Suppress errors for requested session stops

server/src/session/process.rs

@@ -30,6 +30,7 @@ use anyhow::{Context, Result};
 use serde::{Deserialize, Serialize};
 
 const RECORD_FILE: &str = "process.json";
+const STOP_REQUEST_FILE: &str = "stop-requested";
 
 /// A process this server started and expects to outlive it.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -101,6 +102,28 @@ fn path(session_dir: &Path) -> PathBuf {
     session_dir.join(RECORD_FILE)
 }
 
+fn stop_request_path(session_dir: &Path) -> PathBuf {
+    session_dir.join(STOP_REQUEST_FILE)
+}
+
+/// Marks the process as one the server deliberately asked to end, so its watcher reports an exit
+/// without presenting ordinary stderr from the process's lifetime as the cause.
+pub fn mark_stopping(session_dir: &Path) -> Result<()> {
+    std::fs::OpenOptions::new()
+        .create(true)
+        .write(true)
+        .truncate(true)
+        .mode(0o600)
+        .open(stop_request_path(session_dir))
+        .with_context(|| format!("marking {} as stopping", session_dir.display()))?;
+    Ok(())
+}
+
+/// Whether this process's exit was deliberately requested.
+pub fn stopping(session_dir: &Path) -> bool {
+    stop_request_path(session_dir).is_file()
+}
+
 /// The recorded process and whether it is still there, or `None` when nothing
 /// usable is recorded. A record that does not parse reads as no record: the
 /// only way to get one is a crash partway through writing it, and the safe
@@ -179,11 +202,12 @@ pub fn size_of(path: &Path) -> u64 {
 /// Forgets the recorded process -- for one confirmed dead, or a session
 /// being deleted. The path out for [`write`].
 pub fn clear(session_dir: &Path) {
-    let path = path(session_dir);
-    if let Err(err) = std::fs::remove_file(&path)
-        && err.kind() != std::io::ErrorKind::NotFound
-    {
-        tracing::warn!("couldn't remove {}: {err}", path.display());
+    for path in [path(session_dir), stop_request_path(session_dir)] {
+        if let Err(err) = std::fs::remove_file(&path)
+            && err.kind() != std::io::ErrorKind::NotFound
+        {
+            tracing::warn!("couldn't remove {}: {err}", path.display());
+        }
     }
 }
 
@@ -405,8 +429,11 @@ mod tests {
         write(dir.path(), &record);
         assert_eq!(live(dir.path()), Some(record));
 
+        mark_stopping(dir.path()).expect("mark stopping");
+        assert!(stopping(dir.path()));
         clear(dir.path());
         assert_eq!(live(dir.path()), None);
+        assert!(!stopping(dir.path()));
     }
 
     #[test]