public PngChunk([NotNull] PngChunkType chunkType, [NotNull] byte[] bytes)
{
ChunkType = chunkType;
Bytes = bytes;
}
public PngDirectory([NotNull] PngChunkType pngChunkType)
{
_pngChunkType = pngChunkType;
SetDescriptor(new PngDescriptor(this));
}
public IEnumerable <PngChunk> Extract([NotNull] SequentialReader reader, [CanBeNull] ICollection <PngChunkType> desiredChunkTypes)
{
//
// PNG DATA STREAM
//
// Starts with a PNG SIGNATURE, followed by a sequence of CHUNKS.
//
// PNG SIGNATURE
//
// Always composed of these bytes: 89 50 4E 47 0D 0A 1A 0A
//
// CHUNK
//
// 4 - length of the data field (unsigned, but always within 31 bytes), may be zero
// 4 - chunk type, restricted to [65,90] and [97,122] (A-Za-z)
// * - data field
// 4 - CRC calculated from chunk type and chunk data, but not length
//
// CHUNK TYPES
//
// Critical Chunk Types:
//
// IHDR - image header, always the first chunk in the data stream
// PLTE - palette table, associated with indexed PNG images
// IDAT - image data chunk, of which there may be many
// IEND - image trailer, always the last chunk in the data stream
//
// Ancillary Chunk Types:
//
// Transparency information: tRNS
// Colour space information: cHRM, gAMA, iCCP, sBIT, sRGB
// Textual information: iTXt, tEXt, zTXt
// Miscellaneous information: bKGD, hIST, pHYs, sPLT
// Time information: tIME
//
// network byte order
reader = reader.WithByteOrder(isMotorolaByteOrder: true);
if (!_pngSignatureBytes.SequenceEqual(reader.GetBytes(_pngSignatureBytes.Length)))
{
throw new PngProcessingException("PNG signature mismatch");
}
var seenImageHeader = false;
var seenImageTrailer = false;
var chunks = new List <PngChunk>();
var seenChunkTypes = new HashSet <PngChunkType>();
while (!seenImageTrailer)
{
// Process the next chunk.
var chunkDataLength = reader.GetInt32();
if (chunkDataLength < 0)
{
throw new PngProcessingException("PNG chunk length exceeds maximum");
}
var chunkType = new PngChunkType(reader.GetBytes(4));
var willStoreChunk = desiredChunkTypes == null || desiredChunkTypes.Contains(chunkType);
var chunkData = reader.GetBytes(chunkDataLength);
// Skip the CRC bytes at the end of the chunk
// TODO consider verifying the CRC value to determine if we're processing bad data
reader.Skip(4);
if (willStoreChunk && seenChunkTypes.Contains(chunkType) && !chunkType.AreMultipleAllowed)
{
throw new PngProcessingException($"Observed multiple instances of PNG chunk '{chunkType}', for which multiples are not allowed");
}
if (chunkType.Equals(PngChunkType.IHDR))
{
seenImageHeader = true;
}
else if (!seenImageHeader)
{
throw new PngProcessingException($"First chunk should be '{PngChunkType.IHDR}', but '{chunkType}' was observed");
}
if (chunkType.Equals(PngChunkType.IEND))
{
seenImageTrailer = true;
}
if (willStoreChunk)
{
chunks.Add(new PngChunk(chunkType, chunkData));
}
seenChunkTypes.Add(chunkType);
}
return(chunks);
}
private bool Equals([NotNull] PngChunkType other) => _bytes.SequenceEqual(other._bytes);
private bool Equals(PngChunkType other) => _bytes.SequenceEqual(other._bytes);
static PngDirectory ReadTextDirectory(string keyword, byte[] textBytes, PngChunkType pngChunkType)
{
var textPairs = new[] { new KeyValuePair(keyword, new StringValue(textBytes, _latin1Encoding)) };
var directory = new PngDirectory(pngChunkType);
directory.Set(PngDirectory.TagTextualData, textPairs);
return(directory);
}
/// <exception cref="PngProcessingException"/>
/// <exception cref="System.IO.IOException"/>
public IEnumerable<PngChunk> Extract([NotNull] SequentialReader reader, [CanBeNull] ICollection<PngChunkType> desiredChunkTypes)
{
//
// PNG DATA STREAM
//
// Starts with a PNG SIGNATURE, followed by a sequence of CHUNKS.
//
// PNG SIGNATURE
//
// Always composed of these bytes: 89 50 4E 47 0D 0A 1A 0A
//
// CHUNK
//
// 4 - length of the data field (unsigned, but always within 31 bytes), may be zero
// 4 - chunk type, restricted to [65,90] and [97,122] (A-Za-z)
// * - data field
// 4 - CRC calculated from chunk type and chunk data, but not length
//
// CHUNK TYPES
//
// Critical Chunk Types:
//
// IHDR - image header, always the first chunk in the data stream
// PLTE - palette table, associated with indexed PNG images
// IDAT - image data chunk, of which there may be many
// IEND - image trailer, always the last chunk in the data stream
//
// Ancillary Chunk Types:
//
// Transparency information: tRNS
// Colour space information: cHRM, gAMA, iCCP, sBIT, sRGB
// Textual information: iTXt, tEXt, zTXt
// Miscellaneous information: bKGD, hIST, pHYs, sPLT
// Time information: tIME
//
// network byte order
reader.IsMotorolaByteOrder = true;
if (!_pngSignatureBytes.SequenceEqual(reader.GetBytes(_pngSignatureBytes.Length)))
throw new PngProcessingException("PNG signature mismatch");
var seenImageHeader = false;
var seenImageTrailer = false;
var chunks = new List<PngChunk>();
var seenChunkTypes = new HashSet<PngChunkType>();
while (!seenImageTrailer)
{
// Process the next chunk.
var chunkDataLength = reader.GetInt32();
var chunkType = new PngChunkType(reader.GetBytes(4));
var willStoreChunk = desiredChunkTypes == null || desiredChunkTypes.Contains(chunkType);
var chunkData = reader.GetBytes(chunkDataLength);
// Skip the CRC bytes at the end of the chunk
// TODO consider verifying the CRC value to determine if we're processing bad data
reader.Skip(4);
if (willStoreChunk && seenChunkTypes.Contains(chunkType) && !chunkType.AreMultipleAllowed)
throw new PngProcessingException($"Observed multiple instances of PNG chunk '{chunkType}', for which multiples are not allowed");
if (chunkType.Equals(PngChunkType.IHDR))
seenImageHeader = true;
else if (!seenImageHeader)
throw new PngProcessingException($"First chunk should be '{PngChunkType.IHDR}', but '{chunkType}' was observed");
if (chunkType.Equals(PngChunkType.IEND))
seenImageTrailer = true;
if (willStoreChunk)
chunks.Add(new PngChunk(chunkType, chunkData));
seenChunkTypes.Add(chunkType);
}
return chunks;
}
public PngDirectory(PngChunkType pngChunkType)
{
_pngChunkType = pngChunkType;
SetDescriptor(new PngDescriptor(this));
}
