#!/usr/bin/perl
#
# A very simple userv git-daemon wrapper.
#
# This reads the first packet-line of the protocol, checks the syntax
# of the user, pathname, and hostname, then uses userv to invoke the
# real git daemon as the target user with safe arguments.
#
# This was written by Tony Finch <dot@dotat.at>
# You may do anything with it, at your own risk.
# http://creativecommons.org/publicdomain/zero/1.0/

use strict;
use warnings;

use POSIX;

my $USER = qr{[0-9a-z]+};
my $PATH = qr{[-+,._/0-9A-Za-z]+};
my $HOST = qr{[-.0-9A-Za-z]+};

sub xread {
    my $length = shift;
    my $buffer = "";
    my $count = 0;
    while ($length > length $buffer) {
	my $data;
	my $ret = sysread STDIN, $data, $len
	  while not defined $ret and ($! == EINTR or $! == EAGAIN);
	die "read" unless defined $ret;
	die "short read: expected $length bytes, got $count\n" if $ret == 0;
	$buffer .= $data;
	$count += $ret;
    }
    return $buffer;
}

my $len_hex = xread 4;
die "bad packet length" unless $len_hex =~ m{^[0-9a-zA-Z]{4}$};
my $len = hex $len;

my $line = xread $len;
$line =~ m{^git-upload-pack ~($USER)/($PATH[.]git)\0host=($HOST)\0$};
my ($user,$path,$host) = ($1,$2,$3);

# child's output will go directly to inetd
open CHILD, '-|', 'userv', $user,
  qw(git daemon --inetd --strict-paths
     --user-path=public-git --forbid-override=receive-pack)
  or die "open pipe to userv: $!\n";

# proxy command line to child
syswrite CHILD, $len_hex.$line
  or die "write to userv: $!\n";

# relay stdin to child
open STDOUT, ">&CHILD"
  or die "dup: $!\n";
exec 'cat'
  or die "exec: $!\n";

die
