722
723 // verify the chunk length
724 if (chunkLength < 0) {
725 throw new IIOException("Invalid chunk length " + chunkLength);
726 };
727
728 try {
729 stream.mark();
730 stream.seek(stream.getStreamPosition() + chunkLength);
731 chunkCRC = stream.readInt();
732 stream.reset();
733 } catch (IOException e) {
734 throw new IIOException("Invalid chunk length " + chunkLength);
735 }
736
737 switch (chunkType) {
738 case IDAT_TYPE:
739 // If chunk type is 'IDAT', we've reached the image data.
740 if (imageStartPosition == -1L) {
741 /*
742 * PNGs may contain multiple IDAT chunks containing
743 * a portion of image data. We store the position of
744 * the first IDAT chunk and continue with iteration
745 * of other chunks that follow image data.
746 */
747 imageStartPosition = stream.getStreamPosition() - 8;
748 }
749 // Move to the CRC byte location.
750 stream.skipBytes(chunkLength);
751 break;
752 case IEND_TYPE:
753 /*
754 * If the chunk type is 'IEND', we've reached end of image.
755 * Seek to the first IDAT chunk for subsequent decoding.
756 */
757 stream.seek(imageStartPosition);
758
759 /*
760 * flushBefore discards the portion of the stream before
761 * the indicated position. Hence this should be used after
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722
723 // verify the chunk length
724 if (chunkLength < 0) {
725 throw new IIOException("Invalid chunk length " + chunkLength);
726 };
727
728 try {
729 stream.mark();
730 stream.seek(stream.getStreamPosition() + chunkLength);
731 chunkCRC = stream.readInt();
732 stream.reset();
733 } catch (IOException e) {
734 throw new IIOException("Invalid chunk length " + chunkLength);
735 }
736
737 switch (chunkType) {
738 case IDAT_TYPE:
739 // If chunk type is 'IDAT', we've reached the image data.
740 if (imageStartPosition == -1L) {
741 /*
742 * The PNG specification mandates that if colorType is
743 * PNG_COLOR_PALETTE then the PLTE chunk should appear
744 * before the first IDAT chunk.
745 */
746 if (colorType == PNG_COLOR_PALETTE &&
747 !(metadata.PLTE_present))
748 {
749 throw new IIOException("Required PLTE chunk"
750 + " missing");
751 }
752 /*
753 * PNGs may contain multiple IDAT chunks containing
754 * a portion of image data. We store the position of
755 * the first IDAT chunk and continue with iteration
756 * of other chunks that follow image data.
757 */
758 imageStartPosition = stream.getStreamPosition() - 8;
759 }
760 // Move to the CRC byte location.
761 stream.skipBytes(chunkLength);
762 break;
763 case IEND_TYPE:
764 /*
765 * If the chunk type is 'IEND', we've reached end of image.
766 * Seek to the first IDAT chunk for subsequent decoding.
767 */
768 stream.seek(imageStartPosition);
769
770 /*
771 * flushBefore discards the portion of the stream before
772 * the indicated position. Hence this should be used after
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