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

[anonymous]

When adding an attachment to a wiki page (or just clicking the cancel button on the Add Attachment page) I get the error below in the browser (and in the Apache error log). No attachment is saved or added to the wiki page.

Trac version: 1.5.4dev from the trunk at revision 17603

OS: Fedora Server 34

Python version: 3.9.4

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 reporting. That is a duplicate of #13492 and has been fixed in trunk (r17604).

[anonymous]

Confirmed fixed. Thank you.