Flask extension raises StopIteration during certain tests

It seems that the Flask extension is causing the Werkzeug test client to raise a StopIteration exception.

Here’s part of the traceback:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
virtualenv/lib/python2.7/site-packages/werkzeug/test.py:772: in post
    return self.open(*args, **kw)
virtualenv/lib/python2.7/site-packages/flask/testing.py:108: in open
    follow_redirects=follow_redirects)
virtualenv/lib/python2.7/site-packages/werkzeug/test.py:736: in open
    response = self.run_wsgi_app(environ, buffered=buffered)
virtualenv/lib/python2.7/site-packages/werkzeug/test.py:659: in run_wsgi_app
    rv = run_wsgi_app(self.application, environ, buffered=buffered)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

app = <Flask 'honeycomb'>
environ = {'CONTENT_LENGTH': '29', 'CONTENT_TYPE': 'application/json', 'HTTP_CONTENT_LENGTH': '29', 'HTTP_CONTENT_TYPE': 'application/json', ...}
buffered = False

    def run_wsgi_app(app, environ, buffered=False):
        """Return a tuple in the form (app_iter, status, headers) of the
        application output.  This works best if you pass it an application that
        returns an iterator all the time.

        Sometimes applications may use the `write()` callable returned
        by the `start_response` function.  This tries to resolve such edge
        cases automatically.  But if you don't get the expected output you
        should set `buffered` to `True` which enforces buffering.

        If passed an invalid WSGI application the behavior of this function is
        undefined.  Never pass non-conforming WSGI applications to this function.

        :param app: the application to execute.
        :param buffered: set to `True` to enforce buffering.
        :return: tuple in the form ``(app_iter, status, headers)``
        """
        environ = _get_environ(environ)
        response = []
        buffer = []

        def start_response(status, headers, exc_info=None):
            if exc_info is not None:
                reraise(*exc_info)
            response[:] = [status, headers]
            return buffer.append

        app_iter = app(environ, start_response)

        # when buffering we emit the close call early and convert the
        # application iterator into a regular list
        if buffered:
            close_func = getattr(app_iter, 'close', None)
            try:
                app_iter = list(app_iter)
            finally:
                if close_func is not None:
                    close_func()

        # otherwise we iterate the application iter until we have
        # a response, chain the already received data with the already
        # collected data and wrap it in a new `ClosingIterator` if
        # we have a close callable.
        else:
            while not response:
>               buffer.append(next(app_iter))
E               StopIteration

virtualenv/lib/python2.7/site-packages/werkzeug/test.py:873: StopIteration

This only seems to happen for tests that use the test client and make POSTs. Interestingly if I use the Sentry middleware directly, I’m not able to reproduce the error leading me to believe the problem lies in the Flask extension. However, so far I haven’t been able to isolate the exact cause.

[PhilipGarnero]

This is because of sentry wrapping the default wsgi app with its own. To disable this, you can either run your app in debug, init sentry with Sentry(app, wrap_wsgi=False) or sentry.init_app(app, wrap_wsgi=False) or re-override the wsgi_app using

from raven.middleware import Sentry
if isinstance(app.wsgi_app, Sentry):
    app.wsgi_app = app.wsgi_app.application

The sentry middleware needs to be fixed in order to avoid such hacks.

[matteosimone]

+1 Ran into this while integrating sentry, fixed with buffered=True