linux 本地通信实例 AF_UNIX close (sockfd）很重要

原创已于 2023-10-05 20:29:11 修改 · 1.8k 阅读

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#通信 #linux #local socket

于 2013-10-17 14:29:34 首次发布

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程序说明：
程序里包含服务端和客户端两个程序，它们之间使用 AF_UNIX 实现本机数据流通信。使用 AF_UNIX 域实际上是使用本地 socket 文件来通信。

服务器端代码：

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <sys/un.h>
#include <unistd.h>
#include <stdlib.h>
int main ( int argc , char * argv [])
{
         int server_sockfd , client_sockfd ;
         int server_len , client_len ;
         struct sockaddr_un server_address ;       /*声明一个UNIX域套接字结构*/
         struct sockaddr_un client_address ;
         int i , bytes ;
         char ch_send , ch_recv ;
         unlink ( "server_socket" );        /*删除原有server_socket对象*/
         /*创建 socket, 通信协议为AF_UNIX, SCK_STREAM 数据方式*/
         server_sockfd = socket ( AF_UNIX , SOCK_STREAM , 0 );
         /*配置服务器信息(通信协议)*/
         server_address . sun_family = AF_UNIX ;
         /*配置服务器信息(socket 对象)*/
         strcpy ( server_address . sun_path , "server_socket" );
         /*配置服务器信息(服务器地址长度)*/
         server_len = sizeof ( server_address );
         /*绑定 socket 对象*/
         bind ( server_sockfd , ( struct sockaddr * ) & server_address , server_len );
         /*监听网络,队列数为5*/
         listen ( server_sockfd , 5 );
         printf ( "Server is waiting for client connect... \n " );
         client_len = sizeof ( client_address );
         /*接受客户端请求; 第2个参数用来存储客户端地址; 第3个参数用来存储客户端地址的大小*/
         /*建立(返回)一个到客户端的文件描述符,用以对客户端的读写操作*/
         client_sockfd = accept ( server_sockfd , ( struct sockaddr * ) & server_address , ( socklen_t * ) & client_len );
         if ( client_sockfd == - 1 ) {
                 perror ( "accept" );
                 exit ( EXIT_FAILURE );
         }
         printf ( "The server is waiting for client data... \n " );
         for ( i = 0 , ch_send = '1' ; i < 5 ; i ++ , ch_send ++ ) {
                 if (( bytes = read ( client_sockfd , & ch_recv , 1 )) == - 1 ) {
                         perror ( "read" );
                         exit ( EXIT_FAILURE );
                 }
                 printf ( "The character receiver from client is %c \n " , ch_recv );
                 sleep ( 1 );
                 if (( bytes = write ( client_sockfd , & ch_send , 1 )) == - 1 ) {
                         perror ( "read" );
                         exit ( EXIT_FAILURE );
                 }
         }
                 close (client_sockfd) ;
                 unlink ( "server socket" );
}

客户端代码：

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <sys/un.h>
#include <unistd.h>
#include <stdlib.h>

int main ( int argc , char * argv [])
{
     struct sockaddr_un address ;
     int sockfd ;
     int len ;
     int i , bytes ;
     int result ;
     char ch_recv , ch_send ;

     /*创建socket,AF_UNIX通信协议,SOCK_STREAM数据方式*/
     if (( sockfd = socket ( AF_UNIX , SOCK_STREAM , 0 )) == - 1 ) {
             perror ( "socket" );
             exit ( EXIT_FAILURE );
     }

     address . sun_family = AF_UNIX ;
     strcpy ( address . sun_path , "server_socket" );
     len = sizeof ( address );

     /*向服务器发送连接请求*/
     result = connect ( sockfd , ( struct sockaddr * ) & address , len );
     if ( result == - 1 ) {
         printf ( "ensure the server is up \n " );
         perror ( "connect" );
         exit ( EXIT_FAILURE );
     }

     for ( i = 0 , ch_send = 'A' ; i < 5 ; i ++ , ch_send ++ ) {
         if (( bytes = write ( sockfd , & ch_send , 1 )) == - 1 ) { /*发消息给服务器*/
             perror ( "write" );
             exit ( EXIT_FAILURE );
         }

         sleep ( 2 );     /*休息二秒钟再发一次*/

         if (( bytes = read ( sockfd , & ch_recv , 1 )) == - 1 ) { /*接收消息*/
             perror ( "read" );
             exit ( EXIT_FAILURE );
         }

         printf ( "receive from server data is %c \n " , ch_recv );
     }
     close (sockfd);

     return ( 0 );
}

程序说明：
先运行服务器端，然后再运行客户端可以在两边同时看到输出。服务器端先运行后会出现如下提示：

./sock_local_server
Server is waiting for client connect...

这表示，服务器端已经被阻塞到到 accept() 这里，服务器就在此等候客户端的连接。
如果不是先运行服务器端，而直接运行客户端，那么客户端会提示：

./ sock_local_client
ensure the server is up
connect: Connection refused

提示服务器没有准备好，连接被拒绝，从而直接退出程序。

如果服务器和客户端依次运行，可以在两边看到输出：
服务器端：

./sock_local_server
Server is waiting for client connect...
The server is waiting for client data...
The character receiver from client is A
The character receiver from client is B
The character receiver from client is C
The character receiver from client is D
The character receiver from client is E

客户端：

./ sock_local_client
receive from server data is 1
receive from server data is 2
receive from server data is 3
receive from server data is 4
receive from server data is 5

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