1. 域套接字：
(1) 只能用于同一设备上不同进程之间的通信；
(2) 效率高于网络套接字。域套接字仅仅是复制数据，并不走协议栈；
(3) 可靠，全双工；
2. 域套接字地址结构：
struct sockaddr_un { sa_family_t sun_family; /*AF_UNIX*/ char sun_path[108]; /*pathname*/ };
当我们将一个地址绑定至域套接字，系统用该路径名创建一个类型为S_IFSOCK的文件，尽告诉客户端名字，不能打开，也不能通信，
不会自动删除，需要程序完成后删除，若文件已存在则bind失败；
3. 测试代码：
server.c
1 #include <sys/types.h> 2 #include <sys/socket.h> 3 #include <sys/un.h> 4 #include <stdio.h> 5 #include <stdlib.h> 6 7 #define UN_PATH "/var/tmp/test_domain_socket" 8 9 10 int main(int argc, char *argv[]) 11 { 12 int sockfd = -1; 13 struct sockaddr_un un; 14 int len = 0; 15 16 if ((sockfd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){ 17 perror("create socket error "); 18 goto _ERROR; 19 } 20 21 memset(&un, 0, sizeof(un)); 22 un.sun_family = AF_UNIX; 23 strcpy(un.sun_path, UN_PATH); 24 25 len = sizeof(un.sun_family) + sizeof(un.sun_path); 26 27 if (bind(sockfd, (struct sockaddr *)&un, len) < 0){ 28 perror("socket bind error "); 29 goto _ERROR; 30 } 31 32 if (listen(sockfd, 5) < 0){ 33 perror("socket listen error "); 34 } 35 36 int conn = accept(sockfd, (struct sockaddr *)&un, &len); 37 if (conn < 0){ 38 perror("accept error "); 39 goto _ERROR; 40 } 41 char buf[64] = {0}; 42 int n = read(conn, buf, 63); 43 printf("recive-msg:%s", buf); 44 write(conn, buf, n); 45 close(conn); 46 47 close(sockfd); 48 unlink(UN_PATH); 49 return 0; 50 51 _ERROR: 52 if (sockfd != -1){ 53 close(sockfd); 54 } 55 56 return -1; 57 }
client.c
1 #include <sys/types.h> 2 #include <sys/socket.h> 3 #include <sys/un.h> 4 #include <stdio.h> 5 #include <stdlib.h> 6 #include <unistd.h> 7 8 #define UN_PATH "/var/tmp/test_domain_socket" 9 10 11 int main(int argc, char *argv[]) 12 { 13 int sockfd = -1; 14 struct sockaddr_un un; 15 int len = 0; 16 17 if ((sockfd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){ 18 perror("create socket error "); 19 goto _ERROR; 20 } 21 22 memset(&un, 0, sizeof(un)); 23 un.sun_family = AF_UNIX; 24 strcpy(un.sun_path, UN_PATH); 25 26 len = sizeof(un.sun_family) + sizeof(un.sun_path); 27 28 if (connect(sockfd, (struct sockaddr *)&un, len) < 0){ 29 perror("socket connect error "); 30 goto _ERROR; 31 } 32 33 char buf[64] = {0}; 34 int n = read(STDIN_FILENO, buf, 63); 35 write(sockfd, buf, n); 36 printf("send-msg:%s", buf); 37 read(sockfd, buf, 63); 38 buf[64] = ' '; 39 printf("recv-msg:%s", buf); 40 41 close(sockfd); 42 return 0; 43 44 _ERROR: 45 if (sockfd != -1){ 46 close(sockfd); 47 } 48 49 return -1; 50 }