public static IEnumerable <Image> ParseImagesFromSwfFile(Stream stream)
{
using (stream)
{
using var reader = new BittableBinaryReader(stream);
var header = Encoding.ASCII.GetString(reader.ReadBytes(3));
if (header == "ZWS")
{
throw new InvalidOperationException($"Unspported file type '{header}'.");
}
else if (header != "CWS" && header != "FWS")
{
throw new InvalidDataException("Not a valid SWF file.");
}
var versionNumber = reader.ReadByte();
var fileLength = reader.ReadInt32(); //This is the uncompressed length, so won't match file size for CWF
if (header == "CWS")
{
//CWS Files are compressed with Zlib
reader.ReadBytes(2); //Skip the zlib header, since DeflateStream won't process it correctly
using var compressedReader = new BittableBinaryReader(new DeflateStream(reader.BaseStream, CompressionMode.Decompress));
return(ReadHeaderAndImages(compressedReader));
}
return(ReadHeaderAndImages(reader));
}
}
private static List <SwfTag> ReadTags(BittableBinaryReader reader)
{
var tags = new List <SwfTag>();
do
{
tags.Add(ReadTag(reader));
} while (tags[tags.Count - 1].Code != SwfTagCode.End);
return(tags);
}
private static void ReadRect(BittableBinaryReader reader)
{
//This is the "twip" sized boundaries of the SWF
int length = reader.ReadBits(5); //Bit length of bounds
_ = reader.ReadBits(length); //xMin
_ = reader.ReadBits(length); //xMax
_ = reader.ReadBits(length); //yMin
_ = reader.ReadBits(length); //yMax
}
private static IEnumerable <Image> ReadHeaderAndImages(BittableBinaryReader reader)
{
ReadRect(reader);
var framerate = reader.ReadInt16();
var frameCount = reader.ReadInt16();
var tags = ReadTags(reader);
return(tags.Where(t => IMAGE_CODES.Contains(t.Code)).Select(t => HandleImageTag(t)));
}
private static SwfTag ReadTag(BittableBinaryReader reader)
{
uint tagCodeAndLength = reader.ReadUInt16();
uint code = (tagCodeAndLength & 0b1111_1111_1100_0000) >> 6; //upper 10 bits are code
uint length = tagCodeAndLength & 0b0011_1111; //lower 6 bits are length
if (length == 0b0011_1111)
{
//If all length bits are set, this is a large block and uses a UInt to signal size
length = reader.ReadUInt32();
}
var data = reader.ReadBytes((int)length); //This cast isn't safe, probably should check this
return(new SwfTag()
{
Code = (SwfTagCode)code, Data = data
});
}
