Notify superseded plugin processes and support SDK draining

sdk/tests/wasi.rs

@@ -201,6 +201,88 @@ fn protocol() {
     assert_eq!(outgoing["method"], "other.background");
     p.answer(&outgoing, json!({}));
     assert!(p.child.wait().unwrap().success());
+    // Replacement is a notification, not EOF. Drain keeps both endpoint handlers
+    // and background calls alive, while closing idle connections and the listener.
+    assert!(
+        !d["result"]["methods"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .any(|m| m["name"] == "rpc.superseded" || m["name"] == "superseded")
+    );
+    std::fs::remove_file(dir.join("stopped")).unwrap();
+    let mut provider = start(&wasm, &dir);
+    provider.request("serve", json!({}));
+    assert_eq!(provider.read()["result"], Value::Null);
+    provider.request("start", json!({}));
+    let first = provider.read();
+    let second = provider.read();
+    let background = if first["method"] == "other.background" {
+        first
+    } else {
+        second
+    };
+    assert_eq!(background["method"], "other.background");
+    let address = std::fs::read_to_string(dir.join("endpoint"))
+        .unwrap()
+        .split_whitespace()
+        .next()
+        .unwrap()
+        .trim_start_matches("tcp:")
+        .to_owned();
+    let mut idle = std::net::TcpStream::connect(&address).unwrap();
+    idle.set_read_timeout(Some(std::time::Duration::from_secs(4)))
+        .unwrap();
+    writeln!(
+        idle,
+        "{}",
+        json!({"jsonrpc":"2.0","id":0,"method":"rpc.endpoint","params":{}})
+    )
+    .unwrap();
+    let mut idle = BufReader::new(idle);
+    let mut line = String::new();
+    idle.read_line(&mut line).unwrap();
+    assert_eq!(
+        sausage_plugin::serde_json::from_str::<Value>(&line).unwrap()["id"],
+        0
+    );
+    let mut active = std::net::TcpStream::connect(&address).unwrap();
+    active
+        .set_read_timeout(Some(std::time::Duration::from_secs(4)))
+        .unwrap();
+    writeln!(
+        active,
+        "{}",
+        json!({"jsonrpc":"2.0","id":1,"method":"wait","params":{}})
+    )
+    .unwrap();
+    let inflight = provider.read();
+    assert_eq!(inflight["method"], "other.inflight");
+    provider
+        .send(json!({"jsonrpc":"2.0","method":"rpc.superseded","params":{"current":"new-hash"}}));
+    let hook = provider.read();
+    assert_eq!(hook["method"], "other.superseded");
+    assert_eq!(hook["params"]["current"], "new-hash");
+    provider.answer(&hook, json!({}));
+    assert_eq!(provider.read()["params"]["name"], "draining");
+    line.clear();
+    assert_eq!(idle.read_line(&mut line).unwrap(), 0);
+    assert!(std::net::TcpStream::connect(&address).is_err());
+    assert!(provider.child.try_wait().unwrap().is_none());
+    provider.answer(&inflight, json!({}));
+    line.clear();
+    BufReader::new(active).read_line(&mut line).unwrap();
+    assert_eq!(
+        sausage_plugin::serde_json::from_str::<Value>(&line).unwrap()["result"],
+        "finished"
+    );
+    assert!(provider.child.try_wait().unwrap().is_none());
+    provider.answer(&background, json!({}));
+    provider.finishes();
+    assert!(
+        !dir.join("stopped").exists(),
+        "drain is not the EOF stop hook"
+    );
     let provider_doc = &d["result"];
     let imports = target.join("imports");
     std::fs::create_dir_all(&imports).unwrap();