static bool yy_png_validate_animation_chunk_order()

in iOS/WAStickersThirdParty/YYImageCoder.m [309:383]

• 64 lines of code
• 26 McCabe index (conditional complexity)

static bool yy_png_validate_animation_chunk_order(yy_png_chunk_info *chunks,  /* input */
                                                  uint32_t chunk_num,         /* input */
                                                  uint32_t *first_idat_index, /* output */
                                                  bool *first_frame_is_cover  /* output */) {
    /*
     PNG at least contains 3 chunks: IHDR, IDAT, IEND.
     `IHDR` must appear first.
     `IDAT` must appear consecutively.
     `IEND` must appear end.
     
     APNG must contains one `acTL` and at least one 'fcTL' and `fdAT`.
     `fdAT` must appear consecutively.
     `fcTL` must appear before `IDAT` or `fdAT`.
     */
    if (chunk_num <= 2) return false;
    if (chunks->fourcc != YY_FOUR_CC('I', 'H', 'D', 'R')) return false;
    if ((chunks + chunk_num - 1)->fourcc != YY_FOUR_CC('I', 'E', 'N', 'D')) return false;
    
    uint32_t prev_fourcc = 0;
    uint32_t IHDR_num = 0;
    uint32_t IDAT_num = 0;
    uint32_t acTL_num = 0;
    uint32_t fcTL_num = 0;
    uint32_t first_IDAT = 0;
    bool first_frame_cover = false;
    for (uint32_t i = 0; i < chunk_num; i++) {
        yy_png_chunk_info *chunk = chunks + i;
        switch (chunk->fourcc) {
            case YY_FOUR_CC('I', 'H', 'D', 'R'): {  // png header
                if (i != 0) return false;
                if (IHDR_num > 0) return false;
                IHDR_num++;
            } break;
            case YY_FOUR_CC('I', 'D', 'A', 'T'): {  // png data
                if (prev_fourcc != YY_FOUR_CC('I', 'D', 'A', 'T')) {
                    if (IDAT_num == 0)
                        first_IDAT = i;
                    else
                        return false;
                }
                IDAT_num++;
            } break;
            case YY_FOUR_CC('a', 'c', 'T', 'L'): {  // apng control
                if (acTL_num > 0) return false;
                acTL_num++;
            } break;
            case YY_FOUR_CC('f', 'c', 'T', 'L'): {  // apng frame control
                if (i + 1 == chunk_num) return false;
                if ((chunk + 1)->fourcc != YY_FOUR_CC('f', 'd', 'A', 'T') &&
                    (chunk + 1)->fourcc != YY_FOUR_CC('I', 'D', 'A', 'T')) {
                    return false;
                }
                if (fcTL_num == 0) {
                    if ((chunk + 1)->fourcc == YY_FOUR_CC('I', 'D', 'A', 'T')) {
                        first_frame_cover = true;
                    }
                }
                fcTL_num++;
            } break;
            case YY_FOUR_CC('f', 'd', 'A', 'T'): {  // apng data
                if (prev_fourcc != YY_FOUR_CC('f', 'd', 'A', 'T') && prev_fourcc != YY_FOUR_CC('f', 'c', 'T', 'L')) {
                    return false;
                }
            } break;
        }
        prev_fourcc = chunk->fourcc;
    }
    if (IHDR_num != 1) return false;
    if (IDAT_num == 0) return false;
    if (acTL_num != 1) return false;
    if (fcTL_num < acTL_num) return false;
    *first_idat_index = first_IDAT;
    *first_frame_is_cover = first_frame_cover;
    return true;
}