#!/usr/bin/perl

# Try to parse jpeg file, possibly corrupted

require 'jpeg_marker.perl' ;

$/ = undef ;	# read whole file

# Read it all and convert to array of ASCII codes
@data = unpack('C*',<>) ;

$length = scalar @data ;
$s_length = sprintf("%x",$length) ;
print "$s_length (hex), $length (decimal) characters\n" ;
$l_chars = length($s_length) ;

$last_type = -1 ;
#$first_loc = -1 ;
#$last_loc = -1 ;
#$count = 0 ;

# Some common tokens
$APP0 = ord("\xe0") ;
$SOI  = ord("\xd8") ;
$ff   = ord("\xff") ;

$i = 0 ;
# Check for JFIF file header
if ($data[0] != $ff)
{
	print "ERROR: No marker at beginning of file!\n" ;
}
elsif ($data[1] != $SOI)
{
	print "ERROR: Non-SOI marker at beginning of file!\n" ;
}
else
{
	&do_marker(0,$data[1]) ;
	$i = 2 ;
	if ($data[2] != $ff)
	{
		print "WARNING: No marker after initial SOI (not JFIF standard)!\n" ;
	}
	elsif ($data[3] < $APP0 && $data[3] > $APP0+7)
	{
		print "WARNING: Non-APPn marker after initial SOI (not JFIF standard)!\n" ;
	}
	else
	{
		&do_marker(2,$data[3]) ;
		if ($data[3] != $APP0)
		{
			print "WARNING: Non-APP0 marker after initial SOI (not JFIF standard)!\n" ;
			print "         Trying to parse anyway ...\n" ;
		}
		$i = 4 ;
		# length field
		$length1 = $data[4] + 256*$data[5] ;
		$length2 = $data[5] + 256*$data[4] ;
		# look for next marker, check consistency
		#for ($j=6;$j<$length;$j++)
		#{
		#	last if ($data[$j] == $ff &&
		#		$data[$j+1] != 0) ;
		#		#$data[$j+1] != $ff) ;
		#}
		#$length3 = $j - 4 ;
		#print "\tlength: $length1 $length2 $length3\n" ;
		print "\tlength: $length2\n" ;
		#if ($length1 != $length3 && $length2 != $length3)
		#{
		#	print "\tWARNING: inconsistent lengths\n" ;
		#}
		if ($data[$length1+2] == $ff and
		    $data[$length1+3] != $ff and
		    $data[$length1+3] != "\0")
		{
			print "Length1 ($length1) points to a marker.\n" ;
			&do_marker($length1+4,$data[$length1+5]) ;
		}
		if ($data[$length2+2] == $ff and
		    $data[$length2+3] != $ff and
		    $data[$length2+3] != "\0")
		{
			#print "Length2 ($length2) points to a marker:" ;
			print "Skipping to next marker:\n" ;
			$i = $length2+2 ;
			#&do_marker($i,$data[$i+1]) ;
		}
		else
		{
			print "No marker after length, parsing intermediate data:\n" ;
		}
	}
}

for (; $i < (scalar @data); $i++)
{
	if ($data[$i] == $ff)
	{
		$j = $i + 1 ;
		next if ($data[$j] == 0) ;	# skip "stuffed zero"
		next if ($data[$j] == $ff) ;	# skip filler
		&do_marker($i,$data[$j]) ;
	}
}

sub do_marker()
{
	my($loc,$type) = @_ ;
	print sprintf("%${l_chars}x  %4s %s\n",$loc,$mark_code[$type],$mark_text[$type]) ;

}