ReverseServer.c

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

#define S_PORT 43454
#define C_PORT 43455
#define ERROR -1
#define IP_STR "127.0.0.1"

void strrev(char *str, int len) {
    int i, j;
    char temp;
    for (i = 0, j = len -1; i < j; ++i, --j) {
        temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }
}

int main(int argc, char const *argv[]) {
	int sfd, len;
	char *str_buf;
	struct sockaddr_in servaddr, clientaddr;
	sfd = socket(AF_INET, SOCK_DGRAM,IPPROTO_UDP);
	if (sfd == ERROR) {
		perror("Could not open a socket");
		return 1;
	}
	memset((char *) &servaddr, 0, sizeof(servaddr));
	servaddr.sin_family=AF_INET;
	servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
	servaddr.sin_port=htons(S_PORT);

	memset((char *) &clientaddr, 0, sizeof(clientaddr));
	clientaddr.sin_family=AF_INET;
	clientaddr.sin_addr.s_addr=inet_addr(IP_STR);
	clientaddr.sin_port=htons(C_PORT);

	if((bind(sfd,(struct sockaddr *)&servaddr,sizeof(servaddr)))!=0) {
		perror("Could not bind socket");
		return 2;
	}

	printf("Server is running on %s:%d\n", IP_STR, S_PORT);
	while(1) {
		recvfrom(sfd, &len, sizeof(len), 0, (struct sockaddr *)&clientaddr, (socklen_t *)&clientaddr);
		str_buf = (char *) malloc(len*sizeof(char));
		recvfrom(sfd, str_buf, len, 0, (struct sockaddr *)&clientaddr, (socklen_t *)&clientaddr);
		printf("Client: %s\t", str_buf);
		strrev(str_buf,len);  //String Reversal
		sendto(sfd, &len, sizeof(len), 0, (struct sockaddr *)&clientaddr, sizeof(clientaddr));
		sendto(sfd, str_buf, len, 0, (struct sockaddr *)&clientaddr, sizeof(clientaddr));
		printf("\nReverse: %s\n", str_buf);
		free(str_buf);
	}
	return 0;
}