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>

1 files changed, 173 insertions, 0 deletions

diff --git a/users/grfn/xanthous/server/src/pty.rs b/users/grfn/xanthous/server/src/pty.rs
new file mode 100644
index 000000000000..611130f5bcd9
--- /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)
+    }
+}