server/callback-server-json/main.cpp

Author

Pascal JEAN, aka epsilonrt

Copyright

GNU Lesser General Public License

#include <csignal>
#include <thread>
#include <iostream>
#include <modbuspp.h>

using namespace std;
using namespace Modbus;

Server srv; // instantiates new MODBUS Server

/* -----------------------------------------------------------------------------
 * Incoming message handler
 * This function is called each time a MODBUS message is received by the Server
 * class on the backend network (TCP-IP or OSL).
 * Here the function analyzes the message, if it is a message for reading input
 * registers (FC 4), a response is constructed which sends dummy values which
 * are incremented with each reading. The response is sent using the
 * sendRawMessage() function, which automatically completes the message with a
 * header or CRC.
 */
int messageHandler (Message * req, Device * dev) {

  cout << "Receive message, size : " << req->aduSize() << endl;
  if (req->function() == ReadInputRegisters) {
    // the dummy word will be the returned value, incremented after each reading
    static uint16_t dummy = 1;

    // get request parameters
    uint16_t N = req->quantity();
    uint16_t index = req->startingAddress();

    // build response, see page 16 of MODBUS Application Protocol Specification
    Response rsp (*req); // uses copy constructor to keep transaction id
    rsp.setSize (1); // keep until function code
    rsp.setByteCount (N * 2);
    for (uint16_t i = 0; i < N; i++) {

      rsp.setRegisterValue (index + i, dummy++);
    }

    return dev->sendRawMessage (rsp, true);
  }
  return 0;
}

// -----------------------------------------------------------------------------
// Signal trap, triggers during a CTRL+C or if kill is called
void
sighandler (int sig) {

  srv.close();
  cout << "everything was closed." << endl << "Have a nice day !" << endl;
  exit (EXIT_SUCCESS);
}

// -----------------------------------------------------------------------------
int main (int argc, char **argv) {

  if (argc < 2) {

    cerr << "Error: the JSON filename must be provided as a parameter on the command line !" << endl;
    cerr << "e.g. : " << argv[0] << " virtual-server-tcp.json" << endl;
    exit (EXIT_FAILURE);
  }

  string  jsonfile = argv[1];

  cout << "Callback Server" << endl;
  // CTRL+C and kill call triggers the trap sighandler()
  signal (SIGINT, sighandler);
  signal (SIGTERM, sighandler);
  cout << "Press CTRL+C to stop... " << endl << endl;

  try {
    cout << "opening " << jsonfile << "..." << endl;
    srv.setConfig (jsonfile, "modbuspp-server");
    srv.setMessageCallback (messageHandler);

    if (srv.open ()) { // open a connection
      cout << "Listening server on " <<
           srv.connection() << ":" << srv.settings() << "..." << endl << endl;

      srv.run();
      while (srv.isOpen()) {

        // std::this_thread::yield();
        std::this_thread::sleep_for (std::chrono::milliseconds (200));
      }
    }
  }
  catch (std::exception & e) {

    cerr << "Error: " << e.what() << endl;
  }
  catch (...) {

    cerr << "Unattended exception !" << endl;
  }

  return EXIT_FAILURE;
}
/* ========================================================================== */