public static JpegSegmentData ReadSegments(SequentialReader reader, Iterable<JpegSegmentType> segmentTypes)
{
// Must be big-endian
System.Diagnostics.Debug.Assert((reader.IsMotorolaByteOrder()));
// first two bytes should be JPEG magic number
int magicNumber = reader.GetUInt16();
if (magicNumber != unchecked((int)(0xFFD8)))
{
throw new JpegProcessingException("JPEG data is expected to begin with 0xFFD8 (ГїГ�) not 0x" + Sharpen.Extensions.ToHexString(magicNumber));
}
ICollection<sbyte> segmentTypeBytes = null;
if (segmentTypes != null)
{
segmentTypeBytes = new HashSet<sbyte>();
foreach (JpegSegmentType segmentType in segmentTypes)
{
segmentTypeBytes.Add(segmentType.byteValue);
}
}
JpegSegmentData segmentData = new JpegSegmentData();
do
{
// next byte is the segment identifier: 0xFF
short segmentIdentifier = reader.GetUInt8();
if (segmentIdentifier != unchecked((int)(0xFF)))
{
throw new JpegProcessingException("Expected JPEG segment start identifier 0xFF, not 0x" + Sharpen.Extensions.ToHexString(segmentIdentifier));
}
// next byte is the segment type
sbyte segmentType = reader.GetInt8();
if (segmentType == SegmentSos)
{
// The 'Start-Of-Scan' segment's length doesn't include the image data, instead would
// have to search for the two bytes: 0xFF 0xD9 (EOI).
// It comes last so simply return at this point
return segmentData;
}
if (segmentType == MarkerEoi)
{
// the 'End-Of-Image' segment -- this should never be found in this fashion
return segmentData;
}
// next 2-bytes are <segment-size>: [high-byte] [low-byte]
int segmentLength = reader.GetUInt16();
// segment length includes size bytes, so subtract two
segmentLength -= 2;
if (segmentLength < 0)
{
throw new JpegProcessingException("JPEG segment size would be less than zero");
}
// Check whether we are interested in this segment
if (segmentTypeBytes == null || segmentTypeBytes.Contains(segmentType))
{
sbyte[] segmentBytes = reader.GetBytes(segmentLength);
System.Diagnostics.Debug.Assert((segmentLength == segmentBytes.Length));
segmentData.AddSegment(segmentType, segmentBytes);
}
else
{
// Some if the JPEG is truncated, just return what data we've already gathered
if (!reader.TrySkip(segmentLength))
{
return segmentData;
}
}
}
while (true);
}
