transport: replace a bunch of bools with a proper state machine

Change-Id: I42f74aebfd714cd8b3be7fcb3068228935482366

ndn-cxx/face.cpp

@@ -292,7 +292,7 @@ Face::shutdown()
 {
   IO_CAPTURE_WEAK_IMPL(post) {
     impl->shutdown();
-    if (m_transport->isConnected())
+    if (m_transport->getState() != Transport::State::CLOSED)
       m_transport->close();
   } IO_CAPTURE_WEAK_IMPL_END
 }

ndn-cxx/impl/face-impl.hpp

@@ -304,12 +304,12 @@ public: // IO routine
   void
   ensureConnected(bool wantResume)
   {
-    if (!m_face.m_transport->isConnected()) {
+    if (m_face.m_transport->getState() == Transport::State::CLOSED) {
       m_face.m_transport->connect(m_face.getIoService(),
                                   [this] (const Block& wire) { m_face.onReceiveElement(wire); });
     }
 
-    if (wantResume && !m_face.m_transport->isReceiving()) {
+    if (wantResume) {
       m_face.m_transport->resume();
     }
   }

ndn-cxx/transport/detail/stream-transport-impl.hpp

@@ -55,10 +55,10 @@ public:
   void
   connect(const typename Protocol::endpoint& endpoint)
   {
-    if (m_isConnecting) {
+    if (m_transport.getState() == Transport::State::CONNECTING) {
       return;
     }
-    m_isConnecting = true;
+    m_transport.setState(Transport::State::CONNECTING);
 
     // Wait at most 4 seconds to connect
     /// @todo Decide whether this number should be configurable
@@ -76,38 +76,30 @@ public:
   void
   close()
   {
-    m_isConnecting = false;
+    m_transport.setState(Transport::State::CLOSED);
 
     boost::system::error_code error; // to silently ignore all errors
     m_connectTimer.cancel(error);
     m_socket.cancel(error);
     m_socket.close(error);
 
-    m_transport.m_isConnected = false;
-    m_transport.m_isReceiving = false;
     TransmissionQueue{}.swap(m_transmissionQueue); // clear the queue
   }
 
   void
   pause()
   {
-    if (m_isConnecting)
-      return;
-
-    if (m_transport.m_isReceiving) {
-      m_transport.m_isReceiving = false;
+    if (m_transport.getState() == Transport::State::RUNNING) {
       m_socket.cancel();
+      m_transport.setState(Transport::State::PAUSED);
     }
   }
 
   void
   resume()
   {
-    if (m_isConnecting)
-      return;
-
-    if (!m_transport.m_isReceiving) {
-      m_transport.m_isReceiving = true;
+    if (m_transport.getState() == Transport::State::PAUSED) {
+      m_transport.setState(Transport::State::RUNNING);
       m_inputBufferSize = 0;
       asyncReceive();
     }
@@ -118,7 +110,9 @@ public:
   {
     m_transmissionQueue.push(block);
 
-    if (m_transport.m_isConnected && m_transmissionQueue.size() == 1) {
+    if (m_transport.getState() != Transport::State::CLOSED &&
+        m_transport.getState() != Transport::State::CONNECTING &&
+        m_transmissionQueue.size() == 1) {
       asyncWrite();
     }
     // if not connected or there's another transmission in progress (m_transmissionQueue.size() > 1),
@@ -129,16 +123,14 @@ protected:
   void
   connectHandler(const boost::system::error_code& error)
   {
-    m_isConnecting = false;
     m_connectTimer.cancel();
 
     if (error) {
-      m_transport.m_isConnected = false;
       m_transport.close();
       NDN_THROW(Transport::Error(error, "error while connecting to the forwarder"));
     }
 
-    m_transport.m_isConnected = true;
+    m_transport.setState(Transport::State::PAUSED);
 
     if (!m_transmissionQueue.empty()) {
       resume();
@@ -172,8 +164,8 @@ protected:
           NDN_THROW(Transport::Error(error, "error while writing data to socket"));
         }
 
-        if (!m_transport.m_isConnected) {
-          return; // queue has been already cleared
+        if (m_transport.getState() == Transport::State::CLOSED) {
+          return; // queue has already been cleared
         }
 
         BOOST_ASSERT(!m_transmissionQueue.empty());
@@ -249,7 +241,6 @@ protected:
   size_t m_inputBufferSize = 0;
   TransmissionQueue m_transmissionQueue;
   boost::asio::steady_timer m_connectTimer;
-  bool m_isConnecting = false;
 };
 
 } // namespace detail

ndn-cxx/transport/detail/stream-transport-with-resolver-impl.hpp

@@ -42,10 +42,10 @@ public:
   void
   connect(const typename Protocol::resolver::query& query)
   {
-    if (this->m_isConnecting) {
+    if (this->m_transport.getState() == Transport::State::CONNECTING) {
       return;
     }
-    this->m_isConnecting = true;
+    this->m_transport.setState(Transport::State::CONNECTING);
 
     // Wait at most 4 seconds to connect
     /// @todo Decide whether this number should be configurable

ndn-cxx/transport/transport.hpp

@@ -30,7 +30,8 @@
 
 namespace ndn {
 
-/** \brief Provides TLV-block delivery service.
+/**
+ * \brief Provides a "TLV-oriented" delivery service.
  */
 class Transport : noncopyable
 {
@@ -43,9 +44,16 @@ public:
     Error(const boost::system::error_code& code, const std::string& msg);
   };
 
-  using ReceiveCallback = std::function<void(const Block& wire)>;
-  using ErrorCallback = std::function<void()>;
+  enum class State {
+    CLOSED,
+    CONNECTING,
+    RUNNING,
+    PAUSED,
+  };
 
+  using ReceiveCallback = std::function<void(const Block&)>;
+
+public:
   virtual
   ~Transport() = default;
 
@@ -89,29 +97,27 @@ public:
   resume() = 0;
 
   /**
-   * \brief Return whether the transport is connected.
+   * \brief Return the current state of the transport.
    */
-  bool
-  isConnected() const noexcept
+  State
+  getState() const noexcept
   {
-    return m_isConnected;
+    return m_state;
   }
 
-  /**
-   * \retval true incoming packets are expected, the receive callback will be invoked
-   * \retval false incoming packets are not expected, the receive callback will not be invoked
-   */
-  bool
-  isReceiving() const noexcept
+protected:
+  void
+  setState(State state) noexcept
   {
-    return m_isReceiving;
+    m_state = state;
   }
 
 protected:
   boost::asio::io_service* m_ioService = nullptr;
   ReceiveCallback m_receiveCallback;
-  bool m_isConnected = false;
-  bool m_isReceiving = false;
+
+private:
+  State m_state = State::CLOSED;
 };
 
 } // namespace ndn