git wrapper to optimize network use by maintaining a local mirror

git-wrapper.py

#!/usr/bin/env python
# Put me in /usr/local/bin for magic caching (but set cache_root too!)
# Note this expects to run inside Jenkins, so remove line 20 if you don't do that.

import os
import sys
import urlparse

real_git = '/usr/bin/git'
cache_root = '/gitdata'

def find_url(args):
    for arg in args:
        if urlparse.urlparse(arg).scheme != '':
            return arg
    raise Exception("No url in argument list!")

def cache_path(url):
    return os.path.join(cache_root,
                        os.environ['JOB_NAME'],
                        os.path.basename(url))

def update_mirror(url):
    path = cache_path(url)
    if os.path.isdir(path):
        print 'updating mirror of %s' % url
        os.environ['GIT_DIR'] = path
        os.system('%s remote update' % real_git)
    else:
        print 'creating mirror of %s' % url
        os.system('%s clone --mirror %s %s' % (real_git, url, path))

def inject_reference(args):
    return [real_git, 'clone', '--reference',
            cache_path(find_url(args))] + args[2:]

if __name__ == "__main__":
    if sys.argv[1] == 'clone':
        url = find_url(sys.argv)
        update_mirror(url)
        os.execv(real_git, inject_reference(sys.argv))
    else:
        os.execv(real_git, sys.argv)