Allow construction of websocket pong messages (#800)

Fixes #782

src/filters/ws.rs

@@ -291,6 +291,17 @@ impl Message {
         }
     }
 
+    /// Construct a new Pong `Message`.
+    ///
+    /// Note that one rarely needs to manually construct a Pong message because the underlying tungstenite socket
+    /// automatically responds to the Ping messages it receives. Manual construction might still be useful in some cases
+    /// like in tests or to send unidirectional heartbeats.
+    pub fn pong<V: Into<Vec<u8>>>(v: V) -> Message {
+        Message {
+            inner: protocol::Message::Pong(v.into()),
+        }
+    }
+
     /// Construct the default Close `Message`.
     pub fn close() -> Message {
         Message {

tests/ws.rs

@@ -149,6 +149,28 @@ async fn echo_pings() {
     assert_eq!(msg.as_bytes(), &b"clt"[..]);
 }
 
+#[tokio::test]
+async fn pongs_only() {
+    let _ = pretty_env_logger::try_init();
+
+    let mut client = warp::test::ws()
+        .handshake(ws_echo())
+        .await
+        .expect("handshake");
+
+    // construct a pong message and make sure it is correct
+    let msg = Message::pong("clt");
+    assert!(msg.is_pong());
+    assert_eq!(msg.as_bytes(), &b"clt"[..]);
+
+    // send it to echo and wait for `ws_echo` to send it back
+    client.send(msg).await;
+
+    let msg = client.recv().await.expect("recv");
+    assert!(msg.is_pong());
+    assert_eq!(msg.as_bytes(), &b"clt"[..]);
+}
+
 #[tokio::test]
 async fn closed() {
     let _ = pretty_env_logger::try_init();