/* this is a UDP receiver */

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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])
{
	int sockfd;
	socklen_t len;
	struct sockaddr_in servaddr;
	struct sockaddr_in cliaddr;
	char buf[100000];
	// int count = 0;
	FILE *fd;

	if (argc != 2) {
		printf("Usage : a.out port\n");
		exit(0);
	}

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons((int)atoi(argv[1]));
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);

	if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
		perror(": socket");
		exit(0);
	}

	if ((bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)) {
		perror(": bind");
		exit(0);
	}

	if ((fd = fopen("outputfile", "w")) == NULL) {
		printf("can't open outputfile\n");
		exit(0);
	}

	while (1) {
		memset(&cliaddr, 0, sizeof(servaddr));
		len = sizeof (cliaddr);
		recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&cliaddr, &len);
		if ((*buf < 'A') || (*buf > 'Z')) exit(0);
		if (*buf=='Z') fprintf(fd, "%c\n", *buf);
		else fprintf(fd, "%c", *buf);
		/*    printf("message %c from %s %d\n", *buf, 
			  inet_ntoa(cliaddr.sin_addr),
			  cliaddr.sin_port) ;
			  */
		sendto(sockfd, buf, 1, 0, (struct sockaddr *)&cliaddr, len);
	}
}