buffer-codec/com.ditchoom.buffer.codec.annotations/PacketType

PacketType

@Target(allowedTargets = [AnnotationTarget.CLASS])

annotation class PacketType(val value: Int, val wire: Int = -1)

Specifies the discriminator value for a variant of a @ProtocolMessage sealed interface.

The generated dispatch codec reads one byte, matches it against each variant's value, and delegates to the correct variant codec. On encode, wire is written as the type byte.

Simple dispatch (no @DispatchOn): value is both the match value and the wire byte.

@ProtocolMessage
sealed interface Command {
    @ProtocolMessage @PacketType(0x01)
    data class Ping(val timestamp: Long) : Command

    @ProtocolMessage @PacketType(0x02)
    data class Echo(@LengthPrefixed val message: String) : Command
}

Bit-packed dispatch (with @DispatchOn): value is the extracted dispatch value, wire is the raw byte written on encode.

@DispatchOn(MqttFixedHeader::class)
sealed interface MqttPacket {
    @PacketType(value = 1, wire = 0x10)  // type=1, raw byte=0x10
    data class Connect(...) : MqttPacket

    @PacketType(value = 6, wire = 0x62)  // type=6, raw byte=0x62 (flags=0x02)
    data class PubRel(...) : MqttPacket
}

Parameters

value

The discriminator value to match during decode (0-255).

wire

The raw byte to write during encode. Defaults to -1, meaning use value. Required when @DispatchOn extracts a different value than the raw wire byte.

Properties

value

val value: Int

wire

val wire: Int