Message Format
Every JSON message will be sent via a "plugin message" packet. The plugin channel that should be used is called "labymod3:main".The packet's data (a byte-array) consists of two Strings:
1. the message's key (which will be used to find out the message's purpose)
2. the message's contents (a JSON element)
Warning
We changed the plugin channel name from LMC to labymod3:main since LabyMod 3.8.0 to support the latest Minecraft 1.16 version
Note
In our protocol a String consists of two components:
• varint: the string's length
• byte-array: the string's content
Info
This format can be applied to both incoming and outgoing plugin messages.
Utils class
import com.google.gson.JsonElement;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.handler.codec.DecoderException;import io.netty.handler.codec.EncoderException;import java.nio.charset.Charset;import java.util.UUID;public class LabyModProtocol { /** * Send a message to LabyMod * @param player Minecraft Client * @param key LabyMod message key * @param messageContent json object content */ public static void sendLabyModMessage( Player player, String key, JsonElement messageContent ) { byte[] bytes = getBytesToSend( key, messageContent.toString() ); PacketDataSerializer pds = new PacketDataSerializer( Unpooled.wrappedBuffer( bytes ) ); PacketPlayOutCustomPayload payloadPacket = new PacketPlayOutCustomPayload( "labymod3:main", pds ); ((CraftPlayer) player).getHandle().playerConnection.sendPacket( payloadPacket ); } /** * Gets the bytes that are required to send the given message * * @param messageKey the message's key * @param messageContents the message's contents * @return the byte array that should be the payload */ public static byte[] getBytesToSend( String messageKey, String messageContents ) { // Getting an empty buffer ByteBuf byteBuf = Unpooled.buffer(); // Writing the message-key to the buffer writeString( byteBuf, messageKey ); // Writing the contents to the buffer writeString( byteBuf, messageContents ); // Copying the buffer's bytes to the byte array byte[] bytes = new byte[byteBuf.readableBytes()]; byteBuf.readBytes( bytes ); // Release the buffer byteBuf.release(); // Returning the byte array return bytes; } /** * Writes a varint to the given byte buffer * * @param buf the byte buffer the int should be written to * @param input the int that should be written to the buffer */ private static void writeVarIntToBuffer( ByteBuf buf, int input ) { while ( (input & -128) != 0 ) { buf.writeByte( input & 127 | 128 ); input >>>= 7; } buf.writeByte( input ); } /** * Writes a string to the given byte buffer * * @param buf the byte buffer the string should be written to * @param string the string that should be written to the buffer */ private static void writeString( ByteBuf buf, String string ) { byte[] abyte = string.getBytes( Charset.forName( "UTF-8" ) ); if ( abyte.length > Short.MAX_VALUE ) { throw new EncoderException( "String too big (was " + string.length() + " bytes encoded, max " + Short.MAX_VALUE + ")" ); } else { writeVarIntToBuffer( buf, abyte.length ); buf.writeBytes( abyte ); } } /** * Reads a varint from the given byte buffer * * @param buf the byte buffer the varint should be read from * @return the int read */ public static int readVarIntFromBuffer( ByteBuf buf ) { int i = 0; int j = 0; byte b0; do { b0 = buf.readByte(); i |= (b0 & 127) << j++ * 7; if ( j > 5 ) { throw new RuntimeException( "VarInt too big" ); } } while ( (b0 & 128) == 128 ); return i; } /** * Reads a string from the given byte buffer * * @param buf the byte buffer the string should be read from * @param maxLength the string's max-length * @return the string read */ public static String readString( ByteBuf buf, int maxLength ) { int i = readVarIntFromBuffer( buf ); if ( i > maxLength * 4 ) { throw new DecoderException( "The received encoded string buffer length is longer than maximum allowed (" + i + " > " + maxLength * 4 + ")" ); } else if ( i < 0 ) { throw new DecoderException( "The received encoded string buffer length is less than zero! Weird string!" ); } else { byte[] bytes = new byte[i]; buf.readBytes( bytes ); String s = new String( bytes, Charset.forName( "UTF-8" ) ); if ( s.length() > maxLength ) { throw new DecoderException( "The received string length is longer than maximum allowed (" + i + " > " + maxLength + ")" ); } else { return s; } } }}