UDP Echo implementation using C

In the following program, we will demonstrate, how data can be transferred between client and server using Transport Layer Protocol - UDP. This code is self-explanatory. Hence, first, you will learn to develop server-side applications. Then, you will learn to develop client-side applications.

We know that UDP is a connection-less protocol, hence at the time of testing you may not get a response from the server many times.

Source code of Echo Server

#include <stdio.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> int main(void) { int received_data_length; int sent_data_length; int client_address_length; int server_port = 5000; short sock_file_descriptor; char server_ip[] = "127.0.0.1"; char buffer[256]; char *client; struct sockaddr_in server_address; struct sockaddr_in client_address; fflush(stdin); client = (char *) malloc(sizeof(server_address)); sock_file_descriptor = socket(PF_INET, SOCK_DGRAM, 0); if (sock_file_descriptor < 0) { printf("failed"); exit(1); } else { printf("socket created"); } bzero(&server_address, sizeof(server_address)); server_address.sin_family = PF_INET; inet_aton(server_ip, &server_address.sin_addr); server_address.sin_port = htons(server_port); bind(sock_file_descriptor, (struct sockaddr *) &server_address, sizeof(server_address)); received_data_length = recvfrom(sock_file_descriptor, buffer, strlen(buffer), 0, (struct sockaddr *) &client_address, &client_address_length); fflush(stdout); if (received_data_length != -1) printf("\n* receive success *\n"); else printf("\n* receive failure *\n"); sent_data_length = sendto(sock_file_descriptor, buffer, received_data_length, 0, (struct sockaddr *) &client_address, sizeof(client_address)); if (sent_data_length != -1) printf("\n* send success *\n"); else printf("\n* send failure *\n"); close(sock_file_descriptor); return 0; }

---

Source code of Echo Client

#include <sys/types.h> #include <stdio.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> int main(void) { int sock_file_descriptor; int sent_data_length; int received_data_length; unsigned int server_address_len; unsigned short server_port = 5000; char server_ip[] = "127.0.0.1"; char text[] = "Hello"; char buffer[256]; struct sockaddr_in server_address; server_address_len = sizeof(server_address); bzero(&server_address, sizeof(server_address)); server_address.sin_family = PF_INET; server_address.sin_port = htons(server_port); inet_aton(server_ip, &server_address.sin_addr); sock_file_descriptor = socket(PF_INET, SOCK_DGRAM, 0); /* send text to server */ sent_data_length = sendto(sock_file_descriptor, text, strlen(text), 0, (struct sockaddr *) &server_address, sizeof(server_address)); if (sent_data_length != -1) printf("\n* message sent successfully *\n"); else printf("\n* message sent failure *\n"); /* receive data from server */ received_data_length = recvfrom(sock_file_descriptor, buffer, strlen(buffer), 0, (struct sockaddr *) &server_address, &server_address_len); if (received_data_length != -1) { buffer[received_data_length] = '\0'; printf("\n* %s *\n", buffer); } close(sock_file_descriptor); return 0; }

---

Happy Exploring!