pngpread.c 30.7 KB
Newer Older
wester committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085

/* pngpread.c - read a png file in push mode
 *
 * Last changed in libpng 1.6.18 [July 23, 2015]
 * Copyright (c) 1998-2015 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 */

#include "pngpriv.h"

#ifdef PNG_PROGRESSIVE_READ_SUPPORTED

/* Push model modes */
#define PNG_READ_SIG_MODE   0
#define PNG_READ_CHUNK_MODE 1
#define PNG_READ_IDAT_MODE  2
#define PNG_READ_tEXt_MODE  4
#define PNG_READ_zTXt_MODE  5
#define PNG_READ_DONE_MODE  6
#define PNG_READ_iTXt_MODE  7
#define PNG_ERROR_MODE      8

#define PNG_PUSH_SAVE_BUFFER_IF_FULL \
if (png_ptr->push_length + 4 > png_ptr->buffer_size) \
   { png_push_save_buffer(png_ptr); return; }
#define PNG_PUSH_SAVE_BUFFER_IF_LT(N) \
if (png_ptr->buffer_size < N) \
   { png_push_save_buffer(png_ptr); return; }

void PNGAPI
png_process_data(png_structrp png_ptr, png_inforp info_ptr,
    png_bytep buffer, png_size_t buffer_size)
{
   if (png_ptr == NULL || info_ptr == NULL)
      return;

   png_push_restore_buffer(png_ptr, buffer, buffer_size);

   while (png_ptr->buffer_size)
   {
      png_process_some_data(png_ptr, info_ptr);
   }
}

png_size_t PNGAPI
png_process_data_pause(png_structrp png_ptr, int save)
{
   if (png_ptr != NULL)
   {
      /* It's easiest for the caller if we do the save; then the caller doesn't
       * have to supply the same data again:
       */
      if (save != 0)
         png_push_save_buffer(png_ptr);
      else
      {
         /* This includes any pending saved bytes: */
         png_size_t remaining = png_ptr->buffer_size;
         png_ptr->buffer_size = 0;

         /* So subtract the saved buffer size, unless all the data
          * is actually 'saved', in which case we just return 0
          */
         if (png_ptr->save_buffer_size < remaining)
            return remaining - png_ptr->save_buffer_size;
      }
   }

   return 0;
}

png_uint_32 PNGAPI
png_process_data_skip(png_structrp png_ptr)
{
  /* TODO: Deprecate and remove this API.
   * Somewhere the implementation of this seems to have been lost,
   * or abandoned.  It was only to support some internal back-door access
   * to png_struct) in libpng-1.4.x.
   */
   png_app_warning(png_ptr,
"png_process_data_skip is not implemented in any current version of libpng");
   return 0;
}

/* What we do with the incoming data depends on what we were previously
 * doing before we ran out of data...
 */
void /* PRIVATE */
png_process_some_data(png_structrp png_ptr, png_inforp info_ptr)
{
   if (png_ptr == NULL)
      return;

   switch (png_ptr->process_mode)
   {
      case PNG_READ_SIG_MODE:
      {
         png_push_read_sig(png_ptr, info_ptr);
         break;
      }

      case PNG_READ_CHUNK_MODE:
      {
         png_push_read_chunk(png_ptr, info_ptr);
         break;
      }

      case PNG_READ_IDAT_MODE:
      {
         png_push_read_IDAT(png_ptr);
         break;
      }

      default:
      {
         png_ptr->buffer_size = 0;
         break;
      }
   }
}

/* Read any remaining signature bytes from the stream and compare them with
 * the correct PNG signature.  It is possible that this routine is called
 * with bytes already read from the signature, either because they have been
 * checked by the calling application, or because of multiple calls to this
 * routine.
 */
void /* PRIVATE */
png_push_read_sig(png_structrp png_ptr, png_inforp info_ptr)
{
   png_size_t num_checked = png_ptr->sig_bytes, /* SAFE, does not exceed 8 */ 
       num_to_check = 8 - num_checked;

   if (png_ptr->buffer_size < num_to_check)
   {
      num_to_check = png_ptr->buffer_size;
   }

   png_push_fill_buffer(png_ptr, &(info_ptr->signature[num_checked]),
       num_to_check);
   png_ptr->sig_bytes = (png_byte)(png_ptr->sig_bytes + num_to_check);

   if (png_sig_cmp(info_ptr->signature, num_checked, num_to_check))
   {
      if (num_checked < 4 &&
          png_sig_cmp(info_ptr->signature, num_checked, num_to_check - 4))
         png_error(png_ptr, "Not a PNG file");

      else
         png_error(png_ptr, "PNG file corrupted by ASCII conversion");
   }
   else
   {
      if (png_ptr->sig_bytes >= 8)
      {
         png_ptr->process_mode = PNG_READ_CHUNK_MODE;
      }
   }
}

void /* PRIVATE */
png_push_read_chunk(png_structrp png_ptr, png_inforp info_ptr)
{
   png_uint_32 chunk_name;
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
   int keep; /* unknown handling method */
#endif

   /* First we make sure we have enough data for the 4-byte chunk name
    * and the 4-byte chunk length before proceeding with decoding the
    * chunk data.  To fully decode each of these chunks, we also make
    * sure we have enough data in the buffer for the 4-byte CRC at the
    * end of every chunk (except IDAT, which is handled separately).
    */
   if ((png_ptr->mode & PNG_HAVE_CHUNK_HEADER) == 0)
   {
      png_byte chunk_length[4];
      png_byte chunk_tag[4];

      PNG_PUSH_SAVE_BUFFER_IF_LT(8)
      png_push_fill_buffer(png_ptr, chunk_length, 4);
      png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
      png_reset_crc(png_ptr);
      png_crc_read(png_ptr, chunk_tag, 4);
      png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
      png_check_chunk_name(png_ptr, png_ptr->chunk_name);
      png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
   }

   chunk_name = png_ptr->chunk_name;

   if (chunk_name == png_IDAT)
   {
      if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
         png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;

      /* If we reach an IDAT chunk, this means we have read all of the
       * header chunks, and we can start reading the image (or if this
       * is called after the image has been read - we have an error).
       */
      if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
         png_error(png_ptr, "Missing IHDR before IDAT");

      else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
          (png_ptr->mode & PNG_HAVE_PLTE) == 0)
         png_error(png_ptr, "Missing PLTE before IDAT");

      png_ptr->mode |= PNG_HAVE_IDAT;
      png_ptr->process_mode = PNG_READ_IDAT_MODE;

      if ((png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT) == 0)
         if (png_ptr->push_length == 0)
            return;

      if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
         png_benign_error(png_ptr, "Too many IDATs found");
   }

   if (chunk_name == png_IHDR)
   {
      if (png_ptr->push_length != 13)
         png_error(png_ptr, "Invalid IHDR length");

      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_IHDR(png_ptr, info_ptr, png_ptr->push_length);
   }

   else if (chunk_name == png_IEND)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_IEND(png_ptr, info_ptr, png_ptr->push_length);

      png_ptr->process_mode = PNG_READ_DONE_MODE;
      png_push_have_end(png_ptr, info_ptr);
   }

#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
   else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length, keep);

      if (chunk_name == png_PLTE)
         png_ptr->mode |= PNG_HAVE_PLTE;
   }
#endif

   else if (chunk_name == png_PLTE)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_PLTE(png_ptr, info_ptr, png_ptr->push_length);
   }

   else if (chunk_name == png_IDAT)
   {
      png_ptr->idat_size = png_ptr->push_length;
      png_ptr->process_mode = PNG_READ_IDAT_MODE;
      png_push_have_info(png_ptr, info_ptr);
      png_ptr->zstream.avail_out =
          (uInt) PNG_ROWBYTES(png_ptr->pixel_depth,
          png_ptr->iwidth) + 1;
      png_ptr->zstream.next_out = png_ptr->row_buf;
      return;
   }

#ifdef PNG_READ_gAMA_SUPPORTED
   else if (png_ptr->chunk_name == png_gAMA)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_gAMA(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sBIT_SUPPORTED
   else if (png_ptr->chunk_name == png_sBIT)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_sBIT(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_cHRM_SUPPORTED
   else if (png_ptr->chunk_name == png_cHRM)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_cHRM(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sRGB_SUPPORTED
   else if (chunk_name == png_sRGB)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_sRGB(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_iCCP_SUPPORTED
   else if (png_ptr->chunk_name == png_iCCP)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_iCCP(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sPLT_SUPPORTED
   else if (chunk_name == png_sPLT)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_sPLT(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_tRNS_SUPPORTED
   else if (chunk_name == png_tRNS)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_tRNS(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_bKGD_SUPPORTED
   else if (chunk_name == png_bKGD)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_bKGD(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_hIST_SUPPORTED
   else if (chunk_name == png_hIST)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_hIST(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_pHYs_SUPPORTED
   else if (chunk_name == png_pHYs)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_pHYs(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_oFFs_SUPPORTED
   else if (chunk_name == png_oFFs)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_oFFs(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif

#ifdef PNG_READ_pCAL_SUPPORTED
   else if (chunk_name == png_pCAL)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_pCAL(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sCAL_SUPPORTED
   else if (chunk_name == png_sCAL)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_sCAL(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_tIME_SUPPORTED
   else if (chunk_name == png_tIME)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_tIME(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_tEXt_SUPPORTED
   else if (chunk_name == png_tEXt)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_tEXt(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_zTXt_SUPPORTED
   else if (chunk_name == png_zTXt)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_zTXt(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_iTXt_SUPPORTED
   else if (chunk_name == png_iTXt)
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_iTXt(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif

   else
   {
      PNG_PUSH_SAVE_BUFFER_IF_FULL
      png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length,
         PNG_HANDLE_CHUNK_AS_DEFAULT);
   }

   png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
}

void PNGCBAPI
png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, png_size_t length)
{
   png_bytep ptr;

   if (png_ptr == NULL)
      return;

   ptr = buffer;
   if (png_ptr->save_buffer_size != 0)
   {
      png_size_t save_size;

      if (length < png_ptr->save_buffer_size)
         save_size = length;

      else
         save_size = png_ptr->save_buffer_size;

      memcpy(ptr, png_ptr->save_buffer_ptr, save_size);
      length -= save_size;
      ptr += save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }
   if (length != 0 && png_ptr->current_buffer_size != 0)
   {
      png_size_t save_size;

      if (length < png_ptr->current_buffer_size)
         save_size = length;

      else
         save_size = png_ptr->current_buffer_size;

      memcpy(ptr, png_ptr->current_buffer_ptr, save_size);
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
}

void /* PRIVATE */
png_push_save_buffer(png_structrp png_ptr)
{
   if (png_ptr->save_buffer_size != 0)
   {
      if (png_ptr->save_buffer_ptr != png_ptr->save_buffer)
      {
         png_size_t i, istop;
         png_bytep sp;
         png_bytep dp;

         istop = png_ptr->save_buffer_size;
         for (i = 0, sp = png_ptr->save_buffer_ptr, dp = png_ptr->save_buffer;
             i < istop; i++, sp++, dp++)
         {
            *dp = *sp;
         }
      }
   }
   if (png_ptr->save_buffer_size + png_ptr->current_buffer_size >
       png_ptr->save_buffer_max)
   {
      png_size_t new_max;
      png_bytep old_buffer;

      if (png_ptr->save_buffer_size > PNG_SIZE_MAX -
          (png_ptr->current_buffer_size + 256))
      {
         png_error(png_ptr, "Potential overflow of save_buffer");
      }

      new_max = png_ptr->save_buffer_size + png_ptr->current_buffer_size + 256;
      old_buffer = png_ptr->save_buffer;
      png_ptr->save_buffer = (png_bytep)png_malloc_warn(png_ptr,
          (png_size_t)new_max);

      if (png_ptr->save_buffer == NULL)
      {
         png_free(png_ptr, old_buffer);
         png_error(png_ptr, "Insufficient memory for save_buffer");
      }

      memcpy(png_ptr->save_buffer, old_buffer, png_ptr->save_buffer_size);
      png_free(png_ptr, old_buffer);
      png_ptr->save_buffer_max = new_max;
   }
   if (png_ptr->current_buffer_size)
   {
      memcpy(png_ptr->save_buffer + png_ptr->save_buffer_size,
         png_ptr->current_buffer_ptr, png_ptr->current_buffer_size);
      png_ptr->save_buffer_size += png_ptr->current_buffer_size;
      png_ptr->current_buffer_size = 0;
   }
   png_ptr->save_buffer_ptr = png_ptr->save_buffer;
   png_ptr->buffer_size = 0;
}

void /* PRIVATE */
png_push_restore_buffer(png_structrp png_ptr, png_bytep buffer,
   png_size_t buffer_length)
{
   png_ptr->current_buffer = buffer;
   png_ptr->current_buffer_size = buffer_length;
   png_ptr->buffer_size = buffer_length + png_ptr->save_buffer_size;
   png_ptr->current_buffer_ptr = png_ptr->current_buffer;
}

void /* PRIVATE */
png_push_read_IDAT(png_structrp png_ptr)
{
   if ((png_ptr->mode & PNG_HAVE_CHUNK_HEADER) == 0)
   {
      png_byte chunk_length[4];
      png_byte chunk_tag[4];

      /* TODO: this code can be commoned up with the same code in push_read */
      PNG_PUSH_SAVE_BUFFER_IF_LT(8)
      png_push_fill_buffer(png_ptr, chunk_length, 4);
      png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
      png_reset_crc(png_ptr);
      png_crc_read(png_ptr, chunk_tag, 4);
      png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
      png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;

      if (png_ptr->chunk_name != png_IDAT)
      {
         png_ptr->process_mode = PNG_READ_CHUNK_MODE;

         if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
            png_error(png_ptr, "Not enough compressed data");

         return;
      }

      png_ptr->idat_size = png_ptr->push_length;
   }

   if (png_ptr->idat_size != 0 && png_ptr->save_buffer_size != 0)
   {
      png_size_t save_size = png_ptr->save_buffer_size;
      png_uint_32 idat_size = png_ptr->idat_size;

      /* We want the smaller of 'idat_size' and 'current_buffer_size', but they
       * are of different types and we don't know which variable has the fewest
       * bits.  Carefully select the smaller and cast it to the type of the
       * larger - this cannot overflow.  Do not cast in the following test - it
       * will break on either 16-bit or 64-bit platforms.
       */
      if (idat_size < save_size)
         save_size = (png_size_t)idat_size;

      else
         idat_size = (png_uint_32)save_size;

      png_calculate_crc(png_ptr, png_ptr->save_buffer_ptr, save_size);

      png_process_IDAT_data(png_ptr, png_ptr->save_buffer_ptr, save_size);

      png_ptr->idat_size -= idat_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }

   if (png_ptr->idat_size != 0 && png_ptr->current_buffer_size != 0)
   {
      png_size_t save_size = png_ptr->current_buffer_size;
      png_uint_32 idat_size = png_ptr->idat_size;

      /* We want the smaller of 'idat_size' and 'current_buffer_size', but they
       * are of different types and we don't know which variable has the fewest
       * bits.  Carefully select the smaller and cast it to the type of the
       * larger - this cannot overflow.
       */
      if (idat_size < save_size)
         save_size = (png_size_t)idat_size;

      else
         idat_size = (png_uint_32)save_size;

      png_calculate_crc(png_ptr, png_ptr->current_buffer_ptr, save_size);

      png_process_IDAT_data(png_ptr, png_ptr->current_buffer_ptr, save_size);

      png_ptr->idat_size -= idat_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }

   if (png_ptr->idat_size == 0)
   {
      PNG_PUSH_SAVE_BUFFER_IF_LT(4)
      png_crc_finish(png_ptr, 0);
      png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
      png_ptr->mode |= PNG_AFTER_IDAT;
      png_ptr->zowner = 0;
   }
}

void /* PRIVATE */
png_process_IDAT_data(png_structrp png_ptr, png_bytep buffer,
   png_size_t buffer_length)
{
   /* The caller checks for a non-zero buffer length. */
   if (!(buffer_length > 0) || buffer == NULL)
      png_error(png_ptr, "No IDAT data (internal error)");

   /* This routine must process all the data it has been given
    * before returning, calling the row callback as required to
    * handle the uncompressed results.
    */
   png_ptr->zstream.next_in = buffer;
   /* TODO: WARNING: TRUNCATION ERROR: DANGER WILL ROBINSON: */
   png_ptr->zstream.avail_in = (uInt)buffer_length;

   /* Keep going until the decompressed data is all processed
    * or the stream marked as finished.
    */
   while (png_ptr->zstream.avail_in > 0 &&
      (png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
   {
      int ret;

      /* We have data for zlib, but we must check that zlib
       * has someplace to put the results.  It doesn't matter
       * if we don't expect any results -- it may be the input
       * data is just the LZ end code.
       */
      if (!(png_ptr->zstream.avail_out > 0))
      {
         /* TODO: WARNING: TRUNCATION ERROR: DANGER WILL ROBINSON: */
         png_ptr->zstream.avail_out = (uInt)(PNG_ROWBYTES(png_ptr->pixel_depth,
             png_ptr->iwidth) + 1);

         png_ptr->zstream.next_out = png_ptr->row_buf;
      }

      /* Using Z_SYNC_FLUSH here means that an unterminated
       * LZ stream (a stream with a missing end code) can still
       * be handled, otherwise (Z_NO_FLUSH) a future zlib
       * implementation might defer output and therefore
       * change the current behavior (see comments in inflate.c
       * for why this doesn't happen at present with zlib 1.2.5).
       */
      ret = inflate(&png_ptr->zstream, Z_SYNC_FLUSH);

      /* Check for any failure before proceeding. */
      if (ret != Z_OK && ret != Z_STREAM_END)
      {
         /* Terminate the decompression. */
         png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
         png_ptr->zowner = 0;

         /* This may be a truncated stream (missing or
          * damaged end code).  Treat that as a warning.
          */
         if (png_ptr->row_number >= png_ptr->num_rows ||
             png_ptr->pass > 6)
            png_warning(png_ptr, "Truncated compressed data in IDAT");

         else
            png_error(png_ptr, "Decompression error in IDAT");

         /* Skip the check on unprocessed input */
         return;
      }

      /* Did inflate output any data? */
      if (png_ptr->zstream.next_out != png_ptr->row_buf)
      {
         /* Is this unexpected data after the last row?
          * If it is, artificially terminate the LZ output
          * here.
          */
         if (png_ptr->row_number >= png_ptr->num_rows ||
             png_ptr->pass > 6)
         {
            /* Extra data. */
            png_warning(png_ptr, "Extra compressed data in IDAT");
            png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
            png_ptr->zowner = 0;

            /* Do no more processing; skip the unprocessed
             * input check below.
             */
            return;
         }

         /* Do we have a complete row? */
         if (png_ptr->zstream.avail_out == 0)
            png_push_process_row(png_ptr);
      }

      /* And check for the end of the stream. */
      if (ret == Z_STREAM_END)
         png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
   }

   /* All the data should have been processed, if anything
    * is left at this point we have bytes of IDAT data
    * after the zlib end code.
    */
   if (png_ptr->zstream.avail_in > 0)
      png_warning(png_ptr, "Extra compression data in IDAT");
}

void /* PRIVATE */
png_push_process_row(png_structrp png_ptr)
{
   /* 1.5.6: row_info moved out of png_struct to a local here. */
   png_row_info row_info;

   row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
   row_info.color_type = png_ptr->color_type;
   row_info.bit_depth = png_ptr->bit_depth;
   row_info.channels = png_ptr->channels;
   row_info.pixel_depth = png_ptr->pixel_depth;
   row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);

   if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)
   {
      if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
         png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,
            png_ptr->prev_row + 1, png_ptr->row_buf[0]);
      else
         png_error(png_ptr, "bad adaptive filter value");
   }

   /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
    * 1.5.6, while the buffer really is this big in current versions of libpng
    * it may not be in the future, so this was changed just to copy the
    * interlaced row count:
    */
   memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);

#ifdef PNG_READ_TRANSFORMS_SUPPORTED
   if (png_ptr->transformations != 0)
      png_do_read_transformations(png_ptr, &row_info);
#endif

   /* The transformed pixel depth should match the depth now in row_info. */
   if (png_ptr->transformed_pixel_depth == 0)
   {
      png_ptr->transformed_pixel_depth = row_info.pixel_depth;
      if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
         png_error(png_ptr, "progressive row overflow");
   }

   else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
      png_error(png_ptr, "internal progressive row size calculation error");


#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* Expand interlaced rows to full size */
   if (png_ptr->interlaced != 0 &&
       (png_ptr->transformations & PNG_INTERLACE) != 0)
   {
      if (png_ptr->pass < 6)
         png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,
            png_ptr->transformations);

      switch (png_ptr->pass)
      {
         case 0:
         {
            int i;
            for (i = 0; i < 8 && png_ptr->pass == 0; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr); /* Updates png_ptr->pass */
            }

            if (png_ptr->pass == 2) /* Pass 1 might be empty */
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            if (png_ptr->pass == 4 && png_ptr->height <= 4)
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            if (png_ptr->pass == 6 && png_ptr->height <= 4)
            {
                png_push_have_row(png_ptr, NULL);
                png_read_push_finish_row(png_ptr);
            }

            break;
         }

         case 1:
         {
            int i;
            for (i = 0; i < 8 && png_ptr->pass == 1; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 2) /* Skip top 4 generated rows */
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            break;
         }

         case 2:
         {
            int i;

            for (i = 0; i < 4 && png_ptr->pass == 2; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            for (i = 0; i < 4 && png_ptr->pass == 2; i++)
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 4) /* Pass 3 might be empty */
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            break;
         }

         case 3:
         {
            int i;

            for (i = 0; i < 4 && png_ptr->pass == 3; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 4) /* Skip top two generated rows */
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            break;
         }

         case 4:
         {
            int i;

            for (i = 0; i < 2 && png_ptr->pass == 4; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            for (i = 0; i < 2 && png_ptr->pass == 4; i++)
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 6) /* Pass 5 might be empty */
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            break;
         }

         case 5:
         {
            int i;

            for (i = 0; i < 2 && png_ptr->pass == 5; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 6) /* Skip top generated row */
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            break;
         }

         default:
         case 6:
         {
            png_push_have_row(png_ptr, png_ptr->row_buf + 1);
            png_read_push_finish_row(png_ptr);

            if (png_ptr->pass != 6)
               break;

            png_push_have_row(png_ptr, NULL);
            png_read_push_finish_row(png_ptr);
         }
      }
   }
   else
#endif
   {
      png_push_have_row(png_ptr, png_ptr->row_buf + 1);
      png_read_push_finish_row(png_ptr);
   }
}

void /* PRIVATE */
png_read_push_finish_row(png_structrp png_ptr)
{
#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */

   /* Start of interlace block */
   static PNG_CONST png_byte png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};

   /* Offset to next interlace block */
   static PNG_CONST png_byte png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};

   /* Start of interlace block in the y direction */
   static PNG_CONST png_byte png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};

   /* Offset to next interlace block in the y direction */
   static PNG_CONST png_byte png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};

   /* Height of interlace block.  This is not currently used - if you need
    * it, uncomment it here and in png.h
   static PNG_CONST png_byte png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
   */
#endif

   png_ptr->row_number++;
   if (png_ptr->row_number < png_ptr->num_rows)
      return;

#ifdef PNG_READ_INTERLACING_SUPPORTED
   if (png_ptr->interlaced != 0)
   {
      png_ptr->row_number = 0;
      memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);

      do
      {
         png_ptr->pass++;
         if ((png_ptr->pass == 1 && png_ptr->width < 5) ||
             (png_ptr->pass == 3 && png_ptr->width < 3) ||
             (png_ptr->pass == 5 && png_ptr->width < 2))
            png_ptr->pass++;

         if (png_ptr->pass > 7)
            png_ptr->pass--;

         if (png_ptr->pass >= 7)
            break;

         png_ptr->iwidth = (png_ptr->width +
             png_pass_inc[png_ptr->pass] - 1 -
             png_pass_start[png_ptr->pass]) /
             png_pass_inc[png_ptr->pass];

         if ((png_ptr->transformations & PNG_INTERLACE) != 0)
            break;

         png_ptr->num_rows = (png_ptr->height +
             png_pass_yinc[png_ptr->pass] - 1 -
             png_pass_ystart[png_ptr->pass]) /
             png_pass_yinc[png_ptr->pass];

      } while (png_ptr->iwidth == 0 || png_ptr->num_rows == 0);
   }
#endif /* READ_INTERLACING */
}

void /* PRIVATE */
png_push_have_info(png_structrp png_ptr, png_inforp info_ptr)
{
   if (png_ptr->info_fn != NULL)
      (*(png_ptr->info_fn))(png_ptr, info_ptr);
}

void /* PRIVATE */
png_push_have_end(png_structrp png_ptr, png_inforp info_ptr)
{
   if (png_ptr->end_fn != NULL)
      (*(png_ptr->end_fn))(png_ptr, info_ptr);
}

void /* PRIVATE */
png_push_have_row(png_structrp png_ptr, png_bytep row)
{
   if (png_ptr->row_fn != NULL)
      (*(png_ptr->row_fn))(png_ptr, row, png_ptr->row_number,
         (int)png_ptr->pass);
}

#ifdef PNG_READ_INTERLACING_SUPPORTED
void PNGAPI
png_progressive_combine_row(png_const_structrp png_ptr, png_bytep old_row,
    png_const_bytep new_row)
{
   if (png_ptr == NULL)
      return;

   /* new_row is a flag here - if it is NULL then the app callback was called
    * from an empty row (see the calls to png_struct::row_fn below), otherwise
    * it must be png_ptr->row_buf+1
    */
   if (new_row != NULL)
      png_combine_row(png_ptr, old_row, 1/*blocky display*/);
}
#endif /* READ_INTERLACING */

void PNGAPI
png_set_progressive_read_fn(png_structrp png_ptr, png_voidp progressive_ptr,
    png_progressive_info_ptr info_fn, png_progressive_row_ptr row_fn,
    png_progressive_end_ptr end_fn)
{
   if (png_ptr == NULL)
      return;

   png_ptr->info_fn = info_fn;
   png_ptr->row_fn = row_fn;
   png_ptr->end_fn = end_fn;

   png_set_read_fn(png_ptr, progressive_ptr, png_push_fill_buffer);
}

png_voidp PNGAPI
png_get_progressive_ptr(png_const_structrp png_ptr)
{
   if (png_ptr == NULL)
      return (NULL);

   return png_ptr->io_ptr;
}
#endif /* PROGRESSIVE_READ */