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use std::net::{SocketAddr, TcpListener, TcpStream};

use anyhow::{bail, Context};

use argh::FromArgs;

use async_executor::Executor;

use async_io::{block_on, Async};

use either::Either;

use feather_protocol::{

packets::client::HandshakeState, ClientHandshakePacket, ClientPacket, ClientPacketCodec,

ProtocolState, ServerLoginPacket, ServerPacket, ServerPacketCodec,

};

use futures_lite::FutureExt;

use futures_lite::{AsyncReadExt, AsyncWriteExt};

use simple_logger::SimpleLogger;

/// A proxy for debugging and inspecting the Minecraft protocol.

#[derive(Debug, FromArgs)]

struct Args {

/// the port to listen on. Must be different from

/// the vanilla server's port.

#[argh(option, short = 'p')]

port: u16,

/// the port of the server to proxy to.

#[argh(option, short = 's')]

server_port: u16,

}

fn main() -> anyhow::Result<()> {

SimpleLogger::new()

.with_level(log::LevelFilter::Debug)

.init()

.unwrap();

let args: Args = argh::from_env();

let addr = format!("127.0.0.1:{}", args.port);

let listener = TcpListener::bind(&addr)

.with_context(|| format!("failed to bind to port {}", args.port))?;

let mut listener = Async::new(listener)?;

log::info!("Listening on {}", addr);

let executor = Executor::new();

block_on(executor.run(async {

accept_connections(&executor, &mut listener, args.server_port).await;

}));

Ok(())

}

async fn accept_connections(

executor: &Executor<'static>,

listener: &mut Async<TcpListener>,

server_port: u16,

) {

loop {

let (stream, addr) = match listener.accept().await {

Ok(con) => con,

Err(e) => {

log::error!("Failed to accept connection: {}", e);

continue;

}

};

log::info!("Accepting connection from {}", addr);

executor

.spawn(async move {

if let Err(e) = handle_connection(stream, server_port).await {

log::error!("Connection dropped: {:?}", e);

}

})

.detach();

}

struct Connection {

/// The client's username.

username: String,

client_buffer: [u8; 256],

client_codec: ClientPacketCodec,

client: Async<TcpStream>,

server_buffer: [u8; 256],

server_codec: ServerPacketCodec,

server: Async<TcpStream>,

}

impl Connection {

fn set_state(&mut self, state: ProtocolState) {

log::info!("{}: switching to state {:?}", self.username, state);

self.client_codec.set_state(state);

self.server_codec.set_state(state);

}

const MAX_PACKET_DISPLAY: usize = 4000;

async fn handle_connection(client: Async<TcpStream>, server_port: u16) -> anyhow::Result<()> {

let server =

Async::<TcpStream>::connect(format!("127.0.0.1:{}", server_port).parse::<SocketAddr>()?)

.await

.with_context(|| format!("failed to connect to server at localhost:{}", server_port))?;

let mut connection = Connection {

username: String::from("<unknown>"),

client_buffer: [0; 256],

client_codec: ClientPacketCodec::new(),

client,

server_buffer: [0; 256],

server_codec: ServerPacketCodec::new(),

server,

};

let mut buffer = Vec::new();

loop {

let client = &mut connection.client;

let client_buffer = &mut connection.client_buffer;

let server = &mut connection.server;

let server_buffer = &mut connection.server_buffer;

// Attempt to read data from either the server or the client.

let recv_client = async { Either::Left(client.read(client_buffer).await) };

let recv_server = async { Either::Right(server.read(server_buffer).await) };

match recv_client.race(recv_server).await {

Either::Left(client) => {

let mut bytes_read = client?;

if bytes_read == 0 {

bail!("disconnected from client");

}

while let Some(packet) = connection

.client_codec

.decode(&connection.client_buffer[..bytes_read])

.context("failed to decode client packet")?

{

bytes_read = 0;

let mut packet_str = format!("{:?}", packet);

if packet_str.len() > MAX_PACKET_DISPLAY {

packet_str = format!("{} <snip>", &packet_str[..MAX_PACKET_DISPLAY]);

}

log::info!("client @ {}: {}", connection.username, packet_str);

// Attempt to detect state switches.

if let ClientPacket::Handshake(packet) = &packet {

let state = match packet {

ClientHandshakePacket::Handshake(packet) => match packet.next_state {

HandshakeState::Login => ProtocolState::Login,

HandshakeState::Status => ProtocolState::Status,

};

connection.set_state(state)

}

// Forward the packet to the server.

connection.client_codec.encode(&packet, &mut buffer);

connection.server.write_all(&buffer).await?;

buffer.clear();

}

Either::Right(server) => {

let mut bytes_read = server?;

if bytes_read == 9 {

bail!("disconnected from server");

}

while let Some(packet) = connection

.server_codec

.decode(&connection.server_buffer[..bytes_read])

.context("failed to decode server packet")?

{

bytes_read = 0;

let mut packet_str = format!("{:?}", packet);

if packet_str.len() > MAX_PACKET_DISPLAY {

packet_str = format!("{} <snip>", &packet_str[..MAX_PACKET_DISPLAY]);

}

log::info!("server @ {}: {}", connection.username, packet_str);

// Attempt to detect state switches.

if let ServerPacket::Login(ServerLoginPacket::LoginSuccess(packet)) = &packet {

connection.username = packet.username.clone();

connection.set_state(ProtocolState::Play);

}

// Forward the packet to the client.

connection.server_codec.encode(&packet, &mut buffer);

connection.client.write_all(&buffer).await?;

buffer.clear();

}

#[cfg(test)]

mod tests {

use super::*;

#[test]

fn parse_cli_args() {

let args = Args::from_args(&["minecraft-proxy"], &["-p", "25565", "-s", "25566"]).unwrap();

assert_eq!(args.port, 25565);

assert_eq!(args.server_port, 25566);

}

#[test]

fn parse_cli_args_long_port() {

let args = Args::from_args(

&["minecraft-proxy"],

&["--port", "25565", "--server-port", "25566"],

)

.unwrap();

assert_eq!(args.port, 25565);

assert_eq!(args.server_port, 25566);

}