mc-ingress/src/mc_server/mod.rs

use std::{collections::HashMap, sync::Arc};

use async_trait::async_trait;
use tokio::net::TcpStream;
use tracing::Instrument;

use crate::{
    packets::{
        clientbound::status::StatusTrait, serverbound::handshake::Handshake, Packet, SendPacket,
    },
    OpaqueError,
};

pub mod helpers;

#[async_trait::async_trait]
pub trait MinecraftServerHandle: Send + Sync + 'static + Clone {
    async fn start(&self) -> Result<(), OpaqueError>;
    async fn stop(&self) -> Result<(), OpaqueError>;
    async fn query_status(&self) -> Result<ServerDeploymentStatus, OpaqueError>;
    fn get_internal_address(&self) -> &str;
    fn get_internal_id(&self) -> &str;
    fn get_join_addr(&self) -> &str;
    fn get_join_port(&self) -> &str;
    fn get_motd(&self) -> Option<String>;

    async fn query_server_connectable(&self) -> Result<TcpStream, OpaqueError> {
        let address = self.get_internal_address();
        let server_stream = TcpStream::connect(address)
            .await
            .map_err(|_| "failed to connect to minecraft server")?;

        tracing::trace!(
            "successfully connected to backend server; (connectibility check) {:?}",
            server_stream.peer_addr()
        );
        Ok(server_stream)
    }

    /// Takes the already received packets, sends them to the server,
    /// and proceeds to proxy the rest of the connection transparently.
    async fn proxy_status(
        &self,
        handshake: &Handshake,
        status_request: &Packet,
        client_stream: &mut TcpStream,
        server_stream: &mut TcpStream,
    ) -> Result<(), OpaqueError> {
        handshake
            .send_packet(server_stream)
            .await
            .map_err(|_| "failed to forward handshake packet to minecraft server")?;
        status_request
            .send_packet(server_stream)
            .await
            .map_err(|_| "failed to forward status request packet to minecraft server")?;

        let data_amount = tokio::io::copy_bidirectional(client_stream, server_stream)
            .await
            .map_err(|e| {
                format!(
                    "error during bidirectional copy between server and client; err={:?}",
                    e
                )
            })?;
        tracing::trace!("data exchanged while proxying status: {:?}", data_amount);
        Ok(())
    }
    async fn query_description(&self) -> Result<Box<dyn StatusTrait>, OpaqueError> {
        let status = self.query_status().await?;
        match status {
            ServerDeploymentStatus::Connectable(mut tcp_stream) => {
                let handshake = crate::packets::serverbound::handshake::Handshake::create(
                    crate::types::VarInt::from(746).ok_or("could not create VarInt WTF?")?,
                    crate::types::VarString::from(self.get_join_addr().to_string()),
                    crate::types::UShort::from(1234),
                    crate::types::VarInt::from(1).ok_or("could not create VarInt WTF?")?,
                )
                .ok_or("failed to create handshake packet from scratch... WTF?")?;
                handshake
                    .send_packet(&mut tcp_stream)
                    .await
                    .map_err(|_e| "failed to send handshake packet to server")?;
                let status_rq = crate::packets::Packet::from_bytes(0, Vec::new())
                    .ok_or("Failed to create status request packet from scratch")?;
                status_rq
                    .send_packet(&mut tcp_stream)
                    .await
                    .map_err(|_e| "failed to send status request packet to server")?;
                let return_packet = crate::packets::Packet::parse(&mut tcp_stream).await?;
                let status_response =
                    crate::packets::clientbound::status::StatusResponse::parse(return_packet)
                        .await
                        .unwrap();

                return status_response.get_json().ok_or(OpaqueError::create(
                    "failed to parse status response from server",
                ));
            }
            _ => {
                return Err(OpaqueError::create(&format!(
                    "server is not running; status={:?}",
                    status
                )))
            }
        }
    }
}

#[async_trait]
pub trait MinecraftAPI<T>: Send + Sync + 'static {
    async fn query_server(&self, addr: &str, port: &str) -> Result<T, OpaqueError>;
    fn get_map(&self) -> Arc<tokio::sync::Mutex<HashMap<String, tokio::task::JoinHandle<()>>>>;

    /// This should be callable even if there is already a watcher,
    /// and it should handle the collision itself while returning OK().
    async fn start_watch(
        self,
        server: impl MinecraftServerHandle + Send + Sync + 'static,
        frequency: std::time::Duration,
    ) -> Result<(), OpaqueError>
    where
        Self: Clone,
    {
        let internal_id = server.get_internal_id().to_string();

        if let Some(handle) = self.get_map().lock().await.get(&internal_id) {
            if !handle.is_finished() {
                return Ok(());
            }
        }
        let span = tracing::span!(parent: None,tracing::Level::INFO, "server_watcher", internal_id, join_addr = server.get_join_addr(), join_port = server.get_join_port());

        let internal_id_clone = internal_id.clone();
        let api = self.clone();
        let handle = tokio::spawn(
            async move {
                tracing::info!("starting watcher");
                loop {
                    tokio::time::sleep(frequency).await;
                    let status_json = match server.query_description().await {
                        Ok(x) => x,
                        Err(e) => {
                            tracing::error!(
                                err = format!("{}", e.context),
                                "could not query description"
                            );
                            return;
                        }
                    };
                    if status_json.get_players_online() == 0 {
                        // With this I don't need to specify that StatusTrait
                        // should be send as well.

                        // Otherwise I would need to have it be defined as:
                        // trait StatusTrait: Send { ... }
                        drop(status_json);
                        let map = api.get_map();
                        let mut guard = map.lock().await;
                        guard.remove(&internal_id_clone);
                        drop(guard);
                        drop(map);
                        if let Err(err) = server.stop().await {
                            tracing::error!(
                                trace = %err.print_span_trace(),
                                err = err.context,
                                msg = "failed to stop server"
                            );
                        }
                        return;
                    }
                }
            }
            .instrument(span),
        );
        let map = self.get_map();
        let mut guard = map.lock().await;
        guard.insert(internal_id, handle);
        drop(guard);

        Ok(())
    }
}

pub enum ServerDeploymentStatus {
    Connectable(TcpStream),
    Starting,
    PodOk,
    Offline,
    Unavailable(String),
}

pub fn sanitize_addr(addr: &str) -> &str {
    // Thanks to a buggy minecraft, when the client sends a join
    // from a SRV DNS record, it will not use the address typed
    // in the game, but use the address redicted *to* by the
    // DNS record as the address for joining, plus a trailing "."
    //
    // For example:
    // server.example.com (_minecraft._tcp.server.example.com)
    // (the typed address)     I (the DNS SRV record which gets read)
    //                         V
    //            5 25565 server.example.com
    //                         I (the response for the DNS SRV query)
    //                         V
    //                server.example.com.
    //         (the address used in the protocol)
    let addr = addr.trim_end_matches(".");

    // Modded minecraft clients send null terminated strings,
    // after which they have extra data. This just removes them
    // from the addr lookup
    let addr = terminate_at_null(addr);
    addr
}

fn terminate_at_null(str: &str) -> &str {
    match str.split('\0').next() {
        Some(x) => x,
        None => str,
    }
}