udp服務器端demo

#include <sys/types.h>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h> 
#define MAXLINE 20			//報文最大長度
#define SERV_PORT 8840		//端口號

/*
 *向客戶端返回接收到到數據，並在終端打印該客戶端的ip及端口
 * */
void do_echo(int sockfd, struct sockaddr *pcliaddr,socklen_t clilen) {
		int i;		//for循環使用
		int n;		//接收recfrom的返回值
		socklen_t len;
		char str[INET_ADDRSTRLEN];
		unsigned char mesg[MAXLINE]="\0";
	
		for (;;){
				len = clilen;
				bzero(mesg,sizeof(mesg));
				/* waiting for receive data */
				n = recvfrom(sockfd, mesg, MAXLINE, 0,pcliaddr, &len);
			
				for(i=0;i<n;i++){
						printf("%02x ",mesg[i]);
				}
				/* sent data back to client */
				sendto(sockfd, mesg, n, 0, pcliaddr, len);

				printf("\nyour ip is %s at port %d\n",
						inet_ntop(AF_INET, &(((struct sockaddr_in *)pcliaddr)->sin_addr),str,sizeof(str)),
						ntohs(((struct sockaddr_in *)pcliaddr)->sin_port));
		}
}


int main(void) {

		printf("waiting msg\n");

		int sockfd;
		struct sockaddr_in servaddr, cliaddr;

		sockfd = socket(AF_INET, SOCK_DGRAM, 0); /* create a socket */

		/* init servaddr */
		bzero(&servaddr, sizeof(servaddr));
		servaddr.sin_family = AF_INET;
		servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
		servaddr.sin_port = htons(SERV_PORT);

		/* bind address and port to socket */
		if (bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1) {
				perror("bind error");
				exit(1);
		}


		do_echo(sockfd, (struct sockaddr *) &cliaddr,sizeof(cliaddr));

		return 0;
}