would introduce some breaking changes potentially.

Converting this to "Draft" for now as I believe we're blocked on the httpx 1.0 upgrade and to remove this one from the team's review queue while we await that.

Marking this as "pending dependency changes" for now - looks like encode/httpx#3593 may have been closed while encode/httpcore#1019 is still pending?
Keen to support where needed to get this improvement landed! I've commented on encode/httpcore#1019 to see if there's anything else needed as it looks approved and able to merge?

httpcore is abandonware now that httpx 1.0 is under development. I don't expect to ever see another release of httpcore.

We are moving to httpx2, I've merged ur work in httpcore2. I'll update this when #2693 lands.

agronholm added 2 commits June 12, 2025 13:49

Fixed pre-commit errors

0ce5b79

Kludex reviewed Jun 12, 2025

View reviewed changes

agronholm added 3 commits June 13, 2025 11:57

Merge branch 'main' into trio-support

5fec84c

Fixed uses of async generators and removed the pytest warning ignore

83d23ad

Merge branch 'main' into trio-support

3fc76c0

This was referenced Jun 18, 2025

Ensure that all async generators are explicitly closed florimondmanca/httpx-sse#30

Merged

tests: use inline_snapshot.Is on parametrized test #945

Merged

agronholm added 6 commits June 23, 2025 13:39

Use spawn instead of fork to prevent sniffio detecting the wrong asyn…

85c50f2

…c library on the test server

Bumped httpx-sse to v0.4.1

95f0518

Merge branch 'main' into trio-support

b1d242a

Fixed flaky server-side SSE tests

7759fbe

Merge branch 'main' into trio-support

2425453

Removed obsolete comment

62aeec9

ihrpr assigned felixweinberger Jul 8, 2025

felixweinberger self-requested a review July 11, 2025 12:35

felixweinberger reviewed Jul 14, 2025

View reviewed changes

felixweinberger requested a review from ihrpr July 15, 2025 15:56

Kludex mentioned this pull request Jul 17, 2025

Ensure that all async generators are explicitly closed encode/httpcore#1019

Open

3 tasks

felixweinberger added pending upstream changes and removed pending upstream changes labels Sep 17, 2025

felixweinberger requested changes Sep 17, 2025

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felixweinberger added the pending dependency updates label Sep 17, 2025

felixweinberger added v2 Affects the v2 line (2.x on main) needs more eyes labels Sep 17, 2025

felixweinberger marked this pull request as draft September 26, 2025 14:41

felixweinberger added this to the Python SDK v2.0 milestone Sep 30, 2025

felixweinberger removed their assignment Oct 14, 2025

felixweinberger removed pending dependency updates labels Nov 12, 2025

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+                  # This is to avoid test failures on Trio due to httpx's failure to explicitly close
+                  # async generators
+                  "ignore::pytest.PytestUnraisableExceptionWarning"

Improved Trio support by agronholm · Pull Request #946 · modelcontextprotocol/python-sdk · GitHub

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Improved Trio support - #946

Improved Trio support#946agronholm wants to merge 11 commits intomodelcontextprotocol:mainmodelcontextprotocol/python-sdk:mainfrom agronholm:trio-supportagronholm/python-sdk:trio-supportCopy head branch name to clipboard

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agronholm commented Jun 12, 2025

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Kludex commented Jun 2, 2026

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