CN-LAB-V-SEM

Exercise 8: Implementation of Connectionless Iterative Time Service (UDP)

Description

UDP:

• Does not establish a connection before data transmission, making it faster.
• Sends packets directly to the destination without ensuring delivery, order, or integrity.
• Is suitable for time-sensitive applications, although it may result in packet loss.

Source Code

Server Code

The server initializes a UDP socket, receives messages from a client, and sends a response back.

// 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 8080
#define MAXLINE 1024

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 = INADDR_ANY;
    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);

    // Receive message from client
    n = recvfrom(sockfd, (char *)buffer, MAXLINE, MSG_WAITALL, (struct sockaddr *) &cliaddr, &len);
    buffer[n] = '\0';
    printf("Client : %s\n", buffer);

    // Send response to client
    sendto(sockfd, (const char *)hello, strlen(hello), MSG_CONFIRM, (const struct sockaddr *) &cliaddr, len);
    printf("Hello message sent.\n");

    return 0;
}

Client Code

The client initializes a UDP socket, sends a message to the server, and waits for a response.

// Client 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 8080
#define MAXLINE 1024

int main() {
    int sockfd;
    char buffer[MAXLINE];
    char *hello = "Hello from client";
    struct sockaddr_in servaddr;

    // 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));

    // Filling server information
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(PORT);
    servaddr.sin_addr.s_addr = INADDR_ANY;

    int n, len;

    // Send message to server
    sendto(sockfd, (const char *)hello, strlen(hello), MSG_CONFIRM, (const struct sockaddr *) &servaddr, sizeof(servaddr));
    printf("Hello message sent.\n");

    // Receive response from server
    n = recvfrom(sockfd, (char *)buffer, MAXLINE, MSG_WAITALL, (struct sockaddr *) &servaddr, &len);
    buffer[n] = '\0';
    printf("Server : %s\n", buffer);

    close(sockfd);
    return 0;
}

Explanation

1. Server:
   • Creates a UDP socket and binds it to a specified port.
   • Waits for a message from the client and responds with “Hello from server.”
2. Client:
   • Creates a UDP socket and sends “Hello from client” to the server.
   • Receives a response from the server and displays it.

Output Example

Server

$ ./server
Client: Hello from client
Hello message sent.

Client

$ ./client
Hello message sent.
Server : Hello from server