BadZipfile "file is not a zip file"

Steven D'Aprano steve at
Fri Jan 9 11:09:58 CET 2009

On Fri, 09 Jan 2009 00:46:27 -0800, Carl Banks wrote:

> On Jan 9, 2:16 am, Steven D'Aprano <st... at REMOVE-THIS-
>> wrote:
>> On Thu, 08 Jan 2009 16:47:39 -0800, webcomm wrote:
>> > The error...
>> ...
>> > BadZipfile: File is not a zip file
>> > When I look at in Windows, it appears to be a valid zip
>> > file. I am able to uncompress it in Windows XP, and can also
>> > uncompress it with 7-Zip.  It looks like zipfile is not able to read
>> > a "table of contents" in the zip file.  That's not a concept I'm
>> > familiar with.
>> No, ZipFile can read table of contents:
>>     Help on method printdir in module zipfile:
>>     printdir(self) unbound zipfile.ZipFile method
>>         Print a table of contents for the zip file.
>> In my experience, zip files originating from Windows sometimes have
>> garbage at the end of the file. WinZip just ignores the garbage, but
>> other tools sometimes don't -- if I recall correctly, Linux unzip
>> successfully unzips the file but then complains that the file was
>> corrupt. It's possible that you're running into a similar problem.
> The zipfile format is kind of brain dead, you can't tell where the end
> of the file is supposed to be by looking at the header.  If the end of
> file hasn't yet been reached there could be more data.  To make matters
> worse, somehow zip files came to have text comments simply appended to
> the end of them.  (Probably this was for the benefit of people who would
> cat them to the terminal.)
> Anyway, if you see something that doesn't adhere to the zipfile format,
> you don't have any foolproof way to know if it's because the file is
> corrupted or if it's just an appended comment.

Yes, this has lead to a nice little attack vector, using hostile Java 
classes inside JAR files (a variant of ZIP).



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