STR:

In [1]: from mozprocess import ProcessHandler 
In [2]: proc = ProcessHandler(["echo", "foo"])
In [3]: proc.run()

Exception in thread ProcessReader:

Traceback (most recent call last):
File "/home/ahal/.pyenv/versions/3.8.2/lib/python3.8/threading.py", line 932, in _bootstrap_inner                                                                                                                                                                 
    self.run()
  File "/home/ahal/.pyenv/versions/3.8.2/lib/python3.8/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/home/ahal/dev/mozilla-central/testing/mozbase/mozprocess/mozprocess/processhandler.py", line 1099, in _read
    callback(line.rstrip())
  File "/home/ahal/dev/mozilla-central/testing/mozbase/mozprocess/mozprocess/processhandler.py", line 1009, in __call__
    e(*args, **kwargs)
  File "/home/ahal/dev/mozilla-central/testing/mozbase/mozprocess/mozprocess/processhandler.py", line 1150, in __call__
    self.stream.write(line + '\n'.encode('utf8'))
TypeError: write() argument must be str, not bytes

This is happening because we set up a sys.stdout stream by default here:
https://searchfox.org/mozilla-central/source/testing/mozbase/mozprocess/mozprocess/processhandler.py#1205

But on Python 3, sys.stdout requires text not bytes (whereas, the default subprocess output remains bytes).

In general, I think it's reasonable to fail if a user requests bytes from the subprocess and then tries to set up a stream that needs text (or vice versa). But we at least need to fix our default case there.

I think we need something like:

if PY3 and not (kwargs.get("universal_newlines") or kwargs.get("text")):
    use sys.stdout.buffer as the stream (unsure if this has other negative consequences)
else:
    use sys.stdout as the stream

Alternatively we could try/except the call to stream.write() and decode the line if necessary. This way users wouldn't need to worry about string types at all.. Though part of me feels that this shouldn't be mozprocess' responsibility.

Because this bug's Severity has not been changed from the default since it was filed, and it's Priority is P3 (Backlog,) indicating it has been triaged, the bug's Severity is being updated to S3 (normal.)

https://hg.mozilla.org/mozilla-central/rev/4359371ad385