Linux_C socket 数据报之client, server.c

dgrecv.c

/****************************************************************
 * dgrecv.c - datagram receiver
 *              usage: dgrecv portnum
 *             action: listens at the specfied port and reports messages
 */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>

#define oops(m,x) {perror(m); exit(x);}

int make_dgram_server_socket(int);
int get_internet_address(char* , int , int *, struct sockaddr_in *);
void say_who_called(struct sockaddr_in* );

int main(int argc, char* argv[]) {
  int port;
  int sock;
  char buf[BUFSIZ];
  size_t msglen;
  struct sockaddr_in saddr;
  socklen_t saddrlen;
  
  if(argc==1 || (port=atoi(argv[1]))<=0){
    fprintf(stderr, "usage :dgrecv portnumber
");
    exit(1);
  }
  
  /*get a socket and assign it a port number*/
  if((sock=make_dgram_server_socket(port))==-1)
    oops("cannot make server", 2);
  
  /*receive messages on that socket*/
  saddrlen=sizeof(saddr);
  while((msglen=recvfrom(sock ,buf, BUFSIZ, 0, &saddr, &saddrlen))>0) {
    buf[msglen]='';
    printf("dgrecv: got a message: %s
", buf);
    say_who_called(&saddr);
  }
  return 0;
}

//return the sock_id
int make_dgram_server_socket(int port){
  struct sockaddr_in saddr;
  struct hostent *hp;
  char hostname[BUFSIZ];
  int sock;
  
  sock=socket(PF_INET, SOCK_DGRAM, 0);
  if(sock==-1)
    return -1;
  gethostname(hostname, BUFSIZ);
  hp=gethostbyname(hostname);
  bzero((void*)&saddr, sizeof(saddr));
  bcopy(hp->h_addr, (struct sockaddr*)&saddr.sin_addr, hp->h_length);
  saddr.sin_family=AF_INET;
  saddr.sin_port=htons(port);
  if(bind(sock, (struct sockaddr*)&saddr, sizeof(saddr))!=0)
    return -1;
  return sock;
}

int get_internet_address(char* host, int len, int *portp, struct sockaddr_in* addrp) {
  /*
   * extracts host and port from an internet socket address
   * *addrp->(host, port)
   */
  strncpy(host, inet_ntoa(addrp->sin_addr), len);
  *portp=ntohs(addrp->sin_port);
  return 0;
}

void say_who_called(struct sockaddr_in *addrp) {
  char host[BUFSIZ];
  int port;
  
  get_internet_address(host, BUFSIZ, &port, addrp);
  printf("from: %s: %d
", host, port);
}

dgsend.c

/***********************************************************************
 * dgsend.c - datagram sender
 *            usage: dgsend hostname portnumber "message"
 *            action: sends message to hostname : portnumber
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

#define oops(m, x) {perror(m); exit(x);}

int main(int argc, char* argv[]) {
  char *message;
  int cli_sock;
  struct sockaddr_in saddr;
  struct hostent *hp;

  if(argc!=4){
    printf("please cin hostname portnumber and message ./n");
    exit(-1);
  }
  cli_sock=socket(AF_INET, SOCK_DGRAM, 0);
  if(cli_sock==-1) 
    oops("cannot make socket", 2);
  
  message=argv[3];

  /*make internet address*/
  bzero((void*)&saddr, sizeof(saddr));
  hp=gethostbyname(argv[1]);
  bcopy(hp->h_addr, (struct sockaddr*)&saddr.sin_addr, hp->h_length);
  saddr.sin_family=AF_INET;
  saddr.sin_port=htons(atoi(argv[2]));
  
  if(sendto(cli_sock, message, strlen(message), 0, &saddr, sizeof(saddr))==-1)
    oops("sendto failed", 3);
  return 0;
}

其中，注意

为使网络程序具有可移植性,使同样的C代码在大端和小端计算机上编译后都能正常运行,可以调用以下库函数做网络字节序和主机字节序的转换。

#include <arpa/inet.h>
uint32_t
uint16_t
uint32_t
uint16_t
htonl(uint32_t
htons(uint16_t
ntohl(uint32_t
ntohs(uint16_t
hostlong);
hostshort);
netlong);
netshort);
这些函数名很好记,h表示host,n表示network,l表示32位长整数,s表示16位短整数。例
如htonl表示将32位的长整数从主机字节序转换为网络字节序,例如将IP地址转换后准备发送。如果
主机是小端字节序,这些函数将参数做相应的大小端转换然后返回,如果主机是大端字节序,这些
函数不做转换,将参数原封不动地返回。