AttributeError: 'Request' object has no attribute 'prom_start_time'

before_request from export_defaults() is not guaranteed to run if some other before_request hook raises exception, for example for authentication.

Therefore, when after_request is triggered request.prom_start_time might not be set.

Suggested fix would be to skip the histogram section in after_request if request has no prom_start_time attribute.

[nonnib]

That’s an amazing turn-around time, thank you!

[nonnib]

Yes, I’m sorry, I should have elaborated. an unhandled exception will of course just crash in the before_request hook, but if the exception is handled by the app (or flask) before_request handlers which are unlucky enough to be processed after that one won’t get called, but after_request handlers will be called as usual.

Minimal example here:

from flask import Flask
from werkzeug.serving import run_simple
from prometheus_flask_exporter import PrometheusMetrics
from werkzeug.exceptions import HTTPException
app = Flask(__name__)

@app.before_request
def before_request():
    raise HTTPException(404) # or abort(404)

# if we initialize the metrics middleware _after_ our own before_request handler
# we ensure (as much as dict ordering can be ensured) that its `before_request` handlers
# are called after the one above.
metrics = PrometheusMetrics(app)

if __name__ == '__main__':
    run_simple('localhost', 8080, app, use_reloader=False)

navigate to http://localhost:8080 and you should get this error:

Traceback (most recent call last):
...
  File "/venv/lib/python3.6/site-packages/prometheus_flask_exporter/__init__.py", line 239, in after_request
    total_time = max(default_timer() - request.prom_start_time, 0)
  File "/venv/lib/python3.6/site-packages/werkzeug/local.py", line 347, in __getattr__
    return getattr(self._get_current_object(), name)
AttributeError: 'Request' object has no attribute 'prom_start_time'