Linux上C语言写的简易telnet客户端

发表于 | 分类于 | 732
字数统计 509 | 阅读时长 3

telnet.c

  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <sys/socket.h>
  4. #include <arpa/inet.h>  
  5. #include <netinet/in.h> 
  6. #include <netdb.h>
  7. #include <unistd.h>
  8. #include <errno.h>
  9. #include <signal.h>
  10. #include <time.h>
  11. #include <stdarg.h>
  13. #define ERR_EXIT(m, ...) \  
  14.     do { \  
  15.         fprintf(stderr, m"\n", ##__VA_ARGS__); \  
  16.         log(m"\n", ##__VA_ARGS__); \
  17.         exit(EXIT_FAILURE); \  
  18.     } while (0) 
  19. #define MAX_BUFF_LEN 1024
  21. void log(const char *fmt, ...)
  22. {
  23.     char buffer[MAX_BUFF_LEN] = {0};
  24.     va_list args;
  25.     time_t timep;
  26.     time(&timep);
  27.     struct tm *p = gmtime(&timep);
  28.     FILE* fp = fopen("telnet.log", "a+");
  29.     if(fp){
  30.         snprintf(buffer, MAX_BUFF_LEN, "[%.4d-%.2d-%.2d %.2d:%.2d:%.2d][%d]", (1900+p->tm_year),(1+p->tm_mon), p->tm_mday, p->tm_hour, p->tm_min, p->tm_sec, getpid());
  31.         va_start(args, fmt);
  32.         vsnprintf(buffer + strlen(buffer), MAX_BUFF_LEN - strlen(buffer) - 1, fmt, args);
  33.         va_end(args);
  34.         fwrite(buffer, strlen(buffer), 1, fp);
  35.         fclose(fp);
  36.     }
  37. }
  39. ssize_t      /* Write "n" bytes to a descriptor. */
  40. writen(int fd, const void *vptr, size_t n){
  41.     size_t  nleft;
  42.     ssize_t  nwritten;
  43.     const char *ptr;
  44.     ptr = vptr;
  45.     nleft = n;
  46.     while (nleft > 0) {
  47.         if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
  48.             if (nwritten < 0 && errno == EINTR)
  49.                 nwritten = 0;  /* and call write() again */
  50.             else
  51.                 return(-1);   /* error */
  52.         }
  53.         nleft -= nwritten;
  54.         ptr   += nwritten;
  55.     }
  56.     return(n);
  57. }
  59. int main(int argc,char **argv){
  60.     if(argc < 3){
  61.         fprintf(stderr, "Usage: %s ServerIPAddress ServerPort\n",argv[0]);
  62.         return 0;
  63.     }
  65.     fd_set rset;
  66.     FD_ZERO(&rset);
  67.     int sock = socket(AF_INET,SOCK_STREAM,0);
  68.     struct sockaddr_in server_addr;
  69.     memset(&server_addr, 0, sizeof(server_addr));
  70.     server_addr.sin_family = AF_INET;    //internet协议族
  71.     struct hostent *h = gethostbyname(argv[1]);
  72.     server_addr.sin_addr = *((struct in_addr *)h->h_addr);
  73.     server_addr.sin_port = htons(atoi(argv[2]));
  74.     if(connect(sock,(struct sockaddr*)&server_addr, sizeof(struct sockaddr_in)) < 0){
  75.         ERR_EXIT("connect to %s:%s failed", argv[1], argv[2]);
  76.     }
  78.     fprintf(stdout, "% 9d\n", getpid());
  79.     fflush(stdout);
  81.     int nready;  
  82.     int maxfd;  
  83.     int fd_stdin = fileno(stdin);
  84.     int fd_stdout = fileno(stdout);
  85.     if (fd_stdin > sock)  
  86.         maxfd = fd_stdin;  
  87.     else  
  88.         maxfd = sock;  
  89.     char sendbuf[1024*4] = {0};  
  90.     char recvbuf[1024*4] = {0};  
  92.     while (1){  
  93.         FD_SET(fd_stdin, &rset);  
  94.         FD_SET(sock, &rset);  
  95.         nready = select(maxfd + 1, &rset, NULL, NULL, NULL); //select返回表示检测到可读事件  
  96.         if (nready == -1) ERR_EXIT("select error");  
  97.         if (nready == 0) continue;  
  98.         if (FD_ISSET(sock, &rset)){  
  99.             int ret = read(sock, recvbuf, sizeof(recvbuf)); //按行读取  
  100.             if (ret == -1) ERR_EXIT("read from socket error");  
  101.             else if (ret  == 0) ERR_EXIT("server close");  //服务器关闭  
  103.             writen(fd_stdout, recvbuf, ret);
  104.             memset(recvbuf, 0, sizeof(recvbuf));  
  105.         }  
  106.         if (FD_ISSET(fd_stdin, &rset)){  
  107.             int ret = read(fd_stdin, sendbuf, sizeof(sendbuf));
  108.             if(ret > 0) {
  109.                 writen(sock, sendbuf, ret);  
  110.                 memset(sendbuf, 0, sizeof(sendbuf));
  111.             }else{
  112.                 ERR_EXIT("read from stdin error");                
  113.             }
  114.         }  
  115.     }  
  116.     close(sock);  
  117.     exit(0);
  118. }
  COPY

编译方法：

gcc -o telnet telnet.c

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