[网络协议]C/S模型UDP实现

一、处理模型

由于UDP不需要维护连接，程序逻辑简单了很多，但是UDP协议是不可靠的，保证通讯可靠性的机制需要在应用层实现。

二、实现

服务器端：

#include <string.h>
#include <netinet/in.h>
#include <stdio.h>
#include <unistd.h>
#include <strings.h>
#include <arpa/inet.h>
#include <ctype.h>

#define MAXLINE 80
#define SERV_PORT 6666

int main(void)
{
	struct sockaddr_in servaddr, cliaddr;
	socklen_t cliaddr_len;
	int sockfd;
	char buf[MAXLINE];
	char str[INET_ADDRSTRLEN];
	int i, n;
	sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(SERV_PORT);
	bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
	printf("Accepting connections ...\n");
	while (1) 
	{
		cliaddr_len = sizeof(cliaddr);
		n = recvfrom(sockfd, buf, MAXLINE,0, (struct sockaddr *)&cliaddr, &cliaddr_len);
		if (n == -1)
			perror("recvfrom error");
		printf("received from %s at PORT %d\n", inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)),ntohs(cliaddr.sin_port));
		for (i = 0; i < n; i++)
			buf[i] = toupper(buf[i]);
		n = sendto(sockfd, buf, n, 0, (struct sockaddr *)&cliaddr, sizeof(cliaddr));
		if (n == -1)
			perror("sendto error");
	}
	close(sockfd);
	return 0;
}

客户端：

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <strings.h>
#include <ctype.h>

#define MAXLINE 80
#define SERV_PORT 6666

int main(int argc, char *argv[])
{
	struct sockaddr_in servaddr;
	int sockfd, n;
	char buf[MAXLINE];
	sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);
	servaddr.sin_port = htons(SERV_PORT);
	while (fgets(buf, MAXLINE, stdin) != NULL) 
	{
		n = sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr *)&servaddr, sizeof(servaddr));
		if (n == -1)
			perror("sendto error");
		n = recvfrom(sockfd, buf, MAXLINE, 0, NULL, 0);
		if (n == -1)
			perror("recvfrom error");
		write(STDOUT_FILENO, buf, n);
	}
	close(sockfd);
	return 0;
}