MqttFixedHeader() — netty Function Reference

Architecture documentation for the MqttFixedHeader() function in MqttDecoder.java from the netty codebase.

Function java Buffer Allocators calls 1

Entity Profile

Buffer→ Allocators→ MqttFixedHeader() — netty Function Reference

Dependency Diagram

graph TD
  f52b822d_d755_b4dd_2485_216ecd243ffb["MqttFixedHeader()"]
  c4faa729_e212_a3dd_9d90_3e8fd908d755["MqttDecoder"]
  f52b822d_d755_b4dd_2485_216ecd243ffb -->|defined in| c4faa729_e212_a3dd_9d90_3e8fd908d755
  0e76d845_8de4_7a4c_bd45_465942f0d8f3["parseRemainingLength()"]
  f52b822d_d755_b4dd_2485_216ecd243ffb -->|calls| 0e76d845_8de4_7a4c_bd45_465942f0d8f3
  style f52b822d_d755_b4dd_2485_216ecd243ffb fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

codec-mqtt/src/main/java/io/netty/handler/codec/mqtt/MqttDecoder.java lines 185–250

    private static MqttFixedHeader decodeFixedHeader(ChannelHandlerContext ctx, ByteBuf buffer) {
        short b1 = buffer.readUnsignedByte();

        MqttMessageType messageType = MqttMessageType.valueOf(b1 >> 4);
        boolean dupFlag = (b1 & 0x08) == 0x08;
        int qosLevel = (b1 & 0x06) >> 1;
        boolean retain = (b1 & 0x01) != 0;

        switch (messageType) {
            case PUBLISH:
                if (qosLevel == 3) {
                    throw new DecoderException("Illegal QOS Level in fixed header of PUBLISH message ("
                            + qosLevel + ')');
                }
                break;

            case PUBREL:
            case SUBSCRIBE:
            case UNSUBSCRIBE:
                if (dupFlag) {
                    throw new DecoderException("Illegal BIT 3 in fixed header of " + messageType
                            + " message, must be 0, found 1");
                }
                if (qosLevel != 1) {
                    throw new DecoderException("Illegal QOS Level in fixed header of " + messageType
                            + " message, must be 1, found " + qosLevel);
                }
                if (retain) {
                    throw new DecoderException("Illegal BIT 0 in fixed header of " + messageType
                            + " message, must be 0, found 1");
                }
                break;

            case AUTH:
            case CONNACK:
            case CONNECT:
            case DISCONNECT:
            case PINGREQ:
            case PINGRESP:
            case PUBACK:
            case PUBCOMP:
            case PUBREC:
            case SUBACK:
            case UNSUBACK:
                if (dupFlag) {
                    throw new DecoderException("Illegal BIT 3 in fixed header of " + messageType
                            + " message, must be 0, found 1");
                }
                if (qosLevel != 0) {
                    throw new DecoderException("Illegal BIT 2 or 1 in fixed header of " + messageType
                            + " message, must be 0, found " + qosLevel);
                }
                if (retain) {
                    throw new DecoderException("Illegal BIT 0 in fixed header of " + messageType
                            + " message, must be 0, found 1");
                }
                break;
            default:
                throw new DecoderException("Unknown message type, do not know how to validate fixed header");
        }

        int remainingLength = parseRemainingLength(buffer, messageType);
        MqttFixedHeader decodedFixedHeader =
                new MqttFixedHeader(messageType, dupFlag, MqttQoS.valueOf(qosLevel), retain, remainingLength);
        return validateFixedHeader(ctx, resetUnusedFields(decodedFixedHeader));
    }