Implement keep-alives.

TODO.md

@@ -2,7 +2,6 @@
 
 ## Functionality
 
-* Keepalives
 * Initial connection flag
 
 ## Unit Test Coverage
@@ -12,6 +11,7 @@
 * NetworkCommunication class
 * Dispatcher class
 * Storage incoming processing
+* Keepalives
 * Notifiers
 * RPC
 * C++ API

src/Dispatcher.cpp

@@ -213,7 +213,9 @@ void DispatcherBase::DispatchThreadMain() {
       bool reconnect = false;
       for (auto& conn : m_connections) {
         // post outgoing messages if connection is active
-        if (conn->state() == NetworkConnection::kActive) conn->PostOutgoing();
+        // only send keep-alives on client
+        if (conn->state() == NetworkConnection::kActive)
+          conn->PostOutgoing(!m_server);
 
         // if client, reconnect if connection died
         if (!m_server && conn->state() == NetworkConnection::kDead)

src/NetworkConnection.cpp

@@ -250,10 +250,18 @@ void NetworkConnection::QueueOutgoing(std::shared_ptr<Message> msg) {
   }
 }
 
-void NetworkConnection::PostOutgoing() {
+void NetworkConnection::PostOutgoing(bool keep_alive) {
   std::lock_guard<std::mutex> lock(m_pending_mutex);
-  if (m_pending_outgoing.empty()) return;
-  m_outgoing.emplace(std::move(m_pending_outgoing));
-  m_pending_outgoing.resize(0);
-  m_pending_update.resize(0);
+  auto now = std::chrono::steady_clock::now();
+  if (m_pending_outgoing.empty()) {
+    if (!keep_alive) return;
+    // send keep-alives once a second (if no other messages have been sent)
+    if ((now - m_last_post) < std::chrono::seconds(1)) return;
+    m_outgoing.emplace(Outgoing{Message::KeepAlive()});
+  } else {
+    m_outgoing.emplace(std::move(m_pending_outgoing));
+    m_pending_outgoing.resize(0);
+    m_pending_update.resize(0);
+  }
+  m_last_post = now;
 }

src/NetworkConnection.h

@@ -9,6 +9,7 @@
 #define NT_NETWORKCONNECTION_H_
 
 #include <atomic>
+#include <chrono>
 #include <memory>
 #include <thread>
 
@@ -56,7 +57,7 @@ class NetworkConnection {
   NetworkStream& stream() { return *m_stream; }
 
   void QueueOutgoing(std::shared_ptr<Message> msg);
-  void PostOutgoing();
+  void PostOutgoing(bool keep_alive);
 
   unsigned int uid() const { return m_uid; }
 
@@ -95,6 +96,7 @@ class NetworkConnection {
   mutable std::mutex m_remote_id_mutex;
   std::string m_remote_id;
   std::atomic_ullong m_last_update;
+  std::chrono::steady_clock::time_point m_last_post;
 
   std::mutex m_pending_mutex;
   Outgoing m_pending_outgoing;