Unable to diff two file descriptors

[danvk]

I'd expect webdiff <(cmd1) <(cmd2) to work, but it seems not to:

$ webdiff <(jq . /tmp/base-ll.js) <(jq . data/nyc-lat-lons-ny.js)
Serving diffs on http://localhost:59027
Close the browser tab or hit Ctrl-C when you're done.
======== Running on http://localhost:59027 ========
(Press CTRL+C to quit)
grep: /dev/fd/12: Bad file descriptor
Error handling request
Traceback (most recent call last):
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/aiohttp/web_protocol.py", line 452, in _handle_request
    resp = await request_handler(request)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/aiohttp/web_app.py", line 543, in _handle
    resp = await handler(request)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/aiohttp/web_middlewares.py", line 114, in impl
    return await handler(request)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/webdiff/app.py", line 200, in request_time_middleware
    response = await handler(request)
               ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/webdiff/app.py", line 124, in handle_diff_ops
    dataclasses.asdict(op) for op in diff.get_diff_ops(DIFF[idx], options)
                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/webdiff/diff.py", line 52, in get_diff_ops
    num_lines = fast_num_lines(b_path)
                ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danvk/.local/pipx/venvs/webdiff/lib/python3.12/site-packages/webdiff/diff.py", line 39, in fast_num_lines
    return int(subprocess.check_output(['grep', '-c', '', path]))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.4/Frameworks/Python.framework/Versions/3.12/lib/python3.12/subprocess.py", line 466, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.4/Frameworks/Python.framework/Versions/3.12/lib/python3.12/subprocess.py", line 571, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['grep', '-c', '', '/dev/fd/12']' returned non-zero exit status 2.
Shutting down...