chore(flask): emit pre-request web event - #19816
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Pull request overview
This PR introduces a new internal web-framework event (WebFrameworkEvents.WEB_REQUEST_STARTING) and emits it from the Flask integration at WSGI entry, intended to let downstream logic observe method/path before Flask request context and the root web span are created (motivated by the MicroVM /run identity-refresh ordering constraint).
Changes:
- Add
WebFrameworkEvents.WEB_REQUEST_STARTING = "web.request.starting". - Emit the event from
ddtrace.contrib.internal.flask.patch.patched_wsgi_app()as soon asREQUEST_METHODand path info are available in the WSGI environ. - Add Flask tests asserting the event is emitted (including for 404s) and that emission happens before the Flask WSGI middleware runs.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
ddtrace/contrib/_events/web_framework.py |
Adds the new WEB_REQUEST_STARTING enum value. |
ddtrace/contrib/internal/flask/patch.py |
Dispatches the new pre-request event at Flask WSGI entry. |
tests/contrib/flask/test_microvm_identity_refresh.py |
Adds coverage validating the event is emitted and ordered before tracing/middleware. |
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| events = [] | ||
| environ = {"REQUEST_METHOD": "POST", "PATH_INFO": REQUEST_STARTING_PATH, "SCRIPT_NAME": ""} | ||
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| def start_response(status, headers, exc_info=None): | ||
| pass | ||
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| def wrapped(environ, start_response): | ||
| return [] | ||
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| def dispatch(name, args): | ||
| if name == WebFrameworkEvents.WEB_REQUEST_STARTING.value: | ||
| events.append("starting") | ||
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| core.dispatch( | ||
| WebFrameworkEvents.WEB_REQUEST_STARTING.value, (environ.get("REQUEST_METHOD"), environ.get("PATH_INFO")) | ||
| ) |
This was referenced Aug 23, 2026
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This was referenced Aug 23, 2026
This was referenced Aug 23, 2026
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Description
The MicroVM
/runrequest has to be observed before a web root span reads runtime identity. This PR keeps the request-starting event coverage scoped to Flask.This adds a
WebFrameworkEvents.WEB_REQUEST_STARTINGevent and emits it from Flask once method and path are known, before request context/root span creation. The event is intentionally not tied to MicroVMs or runtime-id refresh in this PR.This PR replaces #19779 as renaming the branch from
tianning.li/2-web-request-starting-eventtotianning.li/2-flask-web-request-starting-eventled to PR close while it could no longer be associated with another branch.Testing
scripts/lint fmt ddtrace/contrib/internal/flask/patch.pyscripts/lint format_check ddtrace/contrib/_events/web_framework.py ddtrace/contrib/internal/flask/patch.py tests/contrib/flask/test_microvm_identity_refresh.pyscripts/run-tests tests/contrib/flask/test_microvm_identity_refresh.py --venv 1c6c710 -- -- -q tests/contrib/flask/test_microvm_identity_refresh.py(fails during local pytest setup with stale native extension:ImportError: cannot import name 'process_metrics' from 'ddtrace.internal.native._native')Risks
Low. The event is emitted on Flask request entry, but it has no listener in this PR. The no-listener path should be cheap.
Release note
None. This PR adds an internal event emitter with no customer-visible listener. Use
changelog/no-changelog.Additional Notes
Depends on #19778. Follow-up PR adds stdlib
http.serversupport.