学步园

Linux和UNIX都拥有一个非常实用的工具--UNIX套接字，或称为本地套接字，它可以被用在进程间通讯（IPC）当中。UNIX套接字的运转机制和Internet套接字类似，主要的区别UNIX套接字只能用在一台计算机中，而Internet套接字则可以在不同的计算机之间使用。UNIX套接字定址的方式是作为本地文件系统里的一个文件。

你可能会奇怪为什么要使用UNIX套接字而不使用常规的Internet套接字呢？或许最大的原因就是安全和速度了。无论何时，当你打开任何Internet套接字的时候，你可能就帮远程的黑客打开了入侵之门。

程序：服务器端
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <string.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <sys/un.h>

    #define SOCK_PATH "echo_socket"

    int main(void)
    {
        int s, s2, t, len;
        struct sockaddr_un local, remote;
        char str[100];

        if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
            perror("socket");
            exit(1);
        }

        local.sun_family = AF_UNIX;
        strcpy(local.sun_path, SOCK_PATH);
        unlink(local.sun_path);
        len = strlen(local.sun_path) + sizeof(local.sun_family);
        if (bind(s, (struct sockaddr *)&local, len) == -1) {
            perror("bind");
            exit(1);
        }

        if (listen(s, 5) == -1) {
            perror("listen");
            exit(1);
        }

        for(;;) {
            int done, n;
            printf("Waiting for a connection...\n");
            t = sizeof(remote);
            if ((s2 = accept(s, (struct sockaddr *)&remote, &t)) == -1) {
                perror("accept");
                exit(1);
            }

            printf("Connected.\n");

            done = 0;
            do {
                n = recv(s2, str, 100, 0);
                if (n <= 0) {
                    if (n < 0) perror("recv");
                    done = 1;
                }

                if (!done) 
                    if (send(s2, str, n, 0) < 0) {
                        perror("send");
                        done = 1;
                    }
            } while (!done);

            close(s2);
        }

        return 0;
    }

客户端：
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <string.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <sys/un.h>
    
    #define SOCK_PATH "echo_socket"

    int main(void)
    {
        int s, t, len;
        struct sockaddr_un remote;
        char str[100];

        if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
            perror("socket");
            exit(1);
        }

        printf("Trying to connect...\n");

        remote.sun_family = AF_UNIX;
        strcpy(remote.sun_path, SOCK_PATH);
        len = strlen(remote.sun_path) + sizeof(remote.sun_family);
        if (connect(s, (struct sockaddr *)&remote, len) == -1) {
            perror("connect");
            exit(1);
        }

        printf("Connected.\n");

        while(printf("> "), fgets(str, 100, stdin), !feof(stdin)) {
            if (send(s, str, strlen(str), 0) == -1) {
                perror("send");
                exit(1);
            }

            if ((t=recv(s, str, 100, 0)) > 0) {
                str[t] = '\0';
                printf("echo> %s", str);
            } else {
                if (t < 0) perror("recv");
                else printf("Server closed connection\n");
                exit(1);
            }
        }

        close(s);

        return 0;
    }