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/* timecli.c */
/* Gets the current time from a UDP server */
/* Last modified: September 23, 2005 */
/* http://www.gomorgan89.com */
/* Link with library file wsock32.lib */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <winsock.h>

#define SIZE 500

void usage(void);

int main(int argc, char **argv)
{
    WSADATA w;                                /* Used to open Windows connection */
    unsigned short port_number;                /* The port number to use */
    SOCKET sd;                                /* The socket descriptor */
    int server_length;                        /* Length of server struct */
    char send_buffer[SIZE] = "GET TIME\r\n";/* Data to send */
    time_t current_time;                    /* Time received */
    struct hostent *hp;                        /* Information about the server */
    struct sockaddr_in server;                /* Information about the server */
    struct sockaddr_in client;                /* Information about the client */
    int a1, a2, a3, a4;                        /* Server address components in xxx.xxx.xxx.xxx form */
    int b1, b2, b3, b4;                        /* Client address components in xxx.xxx.xxx.xxx form */
    char host_name[256];                    /* Host name of this computer */

    /* Make sure command line is correct */
    if (argc != 3 && argc != 4)
    {
        usage();
    }
    if (sscanf_s(argv[1], "%d.%d.%d.%d", &a1, &a2, &a3, &a4) != 4)
    {
        usage();
    }
    if (sscanf_s(argv[2], "%u", &port_number) != 1)
    {
        usage();
    }
    if (argc == 4)
    {
        if (sscanf_s(argv[3], "%d.%d.%d.%d", &b1, &b2, &b3, &b4) != 4)
        {
            usage();
        }
    }

    /* Open windows connection */
    if (WSAStartup(0x0101, &w) != 0)
    {
        fprintf(stderr, "Could not open Windows connection.\n");
        exit(0);
    }

    /* Open a datagram socket */
    sd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sd == INVALID_SOCKET)
    {
        fprintf(stderr, "Could not create socket.\n");
        WSACleanup();
        exit(0);
    }

    /* Clear out server struct */
    memset((void *)&server, '\0', sizeof(struct sockaddr_in));

    /* Set family and port */
    server.sin_family = AF_INET;
    server.sin_port = htons(port_number);

    /* Set server address */
    server.sin_addr.S_un.S_un_b.s_b1 = (unsigned char)a1;
    server.sin_addr.S_un.S_un_b.s_b2 = (unsigned char)a2;
    server.sin_addr.S_un.S_un_b.s_b3 = (unsigned char)a3;
    server.sin_addr.S_un.S_un_b.s_b4 = (unsigned char)a4;

    /* Clear out client struct */
    memset((void *)&client, '\0', sizeof(struct sockaddr_in));

    /* Set family and port */
    client.sin_family = AF_INET;
    client.sin_port = htons(0);

    if (argc == 3)
    {
        /* Get host name of this computer */
        gethostname(host_name, sizeof(host_name));
        hp = gethostbyname(host_name);

        /* Check for NULL pointer */
        if (hp == NULL)
        {
            fprintf(stderr, "Could not get host name.\n");
            closesocket(sd);
            WSACleanup();
            exit(0);
        }

        /* Assign the address */
        client.sin_addr.S_un.S_un_b.s_b1 = hp->h_addr_list[0][0];
        client.sin_addr.S_un.S_un_b.s_b2 = hp->h_addr_list[0][1];
        client.sin_addr.S_un.S_un_b.s_b3 = hp->h_addr_list[0][2];
        client.sin_addr.S_un.S_un_b.s_b4 = hp->h_addr_list[0][3];
    }
    else
    {
        client.sin_addr.S_un.S_un_b.s_b1 = (unsigned char)b1;
        client.sin_addr.S_un.S_un_b.s_b2 = (unsigned char)b2;
        client.sin_addr.S_un.S_un_b.s_b3 = (unsigned char)b3;
        client.sin_addr.S_un.S_un_b.s_b4 = (unsigned char)b4;
    }

    /* Bind local address to socket */
    if (bind(sd, (struct sockaddr *)&client, sizeof(struct sockaddr_in)) == -1)
    {
        fprintf(stderr, "Cannot bind address to socket.\n");
        closesocket(sd);
        WSACleanup();
        exit(0);
    }

    /* Tranmsit data to get time */
    server_length = sizeof(struct sockaddr_in);
    if (sendto(sd, send_buffer, (int)strlen(send_buffer) + 1, 0, (struct sockaddr *)&server, server_length) == -1)
    {
        fprintf(stderr, "Error transmitting data.\n");
        closesocket(sd);
        WSACleanup();
        exit(0);
    }

    /* Receive time */
    if (recvfrom(sd, (char *)&current_time, (int)sizeof(current_time), 0, (struct sockaddr *)&server, &server_length) < 0)
    {
        fprintf(stderr, "Error receiving data.\n");
        closesocket(sd);
        WSACleanup();
        exit(0);
    }

    /* Display time */
    printf("Current time: %s", ctime(&current_time));


    closesocket(sd);
    WSACleanup();

    return 0;
}

void usage(void)
{
    fprintf(stderr, "Usage: timecli server_address port [client_address]\n");
    exit(0);
}