ValidJpeg.cc

#include "ValidJpeg.hh"
#include <arpa/inet.h>

bool valid_jpeg_debug = false;

static void debug(const char * msg)
{
  if (valid_jpeg_debug)
    puts(msg);
}

bool ValidJpeg::open( const char * fn ) 
{
  if (fh != 0)
    fclose (fh);
  
  fh = fopen( fn, "r" );
  if (fh == 0) 
    return false;
  else
    return true;
  
}


int ValidJpeg::short_jpeg () 
{
  if( fseek(fh,-2,SEEK_END) ) 
    return -1;

  unsigned char bytes[2];
  int n_read = fread(bytes, 1, 2, fh);
  if ( (n_read==2) and (bytes[0]==0xff) and (bytes[1]==0xd9) )
    return 0;
  return 1;
}


  
int ValidJpeg::valid_jpeg (bool seek_over_entropy) 
{
  char in_entropy=0;

  while (! feof(fh))
    {
      unsigned char marker=0;

      if ( fread(&marker, 1, 1, fh) < 1 )
	return short_file;
      if (marker != 0xff)
	{
	  if (! in_entropy)
	    return missing_ff;
	  continue;
	}

      if ( fread(&marker, 1, 1, fh) < 1 )
	return short_file;
      
      if (marker != 0)
	{
	  in_entropy = 0;
	}
      else
	{
	  if (! in_entropy)
	    return stray_0;
	  continue;
	}
      if (marker == 0xd8)
	debug("got start");
      else if (marker == 0xd9) 
	{
	  unsigned char junk;
	  fread(&junk, 1, 1, fh);
	  if (feof(fh))
	    return ok;
	  else
	    return trailing_junk;
	}
      
      else if ( (marker >= 0xd0) && (marker <= 0xd7) )
	debug("got RST");
      else
	{
	  unsigned short length;

	  if (marker == 0xda) {
	    if ( seek_over_entropy ) 
	      {
		if( fseek(fh,-2,SEEK_END) ) 
		  return -1;
		else
		  continue;
	      }
	    else 
	      {
		in_entropy = 1;
	      }
	  }
	  
	  fread(&length, 2, 1, fh);
	  length = ntohs(length);

	  if (valid_jpeg_debug) printf ("Length is %d\n", length);
#if 1
	  if (length > 512) 
	    fseek(fh,length-2,SEEK_CUR);
	  else
#endif
	    for (int j=2; j<length; ++j)
	      {
		char junk;
		if ( fread(&junk, 1, 1, fh) < 1 )
		  return short_file;
	      }
	}
      
    }
  return short_file;
}