Add initial implementation of the RS framing layer

I have spent a while thinking about the best way to implement this,
especially after I discovered that OSRS treats the packets sent during
the handshake stage as normal packets (see share/doc/protocol/login.md
for a longer explanation).

I have settled on a design where the same Rs2Decoder and Rs2Encoder
instances, which deal with decoding packet opcodes and lengths, will
remain the same for the entire connection - unless it switches into a
mode where a completely different framing scheme is used, such as
JAGGRAB and JS5.

Rs2Decoder and Rs2Encoder both support optional opcode encryption. The
initial cipher is set to NopStreamCipher. It will be set to an
IsaacRandom instance during the login process.

As the scrambled opcodes used in-game overlap with the opcodes used
during the login process, a class called Protocol is used to represent a
set of opcodes that can be used in a particular state. The protocol can
be changed at any time. Rs2Decoder sets isSingleDecode to true initially
to help do this safely, but once in the final in-game state this can be
disabled for performance.

Unlike previous servers, like Apollo and ScapeEmulator, intermediate
frame objects are not used. Rs2Decoder and Rs2Encoder call PacketCodec
to directly translate an inbound ByteBuf into a POJO, or an outbound
POJO into a ByteBuf. This saves a memory allocation per packet.

PacketCodec implementations must provide both an encode() and a decode()
method for every packet. This will ensure the library is usable as both
a client and server, allowing the development of tools, such as a JS5
client, a game server stress-tester or even a proxy server for
inspecting the flow of packets.

PacketCodec implementations may optionally override getLength() to
return their exact length, to optimise the size of the ByteBuf passed to
the decode() method. (It is not necessary to override getLength() for
fixed packets, as the size is already known.)

The 256-element packet length array is automatically generated by the
Protocol class based on the length attribute of the PacketCodec objects
passed to it. This is less error-prone than populating the array
manually. However, it does mean stub implementations of every packet
packet will need to be provided during development - all lengths must be
known in advance to ensure the client and server remain in sync.

For the moment, it is legal to throw NotImplementError from a decode()
method. Rs2Decoder catches this exception, prints a warning and then
proceed to the next packet. Once all packets have been implemented, this
code may be removed.

Signed-off-by: Graham <gpe@openrs2.org>

protocol/build.gradle.kts

@@ -4,6 +4,7 @@ plugins {
 }
 
 dependencies {
+    api(project(":crypto"))
     api("io.netty:netty-codec:${Versions.netty}")
 
     implementation(project(":buffer"))

protocol/src/main/kotlin/org/openrs2/protocol/EmptyPacketCodec.kt

@@ -0,0 +1,16 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+public abstract class EmptyPacketCodec<T : Packet>(
+    private val packet: T,
+    opcode: Int
+) : PacketCodec<T>(packet.javaClass, opcode, length = 0) {
+    override fun decode(input: ByteBuf): T {
+        return packet
+    }
+
+    override fun encode(input: T, output: ByteBuf) {
+        // empty
+    }
+}

protocol/src/main/kotlin/org/openrs2/protocol/Packet.kt

@@ -0,0 +1,3 @@
+package org.openrs2.protocol
+
+public interface Packet

protocol/src/main/kotlin/org/openrs2/protocol/PacketCodec.kt

@@ -0,0 +1,47 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.ByteBufAllocator
+
+public abstract class PacketCodec<T : Packet>(
+    public val type: Class<T>,
+    public val opcode: Int,
+    public val length: Int
+) {
+    init {
+        require(opcode in 0 until 256)
+        require(length >= PacketLength.VARIABLE_SHORT)
+    }
+
+    public abstract fun decode(input: ByteBuf): T
+    public abstract fun encode(input: T, output: ByteBuf)
+
+    public open fun getLength(input: T): Int {
+        return length
+    }
+
+    public fun allocateBuffer(alloc: ByteBufAllocator, input: T, preferDirect: Boolean): ByteBuf {
+        val payloadLen = getLength(input)
+        if (payloadLen < 0) {
+            return if (preferDirect) {
+                alloc.ioBuffer()
+            } else {
+                alloc.heapBuffer()
+            }
+        }
+
+        val headerLen = when (length) {
+            PacketLength.VARIABLE_BYTE -> 2
+            PacketLength.VARIABLE_SHORT -> 3
+            else -> 1
+        }
+
+        val totalLen = headerLen + payloadLen
+
+        return if (preferDirect) {
+            alloc.ioBuffer(totalLen, totalLen)
+        } else {
+            alloc.heapBuffer(totalLen, totalLen)
+        }
+    }
+}

protocol/src/main/kotlin/org/openrs2/protocol/PacketLength.kt

@@ -0,0 +1,6 @@
+package org.openrs2.protocol
+
+public object PacketLength {
+    public const val VARIABLE_SHORT: Int = -2
+    public const val VARIABLE_BYTE: Int = -1
+}

protocol/src/main/kotlin/org/openrs2/protocol/Protocol.kt

@@ -0,0 +1,22 @@
+package org.openrs2.protocol
+
+public class Protocol(vararg codecs: PacketCodec<*>) {
+    private val decoders = arrayOfNulls<PacketCodec<*>>(256)
+    private val encoders = codecs.associateBy(PacketCodec<*>::type)
+
+    init {
+        for (codec in codecs) {
+            decoders[codec.opcode] = codec
+        }
+    }
+
+    public fun getDecoder(opcode: Int): PacketCodec<*>? {
+        require(opcode in decoders.indices)
+        return decoders[opcode]
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    public fun <T : Packet> getEncoder(type: Class<T>): PacketCodec<T>? {
+        return encoders[type] as PacketCodec<T>?
+    }
+}

protocol/src/main/kotlin/org/openrs2/protocol/Rs2Decoder.kt

@@ -0,0 +1,80 @@
+package org.openrs2.protocol
+
+import com.github.michaelbull.logging.InlineLogger
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.ByteToMessageDecoder
+import io.netty.handler.codec.DecoderException
+import org.openrs2.crypto.NopStreamCipher
+import org.openrs2.crypto.StreamCipher
+
+public class Rs2Decoder(public var protocol: Protocol) : ByteToMessageDecoder() {
+    private enum class State {
+        READ_OPCODE,
+        READ_LENGTH,
+        READ_PAYLOAD
+    }
+
+    public var cipher: StreamCipher = NopStreamCipher
+    private var state = State.READ_OPCODE
+    private lateinit var decoder: PacketCodec<*>
+    private var length = 0
+
+    init {
+        isSingleDecode = true
+    }
+
+    override fun decode(ctx: ChannelHandlerContext, input: ByteBuf, out: MutableList<Any>) {
+        if (state == State.READ_OPCODE) {
+            if (!input.isReadable) {
+                return
+            }
+
+            val opcode = (input.readUnsignedByte().toInt() - cipher.nextInt()) and 0xFF
+            decoder = protocol.getDecoder(opcode) ?: throw DecoderException("Unsupported opcode: $opcode")
+            length = decoder.length
+
+            state = State.READ_LENGTH
+        }
+
+        if (state == State.READ_LENGTH) {
+            when (length) {
+                PacketLength.VARIABLE_BYTE -> {
+                    if (!input.isReadable) {
+                        return
+                    }
+
+                    length = input.readUnsignedByte().toInt()
+                }
+                PacketLength.VARIABLE_SHORT -> {
+                    if (input.readableBytes() < 2) {
+                        return
+                    }
+
+                    length = input.readUnsignedShort()
+                }
+            }
+
+            state = State.READ_PAYLOAD
+        }
+
+        if (state == State.READ_PAYLOAD) {
+            if (input.readableBytes() < length) {
+                return
+            }
+
+            out += try {
+                decoder.decode(input.readSlice(length))
+            } catch (ex: NotImplementedError) {
+                // TODO(gpe): remove this catch block when every packet is implemented
+                logger.warn { "Skipping unimplemented packet: ${decoder.javaClass}" }
+            }
+
+            state = State.READ_OPCODE
+        }
+    }
+
+    private companion object {
+        private val logger = InlineLogger()
+    }
+}

protocol/src/main/kotlin/org/openrs2/protocol/Rs2Encoder.kt

@@ -0,0 +1,60 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.EncoderException
+import io.netty.handler.codec.MessageToByteEncoder
+import org.openrs2.crypto.NopStreamCipher
+import org.openrs2.crypto.StreamCipher
+
+public class Rs2Encoder(public var protocol: Protocol) : MessageToByteEncoder<Packet>(Packet::class.java) {
+    public var cipher: StreamCipher = NopStreamCipher
+
+    override fun encode(ctx: ChannelHandlerContext, msg: Packet, out: ByteBuf) {
+        val encoder = protocol.getEncoder(msg.javaClass)
+            ?: throw EncoderException("Unsupported packet type: ${msg.javaClass}")
+
+        out.writeByte(encoder.opcode + cipher.nextInt())
+
+        val len = encoder.length
+        val lenIndex = out.writerIndex()
+        when (len) {
+            PacketLength.VARIABLE_BYTE -> out.writeZero(1)
+            PacketLength.VARIABLE_SHORT -> out.writeZero(2)
+        }
+
+        val payloadIndex = out.writerIndex()
+        encoder.encode(msg, out)
+
+        val written = out.writerIndex() - payloadIndex
+
+        when (len) {
+            PacketLength.VARIABLE_BYTE -> {
+                if (written >= 256) {
+                    throw EncoderException("Variable byte payload too long: $written bytes")
+                }
+
+                out.setByte(lenIndex, written)
+            }
+            PacketLength.VARIABLE_SHORT -> {
+                if (written >= 65536) {
+                    throw EncoderException("Variable short payload too long: $written bytes")
+                }
+
+                out.setShort(lenIndex, written)
+            }
+            else -> {
+                if (written != len) {
+                    throw EncoderException("Fixed payload length mismatch (expected $len bytes, got $written bytes)")
+                }
+            }
+        }
+    }
+
+    override fun allocateBuffer(ctx: ChannelHandlerContext, msg: Packet, preferDirect: Boolean): ByteBuf {
+        val encoder = protocol.getEncoder(msg.javaClass)
+            ?: throw EncoderException("Unsupported packet type: ${msg.javaClass}")
+
+        return encoder.allocateBuffer(ctx.alloc(), msg, preferDirect)
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/EmptyPacket.kt

@@ -0,0 +1,3 @@
+package org.openrs2.protocol
+
+object EmptyPacket : Packet

protocol/src/test/kotlin/org/openrs2/protocol/FixedPacket.kt

@@ -0,0 +1,3 @@
+package org.openrs2.protocol
+
+internal data class FixedPacket(val value: Int) : Packet

protocol/src/test/kotlin/org/openrs2/protocol/FixedPacketCodec.kt

@@ -0,0 +1,18 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+internal object FixedPacketCodec : PacketCodec<FixedPacket>(
+    type = FixedPacket::class.java,
+    opcode = 0,
+    length = 4
+) {
+    override fun decode(input: ByteBuf): FixedPacket {
+        val value = input.readInt()
+        return FixedPacket(value)
+    }
+
+    override fun encode(input: FixedPacket, output: ByteBuf) {
+        output.writeInt(input.value)
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/LengthMismatchPacketCodec.kt

@@ -0,0 +1,18 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+internal object LengthMismatchPacketCodec : PacketCodec<FixedPacket>(
+    type = FixedPacket::class.java,
+    opcode = 0,
+    length = 5
+) {
+    override fun decode(input: ByteBuf): FixedPacket {
+        val value = input.readInt()
+        return FixedPacket(value)
+    }
+
+    override fun encode(input: FixedPacket, output: ByteBuf) {
+        output.writeInt(input.value)
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/Rs2DecoderTest.kt

@@ -0,0 +1,103 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import io.netty.handler.codec.DecoderException
+import org.junit.jupiter.api.assertThrows
+import org.openrs2.buffer.wrappedBuffer
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object Rs2DecoderTest {
+    @Test
+    fun testDecode() {
+        testDecode(byteArrayOf(0, 0x11, 0x22, 0x33, 0x44), FixedPacket(0x11223344))
+        testDecode(byteArrayOf(1, 3, 0x11, 0x22, 0x33), VariableBytePacket(byteArrayOf(0x11, 0x22, 0x33)))
+        testDecode(byteArrayOf(2, 0, 3, 0x11, 0x22, 0x33), VariableShortPacket(byteArrayOf(0x11, 0x22, 0x33)))
+        testDecode(byteArrayOf(5), EmptyPacket)
+    }
+
+    @Test
+    fun testFragmented() {
+        testFragmented(byteArrayOf(0, 0x11, 0x22, 0x33, 0x44), FixedPacket(0x11223344))
+        testFragmented(byteArrayOf(1, 3, 0x11, 0x22, 0x33), VariableBytePacket(byteArrayOf(0x11, 0x22, 0x33)))
+        testFragmented(byteArrayOf(2, 0, 3, 0x11, 0x22, 0x33), VariableShortPacket(byteArrayOf(0x11, 0x22, 0x33)))
+    }
+
+    @Test
+    fun testUnsupported() {
+        val channel = EmbeddedChannel(Rs2Decoder(Protocol()))
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(wrappedBuffer(0))
+        }
+    }
+
+    @Test
+    fun testEncryptedOpcode() {
+        val decoder = Rs2Decoder(Protocol(FixedPacketCodec))
+        decoder.cipher = TestStreamCipher
+
+        val channel = EmbeddedChannel(decoder)
+        channel.writeInbound(wrappedBuffer(10, 0x11, 0x22, 0x33, 0x44))
+
+        val actual = channel.readInbound<Packet>()
+        assertEquals(FixedPacket(0x11223344), actual)
+    }
+
+    @Test
+    fun testSwitchProtocol() {
+        val decoder = Rs2Decoder(Protocol(FixedPacketCodec))
+        val channel = EmbeddedChannel(decoder)
+
+        channel.writeInbound(wrappedBuffer(0, 0x11, 0x22, 0x33, 0x44))
+        channel.readInbound<Packet>()
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(wrappedBuffer(5))
+        }
+
+        decoder.protocol = Protocol(TestEmptyPacketCodec)
+
+        channel.writeInbound(wrappedBuffer(5))
+
+        val actual = channel.readInbound<Packet>()
+        assertEquals(EmptyPacket, actual)
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(wrappedBuffer(0, 0x11, 0x22, 0x33, 0x44))
+        }
+    }
+
+    private fun testDecode(buf: ByteArray, expected: Packet) {
+        val channel = EmbeddedChannel(Rs2Decoder(Protocol(
+            FixedPacketCodec,
+            VariableBytePacketCodec,
+            VariableShortPacketCodec,
+            VariableByteOptimisedPacketCodec,
+            VariableShortOptimisedPacketCodec,
+            TestEmptyPacketCodec
+        )))
+        channel.writeInbound(Unpooled.wrappedBuffer(buf))
+
+        val actual = channel.readInbound<Packet>()
+        assertEquals(expected, actual)
+    }
+
+    private fun testFragmented(buf: ByteArray, expected: Packet) {
+        val channel = EmbeddedChannel(Rs2Decoder(Protocol(
+            FixedPacketCodec,
+            VariableBytePacketCodec,
+            VariableShortPacketCodec,
+            VariableByteOptimisedPacketCodec,
+            VariableShortOptimisedPacketCodec
+        )))
+
+        for (b in buf) {
+            channel.writeInbound(wrappedBuffer(b))
+        }
+
+        val actual = channel.readInbound<Packet>()
+        assertEquals(expected, actual)
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/Rs2EncoderTest.kt

@@ -0,0 +1,127 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import io.netty.handler.codec.EncoderException
+import org.junit.jupiter.api.assertThrows
+import org.openrs2.buffer.use
+import org.openrs2.buffer.wrappedBuffer
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object Rs2EncoderTest {
+    @Test
+    fun testEncode() {
+        testEncode(FixedPacket(0x11223344), byteArrayOf(0, 0x11, 0x22, 0x33, 0x44))
+        testEncode(VariableBytePacket(byteArrayOf(0x11, 0x22, 0x33)), byteArrayOf(1, 3, 0x11, 0x22, 0x33))
+        testEncode(VariableShortPacket(byteArrayOf(0x11, 0x22, 0x33)), byteArrayOf(2, 0, 3, 0x11, 0x22, 0x33))
+        testEncode(EmptyPacket, byteArrayOf(5))
+    }
+
+    @Test
+    fun testTooLong() {
+        val channel = EmbeddedChannel(Rs2Encoder(Protocol(
+            VariableBytePacketCodec,
+            VariableShortPacketCodec
+        )))
+
+        channel.writeOutbound(VariableShortPacket(ByteArray(255)))
+        channel.readOutbound<ByteBuf>().release()
+
+        channel.writeOutbound(VariableShortPacket(ByteArray(65535)))
+        channel.readOutbound<ByteBuf>().release()
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(VariableBytePacket(ByteArray(256)))
+        }
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(VariableShortPacket(ByteArray(65536)))
+        }
+    }
+
+    @Test
+    fun testUnsupported() {
+        val channel = EmbeddedChannel(Rs2Encoder(Protocol()))
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(FixedPacket(0x11223344))
+        }
+    }
+
+    @Test
+    fun testLengthMismatch() {
+        val channel = EmbeddedChannel(Rs2Encoder(Protocol(LengthMismatchPacketCodec)))
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(FixedPacket(0x11223344))
+        }
+    }
+
+    @Test
+    fun testLengthOptimised() {
+        testEncode(VariableByteOptimisedPacket(byteArrayOf(0x11, 0x22, 0x33)), byteArrayOf(3, 3, 0x11, 0x22, 0x33))
+        testEncode(VariableShortOptimisedPacket(byteArrayOf(0x11, 0x22, 0x33)), byteArrayOf(4, 0, 3, 0x11, 0x22, 0x33))
+    }
+
+    @Test
+    fun testEncryptedOpcode() {
+        val encoder = Rs2Encoder(Protocol(FixedPacketCodec))
+        encoder.cipher = TestStreamCipher
+
+        val channel = EmbeddedChannel(encoder)
+        channel.writeOutbound(FixedPacket(0x11223344))
+
+        channel.readOutbound<ByteBuf>().use { actual ->
+            wrappedBuffer(10, 0x11, 0x22, 0x33, 0x44).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+
+    @Test
+    fun testSwitchProtocol() {
+        val encoder = Rs2Encoder(Protocol(FixedPacketCodec))
+        val channel = EmbeddedChannel(encoder)
+
+        channel.writeOutbound(FixedPacket(0x11223344))
+        channel.readOutbound<ByteBuf>().release()
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(EmptyPacket)
+        }
+
+        encoder.protocol = Protocol(TestEmptyPacketCodec)
+
+        channel.writeOutbound(EmptyPacket)
+
+        channel.readOutbound<ByteBuf>().use { actual ->
+            wrappedBuffer(5).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(FixedPacket(0x11223344))
+        }
+    }
+
+    private fun testEncode(packet: Packet, expected: ByteArray) {
+        val channel = EmbeddedChannel(Rs2Encoder(Protocol(
+            FixedPacketCodec,
+            VariableBytePacketCodec,
+            VariableShortPacketCodec,
+            VariableByteOptimisedPacketCodec,
+            VariableShortOptimisedPacketCodec,
+            TestEmptyPacketCodec
+        )))
+        channel.writeOutbound(packet)
+
+        channel.readOutbound<ByteBuf>().use { actual ->
+            Unpooled.wrappedBuffer(expected).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/TestEmptyPacketCodec.kt

@@ -0,0 +1,6 @@
+package org.openrs2.protocol
+
+object TestEmptyPacketCodec : EmptyPacketCodec<EmptyPacket>(
+    packet = EmptyPacket,
+    opcode = 5
+)

protocol/src/test/kotlin/org/openrs2/protocol/TestStreamCipher.kt

@@ -0,0 +1,9 @@
+package org.openrs2.protocol
+
+import org.openrs2.crypto.StreamCipher
+
+object TestStreamCipher : StreamCipher {
+    override fun nextInt(): Int {
+        return 10
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/VariableByteOptimisedPacket.kt

@@ -0,0 +1,3 @@
+package org.openrs2.protocol
+
+internal class VariableByteOptimisedPacket(val value: ByteArray) : Packet

protocol/src/test/kotlin/org/openrs2/protocol/VariableByteOptimisedPacketCodec.kt

@@ -0,0 +1,23 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+internal object VariableByteOptimisedPacketCodec : PacketCodec<VariableByteOptimisedPacket>(
+    type = VariableByteOptimisedPacket::class.java,
+    opcode = 3,
+    length = PacketLength.VARIABLE_BYTE
+) {
+    override fun decode(input: ByteBuf): VariableByteOptimisedPacket {
+        val value = ByteArray(input.readableBytes())
+        input.readBytes(value)
+        return VariableByteOptimisedPacket(value)
+    }
+
+    override fun encode(input: VariableByteOptimisedPacket, output: ByteBuf) {
+        output.writeBytes(input.value)
+    }
+
+    override fun getLength(input: VariableByteOptimisedPacket): Int {
+        return input.value.size
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/VariableBytePacket.kt

@@ -0,0 +1,18 @@
+package org.openrs2.protocol
+
+internal class VariableBytePacket(val value: ByteArray) : Packet {
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as VariableBytePacket
+
+        if (!value.contentEquals(other.value)) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        return value.contentHashCode()
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/VariableBytePacketCodec.kt

@@ -0,0 +1,19 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+internal object VariableBytePacketCodec : PacketCodec<VariableBytePacket>(
+    type = VariableBytePacket::class.java,
+    opcode = 1,
+    length = PacketLength.VARIABLE_BYTE
+) {
+    override fun decode(input: ByteBuf): VariableBytePacket {
+        val value = ByteArray(input.readableBytes())
+        input.readBytes(value)
+        return VariableBytePacket(value)
+    }
+
+    override fun encode(input: VariableBytePacket, output: ByteBuf) {
+        output.writeBytes(input.value)
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/VariableShortOptimisedPacket.kt

@@ -0,0 +1,3 @@
+package org.openrs2.protocol
+
+internal class VariableShortOptimisedPacket(val value: ByteArray) : Packet

protocol/src/test/kotlin/org/openrs2/protocol/VariableShortOptimisedPacketCodec.kt

@@ -0,0 +1,23 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+internal object VariableShortOptimisedPacketCodec : PacketCodec<VariableShortOptimisedPacket>(
+    type = VariableShortOptimisedPacket::class.java,
+    opcode = 4,
+    length = PacketLength.VARIABLE_SHORT
+) {
+    override fun decode(input: ByteBuf): VariableShortOptimisedPacket {
+        val value = ByteArray(input.readableBytes())
+        input.readBytes(value)
+        return VariableShortOptimisedPacket(value)
+    }
+
+    override fun encode(input: VariableShortOptimisedPacket, output: ByteBuf) {
+        output.writeBytes(input.value)
+    }
+
+    override fun getLength(input: VariableShortOptimisedPacket): Int {
+        return input.value.size
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/VariableShortPacket.kt

@@ -0,0 +1,18 @@
+package org.openrs2.protocol
+
+internal class VariableShortPacket(val value: ByteArray) : Packet {
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as VariableShortPacket
+
+        if (!value.contentEquals(other.value)) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        return value.contentHashCode()
+    }
+}

protocol/src/test/kotlin/org/openrs2/protocol/VariableShortPacketCodec.kt

@@ -0,0 +1,19 @@
+package org.openrs2.protocol
+
+import io.netty.buffer.ByteBuf
+
+internal object VariableShortPacketCodec : PacketCodec<VariableShortPacket>(
+    type = VariableShortPacket::class.java,
+    opcode = 2,
+    length = PacketLength.VARIABLE_SHORT
+) {
+    override fun decode(input: ByteBuf): VariableShortPacket {
+        val value = ByteArray(input.readableBytes())
+        input.readBytes(value)
+        return VariableShortPacket(value)
+    }
+
+    override fun encode(input: VariableShortPacket, output: ByteBuf) {
+        output.writeBytes(input.value)
+    }
+}