Cant send minecraft login packet to server?

问题

Minecraft is a game which also can be played on multiplayer servers. Each server has its own IP and the port is for every server "25565". In generell, for this problem you should be familiar with Minecaft protocol(https://wiki.vg/Protocol#Login_Start). Even if not, I created a hyperlink where you can look for this. My goal is to create a Minecraft Chatbot, without even open Minecraftlauncher to join any server. I know, there are already a lot of these existing, but I want to create some new commands which the client should send.

In generell, there are two big steps of the joining process when you join a Minecraft server. First, you need a connection sending a handshake (state 1) and "ping-pong". After this, you are connected to the server. This first step works very well, so I think I needn´t to show you. But the second step is the authentification of every client. Herefor I send a handshake (state 2) and then there comes my problem : I always get "java.io.EOFException" as a error message on my second step, sending my username to the Server.

try {
private String host = "hypixel.net";
socket.connect(host, 25565); //I created already a Socket called "socket"
DataOutputStream output = new DataOutputStream(socket.getOutputStream());
DataInputStream input = new DataInputStream(socket.getInputStream()); //socket is for creating streams
byte[] handShakeMessage = createHandshakeMessageLogin(host, 25565);
writeVarInt(output, handShakeMessage.length);
output.write(handShakeMessage);
System.out.println("Send handShakeMessage!");

output.writeByte(0x01); //hopefully the right packet size
output.writeByte(0x00); //packetID
output.writeUTF("ExamplePlayer"); //sending username 
}

    public void writeVarInt(DataOutputStream out, int paramInt) throws IOException {
    while (true) {
        if ((paramInt & 0xFFFFFF80) == 0) {
          out.writeByte(paramInt);
          return;
        }

        out.writeByte(paramInt & 0x7F | 0x80);
        paramInt >>>= 7;
    }
}

public static byte [] createHandshakeMessageLogin(String host, int port) throws IOException {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();

    DataOutputStream handshake = new DataOutputStream(buffer);
    handshake.writeByte(0x00); //packet id for handshake
    writeVarInt(handshake, 4); //protocol version
    writeString(handshake, host, StandardCharsets.UTF_8);
    handshake.writeShort(port); //port
    writeVarInt(handshake, 2); //state (2 for login)

    return buffer.toByteArray();
}

    public void writeString(DataOutputStream out, String string, Charset charset) throws IOException {
    byte [] bytes = string.getBytes(charset);
    writeVarInt(out, bytes.length);
    out.write(bytes);
}

So, as you can see quite a complicated thing I guess. If somebody could answer me, why I´m getting this error message and how to fix it i would be very very happy! Thank you

EDIT: I found a post, which helped me a lot with the connection! Java sending handshake packets to minecraft server

回答1:

You're writing a packet length prefix of 1, when your packet contains the entire string "ExamplePlayer".

Instead, construct the packet like is done in the createHandshakeMessageLogin function, then send the length as a varint before sending the content of that buffer.

来源：https://stackoverflow.com/questions/61850007/cant-send-minecraft-login-packet-to-server

标签

java

authentication

stream

minecraft

packet