Fix login start packet decoding for 1.18.2 up to 1.20.2 (#421)

Signed-off-by: Fred Heinecke <fred.heinecke@yahoo.com>

mcproto/decode.go

@@ -21,10 +21,11 @@ func DecodeHandshake(data interface{}) (*Handshake, error) {
 	buffer := bytes.NewBuffer(dataBytes)
 	var err error
 
-	handshake.ProtocolVersion, err = ReadVarInt(buffer)
+	protocolVersion, err := ReadVarInt(buffer)
 	if err != nil {
 		return nil, err
 	}
+	handshake.ProtocolVersion = ProtocolVersion(protocolVersion)
 
 	handshake.ServerAddress, err = ReadString(buffer)
 	if err != nil {
@@ -48,13 +49,13 @@ func DecodeHandshake(data interface{}) (*Handshake, error) {
 }
 
 // DecodeLoginStart takes the Packet.Data bytes and decodes a LoginStart message from it
-func DecodeLoginStart(data interface{}) (*LoginStart, error) {
+func DecodeLoginStart(protocolVersion ProtocolVersion, data interface{}) (*LoginStart, error) {
 	dataBytes, ok := data.([]byte)
 	if !ok {
 		return nil, errors.New(invalidPacketDataBytesMsg)
 	}
 
-	loginStart := &LoginStart{}
+	loginStart := NewLoginStart()
 	buffer := bytes.NewBuffer(dataBytes)
 	var err error
 
@@ -63,9 +64,69 @@ func DecodeLoginStart(data interface{}) (*LoginStart, error) {
 		return loginStart, errors.Wrap(err, "failed to read username")
 	}
 
-	loginStart.PlayerUuid, err = ReadUuid(buffer)
-	if err != nil {
-		return loginStart, errors.Wrap(err, "failed to read player uuid")
+	// These versions can send player keypair data. Ignore it.
+	// References:
+	// * https://github.com/MCCTeam/Minecraft-Console-Client/blob/f785f509f228bf787c237ac139e6f666a960819a/MinecraftClient/Protocol/Handlers/Protocol18.cs#L2808-L2828
+	// * https://minecraft.wiki/w/Minecraft_Wiki:Projects/wiki.vg_merge/Protocol?oldid=2772902#Login_Start
+	if protocolVersion >= ProtocolVersion1_19 && protocolVersion <= ProtocolVersion1_19_2 {
+		hasSignatureData, err := ReadBoolean(buffer)
+		if err != nil {
+			return loginStart, errors.Wrap(err, "failed to read has signature data flag")
+		}
+
+		if hasSignatureData {
+			// Read and discard the data
+			_, err = ReadLong(buffer) // Expiration time
+			if err != nil {
+				return loginStart, errors.Wrap(err, "failed to read expiration time")
+			}
+
+			pubKeyLength, err := ReadVarInt(buffer) // Length of the public key
+			if err != nil {
+				return loginStart, errors.Wrap(err, "failed to read public key length")
+			}
+
+			_, err = ReadByteArray(buffer, pubKeyLength) // Public key data
+			if err != nil {
+				return loginStart, errors.Wrap(err, "failed to read public key")
+			}
+
+			signatureLength, err := ReadVarInt(buffer) // Length of the signature
+			if err != nil {
+				return loginStart, errors.Wrap(err, "failed to read signature length")
+			}
+
+			_, err = ReadByteArray(buffer, signatureLength) // Signature data
+			if err != nil {
+				return loginStart, errors.Wrap(err, "failed to read signature")
+			}
+		}
+	}
+
+	// References:
+	// * https://github.com/MCCTeam/Minecraft-Console-Client/blob/f785f509f228bf787c237ac139e6f666a960819a/MinecraftClient/Protocol/Handlers/Protocol18.cs#L2831-L2853
+	// * https://minecraft.wiki/w/Minecraft_Wiki:Projects/wiki.vg_merge/Protocol?oldid=2772944#Login_Start
+	switch {
+	case protocolVersion >= ProtocolVersion1_19_2 && protocolVersion < ProtocolVersion1_20_2:
+		// Check to see if a UUID was provided at all
+		hasUUID, err := ReadBoolean(buffer)
+		if err != nil {
+			return loginStart, errors.Wrap(err, "failed to read has uuid flag")
+		}
+
+		if !hasUUID {
+			break
+		}
+		fallthrough
+	case protocolVersion >= ProtocolVersion1_20_2:
+		// For 1.20.2 and later, the UUID is always present
+		playerUuid, err := ReadUuid(buffer)
+		if err != nil {
+			return loginStart, errors.Wrap(err, "failed to read player uuid")
+		}
+		loginStart.PlayerUuid = playerUuid
+	default:
+		// For versions before 1.19.2, the UUID is not present
 	}
 
 	return loginStart, nil