套接字2

socket套接字（2）

socket编程基本函数

socket编程的基本函数有socket()、bind()、listen()、accept()、send()、sendto()、recv()以及recvfrom()等，函数说明如下：

• socket() ：该函数用于建立一个socket连接，可指定socket类型等信息。在建立了socket连接后，可对sockaddr或sockaddr_in结构体进行初始化，以保存所建立的socket地址信息
• bind()：该函数是用于将本地IP地址绑定到端口号，若绑定其他IP地址则不成成功，主要用于TCP的连接
• listen()：在服务端程序建立套接字和地址绑定之后，还需要准备在该套接字上接收新的连接请求。此时调用listen()函数来创建一个等待队列，在其中存放未处理的客户端连接请求
• accept()：服务端程序调用listen()函数创建等待队列之后，调用accept()函数等待并接收客户端的连接请求。它通常在bind()所创建的等待队列中取出第一个未处理的连接请求
• send()和recv()：分别用于发送和接收数据
• sendto()和recvfrom()：和send()和recv()类似，UDP时可以用在没有使用connect()的情况

socket编程流程

TCP协议

UDP协议

函数介绍

#include <sys/socket.h>
int socket (int family, int type, int protocol);
int bind (int sockfd, struct sockaddr *my_addr, int addrlen);
int listen (int sockfd, int backlog);
int accept (int sockfd, struct sockaddr *addr, socklen_t *addrlen);
int connect (int sockfd, struct sockaddr *serv_addr, int addrlen);
int send (int sockfd, const void *msg, int len, int flags);
int recv (int sockfd, void *buff, int len, unsigned int flags);

示例

service

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

#define PORT            4321
#define BUFF_SIZE       1024
#define MAX_QUE_CONN_NM 5

int main()
{
    struct sockaddr_in server_sockaddr, client_sockaddr;
    int sin_size, recvbytes;
    int sockfd, client_fd;
    char buf[BUFF_SIZE];

    /*建立socket连接*/
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror ("socket");
        exit (1);
    }
    printf ("socket fd = %d\n", sockfd);

    server_sockaddr.sin_family = AF_INET;
    server_sockaddr.sin_port = htons(PORT);
    server_sockaddr.sin_addr.s_addr = INADDR_ANY;
    memset(&(server_sockaddr.sin_zero), 0, 8);

    int i = 1;
    setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &i, sizeof (i));
    if (bind(sockfd, (struct sockaddr *)&server_sockaddr, sizeof (struct sockaddr)) == -1)
    {
        perror ("bind");
        exit (1);
    }
    printf ("Bind success!\n");

    if (listen (sockfd, MAX_QUE_CONN_NM) == -1)
    {
        perror ("listen");
        exit (1);
    }
    printf ("Listening.....\n");

    if ((client_fd = accept (sockfd, (struct sockaddr *)&client_sockaddr, &sin_size)) == -1)
    {
        perror ("accept");
        exit (1);
    }

    memset (buf, 0, sizeof(buf));
    if ((recvbytes = recv (client_fd, buf, BUFF_SIZE, 0)) == -1)
    {
        perror ("recv");
        exit (1);
    }
    printf ("Recv : %s\n", buf);
    close (sockfd);
    exit(0);
}

client

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

#define PORT            4321
#define BUFF_SIZE       1024

int main(int argc, char *argv[])
{
    int sockfd, sendbytes;
    char buf[BUFF_SIZE];
    struct hostent *host;
    struct sockaddr_in serv_addr;

    if (argc < 3)
    {
        fprintf (stderr, "USAGE: ./client Hostname(or ip address) Text\n");
        exit (1);
    }

    if ((host = gethostbyname(argv[1])) == NULL)
    {
        perror ("gethostbyname");
        exit (1);
    }

    memset (buf, 0, sizeof (buf));
    sprintf (buf, "%s", argv[2]);

    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror ("socket");
        exit (1);
    }
    printf ("socket fd = %d\n", sockfd);

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    memset(&(serv_addr.sin_zero), 0, 8);

    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof (struct sockaddr)) == -1)
    {
        perror ("connect");
        exit (1);
    }
    printf ("connect success!\n");

    if ((sendbytes = send (sockfd, buf, BUFF_SIZE, 0)) == -1)
    {
        perror ("send");
        exit (1);
    }
    //printf ("Send : %s\n", buf);
    close (sockfd);
    exit(0);
}