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Date: Thu, 30 Oct 2014 17:01:39 -0700
From: Brent <yhbrent AT yahoo DOT com>
Reply-To: Brent <yhbrent AT yahoo DOT com>
Subject: bug/deficiency in unzip: large files not supported?
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
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I have encountered an inconsistency between cygwin's zip and unzip programs that I think reflects a bug (or incomplete implementation) in unzip.

First, I am using the very latest release of cygwin 64 bit:
    $ uname -a
    CYGWIN_NT-6.1 yhbrent 1.7.32(0.274/5/3) 2014-08-13 23:06 x86_64 Cygwin
And when I installed from setup-x86_64.exe, I added the zip and unzip programs from the Archive section.  Running setup-x86_64.exe just now, I see that the version numbers of what I have installed are:
    zip: 3.0-12
    unzip: 6.0-1

The issue: zip can successfully archive large (> 4 GiB) files that unzip cannot extract.

Consider this cygwin shell session I just did:

    $ ls -al bigFile.txt
    -rwx------+ 1 yhbrent None 5368709120 Oct 30 18:35 bigFile.txt

    $ zip test.zip bigFile.txt
      adding: bigFile.txt (deflated 0%)

    $ mkdir ./tmp

    $ mv test.zip ./tmp/

    $ cd ./tmp/

    $ unzip test.zip
    Archive:  test.zip
    error: End-of-centdir-64 signature not where expected (prepended bytes?)
      (attempting to process anyway)
    warning [test.zip]:  1068461579 extra bytes at beginning or within zipfile
      (attempting to process anyway)
       skipping: bigFile.txt             need PK compat. v4.5 (can do v2.1)

    $ echo $?
    81

In other words, I had a big (5 GiB) file, zip successfuly archved it, but when I tried to unzip it, I got error output and an error exit code of 81.

I know that zip really did work in archiving that large file, because I was able to successfuly extract its payload using 7zip, and confirmed that the result was the same (diff ../bigFile.txt ./bigFile.txt printed out nothing).

Does the error output "need PK compat. v4.5" mean that unzip fails to support the zip64 extensions needed to handle large files?

Given that zip clearly has zip64 support, it is a big issue that you can archive stuff that subsequently cannot be extracted.                             

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