ptyd: harden against transient scan/event-queue errors

Replace two panics (initial scan_requests expect, event-queue read
expect) and a socket-event break with error logging + continuation. A
transient error reading the event queue or scanning requests must not
kill ptyd and take the whole pty subsystem down with it.

(Change found as uncommitted work in the fork; committing to preserve
it and unblock the clean-fork build gate.)

ptyd/src/main.rs

@@ -62,20 +62,32 @@ fn daemon(daemon: daemon::SchemeDaemon) -> ! {
 
     let mut timeout_count = 0u64;
 
-    scan_requests(&mut handler, &mut scheme).expect("pty: could not scan requests");
+    if let Err(err) = scan_requests(&mut handler, &mut scheme) {
+        eprintln!("ptyd: initial scan_requests failed: {err:?}");
+    }
     issue_events(&socket, &mut scheme);
 
     for event_res in event_queue {
-        let event = event_res.expect("pty: failed to read from event queue");
+        let event = match event_res {
+            Ok(event) => event,
+            Err(err) => {
+                // A transient event-queue read error must not kill ptyd. Log and
+                // wait for the next event rather than panicking.
+                eprintln!("ptyd: event queue read failed: {err:?}; continuing");
+                continue;
+            }
+        };
 
         match event.user_data {
             EventSource::Socket => {
-                if scan_requests(&mut handler, &mut scheme).is_err() {
-                    break;
+                if let Err(err) = scan_requests(&mut handler, &mut scheme) {
+                    eprintln!("ptyd: scan_requests failed: {err:?}; continuing");
                 }
             }
             EventSource::Time => {
-                timeout(&mut time_file).expect("pty: failed to set timeout");
+                if let Err(err) = timeout(&mut time_file) {
+                    eprintln!("ptyd: failed to set timeout: {err:?}");
+                }
 
                 timeout_count = timeout_count.wrapping_add(1);
 
@@ -85,9 +97,9 @@ fn daemon(daemon: daemon::SchemeDaemon) -> ! {
                     }
                 }
 
-                handler
-                    .poll_all_requests(&mut scheme)
-                    .expect("ihdad: failed to poll requests");
+                if let Err(err) = handler.poll_all_requests(&mut scheme) {
+                    eprintln!("ptyd: poll_all_requests failed: {err:?}; continuing");
+                }
             }
         }
 
@@ -101,15 +113,13 @@ fn scan_requests(
     handler: &mut ReadinessBased<'_>,
     scheme: &mut PtyScheme,
 ) -> libredox::error::Result<()> {
-    handler
-        .read_and_process_requests(scheme)
-        .expect("pty: failed to read from socket");
-    handler
-        .poll_all_requests(scheme)
-        .expect("pty: error occured in poll_all_requests");
-    handler
-        .write_responses()
-        .expect("pty: failed to write to socket");
+    // Propagate errors instead of panicking: a transient/error return here must
+    // NOT crash ptyd — it is the sole provider of the `pty` scheme, so a panic
+    // takes down every pty (and thus every getty/login/shell console) at once.
+    // The caller logs and continues on error, keeping ptyd alive.
+    handler.read_and_process_requests(scheme)?;
+    handler.poll_all_requests(scheme)?;
+    handler.write_responses()?;
     Ok(())
 }
 
@@ -118,13 +128,14 @@ fn issue_events(socket: &Socket, scheme: &mut PtyScheme) {
         if let Handle::Resource(ref mut res) = handle {
             let events = res.events();
             if events != syscall::EventFlags::empty() {
-                socket
-                    .write_response(
-                        Response::post_fevent(*id, events.bits()),
-                        SignalBehavior::Restart,
-                    )
-                    .expect("pty: failed to send scheme event");
+                if let Err(err) = socket.write_response(
+                    Response::post_fevent(*id, events.bits()),
+                    SignalBehavior::Restart,
+                ) {
+                    eprintln!("ptyd: failed to send scheme event for handle {id}: {err:?}");
+                }
             }
+
         }
     }
 }