Uploading an attachment fails with "AssertionError: write() before start_response()" (mod_fcgid)

[arroz]

Running Trac 1.5.4.dev0 (0182158c5cb676af5b40cf1714c3d29c28a9d632 from the git repository). Not sure if the problem actually happens in 1.5.3, I need to be on trunk due to a different issue, so consider this 1.5dev (that version isn't available in the list).

When uploading an attachment to a ticket, I get the following error on the browser. This doesn't seem to depend on either the name or size of the attachment (a one byte file with a name with no special chars or spaces triggers the problem).

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/trac/web/_fcgi.py", line 572, in run
    protocolStatus, appStatus = self.server.handler(self)
  File "/usr/local/lib/python3.9/site-packages/trac/web/_fcgi.py", line 1250, in handler
    write(b'') # in case body was empty
  File "/usr/local/lib/python3.9/site-packages/trac/web/_fcgi.py", line 1203, in write
    assert headers_set, 'write() before start_response()'
AssertionError: write() before start_response()

[Jun Omae]

Thanks for the report! I get the following traceback on reproducing the issue:

10:54:36 Trac[main] ERROR: [192.168.11.15] Internal Server Error: <RequestWithSession "POST '/attachment/ticket/102'">, referrer 'http://192.168.11.122:3000/1.5-sqlite/attachment/ticket/102/?action=new'
Traceback (most recent call last):
  File "/vol/src/tracdev/git/trac/web/main.py", line 610, in dispatch_request
    dispatcher.dispatch(req)
  File "/vol/src/tracdev/git/trac/web/main.py", line 302, in dispatch
    raise e
  File "/vol/src/tracdev/git/trac/web/main.py", line 207, in dispatch
    if handler.match_request(req):
  File "/vol/src/tracdev/git/trac/attachment.py", line 168, in match_request
    req.args['realm'] = realm
  File "/vol/src/tracdev/git/trac/web/api.py", line 569, in __getattr__
    value = self.callbacks[name](self)
  File "/vol/src/tracdev/git/trac/web/api.py", line 551, in <lambda>
    'args': lambda req: arg_list_to_args(req.arg_list),
  File "/vol/src/tracdev/git/trac/web/api.py", line 569, in __getattr__
    value = self.callbacks[name](self)
  File "/vol/src/tracdev/git/trac/web/api.py", line 943, in _parse_arg_list
    fs = _FieldStorage(fp, environ=self.environ,
  File "/usr/lib/python3.9/cgi.py", line 480, in __init__
    self.read_multi(environ, keep_blank_values, strict_parsing)
  File "/vol/src/tracdev/git/trac/web/api.py", line 272, in read_multi
    cgi.FieldStorage.read_multi(self, *args, **kwargs)
  File "/usr/lib/python3.9/cgi.py", line 617, in read_multi
    first_line = self.fp.readline() # bytes
  File "/vol/src/tracdev/git/trac/web/_fcgi.py", line 185, in readline
    i = self._buf.find('\n', self._pos)
TypeError: argument should be integer or bytes-like object, not 'str'

I've fixed fcgi issue #13403 but the fix was incomplete.

Could you please try the following patch?

trac/web/_fcgi.py

@@ -182 +182 @@
                 self._buf += _bytes_join(self._bufList)
                 self._bufList = []
             # Find newline.
-            i = self._buf.find('\n', self._pos)
+            i = self._buf.find(b'\n', self._pos)
             if i < 0:
                 # Not found?
                 if self._eof:

[Miguel Arroz <miguel.arroz@…>]

Thanks for the super quick feedback.

Yeah, that patch works perfectly! I can now upload attachments without issues. Thank you! 🙏 Sorry for not including the more detailed trace originally.

[Jun Omae]

Committed in [17604]. Thanks for the reporting, again!