source: tools/SkyQualityMonitor/sqm.cpp @ 143

/********************************************************************\

  Interface to the sky quality monitor (essentially a socket interface)
  
  Terminate with CTRL-c. Note that socket is closed automatically by exit().
  
  Oliver Grimm, September 2009

\********************************************************************/

#include <iostream>
#include <sys/socket.h>
#include <netdb.h>
#include <signal.h>
#include <errno.h>
#include <stdarg.h>

#define SERVER_NAME "SQM"       // Name to use in DIM
#include "Evidence.h"

#define READ_CMD "rx"           // Command to read from device
#define BUF_SIZE 1000           // Read and text buffer size


// Main program
int main() {

  int SocketDescriptor;
  struct sockaddr_in SocketAddress;
  fd_set ReadFileDescriptor;
  time_t Time;
  unsigned int Period;
  
  // Start server and request configuration data
  EvidenceServer Srv(SERVER_NAME);
  char *Address = Srv.GetConfig(SERVER_NAME " address");
  unsigned int Port = atoi(Srv.GetConfig(SERVER_NAME " port"));
    
  // Open socket descriptor
  if ((SocketDescriptor = socket(PF_INET, SOCK_STREAM, 0)) == -1) {
    Srv.State(Srv.FATAL, "Could not open socket (%s)", strerror(errno));
  }
    
  // Resolve hostname
  struct hostent *hostent = gethostbyname(Address);
  if (hostent==0) {
    Srv.State(Srv.FATAL, "Could not resolve host name '%s' (%s)", Address, hstrerror(h_errno));
  }

  //  Connect to server
  SocketAddress.sin_family = PF_INET;
  SocketAddress.sin_port = htons((unsigned short) Port);
  SocketAddress.sin_addr = *(struct in_addr*) hostent->h_addr;
  
  if (connect(SocketDescriptor, (struct sockaddr *) &SocketAddress, sizeof(SocketAddress))==-1) {
    Srv.State(Srv.FATAL, "Could not connect to server '%s' on port %d (%s)", Address, Port, strerror(errno));
  }

  Srv.State(Srv.INFO, "Connected to server '%s' on port %d", Address, Port);
  signal(SIGPIPE,SIG_IGN);  // Do not kill process if writing to closed socket

  // Create DIM services
  double sqm_reading=0.0;
  char Buffer[BUF_SIZE];
  
  DimService SQM_Brightness(SERVER_NAME"/NSB", sqm_reading);
  DimService SQM_Response(SERVER_NAME"/Response", NO_LINK);

  while(!EvidenceServer::ExitRequest) {
        // Request measurement period  
    Period = atoi(Srv.GetConfig(SERVER_NAME " period"));

    // Write read command to socket
    if ((write(SocketDescriptor, READ_CMD, strlen(READ_CMD)))<1) { 
      Srv.State(Srv.ERROR, "Could not write read command '%s' to socket.", READ_CMD);
    }
    
        // Wait for response (minimum 100 ms)
        usleep(100000);
        FD_ZERO(&ReadFileDescriptor);   
    FD_SET(SocketDescriptor, &ReadFileDescriptor);
    struct timeval WaitTime = {Period, 0};
    if (select(((int) SocketDescriptor)+1, &ReadFileDescriptor, NULL, NULL, &WaitTime)==-1) {
      Srv.State(Srv.FATAL, "Error with select() (%s)", strerror(errno));
    }

    if (!FD_ISSET(SocketDescriptor, &ReadFileDescriptor)) { 
      Srv.State(Srv.WARN, "Time-out of %d seconds expired before receiving response from socket", Period);
      continue;
    }

    memset(Buffer, 0, BUF_SIZE);
    if(read(SocketDescriptor, Buffer, BUF_SIZE) == 0) {
      Srv.State(Srv.FATAL, "Server not existing anymore, exiting...\n");
    }

    // Update full textual response and brightness reading
    for (int i=0; i<strlen(Buffer); i++) if (Buffer[i] == '\n') Buffer[i] = '\0';
    sqm_reading = strtod(Buffer+2 ,NULL);

    SQM_Brightness.updateService(sqm_reading);
    SQM_Response.updateService(Buffer);    

    Time = time(NULL);
    printf("%s\n %s CTRL-c to exit.\r", Buffer, asctime(localtime(&Time)));
    fflush(stdout);
        
    sleep(Period);
  } // while()

}