Parameter parsing bug on Windows

The parameter parser doesn’t handle escaped characters correctly on Windows.

Running this works on Linux/MacOS, but fails on Windows:

streamlink -p /path/to/vlc -a "--input-title-format \"\\\"\" {filename}" STREAM best

This is related to chrippa/livestreamer#1337 (reported at streamlink/streamlink-twitch-gui#256 and streamlink/streamlink-twitch-gui#362)

I can’t remember if Linux/MacOS were affected by this in Livestreamer. Didn’t test it…

The error log:

[cli][info] Starting player: C:/Program Files (x86)/VideoLAN/VLC/vlc.exe
Traceback (most recent call last):
  File "C:\Program Files (x86)\Streamlink\bin\streamlink-script.py", line 12, in <module>
    main()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 899, in main
    handle_url()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 499, in handle_url
    handle_stream(plugin, streams, stream_name)
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 382, in handle_stream
    success = output_stream(stream)
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 259, in output_stream
    output.open()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\output.py", line 21, in open
    self._open()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\output.py", line 123, in _open
    self._open_subprocess()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\output.py", line 138, in _open_subprocess
    self.player = subprocess.Popen(self._create_arguments(),
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\output.py", line 116, in _create_arguments
    return shlex.split(cmd) + shlex.split(args)
  File "shlex.py", line 273, in split
  File "shlex.py", line 263, in __next__
  File "shlex.py", line 90, in get_token
  File "shlex.py", line 166, in read_token
ValueError: No closing quotation

[beardypig]

Right. As far as shlex is concerned this is the correct behaviour as it implements strict POSIX. From the IEEE Std 1003.1-2008, specifically section 2.2.2.

2.2.2 Single-Quotes Enclosing characters in single-quotes ( ‘’ ) shall preserve the literal value of each character within the single-quotes. A single-quote cannot occur within single-quotes.

In fact, you can reproduce it in sh, bash, zsh, plus any other POSIX compatible shell; you will find that there is still an open quote on the second line:

bash-4.4$ echo 'foo\'s'
> '
foo\s

So the correct thing to do is to always use " 😃

[beardypig]

I have added a test that reproduces this bug, and the most basic reproduction is:

assert shlex.split('--title "\\""') == ['--title', '"'] # passes
assert shlex.split("--title '\\''") == ['--title', "'"] # fails

Wether or not it can be easily fixed remains to be seen, as I workaround I would suggest always using " 😃 I will dig a bit deeper and see if a bug needs to be filed against the Python stdlibs.