Use git through a proxy

Tutorial: how to use git through a proxy

What kind of proxy

The most common are an HTTP proxy, and a SOCKS5 proxy - for example, one opened with the ssh -D command, documented in ssh(1). 

How to open a SOCKS proxy through an SSH tunnel

The ssh command distributed with most Unix-like systems can open a SOCKS proxy on the local machine and forward all connections through the ssh tunnel.
For example

ssh -f -N -D 1080 cmsusr.cms

will connect to the host cmsusr.cms, open a SOCKS proxy on the local host on port 1080 (-D 1080), and put the process in background after a successful connection (-f -N).

How to connect to a git repository using the SSH protocol
If the remote has a format like

git@github.com:cms-sw/cmssw.git
ssh://git@github.com/cms-sw/cmssw.git

then you are connecting to the git server using the SSH protocol.

In this case, git relis on ssh to handle the connection; in order to connect through a SOCKS proxy you have to configure ssh itself, setting the ProxyCommand option in your ~/.ssh/config file:

Host <host_alias>
    Hostname                github.com
    User                    git
    ProxyCommand            nc -X 5 -x localhost:1080 %h %p

For more information, see ssh_config(5).
Using: git clone ssh://<host_alias>/<path/to/git/repo>

How to connect to a git repository using the HTTP or HTTPS protocols

If the remote has a format like

http://github.com/cms-sw/cmssw.git
https://github.com/cms-sw/cmssw.git

then you are connecting to the git server using the HTTP or HTTPS protocols. In the old days, this used to be a dumb protocol, but since git 1.6.6 it uses a smart protocol similar to that used by SSH or GIT.

In this case git uses libcurl to handle the connection; the version of git bundled with CMSSW supports different kinds of proxies: SOCKS4, SOCKS4a, SOCKS5, and HTTP/HTTPS. In order to connect through any proxy supported by libcurl, you can set thehttp.proxy option:

git config --global http.proxy socks5://localhost:1080

For more information, see the --proxy option in curl(1) and the http.proxy entry in git-config(1).

How to connect to a git repository using the GIT protocol

If the remote has a format like

git://github.com/cms-sw/cmssw.git

then you are connecting to the git server using the GIT protocol.

In this case, it is possible to use a helper command to connect through any kind of proxy. A simple script is included with CMSSW, to connect through a SOCKS5 proxy: git-proxy. You can configure git to use it with

git config --global core.gitproxy "git-proxy"
git config --global socks.proxy "localhost:1080"

For more information, see git-proxy --help.