Issues with High-Version Client Construction

[wcr490]

Hi guys,

I have some questions regarding the high-version protocol (1.20.6, which I assume has differences in protocol ID compared to 1.20.4).

I am building a command-line client, and I have successfully implemented the handshake -> login -> configuration process. However, when I attempt to handle the packet with id = 0x40 in the play state (which corresponds to Synchronize Player Position in 1.20.6 and, based on references from this link and this link, appears to match 0x3E in 1.20.4), I encounter an issue.

The problem is that this packet has an extremely inconsistent length, ranging from 30 to 3000 bytes. I would like to ask if you have any insights into what might be causing this issue.

Here is a demo of my implementation:

let mut conn = MCConnTcp::connect("xxx.com:25565")?; 
/*
 * Handshake
 */
// Handshake -> Enter Login
conn.write_packet(&Packet::build(0x00, |packet| {
    packet.write_u16_varint(769)?; // protocol_version
    packet.write_string("xxx.com")?; // server_address
    packet.write_unsigned_short(25565)?; // server_port
    packet.write_u8_varint(2) // next_state
})?)?;

/*
 * Login
 */
// Assign Username and UUID
conn.write_packet(&Packet::build(0x00, |packet| {
    packet.write_string("SKKkkkkk")?;
    packet.write_uuid(&Uuid::from_str("8ea5a373-4847-4d71-b006-34dd1c467d79").unwrap())
})?)?;
let mut packet_after_assign_username = conn.read_packet()?;

// Set compression
if packet_after_assign_username.id() == 0x03 {
    let threshold = packet_after_assign_username.read_i32_varint()?;
    println!("Set compression threshold: {:#?}", threshold);
    conn.set_compression(Some(threshold as usize));
}

// Login success -> Enter configuration
let mut packet_after_set_compression = conn.read_packet()?;
if packet_after_set_compression.id() == 0x02 {
    println!("login success");
    println!("UUID: {}", packet_after_set_compression.read_uuid()?);
    println!("Username: {}", packet_after_set_compression.read_string()?);
    conn.write_packet(&Packet::empty(0x03))?;
}

/*
 * Configuration
 */
// Features
let packet_after_login = conn.read_packet()?;
println!("id: {}", packet_after_login.id());
let mut packet_after_login = conn.read_packet()?;
println!("id: {}", packet_after_login.id());
println!("conf_features_num: {}", packet_after_login.read_u32_varint()?);
println!("features: {}", packet_after_login.read_string()?);

// Known Packs
let mut packet_after_get_features = conn.read_packet()?;
println!("id: {}", packet_after_get_features.id());
println!("packs num: {}", packet_after_get_features.read_u32_varint()?);
println!(
    "namespace: {}\nID: {}\nVersion: {}",
    packet_after_get_features.read_string()?,
    packet_after_get_features.read_string()?,
    packet_after_get_features.read_string()?
);
// Known Packs ACK
conn.write_packet(&Packet::build(0x07, |packet| packet.write_u32_varint(0))?)?;

// Registry data
for _ in 0..13 {
    let mut packet_after_ack_packs = conn.read_packet()?;
    let id = packet_after_ack_packs.id();
    println!("ident: {}", packet_after_ack_packs.read_string()?);
}

let mut packet_after_registry_ident = conn.read_packet()?;
// Configuration finish -> Play
if packet_after_registry_ident.id() == 0x03 {
    println!("configuration finished");
    conn.write_packet(&Packet::empty(0x03))?;
}

let conn = Arc::new(Mutex::new(conn));

let conn_clone = Arc::clone(&conn);
let _handle = task::spawn(async move {
    loop {
        let mut locked_conn = conn_clone.lock().await;
        let mut packet = locked_conn.read_packet()?;

        if packet.id() == 0x40 {
            println!("LEN: {}", packet.len());
            println!("Received 0x40 packet (Synchronize Player Position)");
            let x = packet.read_double()?;
            let y = packet.read_double()?;
            let z = packet.read_double()?;
            let yaw = packet.read_float()?;
            let pitch = packet.read_float()?;
            let flags = packet.read_byte()?;
            let teleport_id = packet.read_u32_varint()?;

            println!(
                "Player position: X={}, Y={}, Z={}, Yaw={}, Pitch={}, Flags={:08b}, Teleport ID={}\n",
                x, y, z, yaw, pitch, flags, teleport_id
            );
            locked_conn
                .write_packet(&Packet::build(0x00, |p| p.write_u32_varint(teleport_id))?)?;
        }
    }

    Ok::<(), ProtocolError>(())
});

loop {}

Here is a small segment of test output data.

LEN: 1165
Received 0x40 packet (Synchronize Player Position)
Player position: X=0.000000000000007724048850828133, Y=0.0000000000002793863302650555, Z=-108304047231387150, Yaw=4424583000000000000000000000000, Pitch=279434860000000000000, Flags=00001000, Teleport ID=116

LEN: 1223
Received 0x40 packet (Synchronize Player Position)
Player position: X=0.000000000000007565091155625899, Y=0.00000000000000000000000029271759837360926, Z=155050391321645740000000000000000000000000000000000000000000000000000000000000000000000000000, Yaw=0.0000027120714, Pitch=72722110000000000000000000000000, Flags=01110101, Teleport ID=114

LEN: 55
Received 0x40 packet (Synchronize Player Position)
Player position: X=0.000000000000007895122508635527, Y=0.00000000000000000000000000000000000000000000000000000000000000000000000002729598918125162, Z=-281158689879342800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000, Yaw=18368851000000000000000000000, Pitch=1088311100000000000000000, Flags=01110101, Teleport ID=0

LEN: 51
Received 0x40 packet (Synchronize Player Position)
Player position: X=0.000000000000007700575092107292, Y=0.0000000000000000000000000000000000000000000000000000000000000000000000000013588551144202216, Z=0.000000000000000000000000000000000000004600727445211243, Yaw=1128596600000000000000000000, Pitch=70363952000000000000000, Flags=00000011, Teleport ID=1

LEN: 1341
Received 0x40 packet (Synchronize Player Position)
Player position: X=0.00000000000000777407012755373, Y=0.0000000000000000000000000000000000000000000000000000000000000012621767488231338, Z=-0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000133590177701754, Yaw=78973150000000000000000000000000, Pitch=0.00000000000000000000000000000000073545355, Flags=01110100, Teleport ID=117

LEN: 1225
Received 0x40 packet (Synchronize Player Position)
Player position: X=0.000000000000007582506572134247, Y=0.0000000000000000000000000000000000000000000000000000000000000000000010704874341073102, Z=2332720554003314600000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000, Yaw=0.0000000026223683, Pitch=0.00000012017136, Flags=01100101, Teleport ID=120

I appreciate your patience in reading through this. Since I am not very familiar with the Minecraft protocol, please feel free to point out any mistakes.

[breadbyte]

Compression? Your data values are wayyyyy too off to be of any use, which may indicate that you're not reading the data correctly, or the data getting sent to you is invalid, which I doubt is the case, or vanilla would cause a tantrum.

One packet, you're parsing
Yaw=1128596600000000000000000000, Pitch=70363952000000000000000
and the next you're parsing
Yaw=78973150000000000000000000000000, Pitch=0.00000000000000000000000000000000073545355

which tells me that you may be trying to read compressed data as actual data.

Also paired with the fact that your packet lengths are inconsistent, sometimes big, sometimes small, which also tells me that packet compression may be at play here.

Try looking into your compression/decompression algorithm and try again, and to test, disable the server's compression and see if that fixes your issue.

[wcr490]

Thanks for the suggestion! I'll give it a try. Really appreciate your help!