Git Transfer Protocol Specifications

Question

I'm playing around with git's transfer protocols, and I was just wondering if there is some detailed specification for them before I attempt to read the source?

Answer 1

Update May 2018: Starting Q2 2018 and Git 2.18, you will have the Git transfer protocol v2: See "How does Git's transfer protocol work".

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Original answer 2013:

First, check the git documentation in the git repo itself (with a good grep, available even on Windows):

git clone https://github.com/git/git
cd git/Documentation
grep -nRHI "receive-pack" *

That will give you pointers to:

• http-protocol But also:
• pack-heuristics
• pack-protocol
• protocol capabilities
• send-pack pipeline

Then you can complete that set of documentation with ones related to the backend commands:

• git-http-backend
• git-receive-pack
• git-remote-ext
• git-send-pack
• gitremote-helpers

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One way at looking at the source is by looking at the recent evolutions around transfer and transport in the git repo:

git clone https://github.com/git/git
cd git
git log -Stransfer

Have a look at:

• commit 4bc444 (Support FTP-over-SSL/TLS for regular FTP)
• commit daebaa (upload/receive-pack: allow hiding ref hierarchies )
• commit 745f7a (fetch-pack: move core code to libgit.a)
• commit fe0435 (Add persistent-https to contrib)
• ...

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Another way is to have a look at other implementation of git:

• Java: jgit, and its Transport.java source (tested in TransportTest.java, which declines into:
  • TCpTransport
  • TransportHttp
  • TransportSftp
  • TransportLocal
  • TransportBundle

 

• C, with libgit2, and its src/transports sources.

• ... and so on

Answer 2

there is also a partially completed documentation hosted on Github Gist.

This metasploit module also poses as a malicious dumb git server, serving bad git trees. You can see how the git trees are constructed.