socket_example.c

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>

#define DATA_SIZE 10
#define PORT_NUMBER 8888

int main(void)
{
    int mysocket, client_socket;
    int testsocket;
    int datainbuffer;
    int result;
    int len = 0;
    int client_addr_size;
    struct sockaddr_in server_addr, client_addr;
    socklen_t mysockaddrlen = sizeof(struct sockaddr);
    char sent_data[DATA_SIZE];

    printf("[+] Starting\n");

    mysocket = socket(AF_INET, SOCK_STREAM, 0);

    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons( PORT_NUMBER );

    bind(mysocket, (struct sockaddr *) &server_addr, sizeof(server_addr));
    listen(mysocket, 2);

    printf("[+] Socket number %d was allocated\n", mysocket);
    printf("[+] Send more than %d bytes of data\n", DATA_SIZE);
    client_socket = accept(mysocket, (struct sockaddr *) &client_addr, (socklen_t*) &client_addr_size);
    recv(client_socket, sent_data, DATA_SIZE, 0);
    printf("[+] Data received - %s\n", sent_data);

    sleep(5);

    result = ioctl(client_socket, FIONREAD, &len);
    if (result == -1)
        printf("[-] Ioctl call failed. Error is %s\n", strerror(errno));
    else
        printf("[+] Queue size is %d!\n", result); // MISTAKE HERE - should have been len instead of result

    return 0;
}