// Server side implementation of UDP client-server model 
#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <string.h> 
#include <sys/types.h> 
#include <sys/socket.h> 
#include <arpa/inet.h> 
#include <netinet/in.h> 
  
#define PORT    26000 
#define MAXLINE 1024 
  
// Driver code 
int main() { 
    int sockfd; 
    char buffer[MAXLINE]; 
    char *hello = "Hello from server"; 
    struct sockaddr_in servaddr, cliaddr; 
      
    // Creating socket file descriptor 
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) { 
        perror("socket creation failed"); 
        exit(EXIT_FAILURE);
    } 
      
    memset(&servaddr, 0, sizeof(servaddr)); 
    memset(&cliaddr,  0, sizeof(cliaddr)); 
      
    // Filling server information 
    servaddr.sin_family      = AF_INET; // IPv4 
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1"); 
    servaddr.sin_port        = htons(PORT); 
      
    // Bind the socket with the server address 
    if ( bind(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0 ) { 
        perror("bind failed"); 
        exit(EXIT_FAILURE); 
    } 
      
    int len, n; 
  
    len = sizeof(cliaddr);  //len is value/resuslt 
  
    n = recvfrom(sockfd, (char *)buffer, MAXLINE, MSG_WAITALL, ( struct sockaddr *)&cliaddr, &len); 
    buffer[n] = '\0'; 

    printf("Client : %s\n", buffer); 
    
    close(sockfd);
    
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }
    
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family      = AF_INET; // IPv4
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    servaddr.sin_port        = htons(26001);
    
    if ( bind(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0 ) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    sendto(sockfd, (const char *)hello, strlen(hello), MSG_CONFIRM, (const struct sockaddr *)&cliaddr, len); 

    printf("Hello message sent.\n");  
      
    return 0; 
}