Trap "ZipImportError: bad local file header.. " and suggest server restart

[admin]

How to Reproduce

While doing a GET operation on /admin/general/plugin, Trac issued an internal error.

(please provide additional details here)

Request parameters:

{'cat_id': u'general', 'panel_id': u'plugin', 'path_info': None}

System Information

Trac	0.11b1
Python	2.5.1 (r251:54863, Mar 13 2008, 12:52:19) [GCC 3.4.6 [FreeBSD] 20060305]
setuptools	0.6c8
SQLite	3.3.17
pysqlite	2.3.5
Genshi	0.4.4
Pygments	0.9
Subversion	1.4.6 (r28521)

Python Traceback

Traceback (most recent call last):
  File "/usr/local/lib/python2.5/site-packages/Trac-0.11b1-py2.5.egg/trac/web/main.py", line 398, in _dispatch_request
    dispatcher.dispatch(req)
  File "/usr/local/lib/python2.5/site-packages/Trac-0.11b1-py2.5.egg/trac/web/main.py", line 195, in dispatch
    resp = chosen_handler.process_request(req)
  File "/usr/local/lib/python2.5/site-packages/Trac-0.11b1-py2.5.egg/trac/admin/web_ui.py", line 108, in process_request
    path_info)
  File "/usr/local/lib/python2.5/site-packages/Trac-0.11b1-py2.5.egg/trac/admin/web_ui.py", line 389, in render_admin_panel
    return self._render_view(req)
  File "/usr/local/lib/python2.5/site-packages/Trac-0.11b1-py2.5.egg/trac/admin/web_ui.py", line 503, in _render_view
    info = get_pkginfo(dist)
  File "/usr/local/lib/python2.5/site-packages/Trac-0.11b1-py2.5.egg/trac/util/__init__.py", line 228, in get_pkginfo
    pkginfo = email.message_from_string(dist.get_metadata('PKG-INFO'))
  File "/usr/local/lib/python2.5/site-packages/setuptools-0.6c8-py2.5.egg/pkg_resources.py", line 1137, in get_metadata
    return self._get(self._fn(self.egg_info,name))
  File "/usr/local/lib/python2.5/site-packages/setuptools-0.6c8-py2.5.egg/pkg_resources.py", line 1195, in _get
    return self.loader.get_data(path)
ZipImportError: bad local file header in /usr/local/lib/python2.5/site-packages/TracAccountManager-0.2dev_r3111-py2.5.egg

[John Hampton]

Please restart your webserver.

This generally happens when a process has the egg cached and the physical egg behind it changes.

Please reopen the ticket if this does not fix your problem.

[Christian Boos]

The ZipImportError exception is raised by pkg_resource in a new process which loads a newly installed .egg while there are still other processes running with the older version of the .egg.

This usually happens after an install, if it is not followed by a server restart, as new processes get spawned. A server restarts always fix the problem without a need to reinstall anything, so the .egg is not actually corrupted.

It would be nice to find a fix or a workaround or at least a more precise explanation of the problem.

[Christian Boos]

This actually happens if those new processes get forked from processes already having loaded the modules from the previous zip file.

In ​Re: py2exe + svn - the final drama, when discussing the reasons for a "bad local file header" exception, David Bollen wrote:

Apparently there are two levels of caching that you've got to defeat if you change the underlying zip:

1. A global file set of file directory cache information for any opened zip file (for all files in the zip). This is held in the zipimport module global _zip_directory_cache.
2. Individual file cached information within the zipimporter instance that is kept in the path importer cache (sys.path_importer_cache). Technically these are just references to the same individual entries being held in the dictionary from (1).

pkg_resources does the same as (2) and stores those "​toc entries" dicts in ​zipinfo property of ZipImporter and EggMetadata.

This is for the explanation of the issue, which is now clear.

Now, for finding a solution, that's far less evident. We could try to modify pkg_resource so that it detects the change and resets the information, but we would then end up doing a kind of reload, which I'm sure would introduce its own set of issues.

Perhaps it's better to simply trap the error and translate it to a simple TracError stating that a full server restart is needed.