linux socket 编程示例

前言

   socket编程现在几乎成了网络编程的代名词，关于这方面的书籍与资料更是不可胜数。比较好的可以推荐一下《Unix 网络编程 卷1：套接字联网API》。

1. TCP

   TCP提供客户与服务器之间的连接(connection),TCP客户先与某个给定服务器之间建立一个连接，再跨该连接与那个服务器交换数据，然后终止这个连接。

   

1.1 TCP server

编程步骤：

socket→初始化struct  sockaddr_in→bind→listen→[accept→send→recv]

tcp_server.c

/*
 * \brief
 * tcp server
 */
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>

#define SERVPORT 8080
#define BACKLOG 10 // max numbef of client connection
#define MAXDATASIZE 100

int main(char argc, char *argv[])
{
  int sockfd, client_fd, addr_size, recvbytes;
  char rcv_buf[MAXDATASIZE], snd_buf[MAXDATASIZE];
  char* val;
  struct sockaddr_in server_addr;
  struct sockaddr_in client_addr;

  char IPdotdec[20];

  /* create a new socket and regiter it to os .
   * SOCK_STREAM means that supply tcp service,
   * and must connect() before data transfort.
   */
  if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
  {
    perror("socket:");
    exit(1);
  }

  /* setting server's socket */
  server_addr.sin_family = AF_INET;         // IPv4 network protocol
  server_addr.sin_port = htons(SERVPORT);
  server_addr.sin_addr.s_addr = INADDR_ANY; // auto IP detect
  memset(&(server_addr.sin_zero),0, 8);

  if (bind(sockfd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr))== -1)
  {
    perror("bind:");
    exit(1);
  }

  /* watting for connection , and server permit to recive the requestion from sockfd */
  if (listen(sockfd, BACKLOG) == -1) // BACKLOG assign thd max number of connection
  {
    perror("listen:");
    exit(1);
  }

  while(1)
  {
    addr_size = sizeof(struct sockaddr_in);

    /* accept the sockfd's connection,
     * return an new socket and assign far host to client_addr
     */
    if ((client_fd = accept(sockfd, (struct sockaddr *)&client_addr, &addr_size)) == -1)
    {
      /* Nonblocking mode */
      perror("accept:");
      continue;
    }

    /* network-digital to ip address */
    inet_ntop(AF_INET, (void*)&client_addr, IPdotdec, 16);
    printf("connetion from:%d : %s\n",client_addr.sin_addr, IPdotdec);

    if (!fork())
    {
      /* child process handle with the client connection */

      /* recive the client's data by client_fd */
      if ((recvbytes = recv(client_fd, rcv_buf, MAXDATASIZE, 0)) == -1)
      {
        perror("recv:");
        exit(1);
      }
      rcv_buf[recvbytes]='\0';
      printf("recv:%s\n", rcv_buf);


      *snd_buf='\0';
      strcat(snd_buf, "welcome");
      /* send the message to far-hosts by client_fd */
      if (send(client_fd, snd_buf, strlen(snd_buf), 0) == -1)
      {
        perror("send:");
        exit(1);
      }
      printf("send:%s\n", snd_buf);

      close(client_fd);
      exit(1);
    }

    close(client_fd);
  }

  return 0;
}

编译：

gcc -g -o tcp_server tcp_server.c

1.2 TCP client

编程步骤：

socket→初始化struct  sockaddr_in→connect→[recv→send]

tcp_client.c

/*
 * \brief
 * tcp client
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>

#define SERVPORT 8080
#define MAXDATASIZE 100

int main(int argc, char *argv[])
{
  int sockfd, recvbytes;
  char rcv_buf[MAXDATASIZE]; /*./client 127.0.0.1 hello */
  char snd_buf[MAXDATASIZE];
  struct hostent *host;             /* struct hostent
                                     * {
                                     * char *h_name; // general hostname
                                     * char **h_aliases; // hostname's alias
                                     * int h_addrtype; // AF_INET
                                     * int h_length;
                                     * char **h_addr_list;
                                     * };
                                     */
  struct sockaddr_in server_addr;

  if (argc < 3)
  {
    printf("Usage:%s [ip address] [any string]\n", argv[0]);
    return 1;
  }

  *snd_buf = '\0';
  strcat(snd_buf, argv[2]);

  if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
  {
    perror("socket:");
    exit(1);
  }

  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(SERVPORT);
  inet_pton(AF_INET, argv[1], &server_addr.sin_addr);
  memset(&(server_addr.sin_zero), 0, 8);

  /* create the connection by socket
   * means that connect "sockfd" to "server_addr"
   */
  if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
  {
    perror("connect");
    exit(1);
  }

  /**/
  if (send(sockfd, snd_buf, sizeof(snd_buf), 0) == -1)
  {
    perror("send:");
    exit(1);
  }
  printf("send:%s\n", snd_buf);

  if ((recvbytes = recv(sockfd, rcv_buf, MAXDATASIZE, 0)) == -1)
  {
    perror("recv:");
    exit(1);
  }

  rcv_buf[recvbytes] = '\0';
  printf("recv:%s\n", rcv_buf);

  close(sockfd);
  return 0;
}

编译：

gcc -o -g tcp_client tcp_client.c

2. UDP

   UDP提供无连接的(connectionless)服务，比如一个UDP客户可以创建一个套接字并发送一个数据报给一个给定的服务器，然后立即用同一个套接字发送另一个数据报给另一个服务器。同样地，一个UDP服务器可以用同一个UDP套接字从若干不同的客户接收数据报，每个客户一个数据报。

2.1 UDP server

编程步骤：

socket→初始化struct  sockaddr_in→bind→[recvfrom→sendto]

udp_server.c

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


#define SERVPORT 8080
#define MAXDATASIZE 100

int main()
{
  int sockfd, addr_size, recvbytes;
  char rcv_buf[MAXDATASIZE], snd_buf[MAXDATASIZE];
  char* val;
  struct sockaddr_in server_addr;

  if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
  {
    perror("socket:");
    exit(1);
  }

  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(SERVPORT);
  server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
  memset(&(server_addr.sin_zero), 0, 8);

  if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))==-1)
  {
    perror("bind:");
    exit(1);
  }

  while(1)
  {
    addr_size = sizeof(struct sockaddr);

    /* receive the data from "server_addr" by "sockfd" and store into "rcv_buf" */
    if ((recvbytes = recvfrom(sockfd, rcv_buf, MAXDATASIZE, 0,
              (struct sockaddr*)&server_addr, &addr_size)) == -1)
    {
      perror("recv:");
      exit(1);
    }
    rcv_buf[recvbytes] = '\0';
    printf("recv:%s : %s\n", inet_ntop(server_addr.sin_addr), rcv_buf);

    *snd_buf = '\0';
    strcat(snd_buf, "welcome");

    /* send the data "snd_buf" to "server_addr" by "sockfd" */
    if (sendto(sockfd, snd_buf, strlen(snd_buf), 0,
            (struct sockaddr*)&server_addr, addr_size) == -1)
    {
      perror("send:");
      exit(1);
    }
    printf("send:%s\n", snd_buf);
    //exit(1);
  }
  close(sockfd);
  return 0;
}

编译：

gcc -g -o udp_server udp_server.c

2.2 UDP client

编程步骤：

socket→初始化struct  sockaddr_in→[sendto→recvfrom]

udp_client.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>

#define SERVPORT 8080
#define MAXDATASIZE 100

int main(int argc, char *argv[])
{
  int server_sockfd, recvbytes,addr_size;
  char rcv_buf[MAXDATASIZE]; /*./client 127.0.0.1 hello*/
  char snd_buf[MAXDATASIZE];
  struct hostent *host;
  struct sockaddr_in server_addr;

  if (argc < 3)
  {
    printf("Usage:%s [ip address] [any string]\n",argv[0]);
    return 1;
  }
  *snd_buf = '\0';
  strcat(snd_buf,argv[2]);

  if ((server_sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
  {
    perror("socket:");
    exit(1);
  }

  server_addr.sin_family=AF_INET;
  server_addr.sin_port=htons(SERVPORT);
  inet_pton(AF_INET,argv[1],&server_addr.sin_addr);
  memset(&(server_addr.sin_zero),0,8);
  addr_size=sizeof(struct sockaddr);

  /* send the data "snd_buf" to "server_addr" by server_sockfd */
  if (sendto(server_sockfd,snd_buf,sizeof(snd_buf),0,
          (struct sockaddr*)&server_addr,addr_size) == -1)
  {
    perror("send:");
    exit(1);
  }
  printf("send:%s\n",snd_buf);

  /* receive the data from "server_addr" by "server_sockfd" and store into rcv_buf */
  if ((recvbytes=recvfrom(server_sockfd,rcv_buf,MAXDATASIZE,0,
            (struct sockaddr*)&server_addr,&addr_size)) ==-1)
  {
    perror("recv:");
    exit(1);
  }
  rcv_buf[recvbytes] = '\0';
  printf("recv:%s\n",rcv_buf);

  close(server_sockfd);
  return 0;
}

编译：

gcc -g -o udp_client udp_client.c

3. UDP multicast

  有时候，本机不止有一张网卡，所以接收UDP组播的数据先要将本机指定的网卡地址加入组播组，才能接收到组播数据。

编程步骤：

socket-->setsockopt-->bind->setsockopt(本机网卡加入组播组)-->[recvfrom --> sendto]

udp_multicast_recv.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define UDPMCASTPORT 1234
#define MAXDATASIZE 1024



int main(char argc, char *argv[])
{
  int udp_sockfd, addr_size, recvbytes;
  char rcv_buf[MAXDATASIZE];

  struct sockaddr_in servaddr, clitaddr;
  struct ip_mreq mreq;

  char* pc_udpmcaddr = "225.1.1.31";
  char* pc_udpmcport = "1234";
  char* pc_localaddr = "192.168.1.73";
  int i_reuse_socket;


  if (argc != 3)
  {
    fprintf(stdout, "SYNTAX: ./udp_mcast_recv <udp_multicast_address> <local_address>\n");
    exit(1);
  }
  else
  {
    pc_udpmcaddr = argv[1];
    pc_localaddr = argv[2];
  }

  memset(&servaddr, 0, sizeof(struct sockaddr_in));
  memset(&clitaddr, 0, sizeof(struct sockaddr_in));
  memset(&mreq, 0, sizeof(struct ip_mreq));

  /* create socket */
  if ((udp_sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
  {
    perror("socket:");
    exit(1);
  }

  i_reuse_socket = 1;
  if (setsockopt(udp_sockfd, SOL_SOCKET, SO_REUSEADDR, &i_reuse_socket, sizeof(int))== -1)
  {
    perror("setsockopt:");
    exit(1);
  }

  servaddr.sin_family = AF_INET;
  servaddr.sin_port = htons(UDPMCASTPORT);

  if (!inet_aton(pc_udpmcaddr, &servaddr.sin_addr))
  {
    perror("inet_aton:");
    exit(1);
  }
  if (bind(udp_sockfd, (struct sockaddr *)&servaddr, sizeof(struct sockaddr))==-1)
  {
    perror("bind:");
    exit(1);
  }

  if (!inet_aton(pc_udpmcaddr, &mreq.imr_multiaddr))
  {
    perror("inet_aton:");
    exit(1);
  }

  if (!inet_aton(pc_localaddr, &mreq.imr_interface))
  {
    perror("inet_aton:");
    exit(1);
  }

  if (setsockopt(udp_sockfd, SOL_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq))==-1)
  {
    perror("setsockopt:");
    exit(1);
  }

  addr_size = sizeof(struct sockaddr);

  while(1)
  {
    if ((recvbytes = recvfrom(udp_sockfd, rcv_buf, MAXDATASIZE, 0,
              (struct sockaddr*)&clitaddr, &addr_size)) == -1)
    {
      perror("recvfrom:");
      exit(1);
    }
    rcv_buf[recvbytes] = '\0';
    fprintf(stdout, "recvfrom:%s:%s", inet_ntoa(clitaddr.sin_addr), rcv_buf);
  }
}

编译：

gcc -g -o udp_multicast_recv udp_multicast_recv.c