Add ping interval to constructor params for WebSocketServer (#497)

* Update .gitignore for CLion compatibility

* Add pingIntervalSeconds to constructor for WebSocketServer

* Add Heartbeat section to WebSocketServer usage documentation

* Fix typo

.gitignore

@@ -8,3 +8,5 @@ ws/.srl
 ixhttpd
 makefile
 a.out
+.idea/
+cmake-build-debug/

docs/usage.md

@@ -445,6 +445,17 @@ server.wait();
 
 ```
 
+### Heartbeat
+
+You can configure an optional heartbeat / keep-alive for the WebSocket server. The heartbeat interval can be adjusted or disabled when constructing the `WebSocketServer`. Setting the interval to `-1` disables the heartbeat feature; this is the default setting. The parameter you set will be applied to every `WebSocket` object that the server creates.
+
+To enable a 45 second heartbeat on a `WebSocketServer`:
+
+```cpp
+int pingIntervalSeconds = 45;
+ix::WebSocketServer server(port, host, backlog, maxConnections, handshakeTimeoutSecs, addressFamily, pingIntervalSeconds);
+```
+
 ## HTTP client API
 
 ```cpp

ixwebsocket/IXWebSocketServer.cpp

@@ -19,17 +19,20 @@ namespace ix
 {
     const int WebSocketServer::kDefaultHandShakeTimeoutSecs(3); // 3 seconds
     const bool WebSocketServer::kDefaultEnablePong(true);
+    const int WebSocketServer::kPingIntervalSeconds(-1); // disable heartbeat
 
     WebSocketServer::WebSocketServer(int port,
                                      const std::string& host,
                                      int backlog,
                                      size_t maxConnections,
                                      int handshakeTimeoutSecs,
-                                     int addressFamily)
+                                     int addressFamily,
+                                     int pingIntervalSeconds)
         : SocketServer(port, host, backlog, maxConnections, addressFamily)
         , _handshakeTimeoutSecs(handshakeTimeoutSecs)
         , _enablePong(kDefaultEnablePong)
         , _enablePerMessageDeflate(true)
+        , _pingIntervalSeconds(pingIntervalSeconds)
     {
     }
 
@@ -93,6 +96,7 @@ namespace ix
         auto webSocket = std::make_shared<WebSocket>();
 
         webSocket->setAutoThreadName(false);
+        webSocket->setPingInterval(_pingIntervalSeconds);
 
         if (_onConnectionCallback)
         {

ixwebsocket/IXWebSocketServer.h

@@ -33,7 +33,8 @@ namespace ix
                         int backlog = SocketServer::kDefaultTcpBacklog,
                         size_t maxConnections = SocketServer::kDefaultMaxConnections,
                         int handshakeTimeoutSecs = WebSocketServer::kDefaultHandShakeTimeoutSecs,
-                        int addressFamily = SocketServer::kDefaultAddressFamily);
+                        int addressFamily = SocketServer::kDefaultAddressFamily,
+                        int pingIntervalSeconds = WebSocketServer::kPingIntervalSeconds);
         virtual ~WebSocketServer();
         virtual void stop() final;
 
@@ -61,6 +62,7 @@ namespace ix
         int _handshakeTimeoutSecs;
         bool _enablePong;
         bool _enablePerMessageDeflate;
+        int _pingIntervalSeconds;
 
         OnConnectionCallback _onConnectionCallback;
         OnClientMessageCallback _onClientMessageCallback;
@@ -69,6 +71,7 @@ namespace ix
         std::set<std::shared_ptr<WebSocket>> _clients;
 
         const static bool kDefaultEnablePong;
+        const static int kPingIntervalSeconds;
 
         // Methods
         virtual void handleConnection(std::unique_ptr<Socket> socket,