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  // for functions for socket #include  // for struct sockaddr_in #include  #include  // for memset #include  // for perror #include  // 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：

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