Re: Reading commit objects

From: Chico Sokol <chico.sokol@gmail.com>
Date: May 21, 2013, 22:18 UTC
Message-ID: <CABx5MBSnpZTthOHECqkbpdbFfkb4e_uSo-rh4owBc8B_oSKjJQ@mail.gmail.com>
In-Reply-To: <CAEBDL5XwrD8ZbRRSrM1iJGtcRgziH5bFVwRHzg9=_PYzaTfgAg@mail.gmail.com>

Ok, we discovered that the commit object actually contains the tree object's sha1, by reading its contents with python zlib library.

So the bug must be with our java code (we're building a java lib).

Is there any non-standard issue in git's zlib compression? We're decompressing its contents with java default zlib api, so it should work normally, here's our code, that's printing that wrong output:

import java.io.File; import java.io.FileInputStream; import java.util.zip.InflaterInputStream; import org.apache.commons.io.IOUtils; ... File obj = new File(".git/objects/25/0f67ef017fcb97b5371a302526872cfcadad21"); InflaterInputStream inflaterInputStream = new InflaterInputStream(new FileInputStream(obj)); System.out.println(IOUtils.readLines(inflaterInputStream));

I know that here it's not the right place to ask about java issues, but we would appreciate any help any help.

-- Chico Sokol

On Tue, May 21, 2013 at 6:37 PM, John Szakmeister <john@szakmeister.net> wrote:

Show 40 quoted lines

> On Tue, May 21, 2013 at 5:21 PM, Chico Sokol <chico.sokol@gmail.com> wrote:
>> Hello,
>>
>> I'm building a library to manipulate git repositories (interacting
>> directly with the filesystem).
>>
>> Currently, we're trying to parse commit objects. After decompressing
>> the contents of a commit object file we got the following output:
>>
>> commit 191
>> author Francisco Sokol <chico.sokol@gmail.com> 1369140112 -0300
>> committer Francisco Sokol <chico.sokol@gmail.com> 1369140112 -0300
>>
>> first commit
>
> Does `git cat-file -p <sha1>` show a tree object?  FWIW, I expected to
> see a tree line there, so maybe this object was created without a
> tree?  I also don't see a parent listed.
>
> I did this on one of my repos:
>
>>>> buf = open('.git/objects/cd/da219e4d7beceae55af73c44cb3c9e1ec56802', 'rb').read()
>>>> import zlib
>>>> zlib.decompress(buf)
> 'commit 246\x00tree 2abfe1a7bedb29672a223a5c5f266b7dc70a8d87\nparent
> 0636e7ff6b79470b0cd53ceacea88e7796f202ce\nauthor John Szakmeister
> <john@szakmeister.net> 1369168481 -0400\ncommitter John Szakmeister
> <john@szakmeister.net> 1369168481 -0400\n\nGot a file listing.\n'
>
> So at least creating the commits with Git, I see a tree.  How was the
> commit you're referencing created?  Perhaps something is wrong with
> that process?
>
>> We hoped to get the same output of a "git cat-file -p <sha1>", but
>> that didn't happened. From a commit object, how can I find tree object
>> hash of this commit?
>
> I'd expect that too.
>
> -John