// the `unsafe` here is so that in the "multiple spans, header crosses spans", we can use stackalloc to
// collate the header bytes in one place, and pass that down for analysis
internal unsafe static bool TryReadFrameHeader(ref ReadableBuffer buffer, out WebSocketsFrame frame)
{
int bytesAvailable = buffer.Length;
if (bytesAvailable < 2)
{
frame = default(WebSocketsFrame);
return(false); // can't read that; frame takes at minimum two bytes
}
var firstSpan = buffer.First;
if (buffer.IsSingleSpan || firstSpan.Length >= MaxHeaderLength)
{
return(TryReadFrameHeader(firstSpan.Length, firstSpan.Span, ref buffer, out frame));
}
else
{
// header is at most 14 bytes; can afford the stack for that - but note that if we aim for 16 bytes instead,
// we will usually benefit from using 2 qword copies
byte *header = stackalloc byte[16];
var slice = buffer.Slice(0, Math.Min(16, bytesAvailable));
var headerSpan = new Span <byte>(header, slice.Length);
slice.CopyTo(headerSpan);
// note that we're using the "slice" above to preview the header, but we
// still want to pass the *original* buffer down below, so that we can
// check the overall length (payload etc)
return(TryReadFrameHeader(slice.Length, headerSpan, ref buffer, out frame));
}
}
internal static Task WriteAsync <T>(WebSocketConnection connection,
WebSocketsFrame.OpCodes opCode,
WebSocketsFrame.FrameFlags flags, ref T message)
where T : struct, IMessageWriter
{
int payloadLength = message.GetPayloadLength();
var buffer = connection.Connection.Output.Alloc(MaxHeaderLength + payloadLength);
int mask = connection.ConnectionType == ConnectionType.Client ? CreateMask() : 0;
WriteFrameHeader(ref buffer, WebSocketsFrame.FrameFlags.IsFinal, opCode, payloadLength, mask);
if (payloadLength != 0)
{
if (mask == 0)
{
message.WritePayload(buffer);
}
else
{
var payloadStart = buffer.AsReadableBuffer().End;
message.WritePayload(buffer);
var payload = buffer.AsReadableBuffer().Slice(payloadStart); // note that this is a different AsReadableBuffer; call twice is good
WebSocketsFrame.ApplyMask(ref payload, mask);
}
}
return(buffer.FlushAsync().AsTask());
}
// TODO: not sure how to do this; basically I want to lease a writable, expandable area
// for a duration, and be able to access it for reading, and release
internal void AddBacklog(ref ReadableBuffer buffer, ref WebSocketsFrame frame)
{
var length = frame.PayloadLength;
if (length == 0)
{
return; // nothing to store!
}
var slicedBuffer = buffer.Slice(0, length);
// unscramble the data
if (frame.MaskLittleEndian != 0)
{
WebSocketsFrame.ApplyMask(ref slicedBuffer, frame.MaskLittleEndian);
}
var backlog = this.backlog;
if (backlog == null)
{
var newBacklog = new List <PreservedBuffer>();
backlog = Interlocked.CompareExchange(ref this.backlog, newBacklog, null) ?? newBacklog;
}
backlog.Add(slicedBuffer.Preserve());
}
internal static bool TryReadFrameHeader(int inspectableBytes, Span <byte> header, ref ReadableBuffer buffer, out WebSocketsFrame frame)
{
bool masked = (header[1] & 128) != 0;
int tmp = header[1] & 127;
int headerLength, maskOffset, payloadLength;
switch (tmp)
{
case 126:
headerLength = masked ? 8 : 4;
if (inspectableBytes < headerLength)
{
frame = default(WebSocketsFrame);
return(false);
}
payloadLength = (header[2] << 8) | header[3];
maskOffset = 4;
break;
case 127:
headerLength = masked ? 14 : 10;
if (inspectableBytes < headerLength)
{
frame = default(WebSocketsFrame);
return(false);
}
int big = header.Slice(2).ReadBigEndian <int>(), little = header.Slice(6).ReadBigEndian <int>();
if (big != 0 || little < 0)
{
throw new ArgumentOutOfRangeException(); // seriously, we're not going > 2GB
}
payloadLength = little;
maskOffset = 10;
break;
default:
headerLength = masked ? 6 : 2;
if (inspectableBytes < headerLength)
{
frame = default(WebSocketsFrame);
return(false);
}
payloadLength = tmp;
maskOffset = 2;
break;
}
if (buffer.Length < headerLength + payloadLength)
{
frame = default(WebSocketsFrame);
return(false); // frame (header+body) isn't intact
}
frame = new WebSocketsFrame(header[0], masked,
masked ? header.Slice(maskOffset).ReadLittleEndian <int>() : 0,
payloadLength);
buffer = buffer.Slice(headerLength); // header is fully consumed now
return(true);
}
private void ApplyMask()
{
if (_mask != 0)
{
WebSocketsFrame.ApplyMask(ref _buffer, _mask);
_mask = 0;
}
}
internal Task OnFrameReceivedAsync(ref WebSocketsFrame frame, ref ReadableBuffer buffer, WebSocketServer server)
{
WebSocketServer.WriteStatus(ConnectionType, frame.ToString());
// note that this call updates the connection state; must be called, even
// if we don't get as far as the 'switch'
var opCode = GetEffectiveOpCode(ref frame);
Message msg;
if (!frame.IsControlFrame)
{
if (frame.IsFinal)
{
if (this.HasBacklog)
{
try
{
// add our data to the existing backlog
this.AddBacklog(ref buffer, ref frame);
// use the backlog buffer to execute the method; note that
// we un-masked *while adding*; don't need mask here
msg = new Message(this.GetBacklog());
if (server != null)
{
return(OnServerAndConnectionFrameReceivedImplAsync(opCode, msg, server));
}
else
{
return(OnConectionFrameReceivedImplAsync(opCode, ref msg));
}
}
finally
{
// and release the backlog
this.ClearBacklog();
}
}
}
else if (BufferFragments)
{
// need to buffer this data against the connection
this.AddBacklog(ref buffer, ref frame);
return(Task.CompletedTask);
}
}
msg = new Message(buffer.Slice(0, frame.PayloadLength), frame.MaskLittleEndian, frame.IsFinal);
if (server != null)
{
return(OnServerAndConnectionFrameReceivedImplAsync(opCode, msg, server));
}
else
{
return(OnConectionFrameReceivedImplAsync(opCode, ref msg));
}
}
internal WebSocketsFrame.OpCodes GetEffectiveOpCode(ref WebSocketsFrame frame)
{
if (frame.IsControlFrame)
{
// doesn't change state
return(frame.OpCode);
}
var frameOpCode = frame.OpCode;
// re-use the previous opcode if we are a continuation
var result = frameOpCode == WebSocketsFrame.OpCodes.Continuation ? lastOpCode : frameOpCode;
// if final, clear the opcode; otherwise: use what we thought of
lastOpCode = frame.IsFinal ? WebSocketsFrame.OpCodes.Continuation : result;
return(result);
}
