private static bool ReadQuery(ref string name, BinaryReaderExt reader, MD5 md5, MemoryStream stream)
{
if (!reader.TryRead(out name))
{
return(false);
}
if (!IsMessageAuthentic(md5, stream, reader))
{
name = null;
return(false);
}
return(true);
}
public static bool TryRead(byte[] message, out string token, out string name, out IPEndPoint endPoint,
out byte[] payload)
{
token = null;
name = null;
endPoint = null;
payload = null;
if (message.Length == 0)
{
return(false);
}
using (var md5 = MD5.Create())
using (var stream = new MemoryStream(message))
using (var reader = new BinaryReaderExt(stream))
{
if (!reader.TryRead(out token))
{
return(false);
}
if (token == P2PQueryToken)
{
return(ReadQuery(ref name, reader, md5, stream));
}
if (token == P2PResponse2Token)
{
return(ReadResponse2(ref name, ref endPoint, ref payload, reader, md5, stream));
}
if (token == P2PResponseLegacyToken)
{
return(ReadLegacyResponse(ref name, ref endPoint, reader, md5, stream));
}
return(false);
}
}
private static bool ReadLegacyResponse(ref string name, ref IPEndPoint endPoint, BinaryReaderExt reader, MD5 md5,
MemoryStream stream)
{
if (!reader.TryRead(out name))
{
return(false);
}
if (!reader.TryRead(out endPoint))
{
return(false);
}
if (!IsMessageAuthentic(md5, stream, reader))
{
name = null;
endPoint = null;
return(false);
}
return(true);
}
private static bool ReadResponse2(ref string name, ref IPEndPoint endPoint, ref byte[] payload,
BinaryReaderExt reader, MD5 md5, MemoryStream stream)
{
// This code is intended to be forwards compatible.
// This means that it needs to be able to deal with content types which
// it does simply not know (yet). Obviously such content would not
// be decoded, however it is super important that we do not discard future
// responses just because we calculated the hash wrong.
// For this reason, we include the total message length here, so that even if we
// do not know the additional content, we include it in our hash code calculation.
var contentLengthStart = (int)stream.Position;
ushort contentLength;
if (!reader.TryRead(out contentLength))
{
return(false);
}
if (reader.BytesLeft < contentLength)
{
return(false);
}
var hashStart = (int)reader.BaseStream.Position;
var hash = reader.ReadBytes(count: 16);
var content = (MessageContent)reader.ReadInt32();
if ((content & MessageContent.Name) == MessageContent.Name)
{
if (!reader.TryRead(out name))
{
return(false);
}
}
if ((content & MessageContent.EndPoint) == MessageContent.EndPoint)
{
if (!reader.TryRead(out endPoint))
{
return(false);
}
}
if ((content & MessageContent.Payload) == MessageContent.Payload)
{
int payloadLength = reader.ReadUInt16();
payload = reader.ReadBytes(payloadLength);
}
// We need to black out the actual hash to 0 before
// we compute the hash of the received content
stream.Position = hashStart;
for (var i = 0; i < 16; ++i)
{
stream.WriteByte(value: 0);
}
var actualHash = md5.ComputeHash(stream.ToArray(), contentLengthStart, contentLength + 2);
if (!AreHashesEqual(hash, actualHash))
{
return(false);
}
return(true);
}