diff --git a/gitosis/serve.py b/gitosis/serve.py
new file mode 100644
index 0000000..cc189ad
--- /dev/null
+++ b/gitosis/serve.py
@@ -0,0 +1,106 @@
+#!/usr/bin/python
+
+"""
+Enforce git-shell to only serve repositories in the given
+directory. The client should refer to them without any directory
+prefix. Repository names are forced to match ALLOW.
+"""
+
+import logging; logging.basicConfig(level=logging.DEBUG)
+
+import sys, os, optparse, re
+from ConfigParser import RawConfigParser
+
+from gitosis import access
+
+def die(msg):
+    print >>sys.stderr, '%s: %s' % (sys.argv[0], msg)
+    sys.exit(1)
+
+def getParser():
+    parser = optparse.OptionParser(
+        usage='%prog [--config=FILE] USER',
+        description='Allow restricted git operations under DIR',
+        )
+    parser.set_defaults(
+        config=os.path.expanduser('~/.gitosis.conf'),
+        )
+    parser.add_option('--config',
+                      metavar='FILE',
+                      help='read config from FILE',
+                      )
+    return parser
+
+ALLOW_RE = re.compile("^(?P<command>git-(?:receive|upload)-pack) '(?P<path>[a-zA-Z][a-zA-Z0-9@._-]*(/[a-zA-Z][a-zA-Z0-9@._-]*)*)'$")
+
+COMMANDS_READONLY = [
+    'git-upload-pack',
+    ]
+
+COMMANDS_WRITE = [
+    'git-receive-pack',
+    ]
+
+def main():
+    os.umask(0022)
+
+    parser = getParser()
+    (options, args) = parser.parse_args()
+    try:
+        (user,) = args
+    except ValueError:
+        parser.error('Missing argument USER.')
+
+    cmd = os.environ.get('SSH_ORIGINAL_COMMAND', None)
+    if cmd is None:
+        die("Need SSH_ORIGINAL_COMMAND in environment.")
+
+    if '\n' in cmd:
+        die("Command may not contain newlines.")
+
+    match = ALLOW_RE.match(cmd)
+    if match is None:
+        die("Command to run looks dangerous")
+
+    cfg = RawConfigParser()
+    cfg.read(options.config)
+
+    os.chdir(os.path.expanduser('~'))
+
+    command = match.group('command')
+    if (command not in COMMANDS_WRITE
+        and command not in COMMANDS_READONLY):
+        die("Unknown command denied.")
+
+    path = match.group('path')
+
+    # write access is always sufficient
+    newpath = access.haveAccess(
+        config=cfg,
+        user=user,
+        mode='writable',
+        path=path)
+
+    if newpath is None:
+        # didn't have write access
+
+        newpath = access.haveAccess(
+            config=cfg,
+            user=user,
+            mode='readonly',
+            path=path)
+
+        if newpath is None:
+            die("Access denied.")
+
+        if command in COMMANDS_WRITE:
+            # didn't have write access and tried to write
+            die("Write access denied.")
+
+    # put the command back together with the new path
+    newcmd = "%(command)s '%(newpath)s'" % dict(
+        command=command,
+        newpath=newpath,
+        )
+    os.execve('/usr/bin/git-shell', ['git-shell', '-c', newcmd], {})
+    die("Cannot execute git-shell.")