feat(gs/xanthous): Add SSH server application r/3015

Add the start of an ssh-compatible server application for playing
Xanthous over ssh. The idea here is that the user can ssh with whatever
username they like (defaulting obviously to their login username) and
then that gets passed as the --name flag to xanthous as they play.

Change-Id: I39eec288ac8e22a165e859479888d78158a58818
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3806
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

2 files changed, 477 insertions, 0 deletions

diff --git a/users/grfn/xanthous/server/src/main.rs b/users/grfn/xanthous/server/src/main.rs
new file mode 100644
index 0000000000..915d1c94db
--- /dev/null
+++ b/users/grfn/xanthous/server/src/main.rs
@@ -0,0 +1,304 @@
+use std::net::SocketAddr;
+
+use std::pin::Pin;
+use std::process::Command;
+use std::sync::Arc;
+
+use clap::Parser;
+use color_eyre::eyre::Result;
+use eyre::{bail, eyre};
+use futures::future::{ready, Ready};
+use futures::Future;
+use nix::pty::Winsize;
+use pty::ChildHandle;
+use thrussh::ChannelId;
+use thrussh::{
+    server::{self, Auth, Session},
+    CryptoVec,
+};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpListener;
+use tokio::select;
+use tracing::{debug, error, info, info_span, trace, warn, Instrument};
+use tracing_subscriber::EnvFilter;
+
+use crate::pty::WaitPid;
+
+mod pty;
+
+/// SSH-compatible server for playing Xanthous
+#[derive(Parser, Debug)]
+struct Opts {
+    /// Address to bind to
+    #[clap(long, short = 'a', default_value = "0.0.0.0:22")]
+    address: String,
+
+    /// Format to use when emitting log events
+    #[clap(
+        long,
+        env = "LOG_FORMAT",
+        default_value = "full",
+        possible_values = &["compact", "full", "pretty", "json"]
+    )]
+    log_format: String,
+
+    /// Full path to the xanthous binary
+    #[clap(long, env = "XANTHOUS_BINARY_PATH")]
+    xanthous_binary_path: String,
+
+    /// Level to log at
+    #[clap(long, env = "LOG_LEVEL", default_value = "info")]
+    log_level: String,
+}
+
+impl Opts {
+    fn ssh_server_config(&self) -> Result<server::Config> {
+        Ok(server::Config {
+            server_id: "SSH-2.0-xanthous".to_owned(),
+            keys: vec![thrussh_keys::key::KeyPair::generate_ed25519()
+                .ok_or_else(|| eyre!("Could not generate ed25519 key"))?],
+            ..Default::default()
+        })
+    }
+
+    fn init_logging(&self) -> Result<()> {
+        let filter = EnvFilter::try_new(&self.log_level)?;
+        let s = tracing_subscriber::fmt().with_env_filter(filter);
+
+        match self.log_format.as_str() {
+            "compact" => s.compact().init(),
+            "full" => s.init(),
+            "pretty" => s.pretty().init(),
+            "json" => s.json().with_current_span(true).init(),
+            _ => bail!("Invalid log format `{}`"),
+        }
+
+        Ok(())
+    }
+}
+
+struct Handler {
+    address: SocketAddr,
+    xanthous_binary_path: &'static str,
+    username: Option<String>,
+    child: Option<ChildHandle>,
+}
+
+async fn run_child(
+    mut child: pty::Child,
+    mut server_handle: server::Handle,
+    channel_id: ChannelId,
+) -> Result<()> {
+    let mut buf = [0; 2048];
+    loop {
+        select! {
+            r = child.tty.read(&mut buf)  => {
+                let read_bytes = r?;
+                if read_bytes == 0 {
+                    info!("EOF received from process");
+                    let _ = server_handle.close(channel_id).await;
+                    return Ok(())
+                } else {
+                    trace!(?read_bytes, "read bytes from child");
+                    let _ = server_handle.data(channel_id, CryptoVec::from_slice(&buf[..read_bytes])).await;
+                }
+            }
+            status = WaitPid::new(child.pid) => {
+                match status {
+                    Ok(_status) => info!("Child exited"),
+                    Err(error) => error!(%error, "Child failed"),
+                }
+                let _ = server_handle.close(channel_id).await;
+                return Ok(())
+            }
+        }
+    }
+}
+
+impl Handler {
+    async fn spawn_shell(
+        &mut self,
+        mut handle: server::Handle,
+        channel_id: ChannelId,
+        term: String,
+        winsize: Winsize,
+    ) -> Result<()> {
+        let mut cmd = Command::new(self.xanthous_binary_path);
+        cmd.env("TERM", term);
+        if let Some(username) = &self.username {
+            cmd.args(["--name", username]);
+        }
+
+        let child = pty::spawn(cmd, Some(winsize), None).await?;
+        info!(pid = %child.pid, "Spawned child");
+        self.child = Some(child.handle().await?);
+        tokio::spawn(
+            async move {
+                let span = info_span!("child", pid = %child.pid);
+                if let Err(error) = run_child(child, handle.clone(), channel_id)
+                    .instrument(span.clone())
+                    .await
+                {
+                    span.in_scope(|| error!(%error, "Error running child"));
+                    let _ = handle.close(channel_id).await;
+                }
+            }
+            .in_current_span(),
+        );
+        Ok(())
+    }
+}
+
+#[allow(clippy::type_complexity)]
+impl server::Handler for Handler {
+    type Error = eyre::Error;
+    type FutureAuth = Ready<Result<(Self, Auth)>>;
+    type FutureUnit = Pin<Box<dyn Future<Output = Result<(Self, Session)>> + Send + 'static>>;
+    type FutureBool = Ready<Result<(Self, Session, bool)>>;
+
+    fn finished_auth(self, auth: Auth) -> Self::FutureAuth {
+        ready(Ok((self, auth)))
+    }
+
+    fn finished_bool(self, b: bool, session: Session) -> Self::FutureBool {
+        ready(Ok((self, session, b)))
+    }
+
+    fn finished(self, session: Session) -> Self::FutureUnit {
+        Box::pin(ready(Ok((self, session))))
+    }
+
+    fn auth_none(mut self, username: &str) -> Self::FutureAuth {
+        info!(%username, "Accepted new connection");
+        self.username = Some(username.to_owned());
+        self.finished_auth(Auth::Accept)
+    }
+
+    fn auth_publickey(
+        mut self,
+        username: &str,
+        _: &thrussh_keys::key::PublicKey,
+    ) -> Self::FutureAuth {
+        info!(%username, "Accepted new connection");
+        self.username = Some(username.to_owned());
+        self.finished_auth(Auth::Accept)
+    }
+
+    fn pty_request(
+        mut self,
+        channel: thrussh::ChannelId,
+        term: &str,
+        col_width: u32,
+        row_height: u32,
+        pix_width: u32,
+        pix_height: u32,
+        modes: &[(thrussh::Pty, u32)],
+        session: Session,
+    ) -> Self::FutureUnit {
+        let term = term.to_owned();
+        let modes = modes.to_vec();
+        Box::pin(async move {
+            debug!(
+                %term,
+                %col_width,
+                %row_height,
+                %pix_width,
+                %pix_height,
+                ?modes,
+                "PTY Requested"
+            );
+
+            self.spawn_shell(
+                session.handle(),
+                channel,
+                term,
+                Winsize {
+                    ws_row: row_height as _,
+                    ws_col: col_width as _,
+                    ws_xpixel: pix_width as _,
+                    ws_ypixel: pix_height as _,
+                },
+            )
+            .await?;
+
+            Ok((self, session))
+        })
+    }
+
+    fn window_change_request(
+        mut self,
+        _channel: ChannelId,
+        col_width: u32,
+        row_height: u32,
+        pix_width: u32,
+        pix_height: u32,
+        session: Session,
+    ) -> Self::FutureUnit {
+        Box::pin(async move {
+            if let Some(child) = self.child.as_mut() {
+                trace!(%row_height, %col_width, "Window resize request received");
+                child
+                    .resize_window(Winsize {
+                        ws_row: row_height as _,
+                        ws_col: col_width as _,
+                        ws_xpixel: pix_width as _,
+                        ws_ypixel: pix_height as _,
+                    })
+                    .await?;
+            } else {
+                warn!("Resize request received without child process; ignoring");
+            }
+
+            Ok((self, session))
+        })
+    }
+
+    fn data(
+        mut self,
+        _channel: thrussh::ChannelId,
+        data: &[u8],
+        session: Session,
+    ) -> Self::FutureUnit {
+        trace!(data = %String::from_utf8_lossy(data), raw_data = ?data);
+        let data = data.to_owned();
+        Box::pin(async move {
+            if let Some(child) = self.child.as_mut() {
+                child.write_all(&data).await?;
+            } else {
+                warn!("Data received without child process; ignoring");
+            }
+
+            Ok((self, session))
+        })
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    color_eyre::install()?;
+    let opts = Box::leak::<'static>(Box::new(Opts::parse()));
+    opts.init_logging()?;
+    let config = Arc::new(opts.ssh_server_config()?);
+    info!(address = %opts.address, "Listening for new SSH connections");
+    let listener = TcpListener::bind(&opts.address).await?;
+
+    loop {
+        let (stream, address) = listener.accept().await?;
+        let config = config.clone();
+        let handler = Handler {
+            xanthous_binary_path: &opts.xanthous_binary_path,
+            address,
+            username: None,
+            child: None,
+        };
+        tokio::spawn(async move {
+            let span = info_span!("client", address = %handler.address);
+            if let Err(error) = server::run_stream(config, stream, handler)
+                .instrument(span.clone())
+                .await
+            {
+                span.in_scope(|| error!(%error));
+            }
+        });
+    }
+}
diff --git a/users/grfn/xanthous/server/src/pty.rs b/users/grfn/xanthous/server/src/pty.rs
new file mode 100644
index 0000000000..611130f5bc
--- /dev/null
+++ b/users/grfn/xanthous/server/src/pty.rs
@@ -0,0 +1,173 @@
+use std::io::{self};
+use std::os::unix::prelude::{AsRawFd, CommandExt, FromRawFd};
+use std::pin::Pin;
+use std::process::{abort, Command};
+use std::task::{Context, Poll};
+
+use eyre::{bail, Result};
+use futures::Future;
+use nix::pty::forkpty;
+use nix::pty::Winsize;
+use nix::sys::termios::Termios;
+use nix::sys::wait::{waitpid, WaitPidFlag, WaitStatus};
+use nix::unistd::{ForkResult, Pid};
+use tokio::fs::File;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tokio::signal::unix::{signal, Signal, SignalKind};
+use tokio::task::spawn_blocking;
+
+mod ioctl {
+    use super::Winsize;
+    use libc::TIOCSWINSZ;
+    use nix::ioctl_write_ptr_bad;
+
+    ioctl_write_ptr_bad!(tiocswinsz, TIOCSWINSZ, Winsize);
+}
+
+async fn asyncify<F, T>(f: F) -> Result<T>
+where
+    F: FnOnce() -> Result<T> + Send + 'static,
+    T: Send + 'static,
+{
+    match spawn_blocking(f).await {
+        Ok(res) => res,
+        Err(_) => bail!("background task failed",),
+    }
+}
+
+pub struct Child {
+    pub tty: File,
+    pub pid: Pid,
+}
+
+pub struct ChildHandle {
+    pub tty: File,
+}
+
+pub struct WaitPid {
+    pid: Pid,
+    signal: Signal,
+}
+
+impl WaitPid {
+    pub fn new(pid: Pid) -> Self {
+        Self {
+            pid,
+            signal: signal(SignalKind::child()).unwrap(),
+        }
+    }
+}
+
+impl Future for WaitPid {
+    type Output = nix::Result<WaitStatus>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let _ = self.signal.poll_recv(cx);
+        match waitpid(self.pid, Some(WaitPidFlag::WNOHANG)) {
+            Ok(WaitStatus::StillAlive) => Poll::Pending,
+            result => Poll::Ready(result),
+        }
+    }
+}
+
+impl Child {
+    pub async fn handle(&self) -> io::Result<ChildHandle> {
+        Ok(ChildHandle {
+            tty: self.tty.try_clone().await?,
+        })
+    }
+}
+
+impl ChildHandle {
+    pub async fn resize_window(&mut self, winsize: Winsize) -> Result<()> {
+        let fd = self.tty.as_raw_fd();
+        asyncify(move || unsafe {
+            ioctl::tiocswinsz(fd, &winsize as *const Winsize)?;
+            Ok(())
+        })
+        .await
+    }
+}
+
+pub async fn spawn(
+    mut cmd: Command,
+    winsize: Option<Winsize>,
+    termios: Option<Termios>,
+) -> Result<Child> {
+    asyncify(move || unsafe {
+        let res = forkpty(winsize.as_ref(), termios.as_ref())?;
+        match res.fork_result {
+            ForkResult::Parent { child } => Ok(Child {
+                pid: child,
+                tty: File::from_raw_fd(res.master),
+            }),
+            ForkResult::Child => {
+                cmd.exec();
+                abort();
+            }
+        }
+    })
+    .await
+}
+
+impl AsyncRead for Child {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut tokio::io::ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.tty).poll_read(cx, buf)
+    }
+}
+
+impl AsyncWrite for Child {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        Pin::new(&mut self.tty).poll_write(cx, buf)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.tty).poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.tty).poll_shutdown(cx)
+    }
+}
+
+impl AsyncRead for ChildHandle {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut tokio::io::ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.tty).poll_read(cx, buf)
+    }
+}
+
+impl AsyncWrite for ChildHandle {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        Pin::new(&mut self.tty).poll_write(cx, buf)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.tty).poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.tty).poll_shutdown(cx)
+    }
+}