sub sync_aria2 {
    -x "/usr/bin/aria2c" or die N("aria2 is missing\n");
    my $options = shift;
    $options = { dir => $options } if !ref $options;
    #- force download to be done in cachedir to avoid polluting cwd.
    (my $cwd) = getcwd() =~ /(.*)/;
    chdir $options->{dir};
    my ($buf, $total, $file) = ('', undef, undef);
    my $aria2c_command = join(" ", map { "'$_'" }
	"/usr/bin/aria2c",
	"--timeout", $CONNECT_TIMEOUT,
	"--max-tries=1", #- aria2 will always retry, even when 404, therefore disable it
	"--allow-overwrite=true",
	"--auto-file-renaming=false",
	($options->{limit_rate} ? "--max-download-limit=$options->{limit_rate}" : ()),
	($options->{resume} ? "--continue" : ()),
	($options->{retry} ? "--max-tries=$options->{retry}" : ()),
	(defined $options->{'aria2-options'} ? split /\s+/, $options->{'aria2-options'} : ()),
	'-d', $options->{dir},		
	($options->{metalink} ? "-M" : ()),
	@_);

    $options->{debug} and $options->{debug}($aria2c_command);

    my $aria2_pid = open (my $aria2, "$aria2c_command |");

    local $/ = \1; #- read input by only one char, this is slow but very nice (and it works!).
    local $_;    

    
    while(<$aria2>) {
	    $buf .= $_;
	if ($_ eq "\r" || $_ eq "\n") {
		if ($options->{callback}) {
		    unless (defined $file) {
			$file = shift @_;
    			propagate_sync_callback($options, 'start', $file);
		    }
    		    if ($buf =~ /\[\#\d*\s+\S+:([\d\.]+)\w*.([\d\.]+)\w*\S+\s+\S+\s*([\d\.]).+/) {
			    my ($total, $percent, $speed, $eta) = ($2, $3, $4, $6);
			    #- $1 = currently downloaded size, $5 = connections
		    if (propagate_sync_callback($options, 'progress', $file, $percent, $total, $eta, $speed) eq 'canceled') {
			kill 15, $aria2_pid;
			close $aria2;
			return;
		    }
	    }
		    if ($_ eq "\n") {
			propagate_sync_callback($options, 'end', $file);
			($total, $file) = (undef, undef);
		    }
	    } else {
		$options->{quiet} or print STDERR $buf;
	    }
	    $buf = '';
	}
    }
    chdir $cwd;
    close $aria2 or _error('aria2');
}