// TODO: Consider creating "CoapMessageDecodeResult" which has Message (null or set) and "DecodeResult" as INTERFACE with all possible errors (VersionInvalidDecodeResult) etc.
public CoapMessage Decode(ArraySegment <byte> buffer)
{
using (var reader = new CoapMessageReader(buffer))
{
var version = reader.ReadBits(2);
if (version != 0x1)
{
throw new CoapProtocolViolationException("Version is not set to 1.");
}
var type = reader.ReadBits(2);
if (type > 2)
{
throw new CoapProtocolViolationException("Type is invalid.");
}
var tokenLength = reader.ReadBits(4);
var code = (byte)reader.ReadBits(8);
var codeClass = (byte)(code >> 5);
var codeDetails = (byte)(0x1F & code);
var id = reader.ReadByte() << 8;
id |= reader.ReadByte();
byte[] token = null;
if (tokenLength > 0)
{
token = reader.ReadBytes(tokenLength);
}
var options = DecodeOptions(reader);
var payload = reader.ReadToEnd();
var message = new CoapMessage
{
Type = (CoapMessageType)type,
Code = new CoapMessageCode(codeClass, codeDetails),
Id = (ushort)id,
Token = token,
Options = options,
Payload = payload
};
return(message);
}
}
List <CoapMessageOption> DecodeOptions(CoapMessageReader reader)
{
var options = new List <CoapMessageOption>();
if (reader.EndOfStream)
{
return(options);
}
var lastNumber = 0;
while (!reader.EndOfStream)
{
var delta = reader.ReadBits(4);
var length = reader.ReadBits(4);
if ((byte)(delta << 4 | length) == 0xFF)
{
// Payload marker.
break;
}
if (delta == 13)
{
delta = reader.ReadBits(8) + 13;
}
else if (delta == 14)
{
delta = reader.ReadBits(16) + 269;
}
if (length == 13)
{
length = reader.ReadBits(8) + 13;
}
else if (length == 14)
{
length = reader.ReadBits(16) + 269;
}
byte[] value = null;
if (length > 0)
{
value = reader.ReadBytes(length);
}
var number = lastNumber + delta;
lastNumber = number;
options.Add(CreateOption((CoapMessageOptionNumber)number, value));
}
return(options);
}