Add -open? method to Socket protocol

SPEC-alpha.md

@@ -274,14 +274,15 @@ A socket must satisfy the `ring.websocket/Socket` protocol:
 
 ```clojure
 (defprotocol Socket
+  (-open? [socket])
   (-send  [socket message])
   (-ping  [socket data])
   (-pong  [socket data])
   (-close [socket status reason]))
 ```
 
 The types of the arguments are the same as those described for the
-`Listener` protocol.
+`Listener` protocol. The `-open?` method must return true or false.
 
 It *may* optionally satisfy the `ring.websocket/AsyncSocket` protocol:
 

ring-core/src/ring/websocket.clj

@@ -15,7 +15,7 @@
     "Called when a pong is received in response to an earlier ping. The client
     may provide additional binary data, represented by the data ByteBuffer.")
   (on-error [listener socket throwable]
-    "Called when an Throwable error is thrown.")
+    "Called when a Throwable error is thrown.")
   (on-close [listener socket code reason]
     "Called when the websocket is closed, along with an integer code and a
     plaintext string reason for being closed."))
@@ -35,6 +35,8 @@
 
 (defprotocol Socket
   "A protocol for sending data via websocket."
+  (-open? [socket]
+    "Returns true if the socket is open; false otherwise.")
   (-send [socket message]
     "Sends a String or ByteBuffer to the client via the websocket.")
   (-ping [socket data]
@@ -83,6 +85,9 @@
     :else (throw (ex-info "message is not a valid text or binary data type"
                           {:message message}))))
 
+(defn open? [socket]
+  (boolean (-open? socket)))
+
 (defn send
   "Sends text or binary data via a websocket, either synchronously or
   asynchronously with callback functions. A convenient wrapper for the -send and

ring-jetty-adapter/src/ring/adapter/jetty.clj

@@ -37,6 +37,8 @@
   (let [remote (.getRemote session)]
     (reify
       ws/Socket
+      (-open? [_]
+        (.isOpen session))
       (-send [_ message]
         (if (string? message)
           (.sendString remote message)

ring-jetty-adapter/test/ring/adapter/test/jetty.clj

@@ -718,6 +718,26 @@
       (is (= [[:ping "foo"] [:pong "foo"]]
              @log))))
 
+  (testing "open?"
+    (let [log     (atom [])
+          handler (constantly
+                   {::ws/listener
+                    (reify ws/Listener
+                      (on-open [_ sock]
+                        (swap! log conj [:open? (ws/open? sock)])
+                        (ws/close sock)
+                        (swap! log conj [:open? (ws/open? sock)]))
+                      (on-message [_ _ _])
+                      (on-pong [_ _ data])
+                      (on-error [_ _ _])
+                      (on-close [_ _ code reason]
+                        (swap! log conj [:close])))})]
+      (with-server handler {:port test-port}
+        (hato/websocket test-websocket-url {})
+        (Thread/sleep 100))
+      (is (= [[:open? true] [:open? false] [:close]]
+             @log))))
+
   (testing "sending websocket messages asynchronously"
     (let [log     (atom [])
           handler (constantly