/// <summary>
/// Calculates the length of the given chunk.
/// </summary>
/// <param name="chunk">The chunk.</param>
/// <exception cref="ImageFormatException">
/// Thrown if the input stream is not valid.
/// </exception>
private void ReadChunkLength(PngChunk chunk)
{
int numBytes = this.currentStream.Read(this.chunkLengthBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
if (numBytes <= 0)
{
chunk.Length = -1;
return;
}
this.chunkLengthBuffer.ReverseBytes();
chunk.Length = BitConverter.ToInt32(this.chunkLengthBuffer, 0);
}
/// <summary>
/// Reads a chunk from the stream.
/// </summary>
/// <returns>
/// The <see cref="PngChunk"/>.
/// </returns>
private PngChunk ReadChunk()
{
PngChunk chunk = new PngChunk();
if (this.ReadChunkLength(chunk) == 0)
{
return(null);
}
if (chunk.Length <= 0)
{
return(null);
}
this.ReadChunkType(chunk);
this.ReadChunkData(chunk);
this.ReadChunkCrc(chunk);
return(chunk);
}
/// <summary>
/// Reads a chunk from the stream.
/// </summary>
/// <returns>
/// The <see cref="PngChunk"/>.
/// </returns>
private PngChunk ReadChunk()
{
var chunk = new PngChunk();
this.ReadChunkLength(chunk);
if (chunk.Length < 0)
{
return null;
}
this.ReadChunkType(chunk);
if (chunk.Type == PngChunkTypes.Data)
{
return chunk;
}
this.ReadChunkData(chunk);
this.ReadChunkCrc(chunk);
return chunk;
}
/// <summary>
/// Identifies the chunk type from the chunk.
/// </summary>
/// <param name="chunk">The chunk.</param>
/// <returns>
/// The <see cref="T:byte[]"/> containing identifying information.
/// </returns>
/// <exception cref="ImageFormatException">
/// Thrown if the input stream is not valid.
/// </exception>
private byte[] ReadChunkType(PngChunk chunk)
{
byte[] typeBuffer = new byte[4];
int numBytes = this.currentStream.Read(typeBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
char[] chars = new char[4];
chars[0] = (char)typeBuffer[0];
chars[1] = (char)typeBuffer[1];
chars[2] = (char)typeBuffer[2];
chars[3] = (char)typeBuffer[3];
chunk.Type = new string(chars);
return(typeBuffer);
}
/// <summary>
/// Reads the cycle redundancy chunk from the data.
/// </summary>
/// <param name="chunk">The chunk.</param>
/// <exception cref="ImageFormatException">
/// Thrown if the input stream is not valid or corrupt.
/// </exception>
private void ReadChunkCrc(PngChunk chunk)
{
int numBytes = this.currentStream.Read(this.crcBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
this.crcBuffer.ReverseBytes();
chunk.Crc = BitConverter.ToUInt32(this.crcBuffer, 0);
this.crc.Reset();
this.crc.Update(this.chunkTypeBuffer);
this.crc.Update(chunk.Data, 0, chunk.Length);
if (this.crc.Value != chunk.Crc)
{
throw new ImageFormatException("CRC Error. PNG Image chunk is corrupt!");
}
}
/// <summary>
/// Reads the chunk data from the stream.
/// </summary>
/// <param name="chunk">The chunk.</param>
private void ReadChunkData(PngChunk chunk)
{
chunk.Data = new byte[chunk.Length];
this.currentStream.Read(chunk.Data, 0, chunk.Length);
}
/// <summary>
/// Reads the chunk data from the stream.
/// </summary>
/// <param name="chunk">The chunk.</param>
private void ReadChunkData(PngChunk chunk)
{
// We rent the buffer here to return it afterwards in Decode()
chunk.Data = ArrayPool<byte>.Shared.Rent(chunk.Length);
this.currentStream.Read(chunk.Data, 0, chunk.Length);
}
