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

struct sockaddr_in *sock_addr = NULL;
struct sockaddr_in *client_addr = NULL;

int sock_udp_server;
#define UDPPORT 55555

/* Interrupt_handler – so that CTRL + C can be used to
* exit the program */
void interrupt_handler (int signum) {
    close(sock_udp_server);

    free(sock_addr);
    free(client_addr);
    printf(“socket connection closed\n”);
    exit(0);
}

int main () {
    socklen_t length, num_of_bytes;
    char buffer[50] = {0};
    char *string = “Hello client\n”;

    signal (SIGINT, interrupt_handler);
    signal (SIGTERM, interrupt_handler);

    /* Part 1: create the server socket */

    if (0 > (sock_udp_server = socket(AF_INET, SOCK_DGRAM, 0))) {
        printf(“Unable to create a socket\n”);
        exit(0);
    }

    /* part 2: fill the structure and bind to socket */

    sock_addr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in));
    if (sock_addr == NULL) {
        printf(“unable to allocate memory\n”);
        goto end;
    }

    sock_addr->sin_family = AF_INET;
    sock_addr->sin_port = htons(UDPPORT);
    sock_addr->sin_addr.s_addr = inet_addr(“127.0.0.1”);

    if (0 != (bind(sock_udp_server, (struct sockaddr *)sock_addr, sizeof(struct             sockaddr_in)))) {
        printf(“unable to bind the socket\n”);
        goto end2;
    }

    /* part 3: read and write data */

    client_addr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in));
    if (client_addr == NULL) {
        printf(“Unable to allocate memory to client address socket\n”);
        goto end2;
    }

    while (1) {
        memset(buffer, 0, sizeof(buffer));
        num_of_bytes = recvfrom(sock_udp_server, buffer, sizeof(buffer), 0,                                                               (struct sockaddr *)client_addr, &length);
        if (num_of_bytes == -1) {
            printf(“unable to read from client\n”);
            goto end1;
       }

    printf(“%s\n”, buffer);
    memset(buffer, 0, sizeof(buffer));
    snprintf(buffer, (strlen(string)+1), “%s”, string);
    num_of_bytes = sendto(sock_udp_server, buffer, sizeof(buffer), 0, (struct                                                   sockaddr *)client_addr, length );
    if (num_of_bytes == -1) {
        printf(“unable to send Message to the client\n”);
        goto end1;
        }

    }
end1:
    free(client_addr);
end2:
    free(sock_addr);
end:
    close(sock_udp_server);

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>

int sock_fd;
struct sockaddr_in *server_addr = NULL;
#define PORT 55555

/* signal_handler – so that CTRL + C can be used to
* exit the program */
void interrupt_handler (int signum) {
    close(sock_fd);
    free(server_addr);
    printf(“socket connection closed\n”);
    exit(0);
}

int main () {
    int length, number_of_bytes;
    char buffer[50];
    char *string = “Hello from client”;

    signal (SIGINT, interrupt_handler);
    signal (SIGTERM, interrupt_handler);

    /* Part 1 – create socket */
    sock_fd = socket(AF_INET, SOCK_DGRAM, 0);

    if (sock_fd < 0) {
        printf(“unable to create socket\n”);
        exit(0);
    }

    /* Part 2 – fill the server structure for the specific interface */
    server_addr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in));
    if (server_addr == NULL) {
        printf(“Unable to allocate memory\n”);
        goto end;
    }

    server_addr->sin_family = AF_INET;
    server_addr->sin_addr.s_addr = inet_addr(“127.0.0.1”);
    server_addr->sin_port = htons(PORT);

    /* Part 3 – read and write data */
    while (1) {
        memset(buffer, 0, sizeof(buffer));
        snprintf(buffer, (strlen(string)+1), “%s”, string);
        if (sendto(sock_fd, buffer, sizeof(buffer),
            0, (struct sockaddr *)server_addr, sizeof(struct sockaddr_in)) !=                        sizeof(buffer)) {
            printf(“send to client failed\n”);
            goto end1;
        }

    memset(buffer, 0, sizeof(buffer));
    printf(“waiting to read from port\n”);

    number_of_bytes = recvfrom(sock_fd, buffer, sizeof(buffer),
                                                          0, NULL, NULL);

    if (number_of_bytes == -1) {
         printf(“Read failed\n”);
         goto end1;
    }
        printf(“%s\n”, buffer);
    }

end1:
    free(server_addr);
end:
    close(sock_fd);
return 0;
}