#27316: Multiple LiveServerTestCase subclasses cannot reuse the same port
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Reporter: Jeremy Bowman | Owner: nobody
Type: Bug | Status: new
Component: Testing framework | Version: 1.10
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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The fix for #26011 ("allow_reuse_address = 1 on WSGIServer can cause
random test failures in LiveServerTestCase on Windows"), released with
Django 1.10, seems to have had the unintended side effect of preventing a
port from being reused for multiple subclasses of LiveServerTestCase in
the same test suite. I maintain a couple of libraries (sbo-selenium and
django-nose-qunit) which facilitate Selenium testing of Django
applications, and while updating them to work with 1.10 I noticed that
both of them now fail with `OSError: [Errno 48] Address already in use`
**after** the first test succeeds. `DJANGO_LIVE_TEST_SERVER_ADDRESS` had
been configured to use only a single port, and after updating it to use a
range and inserting some debugging code, I noticed that subsequent test
classes were needing to increment to ever higher port numbers in the
range. (I'm seeing this behavior at least on Mac OS X El Capitan, haven't
yet tested more widely.)
The underlying problem seems to be described well at https://brokenbad.com
/address-reuse-in-pythons-socketserver/ :
Checking with netstat and ps, I found that although the process itself
is no longer running, the socket is still listening on the port with
status “TIME_WAIT”. Basically the OS waits for a while to make sure this
connection has no remaining packets on the way.
I don't think we want to just revert the change that caused this, because
it's true that we should not blindly ignore port conflicts with other
processes. Maybe it can be changed to set `allow_reuse_address=False`
only for the first `LiveServerThread` in the process (to avoid stomping on
any already-running processes), then flip a variable which would set it to
`True` for all subsequent instances so each test class can reuse the same
port?
As a workaround (and the reason I suspect this hadn't already been
noticed), you can just assign a large range of ports in
`DJANGO_LIVE_TEST_SERVER_ADDRESS` and let the tests cycle through them.
But this doesn't necessarily work in a large test suite with many
subclasses of `LiveServerTestCase`, and there are cases where it's very
useful for integration with other scripts to know deterministically which
port will be used to run the server.
--
Ticket URL: <https://code.djangoproject.com/ticket/27316>
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