TracSpamFilter causes exception on /about page

[Rainer Müller <raimue@…>]

On visiting /about, I encountered the following exception:

2016-10-24 09:59:10,686 Trac[main] ERROR: Internal Server Error: <RequestWithSession "GET '/about'">, referrer None
Traceback (most recent call last):
  File "/var/www/trac/virtualenv/lib/python2.7/site-packages/trac/web/main.py", line 562, in _dispatch_request
    dispatcher.dispatch(req)
  File "/var/www/trac/virtualenv/lib/python2.7/site-packages/trac/web/main.py", line 249, in dispatch
    resp = chosen_handler.process_request(req)
  File "/var/www/trac/virtualenv/lib/python2.7/site-packages/trac/about.py", line 66, in process_request
    data['systeminfo'] = self.env.get_systeminfo()
  File "/var/www/trac/virtualenv/lib/python2.7/site-packages/trac/env.py", line 304, in get_systeminfo
    info.extend(provider.get_system_info() or [])
  File "/var/www/trac/virtualenv/lib/python2.7/site-packages/tracspamfilter/filtersystem.py", line 456, in get_system_info
    yield 'dnspython', get_pkginfo(dns)['version']
KeyError: 'version'

This is on a standard Debian 8 jessie installation, with python-dnspython 1.12.0-1. The trac.util.get_pkginfo function returns an empty dict when asking for the version of the module. This in itself might be another bug in Trac or it needs to be fixed in Debian's packaging.

$ python -c 'import dns; from trac.util import get_pkginfo; print get_pkginfo(dns)'
{}

[Rainer Müller <raimue@…>]

Workaround

[Rainer Müller <raimue@…>]

The attached patch mitigates the problem by using .get('version') to access the value. Instead of throwing an exception, an empty version will be displayed on the /about page if the version cannot be determined.

[Jun Omae]

Hmmm, the python-dnspython package has *.egg-info metadata however it is single file rather than a directory which contains *.egg-info/PKG-INFO. The get_pkginfo() utility doesn't work with metadata as a file.

$ dpkg --listfiles python-dnspython | grep info
/usr/lib/python2.7/dist-packages/dnspython-1.12.0.egg-info
$ ls -la /usr/lib/python2.7/dist-packages/dnspython-1.12.0.egg-info
-rw-r--r--. 1 root root 1280 Sep 15  2014 /usr/lib/python2.7/dist-packages/dnspython-1.12.0.egg-info
$ cat /usr/lib/python2.7/dist-packages/dnspython-1.12.0.egg-info
Metadata-Version: 1.1
Name: dnspython
Version: 1.12.0
Summary: DNS toolkit
Home-page: http://www.dnspython.org
...

[Jun Omae]

Could you try the following patch?

trac/util/__init__.py

@@ -730 +730 @@
     Always returns a dictionary but it will be empty if no Distribution
     instance can be created for the given module.
     """
+    import email
     import types
     if isinstance(dist, types.ModuleType):
-        def has_resource(dist, resource_name):
+        def has_resource(dist, module, resource_name):
             if dist.location.endswith('.egg'):  # installed by easy_install
                 return dist.has_resource(resource_name)
             if dist.has_metadata('installed-files.txt'):  # installed by pip
@@ -747 +748 @@
             if dist.has_metadata('RECORD'):  # *.dist-info/RECORD
                 reader = csv.reader(StringIO(dist.get_metadata('RECORD')))
                 return any(resource_name == row[0] for row in reader)
+            if dist.has_metadata('PKG-INFO'):
+                try:
+                    pkginfo = email.message_from_string(
+                                                dist.get_metadata('PKG-INFO'))
+                    if module.__name__ in pkginfo.get_all('Provides', ()):
+                        return True
+                except (IOError, email.Errors.MessageError):
+                    pass
             toplevel = resource_name.split('/')[0]
             if dist.has_metadata('top_level.txt'):
                 return toplevel in dist.get_metadata_lines('top_level.txt')
@@ -761 +770 @@
             resource_name += '.py'
         for dist in find_distributions(module_path, only=True):
             if os.path.isfile(module_path) or \
-                    has_resource(dist, resource_name):
+                    has_resource(dist, module, resource_name):
                 break
         else:
             return {}
-    import email
     from trac.util.translation import _
     attrs = ('author', 'author-email', 'license', 'home-page', 'summary',
              'description', 'version')

After the patch:

>>> import dns
>>> from trac.util import get_pkginfo
>>> pkginfo = get_pkginfo(dns)
>>> pkginfo['version']
'1.12.0'
>>> pkginfo['summary']
'DNS toolkit'

[Rainer Müller <raimue@…>]

Yes, this patch works for me and would resolve the problem.

[Jun Omae]

Thanks for the feedback. I'll apply the patch to 1.0-stable branch (with unit tests if possible).

[Jun Omae]

Fixed in [15189] and merged in [15190-15191].