internal Dimensions(byte[] buffer)
{
if (buffer == null)
{
throw new ArgumentNullException(nameof(buffer));
}
if (Dimensions.MinHeaderSize > buffer.Length)
{
throw new ArgumentException($"Must contain at at least {Dimensions.MinHeaderSize} bytes.", nameof(buffer));
}
this.Height = Jpeg.ReadLength(buffer, 1);
this.Width = Jpeg.ReadLength(buffer, 3);
}
/// <summary>
/// Reads the passed stream and returns the jpeg image dimensions in pixels.
/// It stops reading the stream when the dimensions are found.
/// </summary>
/// <param name="jpegStream"></param>
/// <exception cref="InvalidJpegException">This exception is thrown when the passed stream does not conform to the jpeg standard.</exception>
/// <exception cref="StreamTooSmallException">This exception is thrown when the passed stream does not contain the required jpeg headers before the end of the stream.</exception>
/// <exception cref="BadSegmentSizeException">This exception is thrown when an attempt to recover from a bad segment size fails due to not finding a section marker before the end of the stream.</exception>
/// <returns>the image dimensions in pixels</returns>
public static Dimensions GetDimensions(Stream jpegStream)
{
Jpeg.ThrowIfNotJpeg(jpegStream);
Dimensions imageDetails = new Dimensions();
byte[] headerBuffer = new byte[4];
do
{
Jpeg.CheckedRead(jpegStream, headerBuffer);
if (headerBuffer[0] != Jpeg.SectionStartMarker)
{
Jpeg.FindNextSegment(jpegStream, headerBuffer);
}
ushort length = Jpeg.ReadLength(headerBuffer, 2);
//TODO make this a seek if we do not need to read the data
byte[] headerData = new byte[length - 2];
Jpeg.CheckedRead(jpegStream, headerData);
if (headerBuffer[1] == Markers.SOF0 || headerBuffer[1] == Markers.SOF2)
{
imageDetails = new Dimensions(headerData);
}
}while (headerBuffer[1] != Markers.SOS && imageDetails.Height == 0);
if (imageDetails.Height == 0)
{
// because it has no Start Of Frame header
throw new InvalidJpegException("Failed to find Start Of Frame header.");
}
return(imageDetails);
}