docs: Add guide on how to simulate real apps in ndnSIM

Change-Id: I3694a8791b9540fc1b926a83ff55421b47e0f2a2
diff --git a/examples/ndn-cxx-simple/real-app.hpp b/examples/ndn-cxx-simple/real-app.hpp
new file mode 100644
index 0000000..0aa2f38
--- /dev/null
+++ b/examples/ndn-cxx-simple/real-app.hpp
@@ -0,0 +1,77 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2011-2015  Regents of the University of California.
+ *
+ * This file is part of ndnSIM. See AUTHORS for complete list of ndnSIM authors and
+ * contributors.
+ *
+ * ndnSIM is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * ndnSIM is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * ndnSIM, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+#ifndef NDNSIM_EXAMPLES_NDN_CXX_SIMPLE_REAL_APP_HPP
+#define NDNSIM_EXAMPLES_NDN_CXX_SIMPLE_REAL_APP_HPP
+
+#include <ndn-cxx/face.hpp>
+#include <ndn-cxx/interest.hpp>
+#include <ndn-cxx/security/key-chain.hpp>
+#include <ndn-cxx/util/scheduler.hpp>
+
+#include <iostream>
+
+namespace app {
+
+class RealApp
+{
+public:
+  RealApp(ndn::KeyChain& keyChain)
+    : m_keyChain(keyChain)
+    , m_faceProducer(m_faceConsumer.getIoService())
+    , m_scheduler(m_faceConsumer.getIoService())
+  {
+    // register prefix and set interest filter on producer face
+    m_faceProducer.setInterestFilter("/hello", std::bind(&RealApp::respondToAnyInterest, this, _2),
+                                     std::bind([]{}), std::bind([]{}));
+
+    // use scheduler to send interest later on consumer face
+    m_scheduler.scheduleEvent(ndn::time::seconds(2), [this] {
+        m_faceConsumer.expressInterest(ndn::Interest("/hello/world"),
+                                       std::bind([] { std::cout << "Hello!" << std::endl; }),
+                                       std::bind([] { std::cout << "Bye!.." << std::endl; }));
+      });
+  }
+
+  void
+  run()
+  {
+    m_faceConsumer.processEvents(); // ok (will not block and do nothing)
+    // m_faceConsumer.getIoService().run(); // will crash
+  }
+
+private:
+  void
+  respondToAnyInterest(const ndn::Interest& interest)
+  {
+    auto data = std::make_shared<ndn::Data>(interest.getName());
+    m_keyChain.sign(*data);
+    m_faceProducer.put(*data);
+  }
+
+private:
+  ndn::KeyChain& m_keyChain;
+  ndn::Face m_faceConsumer;
+  ndn::Face m_faceProducer;
+  ndn::Scheduler m_scheduler;
+};
+
+} // namespace app
+
+#endif // NDNSIM_EXAMPLES_NDN_CXX_SIMPLE_REAL_APP_HPP