mysever.c

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

#include <netinet/in.h>
#include <ctype.h>
#include <arpa/inet.h>

#include <fcntl.h>
#include <netdb.h>

#include <string.h>
#include <strings.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#define MAXFD 2

int main(int argc, char ** argv)
{
    int sockfd, newsockfd, portno; // clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    socklen_t clilen;
    int n;
    char * c;//

    if (argc < 3)
    {
        fprintf(stderr, "usage: %s ip port\n", argv[0]);
        return 0;
    }

    /* Create TCP socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("ERROR opening socket");
        exit(EXIT_FAILURE);
    }

    // reuse the socket if possible
    int const reuse = 1;
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int)) < 0)
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    portno = atoi(argv[2]);

    /* Create address we're going to listen on (given port number)
     - converted to network byte order & any IP address for this machine */
    bzero((char *)&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;//differ
    serv_addr.sin_port = htons(portno); // store in machine-neutral format

    /* Bind address to the socket */
    if (bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        perror("ERROR on binding");
        exit(EXIT_FAILURE);
    }

    /* Listen on socket - means we're ready to accept connections -
     incoming connection requests will be queued */
    listen(sockfd, 5);

    clilen = sizeof(cli_addr);

    /* Accept a connection - block until a connection is ready to
     be accepted. Get back a new file descriptor to communicate on. */
    /*newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clilen);
    if (newsockfd < 0)
    {
        perror("ERROR on accept");
        exit(EXIT_FAILURE);
    }*/

    // initialise an active file descriptors set
    fd_set masterfds;
    FD_ZERO(&masterfds);
    FD_SET(sockfd, &masterfds);
    // record the maximum socket number
    int maxfd = sockfd;

    while (1)
    {
      // monitor file descriptors
      fd_set readfds = masterfds;
      if (select(FD_SETSIZE, &readfds, NULL, NULL, NULL) < 0)
      {
          perror("select");
          exit(EXIT_FAILURE);
      }

      // loop all possible descriptor
      for (int i = 0; i <= maxfd; ++i)
          // determine if the current file descriptor is active
          if (FD_ISSET(i, &readfds))
          {
              // create new socket if there is new incoming connection request
              if (i == sockfd)
              {
                  int newsockfd = accept(sockfd, (struct sockaddr *)&cliaddr, &clilen);
                  if (newsockfd < 0)
                      perror("accept");
                  else
                  {
                      // add the socket to the set
                      FD_SET(newsockfd, &masterfds);
                      // update the maximum tracker
                      if (newsockfd > maxfd)
                          maxfd = newsockfd;
                      // print out the IP and the socket number
                      /*char ip[INET_ADDRSTRLEN];
                      printf(
                          "new connection from %s on socket %d\n",
                          // convert to human readable string
                          inet_ntop(cliaddr.sin_family, &cliaddr.sin_addr, ip, INET_ADDRSTRLEN),
                          newsockfd
                      );*/
                  }
              }
              // a message is sent from the client
              else
              {   /* Read characters from the connection, then process */
                  char buff[256];
                  int n = read(i, buff, 256);
                  if (n <= 0)
                  {
                      if (n < 0)
                          perror("read");
                      else
                          printf("socket %d close the connection\n", i);
                      close(i);
                      FD_CLR(i, &masterfds);
                  }
                  // write back to the client
                  else if (write(i, buff, n) < 0)
                  {
                      perror("write");
                      close(i);
                      FD_CLR(i, &masterfds);
                  }
              }
          }



        if (!strncmp(buffer, "GOODBYE-CLOSE-TCP", 17))
            break;

        /*c = buffer;
        while (*c)
        {
            *c = toupper(*c);
            ++c;
        }*/



    /* close socket */
    //close(sockfd);

    return 0;
}