今天段老师在网络软件设计课上布置了一个题目。

要求是windows环境，现在在linux环境下实现。

运行C/S模式的2个程序，使用UDP协议，发送10次，计算平均时延。

服务器程序如下：

#include <sys/socket.h> // for functions for socket
#include <netinet/in.h> // for struct sockaddr_in
#include <stdlib.h>
#include <memory.h> // for memset
#include <stdio.h> // for perror
#include <errno.h> // for errno
#define BUFLEN 100
int main(void)
{
  int listenfd;
  char buf[BUFLEN];
  socklen_t len;
  struct sockaddr_in serv, cli;
  if ((listenfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
  { // use udp
    perror("socket");
    exit(EXIT_FAILURE);
  }
  memset(&serv, 0, sizeof(serv)); // clear
  serv.sin_family = AF_INET; // use IPv4
  // Listen any ip address and use network
  // byte order
  serv.sin_addr.s_addr = htonl(INADDR_ANY);
  serv.sin_port = htons(9877); // Listen port 9877
  if (bind(listenfd, (struct sockaddr*)&serv, sizeof(serv)) < 0)
  { // bind the socket to the server address
    perror("bind");
    exit(EXIT_FAILURE);
  }
  for ( ; ; )
  {
    len = sizeof(cli);
    if ((recvfrom(listenfd, buf, BUFLEN, 0,
        (struct sockaddr*)&cli, &len)) < 0)
    {   // recvfrom the listenfd
      // put the message into buf
      // no flags (4th argument 0)
      // save the client address and length
      if (errno == EINTR || errno == EAGAIN)
        continue;
      perror("recvfrom");
      exit(EXIT_FAILURE);
    }
    if ((sendto(listenfd, "Got it!", 10, 0,
        (struct sockaddr*)&cli, len)) < 0)
    {   // send the message back
      // send message "Got it!" back
      if (errno == EINTR || errno == EAGAIN)
        continue;
      perror("sendto");
      exit(EXIT_FAILURE);
    }
  }
  return 0;
}

客户端程序如下：

#include <sys/socket.h> // for functions for socket
#include <arpa/inet.h> // for inet_pton
#include <netinet/in.h> // for struct sockaddr_in
#include <stdlib.h>
#include <memory.h> // for memset
#include <stdio.h> // for perror
#include <errno.h> // for errno
#include <time.h>
#define SENDTIMES 10
#define BUFLEN 100
int main(int argc, char* argv[])
{
  struct sockaddr_in serv;
  int sockfd;
  int i;
  clock_t start, finish;
  double duration, total = 0;
  char buf[BUFLEN];
  if (argc != 2)
  {
    fprintf(stderr, "Usage: ./udpcli <IPADDR>\n");
    exit(EXIT_FAILURE);
  }
  if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
  { // use udp
    perror("socket");
    exit(EXIT_FAILURE);
  }
  memset(&serv, 0, sizeof(serv));
  serv.sin_family = AF_INET;
  serv.sin_port = htons(9877);
  if ((inet_pton(AF_INET, argv[1],
    &serv.sin_addr)) == 0)
  { // read the string to the structrue
    perror("inet_pton");
    exit(EXIT_FAILURE);
  }
again:
  if ((connect(sockfd,
      (struct sockaddr*)&serv, sizeof(serv))) < 0)
  { // this connect is for catch the
    // error ICMP packets
    if (errno == EINTR || errno == EAGAIN)
      goto again;
    perror("connect");
    exit(EXIT_FAILURE);
  }
  for (i = 0; i < SENDTIMES; ++i)
  {
    printf("Send %d messages.\n", i + 1);
    start = clock();
again2:
    if ((sendto(sockfd, "A message!", 20, 0,
      (struct sockaddr*)&serv, sizeof(serv))) < 0)
    {
      if (errno == EINTR)
        goto again2;
      perror("sendto");
      exit(EXIT_FAILURE);
    }
again3:
    if ((recvfrom(sockfd, buf, BUFLEN, 0,
      NULL, NULL)) < 0)
    {
      if (errno == EINTR)
        goto again3;
      perror("recvfrom");
      exit(EXIT_FAILURE);
    }
    finish = clock();
    duration = finish - start;
    printf("Spend time: %fms\n", duration);
    total += duration;
  }
  printf("\nAverage time: %fms\n", total / SENDTIMES);
  return 0;
}

运行结果为：

<img src="https://img-blog.csdn.net/20150312120444160?wate%3Ca%20href=" http:="" www.ahlinux.com="" start="" cmd="" 9034.html"="" target="_blank" class="keylink" style="margin: 0px; padding: 3px; border: 1px solid rgb(204, 204, 204); max-width: 660px;">rmark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvcGRjeHMwMDc=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" style="display: block;" />