/*

 * rdjpgcom.c

 *

 * Copyright (C) 1994-1997, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 * This file contains a very simple stand-alone application that displays

 * the text in COM (comment) markers in a JFIF file.

 * This may be useful as an example of the minimum logic needed to parse

 * JPEG markers.

 */



#define JPEG_CJPEG_DJPEG	/* to get the command-line config symbols */

#include "jinclude.h"		/* get auto-config symbols, <stdio.h> */



#include <ctype.h>		/* to declare isupper(), tolower() */

#ifdef USE_SETMODE

#include <fcntl.h>		/* to declare setmode()'s parameter macros */

/* If you have setmode() but not <io.h>, just delete this line: */

#include <io.h>			/* to declare setmode() */

#endif



#ifdef USE_CCOMMAND		/* command-line reader for Macintosh */

#ifdef __MWERKS__

#include <SIOUX.h>              /* Metrowerks needs this */

#include <console.h>		/* ... and this */

#endif

#ifdef THINK_C

#include <console.h>		/* Think declares it here */

#endif

#endif



#ifdef DONT_USE_B_MODE		/* define mode parameters for fopen() */

#define READ_BINARY	"r"

#else

#ifdef VMS			/* VMS is very nonstandard */

#define READ_BINARY	"rb", "ctx=stm"

#else				/* standard ANSI-compliant case */

#define READ_BINARY	"rb"

#endif

#endif



#ifndef EXIT_FAILURE		/* define exit() codes if not provided */

#define EXIT_FAILURE  1

#endif

#ifndef EXIT_SUCCESS

#ifdef VMS

#define EXIT_SUCCESS  1		/* VMS is very nonstandard */

#else

#define EXIT_SUCCESS  0

#endif

#endif





/*

 * These macros are used to read the input file.

 * To reuse this code in another application, you might need to change these.

 */



static FILE * infile;		/* input JPEG file */



/* Return next input byte, or EOF if no more */

#define NEXTBYTE()  getc(infile)





/* Error exit handler */

#define ERREXIT(msg)  (fprintf(stderr, "%s\n", msg), exit(EXIT_FAILURE))





/* Read one byte, testing for EOF */

static int

read_1_byte (void)

{

  int c;



  c = NEXTBYTE();

  if (c == EOF)

    ERREXIT("Premature EOF in JPEG file");

  return c;

}



/* Read 2 bytes, convert to unsigned int */

/* All 2-byte quantities in JPEG markers are MSB first */

static unsigned int

read_2_bytes (void)

{

  int c1, c2;



  c1 = NEXTBYTE();

  if (c1 == EOF)

    ERREXIT("Premature EOF in JPEG file");

  c2 = NEXTBYTE();

  if (c2 == EOF)

    ERREXIT("Premature EOF in JPEG file");

  return (((unsigned int) c1) << 8) + ((unsigned int) c2);

}





/*

 * JPEG markers consist of one or more 0xFF bytes, followed by a marker

 * code byte (which is not an FF).  Here are the marker codes of interest

 * in this program.  (See jdmarker.c for a more complete list.)

 */



#define M_SOF0  0xC0		/* Start Of Frame N */

#define M_SOF1  0xC1		/* N indicates which compression process */

#define M_SOF2  0xC2		/* Only SOF0-SOF2 are now in common use */

#define M_SOF3  0xC3

#define M_SOF5  0xC5		/* NB: codes C4 and CC are NOT SOF markers */

#define M_SOF6  0xC6

#define M_SOF7  0xC7

#define M_SOF9  0xC9

#define M_SOF10 0xCA

#define M_SOF11 0xCB

#define M_SOF13 0xCD

#define M_SOF14 0xCE

#define M_SOF15 0xCF

#define M_SOI   0xD8		/* Start Of Image (beginning of datastream) */

#define M_EOI   0xD9		/* End Of Image (end of datastream) */

#define M_SOS   0xDA		/* Start Of Scan (begins compressed data) */

#define M_APP0	0xE0		/* Application-specific marker, type N */

#define M_APP12	0xEC		/* (we don't bother to list all 16 APPn's) */

#define M_COM   0xFE		/* COMment */





/*

 * Find the next JPEG marker and return its marker code.

 * We expect at least one FF byte, possibly more if the compressor used FFs

 * to pad the file.

 * There could also be non-FF garbage between markers.  The treatment of such

 * garbage is unspecified; we choose to skip over it but emit a warning msg.

 * NB: this routine must not be used after seeing SOS marker, since it will

 * not deal correctly with FF/00 sequences in the compressed image data...

 */



static int

next_marker (void)

{

  int c;

  int discarded_bytes = 0;



  /* Find 0xFF byte; count and skip any non-FFs. */

  c = read_1_byte();

  while (c != 0xFF) {

    discarded_bytes++;

    c = read_1_byte();

  }

  /* Get marker code byte, swallowing any duplicate FF bytes.  Extra FFs

   * are legal as pad bytes, so don't count them in discarded_bytes.

   */

  do {

    c = read_1_byte();

  } while (c == 0xFF);



  if (discarded_bytes != 0) {

    fprintf(stderr, "Warning: garbage data found in JPEG file\n");

  }



  return c;

}





/*

 * Read the initial marker, which should be SOI.

 * For a JFIF file, the first two bytes of the file should be literally

 * 0xFF M_SOI.  To be more general, we could use next_marker, but if the

 * input file weren't actually JPEG at all, next_marker might read the whole

 * file and then return a misleading error message...

 */



static int

first_marker (void)

{

  int c1, c2;



  c1 = NEXTBYTE();

  c2 = NEXTBYTE();

  if (c1 != 0xFF || c2 != M_SOI)

    ERREXIT("Not a JPEG file");

  return c2;

}





/*

 * Most types of marker are followed by a variable-length parameter segment.

 * This routine skips over the parameters for any marker we don't otherwise

 * want to process.

 * Note that we MUST skip the parameter segment explicitly in order not to

 * be fooled by 0xFF bytes that might appear within the parameter segment;

 * such bytes do NOT introduce new markers.

 */



static void

skip_variable (void)

/* Skip over an unknown or uninteresting variable-length marker */

{

  unsigned int length;



  /* Get the marker parameter length count */

  length = read_2_bytes();

  /* Length includes itself, so must be at least 2 */

  if (length < 2)

    ERREXIT("Erroneous JPEG marker length");

  length -= 2;

  /* Skip over the remaining bytes */

  while (length > 0) {

    (void) read_1_byte();

    length--;

  }

}





/*

 * Process a COM marker.

 * We want to print out the marker contents as legible text;

 * we must guard against non-text junk and varying newline representations.

 */



static void

process_COM (void)

{

  unsigned int length;

  int ch;

  int lastch = 0;



  /* Get the marker parameter length count */

  length = read_2_bytes();

  /* Length includes itself, so must be at least 2 */

  if (length < 2)

    ERREXIT("Erroneous JPEG marker length");

  length -= 2;



  while (length > 0) {

    ch = read_1_byte();

    /* Emit the character in a readable form.

     * Nonprintables are converted to \nnn form,

     * while \ is converted to \\.

     * Newlines in CR, CR/LF, or LF form will be printed as one newline.

     */

    if (ch == '\r') {

      printf("\n");

    } else if (ch == '\n') {

      if (lastch != '\r')

	printf("\n");

    } else if (ch == '\\') {

      printf("\\\\");

    } else if (isprint(ch)) {

      putc(ch, stdout);

    } else {

      printf("\\%03o", ch);

    }

    lastch = ch;

    length--;

  }

  printf("\n");

}





/*

 * Process a SOFn marker.

 * This code is only needed if you want to know the image dimensions...

 */



static void

process_SOFn (int marker)

{

  unsigned int length;

  unsigned int image_height, image_width;

  int data_precision, num_components;

  const char * process;

  int ci;



  length = read_2_bytes();	/* usual parameter length count */



  data_precision = read_1_byte();

  image_height = read_2_bytes();

  image_width = read_2_bytes();

  num_components = read_1_byte();



  switch (marker) {

  case M_SOF0:	process = "Baseline";  break;

  case M_SOF1:	process = "Extended sequential";  break;

  case M_SOF2:	process = "Progressive";  break;

  case M_SOF3:	process = "Lossless";  break;

  case M_SOF5:	process = "Differential sequential";  break;

  case M_SOF6:	process = "Differential progressive";  break;

  case M_SOF7:	process = "Differential lossless";  break;

  case M_SOF9:	process = "Extended sequential, arithmetic coding";  break;

  case M_SOF10:	process = "Progressive, arithmetic coding";  break;

  case M_SOF11:	process = "Lossless, arithmetic coding";  break;

  case M_SOF13:	process = "Differential sequential, arithmetic coding";  break;

  case M_SOF14:	process = "Differential progressive, arithmetic coding"; break;

  case M_SOF15:	process = "Differential lossless, arithmetic coding";  break;

  default:	process = "Unknown";  break;

  }



  printf("JPEG image is %uw * %uh, %d color components, %d bits per sample\n",

	 image_width, image_height, num_components, data_precision);

  printf("JPEG process: %s\n", process);



  if (length != (unsigned int) (8 + num_components * 3))

    ERREXIT("Bogus SOF marker length");



  for (ci = 0; ci < num_components; ci++) {

    (void) read_1_byte();	/* Component ID code */

    (void) read_1_byte();	/* H, V sampling factors */

    (void) read_1_byte();	/* Quantization table number */

  }

}





/*

 * Parse the marker stream until SOS or EOI is seen;

 * display any COM markers.

 * While the companion program wrjpgcom will always insert COM markers before

 * SOFn, other implementations might not, so we scan to SOS before stopping.

 * If we were only interested in the image dimensions, we would stop at SOFn.

 * (Conversely, if we only cared about COM markers, there would be no need

 * for special code to handle SOFn; we could treat it like other markers.)

 */



static int

scan_JPEG_header (int verbose)

{

  int marker;



  /* Expect SOI at start of file */

  if (first_marker() != M_SOI)

    ERREXIT("Expected SOI marker first");



  /* Scan miscellaneous markers until we reach SOS. */

  for (;;) {

    marker = next_marker();

    switch (marker) {

      /* Note that marker codes 0xC4, 0xC8, 0xCC are not, and must not be,

       * treated as SOFn.  C4 in particular is actually DHT.

       */

    case M_SOF0:		/* Baseline */

    case M_SOF1:		/* Extended sequential, Huffman */

    case M_SOF2:		/* Progressive, Huffman */

    case M_SOF3:		/* Lossless, Huffman */

    case M_SOF5:		/* Differential sequential, Huffman */

    case M_SOF6:		/* Differential progressive, Huffman */

    case M_SOF7:		/* Differential lossless, Huffman */

    case M_SOF9:		/* Extended sequential, arithmetic */

    case M_SOF10:		/* Progressive, arithmetic */

    case M_SOF11:		/* Lossless, arithmetic */

    case M_SOF13:		/* Differential sequential, arithmetic */

    case M_SOF14:		/* Differential progressive, arithmetic */

    case M_SOF15:		/* Differential lossless, arithmetic */

      if (verbose)

	process_SOFn(marker);

      else

	skip_variable();

      break;



    case M_SOS:			/* stop before hitting compressed data */

      return marker;



    case M_EOI:			/* in case it's a tables-only JPEG stream */

      return marker;



    case M_COM:

      process_COM();

      break;



    case M_APP12:

      /* Some digital camera makers put useful textual information into

       * APP12 markers, so we print those out too when in -verbose mode.

       */

      if (verbose) {

	printf("APP12 contains:\n");

	process_COM();

      } else

	skip_variable();

      break;



    default:			/* Anything else just gets skipped */

      skip_variable();		/* we assume it has a parameter count... */

      break;

    }

  } /* end loop */

}





/* Command line parsing code */



static const char * progname;	/* program name for error messages */





static void

usage (void)

/* complain about bad command line */

{

  fprintf(stderr, "rdjpgcom displays any textual comments in a JPEG file.\n");



  fprintf(stderr, "Usage: %s [switches] [inputfile]\n", progname);



  fprintf(stderr, "Switches (names may be abbreviated):\n");

  fprintf(stderr, "  -verbose    Also display dimensions of JPEG image\n");



  exit(EXIT_FAILURE);

}





static int

keymatch (char * arg, const char * keyword, int minchars)

/* Case-insensitive matching of (possibly abbreviated) keyword switches. */

/* keyword is the constant keyword (must be lower case already), */

/* minchars is length of minimum legal abbreviation. */

{

  register int ca, ck;

  register int nmatched = 0;



  while ((ca = *arg++) != '\0') {

    if ((ck = *keyword++) == '\0')

      return 0;			/* arg longer than keyword, no good */

    if (isupper(ca))		/* force arg to lcase (assume ck is already) */

      ca = tolower(ca);

    if (ca != ck)

      return 0;			/* no good */

    nmatched++;			/* count matched characters */

  }

  /* reached end of argument; fail if it's too short for unique abbrev */

  if (nmatched < minchars)

    return 0;

  return 1;			/* A-OK */

}





/*

 * The main program.

 */



int

main (int argc, char **argv)

{

  int argn;

  char * arg;

  int verbose = 0;



  /* On Mac, fetch a command line. */

#ifdef USE_CCOMMAND

  argc = ccommand(&argv);

#endif



  progname = argv[0];

  if (progname == NULL || progname[0] == 0)

    progname = "rdjpgcom";	/* in case C library doesn't provide it */



  /* Parse switches, if any */

  for (argn = 1; argn < argc; argn++) {

    arg = argv[argn];

    if (arg[0] != '-')

      break;			/* not switch, must be file name */

    arg++;			/* advance over '-' */

    if (keymatch(arg, "verbose", 1)) {

      verbose++;

    } else

      usage();

  }



  /* Open the input file. */

  /* Unix style: expect zero or one file name */

  if (argn < argc-1) {

    fprintf(stderr, "%s: only one input file\n", progname);

    usage();

  }

  if (argn < argc) {

    if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {

      fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);

      exit(EXIT_FAILURE);

    }

  } else {

    /* default input file is stdin */

#ifdef USE_SETMODE		/* need to hack file mode? */

    setmode(fileno(stdin), O_BINARY);

#endif

#ifdef USE_FDOPEN		/* need to re-open in binary mode? */

    if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {

      fprintf(stderr, "%s: can't open stdin\n", progname);

      exit(EXIT_FAILURE);

    }

#else

    infile = stdin;

#endif

  }



  /* Scan the JPEG headers. */

  (void) scan_JPEG_header(verbose);



  /* All done. */

  exit(EXIT_SUCCESS);

  return 0;			/* suppress no-return-value warnings */

}

