media/libpng/pngpread.c

   1
   2 /* pngpread.c - read a png file in push mode
   3  *
   4  * Copyright (c) 2018 Cosmin Truta
   5  * Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
   6  * Copyright (c) 1996-1997 Andreas Dilger
   7  * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
   8  *
   9  * This code is released under the libpng license.
  10  * For conditions of distribution and use, see the disclaimer
  11  * and license in png.h
  12  */
  13
  14 #include "pngpriv.h"
  15
  16 #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
  17
  18 /* Push model modes */
  19 #define PNG_READ_SIG_MODE   0
  20 #define PNG_READ_CHUNK_MODE 1
  21 #define PNG_READ_IDAT_MODE  2
  22 #define PNG_READ_tEXt_MODE  4
  23 #define PNG_READ_zTXt_MODE  5
  24 #define PNG_READ_DONE_MODE  6
  25 #define PNG_READ_iTXt_MODE  7
  26 #define PNG_ERROR_MODE      8
  27
  28 #define PNG_PUSH_SAVE_BUFFER_IF_FULL \
  29 if (png_ptr->push_length + 4 > png_ptr->buffer_size) \
  30    { png_push_save_buffer(png_ptr); return; }
  31 #define PNG_PUSH_SAVE_BUFFER_IF_LT(N) \
  32 if (png_ptr->buffer_size < N) \
  33    { png_push_save_buffer(png_ptr); return; }
  34
  35 void PNGAPI
  36 png_process_data(png_structrp png_ptr, png_inforp info_ptr,
  37     png_bytep buffer, size_t buffer_size)
  38 {
  39    if (png_ptr == NULL || info_ptr == NULL)
  40       return;
  41
  42    png_push_restore_buffer(png_ptr, buffer, buffer_size);
  43
  44    while (png_ptr->buffer_size)
  45    {
  46       png_process_some_data(png_ptr, info_ptr);
  47    }
  48 }
  49
  50 size_t PNGAPI
  51 png_process_data_pause(png_structrp png_ptr, int save)
  52 {
  53    if (png_ptr != NULL)
  54    {
  55       /* It's easiest for the caller if we do the save; then the caller doesn't
  56        * have to supply the same data again:
  57        */
  58       if (save != 0)
  59          png_push_save_buffer(png_ptr);
  60       else
  61       {
  62          /* This includes any pending saved bytes: */
  63          size_t remaining = png_ptr->buffer_size;
  64          png_ptr->buffer_size = 0;
  65
  66          /* So subtract the saved buffer size, unless all the data
  67           * is actually 'saved', in which case we just return 0
  68           */
  69          if (png_ptr->save_buffer_size < remaining)
  70             return remaining - png_ptr->save_buffer_size;
  71       }
  72    }
  73
  74    return 0;
  75 }
  76
  77 png_uint_32 PNGAPI
  78 png_process_data_skip(png_structrp png_ptr)
  79 {
  80 /* TODO: Deprecate and remove this API.
  81  * Somewhere the implementation of this seems to have been lost,
  82  * or abandoned.  It was only to support some internal back-door access
  83  * to png_struct) in libpng-1.4.x.
  84  */
  85    png_app_warning(png_ptr,
  86 "png_process_data_skip is not implemented in any current version of libpng");
  87    return 0;
  88 }
  89
  90 /* What we do with the incoming data depends on what we were previously
  91  * doing before we ran out of data...
  92  */
  93 void /* PRIVATE */
  94 png_process_some_data(png_structrp png_ptr, png_inforp info_ptr)
  95 {
  96    if (png_ptr == NULL)
  97       return;
  98
  99    switch (png_ptr->process_mode)
 100    {
 101       case PNG_READ_SIG_MODE:
 102       {
 103          png_push_read_sig(png_ptr, info_ptr);
 104          break;
 105       }
 106
 107       case PNG_READ_CHUNK_MODE:
 108       {
 109          png_push_read_chunk(png_ptr, info_ptr);
 110          break;
 111       }
 112
 113       case PNG_READ_IDAT_MODE:
 114       {
 115          png_push_read_IDAT(png_ptr);
 116          break;
 117       }
 118
 119       default:
 120       {
 121          png_ptr->buffer_size = 0;
 122          break;
 123       }
 124    }
 125 }
 126
 127 /* Read any remaining signature bytes from the stream and compare them with
 128  * the correct PNG signature.  It is possible that this routine is called
 129  * with bytes already read from the signature, either because they have been
 130  * checked by the calling application, or because of multiple calls to this
 131  * routine.
 132  */
 133 void /* PRIVATE */
 134 png_push_read_sig(png_structrp png_ptr, png_inforp info_ptr)
 135 {
 136    size_t num_checked = png_ptr->sig_bytes; /* SAFE, does not exceed 8 */
 137    size_t num_to_check = 8 - num_checked;
 138
 139    if (png_ptr->buffer_size < num_to_check)
 140    {
 141       num_to_check = png_ptr->buffer_size;
 142    }
 143
 144    png_push_fill_buffer(png_ptr, &(info_ptr->signature[num_checked]),
 145        num_to_check);
 146    png_ptr->sig_bytes = (png_byte)(png_ptr->sig_bytes + num_to_check);
 147
 148    if (png_sig_cmp(info_ptr->signature, num_checked, num_to_check))
 149    {
 150       if (num_checked < 4 &&
 151           png_sig_cmp(info_ptr->signature, num_checked, num_to_check - 4))
 152          png_error(png_ptr, "Not a PNG file");
 153
 154       else
 155          png_error(png_ptr, "PNG file corrupted by ASCII conversion");
 156    }
 157    else
 158    {
 159       if (png_ptr->sig_bytes >= 8)
 160       {
 161          png_ptr->process_mode = PNG_READ_CHUNK_MODE;
 162       }
 163    }
 164 }
 165
 166 void /* PRIVATE */
 167 png_push_read_chunk(png_structrp png_ptr, png_inforp info_ptr)
 168 {
 169    png_uint_32 chunk_name;
 170 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
 171    int keep; /* unknown handling method */
 172 #endif
 173
 174    /* First we make sure we have enough data for the 4-byte chunk name
 175     * and the 4-byte chunk length before proceeding with decoding the
 176     * chunk data.  To fully decode each of these chunks, we also make
 177     * sure we have enough data in the buffer for the 4-byte CRC at the
 178     * end of every chunk (except IDAT, which is handled separately).
 179     */
 180    if ((png_ptr->mode & PNG_HAVE_CHUNK_HEADER) == 0)
 181    {
 182       png_byte chunk_length[4];
 183       png_byte chunk_tag[4];
 184
 185       PNG_PUSH_SAVE_BUFFER_IF_LT(8)
 186       png_push_fill_buffer(png_ptr, chunk_length, 4);
 187       png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
 188       png_reset_crc(png_ptr);
 189       png_crc_read(png_ptr, chunk_tag, 4);
 190       png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
 191       png_check_chunk_name(png_ptr, png_ptr->chunk_name);
 192       png_check_chunk_length(png_ptr, png_ptr->push_length);
 193       png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
 194    }
 195
 196    chunk_name = png_ptr->chunk_name;
 197
 198 #ifdef PNG_READ_APNG_SUPPORTED
 199    if (png_ptr->num_frames_read > 0 &&
 200        png_ptr->num_frames_read < info_ptr->num_frames)
 201    {
 202       if (chunk_name == png_IDAT)
 203       {
 204          /* Discard trailing IDATs for the first frame */
 205          if ((png_ptr->mode & PNG_HAVE_fcTL) != 0 ||
 206              png_ptr->num_frames_read > 1)
 207             png_error(png_ptr, "out of place IDAT");
 208
 209          PNG_PUSH_SAVE_BUFFER_IF_FULL
 210          png_crc_finish(png_ptr, png_ptr->push_length);
 211          png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 212       }
 213
 214       else if (chunk_name == png_fdAT)
 215       {
 216          PNG_PUSH_SAVE_BUFFER_IF_LT(4)
 217          png_ensure_sequence_number(png_ptr, 4);
 218
 219          if ((png_ptr->mode & PNG_HAVE_fcTL) == 0)
 220          {
 221             /* Discard trailing fdATs for frames other than the first */
 222             if (png_ptr->num_frames_read < 2)
 223                png_error(png_ptr, "out of place fdAT");
 224
 225             PNG_PUSH_SAVE_BUFFER_IF_FULL
 226             png_crc_finish(png_ptr, png_ptr->push_length);
 227             png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 228          }
 229
 230          else
 231          {
 232             /* frame data follows */
 233             png_ptr->idat_size = png_ptr->push_length - 4;
 234             png_ptr->mode |= PNG_HAVE_IDAT;
 235             png_ptr->process_mode = PNG_READ_IDAT_MODE;
 236          }
 237       }
 238
 239       else if (chunk_name == png_fcTL)
 240       {
 241          PNG_PUSH_SAVE_BUFFER_IF_FULL
 242          png_read_reset(png_ptr);
 243          png_ptr->mode &= ~PNG_HAVE_fcTL;
 244
 245          png_handle_fcTL(png_ptr, info_ptr, png_ptr->push_length);
 246
 247          if ((png_ptr->mode & PNG_HAVE_fcTL) == 0)
 248             png_error(png_ptr, "missing required fcTL chunk");
 249
 250          png_read_reinit(png_ptr, info_ptr);
 251          png_progressive_read_reset(png_ptr);
 252
 253          if (png_ptr->frame_info_fn != NULL)
 254             (*(png_ptr->frame_info_fn))(png_ptr, png_ptr->num_frames_read);
 255
 256          png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 257       }
 258
 259       else if (chunk_name == png_IEND)
 260       {
 261          PNG_PUSH_SAVE_BUFFER_IF_FULL
 262          png_warning(png_ptr, "Number of actual frames fewer than expected");
 263          png_crc_finish(png_ptr, png_ptr->push_length);
 264          png_ptr->process_mode = PNG_READ_DONE_MODE;
 265          png_push_have_end(png_ptr, info_ptr);
 266       }
 267
 268       else
 269       {
 270          PNG_PUSH_SAVE_BUFFER_IF_FULL
 271          png_warning(png_ptr, "Skipped (ignored) a chunk "
 272                               "between APNG chunks");
 273          png_crc_finish(png_ptr, png_ptr->push_length);
 274          png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 275       }
 276
 277       return;
 278    }
 279 #endif /* READ_APNG */
 280
 281    if (chunk_name == png_IDAT)
 282    {
 283       if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
 284          png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;
 285
 286       /* If we reach an IDAT chunk, this means we have read all of the
 287        * header chunks, and we can start reading the image (or if this
 288        * is called after the image has been read - we have an error).
 289        */
 290       if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
 291          png_error(png_ptr, "Missing IHDR before IDAT");
 292
 293       else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
 294           (png_ptr->mode & PNG_HAVE_PLTE) == 0)
 295          png_error(png_ptr, "Missing PLTE before IDAT");
 296
 297       png_ptr->process_mode = PNG_READ_IDAT_MODE;
 298
 299       if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
 300          if ((png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT) == 0)
 301             if (png_ptr->push_length == 0)
 302                return;
 303
 304       png_ptr->mode |= PNG_HAVE_IDAT;
 305
 306       if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
 307          png_benign_error(png_ptr, "Too many IDATs found");
 308    }
 309
 310    if (chunk_name == png_IHDR)
 311    {
 312       if (png_ptr->push_length != 13)
 313          png_error(png_ptr, "Invalid IHDR length");
 314
 315       PNG_PUSH_SAVE_BUFFER_IF_FULL
 316       png_handle_IHDR(png_ptr, info_ptr, png_ptr->push_length);
 317    }
 318
 319    else if (chunk_name == png_IEND)
 320    {
 321       PNG_PUSH_SAVE_BUFFER_IF_FULL
 322       png_handle_IEND(png_ptr, info_ptr, png_ptr->push_length);
 323
 324       png_ptr->process_mode = PNG_READ_DONE_MODE;
 325       png_push_have_end(png_ptr, info_ptr);
 326    }
 327
 328 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
 329    else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
 330    {
 331       PNG_PUSH_SAVE_BUFFER_IF_FULL
 332       png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length, keep);
 333
 334       if (chunk_name == png_PLTE)
 335          png_ptr->mode |= PNG_HAVE_PLTE;
 336    }
 337 #endif
 338
 339    else if (chunk_name == png_PLTE)
 340    {
 341       PNG_PUSH_SAVE_BUFFER_IF_FULL
 342       png_handle_PLTE(png_ptr, info_ptr, png_ptr->push_length);
 343    }
 344
 345    else if (chunk_name == png_IDAT)
 346    {
 347 #ifdef PNG_READ_APNG_SUPPORTED
 348       png_have_info(png_ptr, info_ptr);
 349 #endif
 350       png_ptr->idat_size = png_ptr->push_length;
 351       png_ptr->process_mode = PNG_READ_IDAT_MODE;
 352       png_push_have_info(png_ptr, info_ptr);
 353       png_ptr->zstream.avail_out =
 354           (uInt) PNG_ROWBYTES(png_ptr->pixel_depth,
 355           png_ptr->iwidth) + 1;
 356       png_ptr->zstream.next_out = png_ptr->row_buf;
 357       return;
 358    }
 359
 360 #ifdef PNG_READ_gAMA_SUPPORTED
 361    else if (png_ptr->chunk_name == png_gAMA)
 362    {
 363       PNG_PUSH_SAVE_BUFFER_IF_FULL
 364       png_handle_gAMA(png_ptr, info_ptr, png_ptr->push_length);
 365    }
 366
 367 #endif
 368 #ifdef PNG_READ_sBIT_SUPPORTED
 369    else if (png_ptr->chunk_name == png_sBIT)
 370    {
 371       PNG_PUSH_SAVE_BUFFER_IF_FULL
 372       png_handle_sBIT(png_ptr, info_ptr, png_ptr->push_length);
 373    }
 374
 375 #endif
 376 #ifdef PNG_READ_cHRM_SUPPORTED
 377    else if (png_ptr->chunk_name == png_cHRM)
 378    {
 379       PNG_PUSH_SAVE_BUFFER_IF_FULL
 380       png_handle_cHRM(png_ptr, info_ptr, png_ptr->push_length);
 381    }
 382
 383 #endif
 384 #ifdef PNG_READ_sRGB_SUPPORTED
 385    else if (chunk_name == png_sRGB)
 386    {
 387       PNG_PUSH_SAVE_BUFFER_IF_FULL
 388       png_handle_sRGB(png_ptr, info_ptr, png_ptr->push_length);
 389    }
 390
 391 #endif
 392 #ifdef PNG_READ_iCCP_SUPPORTED
 393    else if (png_ptr->chunk_name == png_iCCP)
 394    {
 395       PNG_PUSH_SAVE_BUFFER_IF_FULL
 396       png_handle_iCCP(png_ptr, info_ptr, png_ptr->push_length);
 397    }
 398
 399 #endif
 400 #ifdef PNG_READ_sPLT_SUPPORTED
 401    else if (chunk_name == png_sPLT)
 402    {
 403       PNG_PUSH_SAVE_BUFFER_IF_FULL
 404       png_handle_sPLT(png_ptr, info_ptr, png_ptr->push_length);
 405    }
 406
 407 #endif
 408 #ifdef PNG_READ_tRNS_SUPPORTED
 409    else if (chunk_name == png_tRNS)
 410    {
 411       PNG_PUSH_SAVE_BUFFER_IF_FULL
 412       png_handle_tRNS(png_ptr, info_ptr, png_ptr->push_length);
 413    }
 414
 415 #endif
 416 #ifdef PNG_READ_bKGD_SUPPORTED
 417    else if (chunk_name == png_bKGD)
 418    {
 419       PNG_PUSH_SAVE_BUFFER_IF_FULL
 420       png_handle_bKGD(png_ptr, info_ptr, png_ptr->push_length);
 421    }
 422
 423 #endif
 424 #ifdef PNG_READ_hIST_SUPPORTED
 425    else if (chunk_name == png_hIST)
 426    {
 427       PNG_PUSH_SAVE_BUFFER_IF_FULL
 428       png_handle_hIST(png_ptr, info_ptr, png_ptr->push_length);
 429    }
 430
 431 #endif
 432 #ifdef PNG_READ_pHYs_SUPPORTED
 433    else if (chunk_name == png_pHYs)
 434    {
 435       PNG_PUSH_SAVE_BUFFER_IF_FULL
 436       png_handle_pHYs(png_ptr, info_ptr, png_ptr->push_length);
 437    }
 438
 439 #endif
 440 #ifdef PNG_READ_oFFs_SUPPORTED
 441    else if (chunk_name == png_oFFs)
 442    {
 443       PNG_PUSH_SAVE_BUFFER_IF_FULL
 444       png_handle_oFFs(png_ptr, info_ptr, png_ptr->push_length);
 445    }
 446 #endif
 447
 448 #ifdef PNG_READ_pCAL_SUPPORTED
 449    else if (chunk_name == png_pCAL)
 450    {
 451       PNG_PUSH_SAVE_BUFFER_IF_FULL
 452       png_handle_pCAL(png_ptr, info_ptr, png_ptr->push_length);
 453    }
 454
 455 #endif
 456 #ifdef PNG_READ_sCAL_SUPPORTED
 457    else if (chunk_name == png_sCAL)
 458    {
 459       PNG_PUSH_SAVE_BUFFER_IF_FULL
 460       png_handle_sCAL(png_ptr, info_ptr, png_ptr->push_length);
 461    }
 462
 463 #endif
 464 #ifdef PNG_READ_tIME_SUPPORTED
 465    else if (chunk_name == png_tIME)
 466    {
 467       PNG_PUSH_SAVE_BUFFER_IF_FULL
 468       png_handle_tIME(png_ptr, info_ptr, png_ptr->push_length);
 469    }
 470
 471 #endif
 472 #ifdef PNG_READ_tEXt_SUPPORTED
 473    else if (chunk_name == png_tEXt)
 474    {
 475       PNG_PUSH_SAVE_BUFFER_IF_FULL
 476       png_handle_tEXt(png_ptr, info_ptr, png_ptr->push_length);
 477    }
 478
 479 #endif
 480 #ifdef PNG_READ_zTXt_SUPPORTED
 481    else if (chunk_name == png_zTXt)
 482    {
 483       PNG_PUSH_SAVE_BUFFER_IF_FULL
 484       png_handle_zTXt(png_ptr, info_ptr, png_ptr->push_length);
 485    }
 486
 487 #endif
 488 #ifdef PNG_READ_iTXt_SUPPORTED
 489    else if (chunk_name == png_iTXt)
 490    {
 491       PNG_PUSH_SAVE_BUFFER_IF_FULL
 492       png_handle_iTXt(png_ptr, info_ptr, png_ptr->push_length);
 493    }
 494 #endif
 495
 496 #ifdef PNG_READ_APNG_SUPPORTED
 497    else if (chunk_name == png_acTL)
 498    {
 499       PNG_PUSH_SAVE_BUFFER_IF_FULL
 500       png_handle_acTL(png_ptr, info_ptr, png_ptr->push_length);
 501    }
 502
 503    else if (chunk_name == png_fcTL)
 504    {
 505       PNG_PUSH_SAVE_BUFFER_IF_FULL
 506       png_handle_fcTL(png_ptr, info_ptr, png_ptr->push_length);
 507    }
 508
 509 #endif /* READ_APNG */
 510    else
 511    {
 512       PNG_PUSH_SAVE_BUFFER_IF_FULL
 513       png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length,
 514           PNG_HANDLE_CHUNK_AS_DEFAULT);
 515    }
 516
 517    png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 518 }
 519
 520 void PNGCBAPI
 521 png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, size_t length)
 522 {
 523    png_bytep ptr;
 524
 525    if (png_ptr == NULL)
 526       return;
 527
 528    ptr = buffer;
 529    if (png_ptr->save_buffer_size != 0)
 530    {
 531       size_t save_size;
 532
 533       if (length < png_ptr->save_buffer_size)
 534          save_size = length;
 535
 536       else
 537          save_size = png_ptr->save_buffer_size;
 538
 539       memcpy(ptr, png_ptr->save_buffer_ptr, save_size);
 540       length -= save_size;
 541       ptr += save_size;
 542       png_ptr->buffer_size -= save_size;
 543       png_ptr->save_buffer_size -= save_size;
 544       png_ptr->save_buffer_ptr += save_size;
 545    }
 546    if (length != 0 && png_ptr->current_buffer_size != 0)
 547    {
 548       size_t save_size;
 549
 550       if (length < png_ptr->current_buffer_size)
 551          save_size = length;
 552
 553       else
 554          save_size = png_ptr->current_buffer_size;
 555
 556       memcpy(ptr, png_ptr->current_buffer_ptr, save_size);
 557       png_ptr->buffer_size -= save_size;
 558       png_ptr->current_buffer_size -= save_size;
 559       png_ptr->current_buffer_ptr += save_size;
 560    }
 561 }
 562
 563 void /* PRIVATE */
 564 png_push_save_buffer(png_structrp png_ptr)
 565 {
 566    if (png_ptr->save_buffer_size != 0)
 567    {
 568       if (png_ptr->save_buffer_ptr != png_ptr->save_buffer)
 569       {
 570          size_t i, istop;
 571          png_bytep sp;
 572          png_bytep dp;
 573
 574          istop = png_ptr->save_buffer_size;
 575          for (i = 0, sp = png_ptr->save_buffer_ptr, dp = png_ptr->save_buffer;
 576              i < istop; i++, sp++, dp++)
 577          {
 578             *dp = *sp;
 579          }
 580       }
 581    }
 582    if (png_ptr->save_buffer_size + png_ptr->current_buffer_size >
 583        png_ptr->save_buffer_max)
 584    {
 585       size_t new_max;
 586       png_bytep old_buffer;
 587
 588       if (png_ptr->save_buffer_size > PNG_SIZE_MAX -
 589           (png_ptr->current_buffer_size + 256))
 590       {
 591          png_error(png_ptr, "Potential overflow of save_buffer");
 592       }
 593
 594       new_max = png_ptr->save_buffer_size + png_ptr->current_buffer_size + 256;
 595       old_buffer = png_ptr->save_buffer;
 596       png_ptr->save_buffer = (png_bytep)png_malloc_warn(png_ptr,
 597           (size_t)new_max);
 598
 599       if (png_ptr->save_buffer == NULL)
 600       {
 601          png_free(png_ptr, old_buffer);
 602          png_error(png_ptr, "Insufficient memory for save_buffer");
 603       }
 604
 605       if (old_buffer)
 606          memcpy(png_ptr->save_buffer, old_buffer, png_ptr->save_buffer_size);
 607       else if (png_ptr->save_buffer_size)
 608          png_error(png_ptr, "save_buffer error");
 609       png_free(png_ptr, old_buffer);
 610       png_ptr->save_buffer_max = new_max;
 611    }
 612    if (png_ptr->current_buffer_size)
 613    {
 614       memcpy(png_ptr->save_buffer + png_ptr->save_buffer_size,
 615          png_ptr->current_buffer_ptr, png_ptr->current_buffer_size);
 616       png_ptr->save_buffer_size += png_ptr->current_buffer_size;
 617       png_ptr->current_buffer_size = 0;
 618    }
 619    png_ptr->save_buffer_ptr = png_ptr->save_buffer;
 620    png_ptr->buffer_size = 0;
 621 }
 622
 623 void /* PRIVATE */
 624 png_push_restore_buffer(png_structrp png_ptr, png_bytep buffer,
 625     size_t buffer_length)
 626 {
 627    png_ptr->current_buffer = buffer;
 628    png_ptr->current_buffer_size = buffer_length;
 629    png_ptr->buffer_size = buffer_length + png_ptr->save_buffer_size;
 630    png_ptr->current_buffer_ptr = png_ptr->current_buffer;
 631 }
 632
 633 void /* PRIVATE */
 634 png_push_read_IDAT(png_structrp png_ptr)
 635 {
 636    if ((png_ptr->mode & PNG_HAVE_CHUNK_HEADER) == 0)
 637    {
 638       png_byte chunk_length[4];
 639       png_byte chunk_tag[4];
 640
 641       /* TODO: this code can be commoned up with the same code in push_read */
 642 #ifdef PNG_READ_APNG_SUPPORTED
 643       PNG_PUSH_SAVE_BUFFER_IF_LT(12)
 644 #else
 645       PNG_PUSH_SAVE_BUFFER_IF_LT(8)
 646 #endif
 647       png_push_fill_buffer(png_ptr, chunk_length, 4);
 648       png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
 649       png_reset_crc(png_ptr);
 650       png_crc_read(png_ptr, chunk_tag, 4);
 651       png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
 652       png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
 653
 654 #ifdef PNG_READ_APNG_SUPPORTED
 655       if (png_ptr->chunk_name != png_fdAT && png_ptr->num_frames_read > 0)
 656       {
 657           if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) != 0)
 658           {
 659               png_ptr->process_mode = PNG_READ_CHUNK_MODE;
 660               if (png_ptr->frame_end_fn != NULL)
 661                  (*(png_ptr->frame_end_fn))(png_ptr, png_ptr->num_frames_read);
 662               png_ptr->num_frames_read++;
 663               return;
 664           }
 665           else
 666           {
 667               if (png_ptr->chunk_name == png_IEND)
 668                   png_error(png_ptr, "Not enough image data");
 669               PNG_PUSH_SAVE_BUFFER_IF_FULL
 670               png_warning(png_ptr, "Skipping (ignoring) a chunk between "
 671                                    "APNG chunks");
 672               png_crc_finish(png_ptr, png_ptr->push_length);
 673               png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 674               return;
 675           }
 676       }
 677       else
 678 #endif
 679 #ifdef PNG_READ_APNG_SUPPORTED
 680       if (png_ptr->chunk_name != png_IDAT && png_ptr->num_frames_read == 0)
 681 #else
 682       if (png_ptr->chunk_name != png_IDAT)
 683 #endif
 684       {
 685          png_ptr->process_mode = PNG_READ_CHUNK_MODE;
 686
 687          if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
 688             png_error(png_ptr, "Not enough compressed data");
 689
 690 #ifdef PNG_READ_APNG_SUPPORTED
 691          if (png_ptr->frame_end_fn != NULL)
 692             (*(png_ptr->frame_end_fn))(png_ptr, png_ptr->num_frames_read);
 693          png_ptr->num_frames_read++;
 694 #endif
 695
 696          return;
 697       }
 698
 699       png_ptr->idat_size = png_ptr->push_length;
 700
 701 #ifdef PNG_READ_APNG_SUPPORTED
 702       if (png_ptr->num_frames_read > 0)
 703       {
 704          png_ensure_sequence_number(png_ptr, 4);
 705          png_ptr->idat_size -= 4;
 706       }
 707 #endif
 708    }
 709
 710    if (png_ptr->idat_size != 0 && png_ptr->save_buffer_size != 0)
 711    {
 712       size_t save_size = png_ptr->save_buffer_size;
 713       png_uint_32 idat_size = png_ptr->idat_size;
 714
 715       /* We want the smaller of 'idat_size' and 'current_buffer_size', but they
 716        * are of different types and we don't know which variable has the fewest
 717        * bits.  Carefully select the smaller and cast it to the type of the
 718        * larger - this cannot overflow.  Do not cast in the following test - it
 719        * will break on either 16-bit or 64-bit platforms.
 720        */
 721       if (idat_size < save_size)
 722          save_size = (size_t)idat_size;
 723
 724       else
 725          idat_size = (png_uint_32)save_size;
 726
 727       png_calculate_crc(png_ptr, png_ptr->save_buffer_ptr, save_size);
 728
 729       png_process_IDAT_data(png_ptr, png_ptr->save_buffer_ptr, save_size);
 730
 731       png_ptr->idat_size -= idat_size;
 732       png_ptr->buffer_size -= save_size;
 733       png_ptr->save_buffer_size -= save_size;
 734       png_ptr->save_buffer_ptr += save_size;
 735    }
 736
 737    if (png_ptr->idat_size != 0 && png_ptr->current_buffer_size != 0)
 738    {
 739       size_t save_size = png_ptr->current_buffer_size;
 740       png_uint_32 idat_size = png_ptr->idat_size;
 741
 742       /* We want the smaller of 'idat_size' and 'current_buffer_size', but they
 743        * are of different types and we don't know which variable has the fewest
 744        * bits.  Carefully select the smaller and cast it to the type of the
 745        * larger - this cannot overflow.
 746        */
 747       if (idat_size < save_size)
 748          save_size = (size_t)idat_size;
 749
 750       else
 751          idat_size = (png_uint_32)save_size;
 752
 753       png_calculate_crc(png_ptr, png_ptr->current_buffer_ptr, save_size);
 754
 755       png_process_IDAT_data(png_ptr, png_ptr->current_buffer_ptr, save_size);
 756
 757       png_ptr->idat_size -= idat_size;
 758       png_ptr->buffer_size -= save_size;
 759       png_ptr->current_buffer_size -= save_size;
 760       png_ptr->current_buffer_ptr += save_size;
 761    }
 762
 763    if (png_ptr->idat_size == 0)
 764    {
 765       PNG_PUSH_SAVE_BUFFER_IF_LT(4)
 766       png_crc_finish(png_ptr, 0);
 767       png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
 768       png_ptr->mode |= PNG_AFTER_IDAT;
 769       png_ptr->zowner = 0;
 770    }
 771 }
 772
 773 void /* PRIVATE */
 774 png_process_IDAT_data(png_structrp png_ptr, png_bytep buffer,
 775     size_t buffer_length)
 776 {
 777    /* The caller checks for a non-zero buffer length. */
 778    if (!(buffer_length > 0) || buffer == NULL)
 779       png_error(png_ptr, "No IDAT data (internal error)");
 780
 781 #ifdef PNG_READ_APNG_SUPPORTED
 782    /* If the app is not APNG-aware, decode only the first frame */
 783    if ((png_ptr->apng_flags & PNG_APNG_APP) == 0 &&
 784       png_ptr->num_frames_read > 0)
 785    {
 786       png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
 787       return;
 788    }
 789 #endif
 790
 791    /* This routine must process all the data it has been given
 792     * before returning, calling the row callback as required to
 793     * handle the uncompressed results.
 794     */
 795    png_ptr->zstream.next_in = buffer;
 796    /* TODO: WARNING: TRUNCATION ERROR: DANGER WILL ROBINSON: */
 797    png_ptr->zstream.avail_in = (uInt)buffer_length;
 798
 799    /* Keep going until the decompressed data is all processed
 800     * or the stream marked as finished.
 801     */
 802    while (png_ptr->zstream.avail_in > 0 &&
 803       (png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
 804    {
 805       int ret;
 806
 807       /* We have data for zlib, but we must check that zlib
 808        * has someplace to put the results.  It doesn't matter
 809        * if we don't expect any results -- it may be the input
 810        * data is just the LZ end code.
 811        */
 812       if (!(png_ptr->zstream.avail_out > 0))
 813       {
 814          /* TODO: WARNING: TRUNCATION ERROR: DANGER WILL ROBINSON: */
 815          png_ptr->zstream.avail_out = (uInt)(PNG_ROWBYTES(png_ptr->pixel_depth,
 816              png_ptr->iwidth) + 1);
 817
 818          png_ptr->zstream.next_out = png_ptr->row_buf;
 819       }
 820
 821       /* Using Z_SYNC_FLUSH here means that an unterminated
 822        * LZ stream (a stream with a missing end code) can still
 823        * be handled, otherwise (Z_NO_FLUSH) a future zlib
 824        * implementation might defer output and therefore
 825        * change the current behavior (see comments in inflate.c
 826        * for why this doesn't happen at present with zlib 1.2.5).
 827        */
 828       ret = PNG_INFLATE(png_ptr, Z_SYNC_FLUSH);
 829
 830       /* Check for any failure before proceeding. */
 831       if (ret != Z_OK && ret != Z_STREAM_END)
 832       {
 833          /* Terminate the decompression. */
 834          png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
 835          png_ptr->zowner = 0;
 836
 837          /* This may be a truncated stream (missing or
 838           * damaged end code).  Treat that as a warning.
 839           */
 840          if (png_ptr->row_number >= png_ptr->num_rows ||
 841              png_ptr->pass > 6)
 842             png_warning(png_ptr, "Truncated compressed data in IDAT");
 843
 844          else
 845          {
 846             if (ret == Z_DATA_ERROR)
 847                png_benign_error(png_ptr, "IDAT: ADLER32 checksum mismatch");
 848             else
 849                png_error(png_ptr, "Decompression error in IDAT");
 850          }
 851
 852          /* Skip the check on unprocessed input */
 853          return;
 854       }
 855
 856       /* Did inflate output any data? */
 857       if (png_ptr->zstream.next_out != png_ptr->row_buf)
 858       {
 859          /* Is this unexpected data after the last row?
 860           * If it is, artificially terminate the LZ output
 861           * here.
 862           */
 863          if (png_ptr->row_number >= png_ptr->num_rows ||
 864              png_ptr->pass > 6)
 865          {
 866             /* Extra data. */
 867             png_warning(png_ptr, "Extra compressed data in IDAT");
 868             png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
 869             png_ptr->zowner = 0;
 870
 871             /* Do no more processing; skip the unprocessed
 872              * input check below.
 873              */
 874             return;
 875          }
 876
 877          /* Do we have a complete row? */
 878          if (png_ptr->zstream.avail_out == 0)
 879             png_push_process_row(png_ptr);
 880       }
 881
 882       /* And check for the end of the stream. */
 883       if (ret == Z_STREAM_END)
 884          png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
 885    }
 886
 887    /* All the data should have been processed, if anything
 888     * is left at this point we have bytes of IDAT data
 889     * after the zlib end code.
 890     */
 891    if (png_ptr->zstream.avail_in > 0)
 892       png_warning(png_ptr, "Extra compression data in IDAT");
 893 }
 894
 895 void /* PRIVATE */
 896 png_push_process_row(png_structrp png_ptr)
 897 {
 898    /* 1.5.6: row_info moved out of png_struct to a local here. */
 899    png_row_info row_info;
 900
 901    row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
 902    row_info.color_type = png_ptr->color_type;
 903    row_info.bit_depth = png_ptr->bit_depth;
 904    row_info.channels = png_ptr->channels;
 905    row_info.pixel_depth = png_ptr->pixel_depth;
 906    row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);
 907
 908    if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)
 909    {
 910       if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
 911          png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,
 912             png_ptr->prev_row + 1, png_ptr->row_buf[0]);
 913       else
 914          png_error(png_ptr, "bad adaptive filter value");
 915    }
 916
 917    /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
 918     * 1.5.6, while the buffer really is this big in current versions of libpng
 919     * it may not be in the future, so this was changed just to copy the
 920     * interlaced row count:
 921     */
 922    memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);
 923
 924 #ifdef PNG_READ_TRANSFORMS_SUPPORTED
 925    if (png_ptr->transformations != 0)
 926       png_do_read_transformations(png_ptr, &row_info);
 927 #endif
 928
 929    /* The transformed pixel depth should match the depth now in row_info. */
 930    if (png_ptr->transformed_pixel_depth == 0)
 931    {
 932       png_ptr->transformed_pixel_depth = row_info.pixel_depth;
 933       if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
 934          png_error(png_ptr, "progressive row overflow");
 935    }
 936
 937    else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
 938       png_error(png_ptr, "internal progressive row size calculation error");
 939
 940
 941 #ifdef PNG_READ_INTERLACING_SUPPORTED
 942    /* Expand interlaced rows to full size */
 943    if (png_ptr->interlaced != 0 &&
 944        (png_ptr->transformations & PNG_INTERLACE) != 0)
 945    {
 946       if (png_ptr->pass < 6)
 947          png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,
 948              png_ptr->transformations);
 949
 950       switch (png_ptr->pass)
 951       {
 952          case 0:
 953          {
 954             int i;
 955             for (i = 0; i < 8 && png_ptr->pass == 0; i++)
 956             {
 957                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
 958                png_read_push_finish_row(png_ptr); /* Updates png_ptr->pass */
 959             }
 960
 961             if (png_ptr->pass == 2) /* Pass 1 might be empty */
 962             {
 963                for (i = 0; i < 4 && png_ptr->pass == 2; i++)
 964                {
 965                   png_push_have_row(png_ptr, NULL);
 966                   png_read_push_finish_row(png_ptr);
 967                }
 968             }
 969
 970             if (png_ptr->pass == 4 && png_ptr->height <= 4)
 971             {
 972                for (i = 0; i < 2 && png_ptr->pass == 4; i++)
 973                {
 974                   png_push_have_row(png_ptr, NULL);
 975                   png_read_push_finish_row(png_ptr);
 976                }
 977             }
 978
 979             if (png_ptr->pass == 6 && png_ptr->height <= 4)
 980             {
 981                 png_push_have_row(png_ptr, NULL);
 982                 png_read_push_finish_row(png_ptr);
 983             }
 984
 985             break;
 986          }
 987
 988          case 1:
 989          {
 990             int i;
 991             for (i = 0; i < 8 && png_ptr->pass == 1; i++)
 992             {
 993                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
 994                png_read_push_finish_row(png_ptr);
 995             }
 996
 997             if (png_ptr->pass == 2) /* Skip top 4 generated rows */
 998             {
 999                for (i = 0; i < 4 && png_ptr->pass == 2; i++)
1000                {
1001                   png_push_have_row(png_ptr, NULL);
1002                   png_read_push_finish_row(png_ptr);
1003                }
1004             }
1005
1006             break;
1007          }
1008
1009          case 2:
1010          {
1011             int i;
1012
1013             for (i = 0; i < 4 && png_ptr->pass == 2; i++)
1014             {
1015                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
1016                png_read_push_finish_row(png_ptr);
1017             }
1018
1019             for (i = 0; i < 4 && png_ptr->pass == 2; i++)
1020             {
1021                png_push_have_row(png_ptr, NULL);
1022                png_read_push_finish_row(png_ptr);
1023             }
1024
1025             if (png_ptr->pass == 4) /* Pass 3 might be empty */
1026             {
1027                for (i = 0; i < 2 && png_ptr->pass == 4; i++)
1028                {
1029                   png_push_have_row(png_ptr, NULL);
1030                   png_read_push_finish_row(png_ptr);
1031                }
1032             }
1033
1034             break;
1035          }
1036
1037          case 3:
1038          {
1039             int i;
1040
1041             for (i = 0; i < 4 && png_ptr->pass == 3; i++)
1042             {
1043                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
1044                png_read_push_finish_row(png_ptr);
1045             }
1046
1047             if (png_ptr->pass == 4) /* Skip top two generated rows */
1048             {
1049                for (i = 0; i < 2 && png_ptr->pass == 4; i++)
1050                {
1051                   png_push_have_row(png_ptr, NULL);
1052                   png_read_push_finish_row(png_ptr);
1053                }
1054             }
1055
1056             break;
1057          }
1058
1059          case 4:
1060          {
1061             int i;
1062
1063             for (i = 0; i < 2 && png_ptr->pass == 4; i++)
1064             {
1065                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
1066                png_read_push_finish_row(png_ptr);
1067             }
1068
1069             for (i = 0; i < 2 && png_ptr->pass == 4; i++)
1070             {
1071                png_push_have_row(png_ptr, NULL);
1072                png_read_push_finish_row(png_ptr);
1073             }
1074
1075             if (png_ptr->pass == 6) /* Pass 5 might be empty */
1076             {
1077                png_push_have_row(png_ptr, NULL);
1078                png_read_push_finish_row(png_ptr);
1079             }
1080
1081             break;
1082          }
1083
1084          case 5:
1085          {
1086             int i;
1087
1088             for (i = 0; i < 2 && png_ptr->pass == 5; i++)
1089             {
1090                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
1091                png_read_push_finish_row(png_ptr);
1092             }
1093
1094             if (png_ptr->pass == 6) /* Skip top generated row */
1095             {
1096                png_push_have_row(png_ptr, NULL);
1097                png_read_push_finish_row(png_ptr);
1098             }
1099
1100             break;
1101          }
1102
1103          default:
1104          case 6:
1105          {
1106             png_push_have_row(png_ptr, png_ptr->row_buf + 1);
1107             png_read_push_finish_row(png_ptr);
1108
1109             if (png_ptr->pass != 6)
1110                break;
1111
1112             png_push_have_row(png_ptr, NULL);
1113             png_read_push_finish_row(png_ptr);
1114          }
1115       }
1116    }
1117    else
1118 #endif
1119    {
1120       png_push_have_row(png_ptr, png_ptr->row_buf + 1);
1121       png_read_push_finish_row(png_ptr);
1122    }
1123 }
1124
1125 void /* PRIVATE */
1126 png_read_push_finish_row(png_structrp png_ptr)
1127 {
1128 #ifdef PNG_READ_INTERLACING_SUPPORTED
1129    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
1130
1131    /* Start of interlace block */
1132    static const png_byte png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};
1133
1134    /* Offset to next interlace block */
1135    static const png_byte png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};
1136
1137    /* Start of interlace block in the y direction */
1138    static const png_byte png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};
1139
1140    /* Offset to next interlace block in the y direction */
1141    static const png_byte png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};
1142
1143    /* Height of interlace block.  This is not currently used - if you need
1144     * it, uncomment it here and in png.h
1145    static const png_byte png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
1146    */
1147 #endif
1148
1149    png_ptr->row_number++;
1150    if (png_ptr->row_number < png_ptr->num_rows)
1151       return;
1152
1153 #ifdef PNG_READ_INTERLACING_SUPPORTED
1154    if (png_ptr->interlaced != 0)
1155    {
1156       png_ptr->row_number = 0;
1157       memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
1158
1159       do
1160       {
1161          png_ptr->pass++;
1162          if ((png_ptr->pass == 1 && png_ptr->width < 5) ||
1163              (png_ptr->pass == 3 && png_ptr->width < 3) ||
1164              (png_ptr->pass == 5 && png_ptr->width < 2))
1165             png_ptr->pass++;
1166
1167          if (png_ptr->pass > 7)
1168             png_ptr->pass--;
1169
1170          if (png_ptr->pass >= 7)
1171             break;
1172
1173          png_ptr->iwidth = (png_ptr->width +
1174              png_pass_inc[png_ptr->pass] - 1 -
1175              png_pass_start[png_ptr->pass]) /
1176              png_pass_inc[png_ptr->pass];
1177
1178          if ((png_ptr->transformations & PNG_INTERLACE) != 0)
1179             break;
1180
1181          png_ptr->num_rows = (png_ptr->height +
1182              png_pass_yinc[png_ptr->pass] - 1 -
1183              png_pass_ystart[png_ptr->pass]) /
1184              png_pass_yinc[png_ptr->pass];
1185
1186       } while (png_ptr->iwidth == 0 || png_ptr->num_rows == 0);
1187    }
1188 #endif /* READ_INTERLACING */
1189 }
1190
1191 void /* PRIVATE */
1192 png_push_have_info(png_structrp png_ptr, png_inforp info_ptr)
1193 {
1194    if (png_ptr->info_fn != NULL)
1195       (*(png_ptr->info_fn))(png_ptr, info_ptr);
1196 }
1197
1198 void /* PRIVATE */
1199 png_push_have_end(png_structrp png_ptr, png_inforp info_ptr)
1200 {
1201    if (png_ptr->end_fn != NULL)
1202       (*(png_ptr->end_fn))(png_ptr, info_ptr);
1203 }
1204
1205 void /* PRIVATE */
1206 png_push_have_row(png_structrp png_ptr, png_bytep row)
1207 {
1208    if (png_ptr->row_fn != NULL)
1209       (*(png_ptr->row_fn))(png_ptr, row, png_ptr->row_number,
1210           (int)png_ptr->pass);
1211 }
1212
1213 #ifdef PNG_READ_INTERLACING_SUPPORTED
1214 void PNGAPI
1215 png_progressive_combine_row(png_const_structrp png_ptr, png_bytep old_row,
1216     png_const_bytep new_row)
1217 {
1218    if (png_ptr == NULL)
1219       return;
1220
1221    /* new_row is a flag here - if it is NULL then the app callback was called
1222     * from an empty row (see the calls to png_struct::row_fn below), otherwise
1223     * it must be png_ptr->row_buf+1
1224     */
1225    if (new_row != NULL)
1226       png_combine_row(png_ptr, old_row, 1/*blocky display*/);
1227 }
1228 #endif /* READ_INTERLACING */
1229
1230 void PNGAPI
1231 png_set_progressive_read_fn(png_structrp png_ptr, png_voidp progressive_ptr,
1232     png_progressive_info_ptr info_fn, png_progressive_row_ptr row_fn,
1233     png_progressive_end_ptr end_fn)
1234 {
1235    if (png_ptr == NULL)
1236       return;
1237
1238    png_ptr->info_fn = info_fn;
1239    png_ptr->row_fn = row_fn;
1240    png_ptr->end_fn = end_fn;
1241
1242    png_set_read_fn(png_ptr, progressive_ptr, png_push_fill_buffer);
1243 }
1244
1245 #ifdef PNG_READ_APNG_SUPPORTED
1246 void PNGAPI
1247 png_set_progressive_frame_fn(png_structp png_ptr,
1248    png_progressive_frame_ptr frame_info_fn,
1249    png_progressive_frame_ptr frame_end_fn)
1250 {
1251    png_ptr->frame_info_fn = frame_info_fn;
1252    png_ptr->frame_end_fn = frame_end_fn;
1253    png_ptr->apng_flags |= PNG_APNG_APP;
1254 }
1255 #endif
1256
1257 png_voidp PNGAPI
1258 png_get_progressive_ptr(png_const_structrp png_ptr)
1259 {
1260    if (png_ptr == NULL)
1261       return (NULL);
1262
1263    return png_ptr->io_ptr;
1264 }
1265 #endif /* PROGRESSIVE_READ */