/// <summary>
/// Reads the length of the payload according to the contents of byte2
/// </summary>
private static async Task <uint> ReadLength(byte byte2, ArraySegment <byte> smallBuffer, Stream fromStream, CancellationToken cancellationToken)
{
byte payloadLenFlag = 0x7F;
uint len = (uint)(byte2 & payloadLenFlag);
// read a short length or a long length depending on the value of len
if (len == 126)
{
len = await BinaryReaderWriter.ReadUShortExactly(fromStream, false, smallBuffer, cancellationToken);
}
else if (len == 127)
{
len = (uint)await BinaryReaderWriter.ReadULongExactly(fromStream, false, smallBuffer, cancellationToken);
const uint maxLen = 2147483648; // 2GB - not part of the spec but just a precaution. Send large volumes of data in smaller frames.
// protect ourselves against bad data
if (len > maxLen || len < 0)
{
throw new ArgumentOutOfRangeException($"Payload length out of range. Min 0 max 2GB. Actual {len:#,##0} bytes.");
}
}
return(len);
}
/// <summary>
/// Read a WebSocket frame from the stream
/// </summary>
/// <param name="fromStream">The stream to read from</param>
/// <param name="intoBuffer">The buffer to read into</param>
/// <param name="cancellationToken">the cancellation token</param>
/// <returns>A websocket frame</returns>
public static async Task <WebSocketFrame> ReadAsync(Stream fromStream, ArraySegment <byte> intoBuffer, CancellationToken cancellationToken)
{
// allocate a small buffer to read small chunks of data from the stream
var smallBuffer = new ArraySegment <byte>(new byte[8]);
await BinaryReaderWriter.ReadExactly(2, fromStream, smallBuffer, cancellationToken);
byte byte1 = smallBuffer.Array[0];
byte byte2 = smallBuffer.Array[1];
// process first byte
byte finBitFlag = 0x80;
byte opCodeFlag = 0x0F;
bool isFinBitSet = (byte1 & finBitFlag) == finBitFlag;
WebSocketOpCode opCode = (WebSocketOpCode)(byte1 & opCodeFlag);
// read and process second byte
byte maskFlag = 0x80;
bool isMaskBitSet = (byte2 & maskFlag) == maskFlag;
uint len = await ReadLength(byte2, smallBuffer, fromStream, cancellationToken);
int count = (int)len;
// use the masking key to decode the data if needed
if (isMaskBitSet)
{
ArraySegment <byte> maskKey = new ArraySegment <byte>(smallBuffer.Array, 0, WebSocketFrameCommon.MaskKeyLength);
await BinaryReaderWriter.ReadExactly(maskKey.Count, fromStream, maskKey, cancellationToken);
await BinaryReaderWriter.ReadExactly(count, fromStream, intoBuffer, cancellationToken);
ArraySegment <byte> payloadToMask = new ArraySegment <byte>(intoBuffer.Array, intoBuffer.Offset, count);
WebSocketFrameCommon.ToggleMask(maskKey, payloadToMask);
}
else
{
await BinaryReaderWriter.ReadExactly(count, fromStream, intoBuffer, cancellationToken);
}
if (opCode == WebSocketOpCode.ConnectionClose)
{
return(DecodeCloseFrame(isFinBitSet, opCode, count, intoBuffer));
}
else
{
// note that by this point the payload will be populated
return(new WebSocketFrame(isFinBitSet, opCode, count));
}
}
/// <summary>
/// No async await stuff here because we are dealing with a memory stream
/// </summary>
/// <param name="opCode">The web socket opcode</param>
/// <param name="fromPayload">Array segment to get payload data from</param>
/// <param name="toStream">Stream to write to</param>
/// <param name="isLastFrame">True is this is the last frame in this message (usually true)</param>
public static void Write(WebSocketOpCode opCode, ArraySegment <byte> fromPayload, MemoryStream toStream, bool isLastFrame, bool isClient)
{
MemoryStream memoryStream = toStream;
byte finBitSetAsByte = isLastFrame ? (byte)0x80 : (byte)0x00;
byte byte1 = (byte)(finBitSetAsByte | (byte)opCode);
memoryStream.WriteByte(byte1);
// NB, set the mask flag if we are constructing a client frame
byte maskBitSetAsByte = isClient ? (byte)0x80 : (byte)0x00;
// depending on the size of the length we want to write it as a byte, ushort or ulong
if (fromPayload.Count < 126)
{
byte byte2 = (byte)(maskBitSetAsByte | (byte)fromPayload.Count);
memoryStream.WriteByte(byte2);
}
else if (fromPayload.Count <= ushort.MaxValue)
{
byte byte2 = (byte)(maskBitSetAsByte | 126);
memoryStream.WriteByte(byte2);
BinaryReaderWriter.WriteUShort((ushort)fromPayload.Count, memoryStream, false);
}
else
{
byte byte2 = (byte)(maskBitSetAsByte | 127);
memoryStream.WriteByte(byte2);
BinaryReaderWriter.WriteULong((ulong)fromPayload.Count, memoryStream, false);
}
// if we are creating a client frame then we MUST mack the payload as per the spec
if (isClient)
{
byte[] maskKey = new byte[WebSocketFrameCommon.MaskKeyLength];
_random.NextBytes(maskKey);
memoryStream.Write(maskKey, 0, maskKey.Length);
// mask the payload
ArraySegment <byte> maskKeyArraySegment = new ArraySegment <byte>(maskKey, 0, maskKey.Length);
WebSocketFrameCommon.ToggleMask(maskKeyArraySegment, fromPayload);
}
memoryStream.Write(fromPayload.Array, fromPayload.Offset, fromPayload.Count);
}
