套接字socket---網路套接字

網路套接字

• 採用迴路網路連線到一個網路套接字
• 迴路網路只包含一臺計算機，通常稱為localhost，IP地址為127.0.0.1，可以在/etc/hosts檔案中找到

例子：

客戶端發一個A給伺服器，伺服器收到A，加1改成B，返回給客戶端，客戶端顯示收到的字元

server1.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

int main()
{
	int server_sockfd, client_sockfd;
	int server_len, client_len;
	//sockaddr_in:網路套接字的地址
	struct sockaddr_in server_address;
	struct sockaddr_in client_address;
	//第一個引數域AF_INET
	server_sockfd = socket(AF_INET, SOCK_STREAM, 0);
	//命名網路套接字
	server_address.sin_family = AF_INET;
	//inet_addr:把一個字串形式的IP地址變成整數
	server_address.sin_addr.s_addr = inet_addr("127.0.0.1");
	server_address.sin_port = 9734;
	server_len = sizeof(server_address);
	//套接字命名
	bind(server_sockfd, (struct sockaddr *)&server_address, server_len);
	//建立長度為5的監聽佇列
	listen(server_sockfd, 5);
	while(1)
	{
		char ch;
		printf("server waiting\n");
		client_len = sizeof(client_address);
		client_sockfd = accept(server_sockfd, (struct sockaddr *)&client_address, &client_len);
		read(client_sockfd, &ch, 1);
		ch++;
		write(client_sockfd, &ch, 1);
		close(client_sockfd);
	}
}
 

client1.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
int main()
{
	int sockfd;
	int len;
	struct sockaddr_in address;//地址格式
	int result;
	char ch = 'A';
	sockfd = socket(AF_INET, SOCK_STREAM, 0);//生成套接字
	address.sin_family = AF_INET;
	//inet_addr的返回值已經是網路位元組序
	address.sin_addr.s_addr = inet_addr("127.0.0.1");//格式轉換
	address.sin_port = 9734;
	len = sizeof(address);
	result = connect(sockfd, (struct sockaddr *)&address, len);
	if (result == -1)
	{
		perror("oops:client2");
		exit(1);
	}
	write(sockfd, &ch, 1);
	read(sockfd, &ch, 1);
	printf("char from server = %c\n", ch);
	close(sockfd);
	exit(0);

}
 

位元組序問題

不同計算機的位元組序不一樣，例如intel機器一般採用小端方式，而motorola一般採用大端方式，因此傳輸資訊時會造成混亂。

網路位元組序：客戶和伺服器在傳輸之前，將內部整數表示方式轉換為網路位元組序可解決位元組序問題。

#include <netinet/in.h>
unsigned long int htonl(unsigned long int hostlong);       //host to net本地位元組序轉換為網路位元組序
unsigned short int htons(unsigned short

server2.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

int main()
{
	int server_sockfd, client_sockfd;
	int server_len, client_len;
	//sockaddr_in:網路套接字的地址
	struct sockaddr_in server_address;
	struct sockaddr_in client_address;
	//第一個引數域AF_INET
	server_sockfd = socket(AF_INET, SOCK_STREAM, 0);
	//命名網路套接字
	server_address.sin_family = AF_INET;
	//INADDR_ANY:任何機器都允許連線伺服器上
	server_address.sin_addr.s_addr = htonl(INADDR_ANY);
	server_address.sin_port = htons(9734);
	server_len = sizeof(server_address);
	//套接字命名
	bind(server_sockfd, (struct sockaddr *)&server_address, server_len);
	//建立長度為5的監聽佇列
	listen(server_sockfd, 5);
	while(1)
	{
		char ch;
		printf("server waiting\n");
		client_len = sizeof(client_address);
		client_sockfd = accept(server_sockfd, (struct sockaddr *)&client_address, &client_len);
		read(client_sockfd, &ch, 1);
		ch++;
		write(client_sockfd, &ch, 1);
		close(client_sockfd);
	}
}

client2.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
int main()
{
	int sockfd;
	int len;
	struct sockaddr_in address;//地址格式
	int result;
	char ch = 'A';
	sockfd = socket(AF_INET, SOCK_STREAM, 0);//生成套接字
	address.sin_family = AF_INET;
	//inet_addr的返回值已經是網路位元組序
	address.sin_addr.s_addr = inet_addr("127.0.0.1");//格式轉換
	address.sin_port = htons(9734);
	len = sizeof(address);
	result = connect(sockfd, (struct sockaddr *)&address, len);
	if (result == -1)
	{
		perror("oops:client2");
		exit(1);
	}
	write(sockfd, &ch, 1);
	read(sockfd, &ch, 1);
	printf("char from server = %c\n", ch);
	close(sockfd);
	exit(0);

}