udp_client.c

采用UDP协议实现的UNIX/Linux环境下的聊天服务器和客户端程序

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <errno.h>

#define BUFFER_SIZE	1024

int main(int argc, char **argv)
{
  int fd;

  // XXX: step 1, socket();

  int socket(int domain, int type, int protocol);

  if ((fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
  {
    fprintf(stderr, "Create a new UDP socket failed: %s\n", strerror(errno));
    exit(1);
  }

  // XXX: step 2, bind(); optional
  // XXX: step 3, connect(), optional

  char line[BUFFER_SIZE];
  struct sockaddr_in remote_address;
  ssize_t sent;

  memset(&remote_address, 0, sizeof(remote_address));

  remote_address.sin_family = PF_INET;
  remote_address.sin_port = htons(atoi(argv[2]));
  remote_address.sin_addr.s_addr = inet_addr(argv[1]);

  // char *fgets(char *s, int size, FILE *stream);
  while (fgets(line, BUFFER_SIZE, stdin))
  {
    // XXX: step 4, sendto()/recvfrom
  resend:
    // ssize_t  sendto(int  s,  const  void  *buf,  size_t len, int flags, const struct sockaddr *to, socklen_t tolen);
    if ((sent = sendto(fd, line, strlen(line), 0, (struct sockaddr *) &remote_address, sizeof(remote_address))) < 0)
    {
      if (errno == EINTR)
      {
	goto resend;
      }
      else
      {
	fprintf(stderr, "sendto() failed: %s\n", strerror(errno));
      }
    }
    else
    {
      fprintf(stdout, "Sent %d bytes to remote host.\n", sent);
    }

    struct sockaddr_in peer_address;
    socklen_t peer_address_length;
    ssize_t n;

    peer_address_length = sizeof(peer_address);

  re_receive:
    //ssize_t recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);
    if ((n = recvfrom(fd, line, BUFFER_SIZE, 0, (struct sockaddr *) &peer_address, &peer_address_length)) < 0)
    {
      if (errno == EINTR)
      {
	goto re_receive;
      }
      else
      {
	fprintf(stderr, "recvfrom() failed: %s\n", strerror(errno));
      }
    }
    else
    {
      fprintf(stdout, "INFO: read %d bytes from %s:%d\n", n, inet_ntoa(peer_address.sin_addr), ntohs(peer_address.sin_port));

#if 0
      int i;

      for (i = 0; i < n; i++)
      {
	fprintf(stdout, "0x%x", buffer[i]);
      }
#endif

      line[n] = '\0';
      fprintf(stdout, "DEBUG: %s\n", line);
    }
  }

  // XXX: step 5, close()

  return 0;
}