TCP套接口编程(Socket)

TCP套接口编程(Socket)

socket起源于Unix，而Unix/Linux基本哲学之一就是“一切皆文件”，都可以用“打开open –> 读写write/read –> 关闭close”模式来操作。我的理解就是Socket就是该模式的一个实现，socket即是一种特殊的文件，一些socket函数就是对其进行的操作（读/写IO、打开、关闭）。

1.套接口的数据结构。在<sys/socket.h>头文件中，其数据结构定义如下

struct  sockaddr{uint8_t sa_len;                uint8_t 是POSIX.1要求的数据类型。sa_family_t   sa_family;    套接口的协议族cahr   sa_data[14];             协议地址的大小}struct socketaddr_in{uint8_t  sin_len;              sa_family_t   sin_family;in_port_t     sin_port;struct  in_addr   sin_addr;unsigned char     sin_zero[8];};

以上是通用的套接口的数据结构，在平常中我们用到的是ipv4套接口的地址数据结构。

在tcp套接口编程中。server端和client端相互通信，其步骤如下：

上面是基本的socket编程，通信模型。

1. server.c

#include <stdlib.h>#include <stdio.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>#define MAXSIZE 1024     /*定义数据缓冲区大小*/int main(int argc, char *argv[]){struct sockaddr_in server_addr;//定义服务端套接口数据结构server_addrint sock_fd, new_fd, ret;int sin_size, portno;char buffer[MAXSIZE] = { 0 };//发送缓存区大小if( argc != 2){fprintf(stderr, "Usage:%s [port-number]\n", argv[0]);exit(EXIT_FAILURE);}portno = atoi(argv[1]);//参数二的端口//第一步创建套接口sock_fd = socket(AF_INET, SOCK_STREAM, 0);if (sock_fd == -1){fprintf(stderr, "Create socket failed, reason: %s\n", strerror(errno));exit(EXIT_FAILURE);}else fprintf(stdout, "Create socket success.\n");//第二步填充套接字bzero(&server_addr, sizeof(server_addr));server_addr.sin_family = AF_INET;server_addr.sin_addr.s_addr = htonl(INADDR_ANY);server_addr.sin_port = htons(portno);ret = bind(sock_fd, (struct sockaddr *)(&server_addr), sizeof(struct sockaddr));if (ret == -1){fprintf(stderr, "bind port failed, reason: %s\n", strerror(errno));exit(EXIT_FAILURE);}else fprintf(stdout, "bind port success.\n");//第三步监听客户端的请求，最大请求数为5if( listen(sock_fd, 5) == -1){fprintf(stderr, "listen failed, reason: %s\n", strerror(errno));exit(EXIT_FAILURE);}else fprintf(stdout, "listen success.\n");//第四步接收请求accept()while (1)//服务端采用阻塞模式，等待客户端请求{bzero(&client_addr, sizeof(client_addr));sin_size = sizeof(struct sockaddr_in); new_fd = accept(sock_fd, NULL, NULL);<span style="white-space:pre"></span><span style="font-family: 'Courier New';">//调用accept接收一次请求 </span>if (new_fd == -1){fprintf(stderr, "server accept failed, reason: %s\n", strerror(errno));exit(EXIT_FAILURE);}printf("connected sucessful, please enter reply message: ");fgets(buffer, MAXSIZE, stdin);if( write(new_fd, buffer, strlen(buffer)) == -1){fprintf(stderr, "write failed, reason: %\n", strerror(errno));exit(EXIT_FAILURE);}close(new_fd);//本次通信接收，关闭客户端的套接口，等待接收下次usleep(30000);}close(sock_fd);//服务端进程终止，关闭服务端套接口return 0;}

2. client.c

#include <stdlib.h>#include <stdio.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#define MAXSIZE 1024int main(int argc, char *argv[]){int sock_fd, ret;char buffer[MAXSIZE] = { 0 };struct sockaddr_in server_addr;struct hostent *host = NULL;int portno, nbytes;if (argc != 3){fprintf(stderr, "Usage:%s -h[hostname]/-a[ip] -p[portnumber]\n", argv[0]);exit(EXIT_FAILURE);}//预先处理：通过主机名或者IP地址获得主机信息if (argv[1][1] == 'h')host = gethostbyname(argv[1]+2);else if (argv[1][1] == 'a'){char IPaddr[128] = { 0 };int sta = inet_pton(AF_INET, argv[1] + 2, IPaddr);printf("%s %s IPaddr: %s\n", argv[1] + 2, argv[2] + 2, IPaddr);if (sta == 0){fprintf(stderr, "IP address invalid.\n");exit(EXIT_FAILURE);}else if(sta == -1){fprintf(stderr, "inet_pton failed, reason: %s\n", strerror(errno));exit(EXIT_FAILURE);}host = gethostbyaddr(IPaddr, sizeof(struct in_addr), AF_INET);}if (host == NULL){fprintf(stderr, "get host by name/address failed, reason: %s\n",hstrerror(h_errno));exit(EXIT_FAILURE);}else fprintf(stdout, "get host success.\n");//第一步创建客户端套接字sock_fd = socket(AF_INET, SOCK_STREAM, 0);if (sock_fd == -1){fprintf(stderr, "create socket failed, reason: %s\n", strerror(errno));exit(EXIT_FAILURE);}else fprintf(stdout, "create socket success.\n");portno = atoi(argv[2] + 2);//第二步填充套接字bzero(&server_addr, sizeof(struct sockaddr));server_addr.sin_family = AF_INET;server_addr.sin_addr = *((struct in_addr *)(host->h_addr));server_addr.sin_port = htons(portno);//第四步connect服务端ret = connect(sock_fd, (struct sockaddr *)(&server_addr), sizeof(struct sockaddr));if (ret == -1){fprintf(stderr, "connected server failed, reason: %s\n",strerror(errno));exit(EXIT_FAILURE);}else fprintf(stdout, "connected server success.\n");//第五步链接成功后，读取服务端的数据nbytes = read(sock_fd, buffer, MAXSIZE);fprintf(stdout,"client received msg(TCP): %s\n", buffer);//客户端受到服务端的数据后，关闭服务端套接口，结束通信close(sock_fd);return 0;}

注意：当运行测试时，可能出现问题，情况很多如防火墙，地址不对，主机找不到，端口被占用等等，这些问题都要确保解决后，方能运行成功。