如何从github上仅下载/.git/objects/中的commit对象？

Question

由于我的工作需要，我需要从远程的git仓库中仅下载./git/objects里的commit对象。.git metadata 包含了一些有用的信息。但在pack文件中包括commit/tree/blob对象，其中tree和blob对象很大，所以不下载tree/blob对象。或许我需要重新客户端或者写python脚本。
我看到一些项目（https://github.com/lijiejie/G...），通过解析index一步步下载文件，并且下载之后commit/tree/blob对象是分隔开的。
但这种方法是通过HTTP的方式访问.git文件夹，无法直接从github上下载index文件。我不理解github与git客户端之间是如何通信的。
我尝试过查看C和Java的底层源码，但复杂的结构让我困惑。
有什么办法可以实现仅下载commit对象的功能吗？或者如何能够帮助我在底层源码里找到关键代码。

不清楚segmentfault上又没有国外的朋友，贴上英文版：

Since my work needs, I need to download only the commit object in ./git/objects from the remote git repository. /.git/ metadata contains some useful information. But in the pack file include the commit/tree/blob object. the tree/blob objects are too large, so the tree/blob object Should not be download. Maybe I need to rebuild the git client or write a python script.

I saw some projects (like https://github.com/lijiejie/G... downloading the files step by step by parsing the index file, and finaly the commit/tree/blob objects are separated after the download.

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But this method need to access the .git folder via HTTP, and you can't download the index file directly from github.

I don't understand how github communicates with the git client.

I tried to look at the underlying source code for C(https://github.com/git/git) and Java(https://github.com/eclipse/jg... but the complicated structure puzzled me.

Is there any way to implement the function of downloading only the commit object? Or how can I help myself find the key code in the underlying source code.

If you know how to do this, please let me know. thank you very much.