def decodeControlPacket()

in mqtt-streaming/src/main/scala/org/apache/pekko/stream/connectors/mqtt/streaming/model.scala [792:840]
49 lines of code
25 McCabe index (conditional complexity)

    def decodeControlPacket(maxPacketSize: Int): Either[DecodeError, ControlPacket] =
      try {
        val b = v.getByte & 0xFF
        v.decodeRemainingLength() match {
          case Right(l) if l <= maxPacketSize =>
            (ControlPacketType(b >> 4), ControlPacketFlags(b & 0xF)) match {
              case (ControlPacketType.Reserved1, ControlPacketFlags.ReservedGeneral) =>
                Right(Reserved1)
              case (ControlPacketType.Reserved2, ControlPacketFlags.ReservedGeneral) =>
                Right(Reserved2)
              case (ControlPacketType.CONNECT, ControlPacketFlags.ReservedGeneral) =>
                v.decodeConnect()
              case (ControlPacketType.CONNACK, ControlPacketFlags.ReservedGeneral) =>
                v.decodeConnAck()
              case (ControlPacketType.PUBLISH, flags) =>
                v.decodePublish(l, flags)
              case (ControlPacketType.PUBACK, ControlPacketFlags.ReservedGeneral) =>
                v.decodePubAck()
              case (ControlPacketType.PUBREC, ControlPacketFlags.ReservedGeneral) =>
                v.decodePubRec()
              case (ControlPacketType.PUBREL, ControlPacketFlags.ReservedPubRel) =>
                v.decodePubRel()
              case (ControlPacketType.PUBCOMP, ControlPacketFlags.ReservedGeneral) =>
                v.decodePubComp()
              case (ControlPacketType.SUBSCRIBE, ControlPacketFlags.ReservedSubscribe) =>
                v.decodeSubscribe(l)
              case (ControlPacketType.SUBACK, ControlPacketFlags.ReservedGeneral) =>
                v.decodeSubAck(l)
              case (ControlPacketType.UNSUBSCRIBE, ControlPacketFlags.ReservedUnsubscribe) =>
                v.decodeUnsubscribe(l)
              case (ControlPacketType.UNSUBACK, ControlPacketFlags.ReservedUnsubAck) =>
                v.decodeUnsubAck()
              case (ControlPacketType.PINGREQ, ControlPacketFlags.ReservedGeneral) =>
                Right(PingReq)
              case (ControlPacketType.PINGRESP, ControlPacketFlags.ReservedGeneral) =>
                Right(PingResp)
              case (ControlPacketType.DISCONNECT, ControlPacketFlags.ReservedGeneral) =>
                Right(Disconnect)
              case (packetType, flags) =>
                Left(UnknownPacketType(packetType, flags))
            }
          case Right(l) =>
            Left(InvalidPacketSize(l, maxPacketSize))
          case Left(BufferUnderflow) => Left(BufferUnderflow)
          case other @ Left(_)       => throw new MatchError(other)
        }
      } catch {
        case _: NoSuchElementException => Left(BufferUnderflow)
      }