# dlib C++ Library - rdjpgcom.c

    /*
     * rdjpgcom.c
     *
     * Copyright (C) 1994-1997, Thomas G. Lane.
     * Modified 2009 by Bill Allombert, Guido Vollbeding.
     * 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> */

    #ifdef HAVE_LOCALE_H
    #include <locale.h>		/* Bill Allombert: use locale for isprint */
    #endif
    #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 (int raw)
    {
      unsigned int length;
      int ch;
      int lastch = 0;

      /* Bill Allombert: set locale properly for isprint */
    #ifdef HAVE_LOCALE_H
      setlocale(LC_CTYPE, "");
    #endif

      /* 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();
        if (raw) {
          putc(ch, stdout);
        /* 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.
         */
        } else 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");

      /* Bill Allombert: revert to C locale */
    #ifdef HAVE_LOCALE_H
      setlocale(LC_CTYPE, "C");
    #endif
    }

    /*
     * 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 raw)
    {
      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(raw);
          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(raw);
          } 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, "  -raw        Display non-printable characters in comments (unsafe)\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, raw = 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 if (keymatch(arg, "raw", 1)) {
          raw = 1;
        } 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, raw);

      /* All done. */
      exit(EXIT_SUCCESS);
      return 0;			/* suppress no-return-value warnings */
    }