[wpiutil] WebSocket: Add GetLastReceivedTime

This allows getting the timestamp that any data has been received.

wpinet/src/main/native/cpp/WebSocket.cpp

@@ -418,6 +418,8 @@ static inline void Unmask(std::span<uint8_t> data,
 }
 
 void WebSocket::HandleIncoming(uv::Buffer& buf, size_t size) {
+  m_lastReceivedTime = m_stream.GetLoopRef().Now().count();
+
   // ignore incoming data if we're failed or closed
   if (m_state == FAILED || m_state == CLOSED) {
     return;

wpinet/src/main/native/include/wpinet/WebSocket.h

@@ -457,6 +457,12 @@ class WebSocket : public std::enable_shared_from_this<WebSocket> {
    */
   void Shutdown();
 
+  /**
+   * Gets the last time data was received on the stream.
+   * @return Timestamp
+   */
+  uint64_t GetLastReceivedTime() const { return m_lastReceivedTime; }
+
   /**
    * Open event.  Emitted when the connection is open and ready to communicate.
    * The parameter is the selected subprotocol.
@@ -521,6 +527,7 @@ class WebSocket : public std::enable_shared_from_this<WebSocket> {
   State m_state = CONNECTING;
 
   // incoming message buffers/state
+  uint64_t m_lastReceivedTime = 0;
   SmallVector<uint8_t, 14> m_header;
   size_t m_headerSize = 0;
   SmallVector<uint8_t, 1024> m_payload;