本地套接字对比网络套接字

本地套接字通过文件名来建立连接，网络套接字通过ip+port建立连接。

实现上的不同：

    1. int socket(int domain, int type, int protocol); 参数 domain：AF_INET --> AF_UNIX/AF_LOCAL 

                                                              type: SOCK_STREAM/SOCK_DGRAM  都可以。    

    2. 地址结构：  sockaddr_in --> sockaddr_un

        struct sockaddr_in srv_addr; --> struct sockaddr_un srv_adrr;

        srv_addr.sin_family = AF_INET;  --> srv_addr.sun_family = AF_UNIX;
    ·
        srv_addr.sin_port = htons(8888);    strcpy(srv_addr.sun_path, "srv.socket")

        srv_addr.sin_addr.s_addr = htonl(INADDR_ANY);           len = offsetof(struct sockaddr_un, sun_path) + strlen("srv.socket");

        bind(fd, (struct sockaddr *)&srv_addr, sizeof(srv_addr));  -->  bind(fd, (struct sockaddr *)&srv_addr, len); 


    3. bind()函数调用成功，会创建一个 socket。因此为保证bind成功，通常我们在 bind之前， 可以使用 unlink("srv.socket");


    4. 客户端不能依赖 “隐式绑定”。并且应该在通信建立过程中，创建且初始化2个地址结构：

        1） client_addr --> bind()

        2)  server_addr --> connect();

对比：

                    网络套接字                       本地套接字
server:                 

lfd = socket(AF_INET, SOCK_STREAM, 0);                lfd = socket(AF_UNIX, SOCK_STREAM, 0);

bzero() ---- struct sockaddr_in serv_addr;            bzero() ---- struct sockaddr_un serv_addr, clie_addr;

serv_addr.sin_family = AF_INET;                        serv_addr.sun_family = AF_UNIX;  
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);          strcpy（serv_addr.sun_path, "套接字文件名"）
serv_addr.sin_port = htons(8888);                       len = offsetof(sockaddr_un, sun_path) + strlen();

bind(lfd, (struct sockaddr *)&serv_addr, sizeof());    unlink("套接字文件名");
                                                       bind(lfd, (struct sockaddr *)&serv_addr, len);  

Listen(lfd, 128);                                       Listen(lfd, 128);

cfd = Accept(lfd, ()&clie_addr, &len);                  cfd = Accept(lfd, ()&clie_addr, &len);  


client： 

    lfd = socket(AF_INET, SOCK_STREAM, 0);          lfd = socket(AF_UNIX, SOCK_STREAM, 0);

    " 隐式绑定 IP+port"                             bzero() ---- struct sockaddr_un clie_addr;
                                                    clie_addr.sun_family = AF_UNIX;
                                                    strcpy（clie_addr.sun_path, "client套接字文件名"）
                                                    len = offsetof(sockaddr_un, sun_path) + strlen();
                                                    unlink( "client套接字文件名");
                                                    bind(lfd, (struct sockaddr *)&clie_addr, len);

    bzero() ---- struct sockaddr_in serv_addr;       bzero() ---- struct sockaddr_un serv_addr;

    serv_addr.sin_family = AF_INET;                  serv_addr.sun_family = AF_UNIX;

    inet_pton(AF_INT, "服务器IP", &sin_addr.s_addr)                                                            serv_addr.sin_port = htons("服务器端口");          strcpy（serv_addr.sun_path, "server套接字文件名"）

                                                        len = offsetof(sockaddr_un, sun_path) + strlen();

    connect(lfd, &serv_addr, sizeof());         connect(lfd, &serv_addr, len);

本地套接字实现进程间通信

server.c

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <strings.h>
#include <string.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <stddef.h>

#include "wrap.h"

#define SERV_ADDR  "serv.socket"

int main(void)
{
    int lfd, cfd, len, size, i;
    struct sockaddr_un servaddr, cliaddr;
    char buf[4096];

    lfd = Socket(AF_UNIX, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sun_family = AF_UNIX;
    strcpy(servaddr.sun_path, SERV_ADDR);

    len = offsetof(struct sockaddr_un, sun_path) + strlen(servaddr.sun_path);     /* servaddr total len */

    unlink(SERV_ADDR);                              /* 确保bind之前serv.sock文件不存在,bind会创建该文件 */
    Bind(lfd, (struct sockaddr *)&servaddr, len);           /* 参3不能是sizeof(servaddr) */

    Listen(lfd, 20);

    printf("Accept ...\n");
    while (1) {
        len = sizeof(cliaddr);  //AF_UNIX大小+108B

        cfd = Accept(lfd, (struct sockaddr *)&cliaddr, (socklen_t *)&len);

        len -= offsetof(struct sockaddr_un, sun_path);      /* 得到文件名的长度 */
        cliaddr.sun_path[len] = '\0';                       /* 确保打印时,没有乱码出现 */

        printf("client bind filename %s\n", cliaddr.sun_path);

        while ((size = read(cfd, buf, sizeof(buf))) > 0) {
            for (i = 0; i < size; i++)
                buf[i] = toupper(buf[i]);
            write(cfd, buf, size);
        }
        close(cfd);
    }
    close(lfd);

    return 0;
}


client.c

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>         
#include <sys/socket.h>
#include <strings.h>
#include <string.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <stddef.h>

#include "wrap.h"

#define SERV_ADDR "serv.socket"
#define CLIE_ADDR "clie.socket"

int main(void)
{
    int  cfd, len;
    struct sockaddr_un servaddr, cliaddr;
    char buf[4096];

    cfd = Socket(AF_UNIX, SOCK_STREAM, 0);

    bzero(&cliaddr, sizeof(cliaddr));
    cliaddr.sun_family = AF_UNIX;
    strcpy(cliaddr.sun_path,CLIE_ADDR);

    len = offsetof(struct sockaddr_un, sun_path) + strlen(cliaddr.sun_path);     /* 计算客户端地址结构有效长度 */

    unlink(CLIE_ADDR);
    Bind(cfd, (struct sockaddr *)&cliaddr, len);                                 /* 客户端也需要bind, 不能依赖自动绑定*/


    bzero(&servaddr, sizeof(servaddr));                                          /* 构造server 地址 */
    servaddr.sun_family = AF_UNIX;
    strcpy(servaddr.sun_path, SERV_ADDR);

    len = offsetof(struct sockaddr_un, sun_path) + strlen(servaddr.sun_path);   /* 计算服务器端地址结构有效长度 */

    Connect(cfd, (struct sockaddr *)&servaddr, len);

    while (fgets(buf, sizeof(buf), stdin) != NULL) {
        write(cfd, buf, strlen(buf));
        len = read(cfd, buf, sizeof(buf));
        write(STDOUT_FILENO, buf, len);
    }

    close(cfd);

    return 0;
}