C建立socket连接的简单实例

建立 Socket连接至少需要一对套接字,其中一个运行于客户端,称为 ClientSocket,另一个运行于服务器端,称为 ServerSocket套接字之间的连接过程可以分为三个步骤:服务器监听,客户端请求,连接确认。

1.首先建立客户端的socket

vi client1.c

#include <sys/types.h>#include <sys/socket.h>#include <stdio.h>#include <sys/un.h>#include <unistd.h>#include <stdlib.h>#include <string.h>int main(){        int sockfd;        int len;        struct sockaddr_un address;        int result;        char ch = 'A';        sockfd = socket(AF_UNIX, SOCK_STREAM, 0);        address.sun_family = AF_UNIX;        strcpy(address.sun_path, "server_socket");        len = sizeof(address);        result = connect (sockfd, (struct sockaddr *)&address, len);        if(result == -1){                perror("oops:client1");                exit(1);        }        write(sockfd, &ch, 1);        read(sockfd, &ch, 1);        printf("char from server = %c\n", ch);        close(sockfd);        exit(0);}

然后编译

gcc client1.c -o client1

运行client1

./client1

运行后会提示：

oops: client1: No such file or directy

运行的时候会失败，因为还没有创建服务器端的socket

2.接下来创建一个非常简单的服务端socket程序 server1.c

#include <sys/types.h>#include <sys/socket.h>#include <stdio.h>#include <sys/un.h>#include <unistd.h>#include <stdlib.h>#include <string.h>int main(){        int server_sockfd, client_sockfd;        int server_len, client_len;        struct sockaddr_un server_address;        struct sockaddr_un client_address;        //用完的socket文件必须清理掉        unlink("server_socket");        server_sockfd = socket(AF_UNIX, SOCK_STREAM, 0);        server_address.sun_family = AF_UNIX;        strcpy(server_address.sun_path, "server_socket");        server_len = sizeof(server_address);        bind(server_sockfd, (struct sockaddr *)&server_address, server_len);        listen(server_sockfd, 5);        while(1){                char ch;                printf("server waiting\n");                client_len = sizeof(client_address);                client_sockfd = accept (server_sockfd, (struct sockaddr *)&server_address, (socklen_t *)&client_len);                read(client_sockfd, &ch, 1);                ch++;                write(client_sockfd, &ch, 1);                close(client_sockfd);        }}

编译文件后运行

gcc server1.c -o server1 & ./server1 &

[1] 2552
server waiting

这时候表明服务端的socket进程监听和等待客户端的连接，使用ps命令可以看到当前的进程正在后台运行，并且处于休眠状态，因此它没有消耗CPU资源。

ps lx | grep './server1'

    0  2552  2286   0  31  0  2432748    524 -      S    s000    0:00.00 ./server1
    0  2556  2286   0  31  0  2433772    536 -      S    s000    0:00.00 ./server1
    0  2616  2286   0  31  0  2432748    524 -      S    s000    0:00.00 ./server1
    0  2626  2286   0  31  0  2432748    524 -      S    s000    0:00.00 ./server1

3.客户端连接服务端socket

现在我们可以建立连接了，新开一个terminal窗口，使用命令：

./client1

将会响应：
char from server = B

而之前的server终端将显示
server waiting

如果同时运行多个客户，server端会依次服务

./client1 & ./client1 & ./client1 & ./client1

响应：
[1] 2641
[2] 2642
[3] 2643
char from server = B
char from server = B
char from server = B
char from server = B
[1]   Done                    ./client1
[2]-  Done                    ./client1
[3]+  Done                    ./client1


That's it~