网络通信

Socket通信的3要素

通信的目的地址
使用的端口号
使用的传输层协议(如TCP、UDP)

Socket通信模型

简单的回声服务器实现

服务端

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


#define SERVER_PORT 666

int main(void){

	int sock;//信箱

	struct sockaddr_in server_addr;


	//创建信箱
	sock = socket(AF_INET,SOCK_STREAM,0);
	
	
	//清空标签
	bzero(&server_addr,sizeof(server_addr));	
	//写上地址和端口号
	server_addr.sin_family = AF_INET;		//选择协议族ipv4
	server_addr.sin_addr.s_addr = htonl(INADDR_ANY);//监听本地所有IP地址-几个网卡就有几个IP地址
	server_addr.sin_port = htons(SERVER_PORT);	//绑定端口号

	//实现标签贴到收信的信箱上
	bind(sock,(struct sockaddr*)&server_addr,sizeof(server_addr));

	//邮箱一次性只能接收128封信件
	listen(sock,128);

	printf("等待客户端链接\n");

	int done = 1;
	
	while(done){
		struct sockaddr_in client;
		
		int client_socket;		
		int len;

		char client_ip[64];
		
		char buf[256];

		socklen_t client_addr_len;

		client_addr_len = sizeof(client);	
			
		client_socket = accept(sock,(struct sockaddr*)&client,&client_addr_len);

		printf("客户端地址:%s\t端口:%d\n",inet_ntop(AF_INET,&client.sin_addr.s_addr,client_ip,sizeof(client_ip)),ntohs(client.sin_port));

		//读取数据
		len = read(client_socket,buf,sizeof(buf)-1);

		buf[len] = '\n';//read读过来的数据不会自动加字符串结束符

		printf("收到[%d]：%s\n",len,buf);

		len = write(client_socket,buf,len);//发回去

		printf("写完，len:%d",len);

		close(client_socket);
	}

	return 0;
}

**可以使用telnet来模拟客户端链接服务器。**例如:

客户端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define SERVER_PORT 666
#define SERVER_IP "127.0.0.1"


int main(int argc, char* argv[]) {

	int sockfd;
	char* message;

	struct sockaddr_in servaddr;

	int n;

	char buf[64];

	//echo_client "xxxx"   ——所以判断是否为2
	if (argc != 2) {
		fputs("Usage: ./echo_client message \n",stderr);
		exit(1);
	}

	message = argv[1];
	printf("message: %s\n",message);


	sockfd = socket(AF_INET,SOCK_STREAM,0);

	memset(&servaddr,'\0',sizeof(struct sockaddr_in));

	servaddr.sin_family = AF_INET;

	//inet_pton(AF_INET,SERVER_IP,&servaddr.sin_addr);
	inet_pton(AF_INET, SERVER_IP, &servaddr.sin_addr);
	servaddr.sin_port = htons(SERVER_PORT); //转换为网络字节序

	connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr));

	write(sockfd,message,strlen(message));

	n = read(sockfd, buf, sizeof(buf)-1);

	if (n > 0) {
		buf[n] = '\n';
		printf("receive: %s\n",buf);
	} else {
		perror("error!");
	}

	printf("finished!\n");
	close(sockfd);

	return 0;
}

测试