[core] Ensure EncryptorFactory actually receives the data we requested

If the initial buffer is unencrypted we can return it straight away
if plain text connections are supported.

If the initial buffer is encrypted, then it will be consumed as part
of the normal encrypted connection negotiation, so we'll need to
receive the actual data before returning.

src/MonoTorrent/MonoTorrent.Client.Encryption/EncryptorFactory.cs

@@ -82,9 +82,8 @@ static async Task<EncryptorResult> DoCheckIncomingConnectionAsync(IConnection co
             message.Decode(buffer, 0, buffer.Length);
 
             if (message.ProtocolString == VersionInfo.ProtocolStringV100) {
-                if (supportsPlainText) {
+                if (supportsPlainText)
                     return new EncryptorResult (PlainTextEncryption.Instance, PlainTextEncryption.Instance, buffer);
-                }
             }
             else if (supportsRC4Header || supportsRC4Full)
             {
@@ -96,7 +95,15 @@ static async Task<EncryptorResult> DoCheckIncomingConnectionAsync(IConnection co
                 if (encSocket.Decryptor is RC4 && !supportsRC4Full)
                     throw new EncryptionException("Decryptor was RC4Full but that is not allowed");
 
+                // As the connection was encrypted, the data we got from the initial Receive call will have
+                // been consumed during the crypto handshake process. Now that the encrypted handshake has
+                // been established, we should ensure we read the data again.
                 var data = encSocket.InitialData?.Length > 0 ? encSocket.InitialData : null;
+                if (data == null && bytesToReceive > 0) {
+                    data = buffer;
+                    await NetworkIO.ReceiveAsync (connection, data, 0, data.Length, null, null, null);
+                    encSocket.Decryptor.Decrypt (data);
+                }
                 return new EncryptorResult (encSocket.Decryptor, encSocket.Encryptor, data);
             }
 

src/MonoTorrent/MonoTorrent.Client/Managers/ListenManager.cs

@@ -109,23 +109,9 @@ private async void ConnectionReceived(object sender, NewConnectionEventArgs e)
                 var result = await EncryptorFactory.CheckIncomingConnectionAsync(id.Connection, id.Peer.Encryption, Engine.Settings, HandshakeMessage.HandshakeLength, skeys.ToArray());
                 id.Decryptor = result.Decryptor;
                 id.Encryptor = result.Encryptor;
-                var initialData = result.InitialData;
-                if (initialData != null && initialData.Length != HandshakeMessage.HandshakeLength)
-                {
-                    e.Connection.Dispose();
-                    return;
-                }
 
-                HandshakeMessage handshake;
-                if (initialData == null)
-                {
-                    handshake = await PeerIO.ReceiveHandshakeAsync(id.Connection, id.Decryptor);
-                }
-                else
-                {
-                    handshake = new HandshakeMessage();
-                    handshake.Decode(initialData, 0, initialData.Length);
-                }
+                var handshake = new HandshakeMessage();
+                handshake.Decode(result.InitialData, 0, result.InitialData.Length);
                 if (!await HandleHandshake(id, handshake))
                     e.Connection.Dispose();
             }