#!/usr/bin/perl
#
# git caching proxy
#
# usage: run it on some port, and then clone or fetch
#  git://<realhost>:<realport>/<real-git-url>
# where <real-git-url> is http://<host>/... or git://<host>/...

use strict;
use warnings;

use POSIX;
use Socket;
use Sys::Syslog;

our $us = 'git-cache-proxy';
our $log; # filehandle (ref), or "1" meaning syslog
our $fetchtimeout = 1800;
our $maxfetchtimeout = 3600;

sub ntoa {
    my $sockaddr = shift;
    return ('(local)') unless defined $sockaddr;
    my ($port,$addr) = sockaddr_in $sockaddr;
    $addr = inet_ntoa $addr;
    return ("[$addr]:$port",$addr,$port);
}

our ($client,$client_addr,$client_port) = ntoa getpeername STDIN;
our ($server,$server_addr,$server_port) = ntoa getsockname STDIN;

sub ensurelog () {
    return if $log;
    openlog $us, qw(pid), 'daemon';
    $log = 1;
}

sub log ($) {
    my ($pri, $msg) = @_;
    ensurelog();
    my $mainmsg = sprintf "%s-%s: %s", $server, $client, $msg;
    if (ref $log) {
	my $wholemsg = sprintf("%s [%d] %s: %s\n",
			       strftime("%Y-%m-%d %H:%M:%S Z", gmtime),
			       $$,
			       $pri,
			       $mainmsg);
	print $log $wholemsg;
    } else {
	syslog $pri, $mainmsg;
    }
}

sub fail ($) {
    my ($msg) = @_;
    log 'error', $msg;
    exit 1;
}

sub gitfail ($) {
    my ($msg) = @_;
    log 'warning', $msg;
    my $gitmsg = "ERR $us: $msg";
    $gitmsg = substr($gitmsg,0,65535); # just in case
    printf "%04x%s", length($gitmsg)+4, $gitmsg;
    flush STDOUT;
    exit 1;
}

our $cachedir = '/var/cache/git-cache-proxy';

for (;;) {
    last unless @ARGV;
    last unless $ARGV[0] =~ m/^-/;
    $_ = shift @ARGV;
    for (;;) {
	last unless m/^-./;
	if (s/^-L(.*)$//) {
	    my $logfile = $_;
	    open STDERR, ">>", $logfile or fail "open $logfile: $!";
	    $log = \*STDERR;
	} elsif (s/^-d(.*)$//) {
	    $cachedir = $1;
	} elsif (s/^--(maxfetchtimeout|fetchtimeout)=(\d+)$//) {
	    ${ $::{$1} } = $2;
	} else {
	    fail "bad usage: unknown option `$_'";
	}
    }
}

!@ARGV or fail "bad usage: no non-option arguments permitted";

chdir $cachedir or fail "chdir $cachedir: $!";

our ($service,$specpath,$spechost);

$SIG{ALRM} = sub { fail "timeout" };
alarm 30;

sub xread {
    my $length = shift;
    my $buffer = "";
    while ($length > length $buffer) {
        my $ret = sysread STDIN, $buffer, $length, length $buffer;
        fail "Expected $length bytes, got ".length $buffer
                            if defined $ret and $ret == 0;
        fail "read: $!" if not defined $ret and $! != EINTR and $! != EAGAIN;
    }
    return $buffer;
}
my $hex_len = xread 4;
fail "Bad hex in packet length" unless $hex_len =~ m|^[0-9a-fA-F]{4}$|;
my $line = xread -4 + hex $hex_len;
unless (($service,$specpath,$spechost) = $line =~
        m|^(git-[a-z-]+) /*([!-~]+)\0host=([!-~]+)\0$|) {
    $line =~ s|[^ -~]+| |g;
    fail "Could not parse \"$line\""
}

alarm 0;

$service eq 'git-upload-pack'
    or gitfail "unknown/unsupported service `$service'";

my $fetch = 2; # 0:don't; 1:try; 2:force
my $url = $specpath;

while ($url =~ s#^(\[)([^][{}])+\]## ||
       $url =~ s#^(\{)([^][{}])+\}##) {
    $_ = $2;
    my $must = $1 eq '{';
    if (m/^relaxed$/) {
	$fetch = 1;
    } elsif (m/^nofetch$/) {
	$fetch = 0;
    } elsif (m/^timeout=(\d+)$/) {
	$fetchtimeout = $1 <= $maxfetchtimeout ? $1 : $maxfetchtimeout;
    } elsif ($must) {
	gitfail "unknown/unsupported option `$_'";
    }
}

$url =~ m{^(?:https?|git)://[-.0-9a-z]+/}
    or gitfail "unknown/unsupported url scheme or format `$url'";

our $subdir = $url;
$subdir =~ s|\\|\\\\|g;
$subdir =~ s|,|\\,|g;
$subdir =~ s|/|,|g;

log 'info', "$specpath locking";

my $tmpd= "$subdir\\.tmp";
my $gitd= "$subdir\\.git";
my $lock = "$subdir\\.lock";

open LOCK, "+>", $lock or fail "open/create $lock: $!";
flock LOCK, LOCK_EX or fail "lock $lock: $!";

$exists = stat $gitd;
$exists or $!==ENOENT or FAIL "stat $gitd: $!";

if ($fetch) {

    our @cmd;

    if (!$exists) {
	system qw(rm -rf --), $tmpd;
	@cmd = qw(git clone -q --mirror), $url;
	log 'info', "$specpath cloning";
    } else {
	@cmd = qw(git remote update --prune), $url;
	log 'info', "$specpath fetching";
    }

    my $child = open P, "-|";
    defined $child or fail "fork: $!";
    if (!$child) {
	if ($exists) {
	    chdir $gitd or fail "chdir $gitd: $!";
	}
	setpgrp or fail "setpgrp: $!";
	open STDERR, ">&STDOUT" or fail "redirect stderr: $!";
	exec @cmd or fail "exec $cmd[0]: $!";
    }

    local $SIG{ALARM} = sub {
	kill 9, -$child;
	
	} or log 'crit', 
    };

    alarm($fetchtimeout);
    

printf STDERR "%s [$$] %s %s\n",
    strftime("%Y-%m-%d %H:%M:%S %Z", localtime), $server, $client;





$service eq '

@@READ_URLMAP@@

fail "No global mapping for $uri" unless defined $serve_user;

my ($hn,$ha,$at,$naddrs,@addrs) = gethostbyname $spechost;
fail "hostname/address mismatch ($spechost $server_addr)" unless grep {
    $server_addr eq inet_ntoa $_
    } @addrs;

our @opts;

push @opts, "-D$_=${$::{$_}}"
    for qw(service specpath spechost
	   client client_addr client_port
	   server server_addr server_port);

fail "no user $serve_user" unless getpwnam($serve_user);

syslog 'notice', "$client $service $uri $serve_user";

my @cmd = ('userv', '-t300', @opts, $serve_user, $service);
no warnings; # suppress errors to stderr
exec @cmd or fail "exec userv: $!";

# end