[flask] avoid double instrumentation when TraceMiddleware is used #538
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Kyle-Verhoog
requested changes
Aug 13, 2018
| def handle_me(): | ||
| raise HandleMe() | ||
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| @app.route('/fatal') |
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moving this route handler to this file breaks this line of this test:
dd-trace-py/tests/contrib/flask/test_flask.py
Line 274 in 23287fe
since now the error is in contrib/flask/web.py
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nice catch! thank you very much!
Kyle-Verhoog
approved these changes
Aug 13, 2018
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Overview
In some cases it's possible to instrument the framework twice. For instance, using
ddtrace-runand theTraceMiddlewaretogether will produce unexpected behavior. Using both is not the right behavior and it's possible to hit this code-path, causing traces to not be sent.This safe-guard ensures that signals and callbacks are attached to the Flask application only once, making the instrumentation idempotent and safe.
Note
I've refactored also the test suite, to make these tests possible. The main change is explained here: 23287fe