From 64a66f76d6d52f5d439e8d44060d0f398f97cd02 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Fri, 21 Feb 2025 11:17:03 +0000
Subject: [PATCH] fix(asm): improve BlockingException catch for fastapi
 [backport 2.20] (#12422)

Backport f3e0eb3f30fd884710d967f5d1da0c88514675b3 from #12413 to 2.20.

Fastapi middleware use BaseExceptionGroup on python 3.11. With a custom
middleware, this mechanism could encapsulate BlockingException raised by
our blocking mechanism, preventing it to be properly caught to generate
a proper blocking response.

This will be tested permanently by the `fastapi` weblog, as
https://github.com/DataDog/system-tests/pull/4125 adds a custom
middleware to simulate ATO automatic instrumentation.

Due to our mandatory compatibility with previous python version, we
can't use syntaxic sugar to handle exception group.


## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Christophe Papazian <114495376+christophe-papazian@users.noreply.github.com>
---
 ddtrace/contrib/internal/asgi/middleware.py               | 8 ++++++++
 ...cking_on_fastapi_with_middleware-08ac58a6b112e29f.yaml | 5 +++++
 2 files changed, 13 insertions(+)
 create mode 100644 releasenotes/notes/fix_blocking_on_fastapi_with_middleware-08ac58a6b112e29f.yaml

diff --git a/ddtrace/contrib/internal/asgi/middleware.py b/ddtrace/contrib/internal/asgi/middleware.py
index 7da2b11b929..9cb52608f80 100644
--- a/ddtrace/contrib/internal/asgi/middleware.py
+++ b/ddtrace/contrib/internal/asgi/middleware.py
@@ -318,6 +318,14 @@ async def wrapped_blocked_send(message):
                 span.set_exc_info(exc_type, exc_val, exc_tb)
                 self.handle_exception_span(exc, span)
                 raise
+            except BaseException as exception:
+                # managing python 3.11+ BaseExceptionGroup with compatible code for 3.10 and below
+                if exception.__class__.__name__ == "BaseExceptionGroup":
+                    for exc in exception.exceptions:
+                        if isinstance(exc, BlockingException):
+                            set_blocked(exc.args[0])
+                            return await _blocked_asgi_app(scope, receive, wrapped_blocked_send)
+                raise
             finally:
                 if span in scope["datadog"]["request_spans"]:
                     scope["datadog"]["request_spans"].remove(span)
diff --git a/releasenotes/notes/fix_blocking_on_fastapi_with_middleware-08ac58a6b112e29f.yaml b/releasenotes/notes/fix_blocking_on_fastapi_with_middleware-08ac58a6b112e29f.yaml
new file mode 100644
index 00000000000..5395a247dfa
--- /dev/null
+++ b/releasenotes/notes/fix_blocking_on_fastapi_with_middleware-08ac58a6b112e29f.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    ASM: This fix resolves an issue where blocking mechanism could partially fail with a 500 error on fastapi with python>=3.11 with a custom middleware.
+