ipod.c

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

int udp; /* udp fd */
double uptime;

void set_up_udp_sock()
{
    struct sockaddr_in sockaddr;
    memset(&sockaddr, 0, sizeof(sockaddr));

    udp = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (udp < 0) exit(1);

    sockaddr.sin_family = AF_INET;
    sockaddr.sin_port = htons(4444);
    sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(udp, (struct sockaddr*)&sockaddr, sizeof(sockaddr)) == -1)
        exit(1);
}

void process_udp_message(int fd)
{
    char msg[1024];
    struct sockaddr_in sockaddr;
    memset(&sockaddr, 0, sizeof(sockaddr));

    socklen_t sockaddr_len = sizeof(struct sockaddr_in);
    struct sockaddr *saddr = (struct sockaddr *)&sockaddr;
    ssize_t length;

    length = recvfrom(fd, msg, sizeof(msg) - 1, 0, saddr, &sockaddr_len);
    if (length <= 0) return;
    msg[length] = '\0';

    int request = atoi(msg);

    switch (request)
    {
        case 0:
        {
            snprintf(msg, sizeof(msg), "uptime=%lf\n", uptime);
            break;
        }
    }

    char msg2[sizeof(msg)];
    strcpy(msg2, msg);
    length = snprintf(msg, sizeof(msg), "%d\n%s", request, msg2);
    if (length <= 0) return;

    sendto(fd, msg, length, 0, saddr, sockaddr_len);
}

int process_udp(int wait)
{
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(udp, &fds);

    struct timeval tv;

    tv.tv_sec = wait / 1000;
    tv.tv_usec = (wait % 1000) * 1000;

    int ret = select(udp + 1, &fds, NULL, NULL, &tv);

    if (ret > 0)
    {
        if (FD_ISSET(udp, &fds))
            process_udp_message(udp);
    }
    else if (ret < 0)
    {
        return -1;
    }

    return 0;
}

void update()
{
    struct timeval boot_time;
    struct timeval current_time;
    size_t len = sizeof(boot_time);
    int mib[2] = { CTL_KERN, KERN_BOOTTIME };
    if (sysctl(mib, 2, &boot_time, &len, NULL, 0) >= 0)
    {
        long long usec;
        long long current_usec;
    
        usec = boot_time.tv_sec * 1000000LL;
        usec += boot_time.tv_usec;

        if (gettimeofday(&current_time, NULL) < 0)
        {
            uptime = 0.0;
        }
        else
        {
            current_usec = current_time.tv_sec * 1000000LL;
            current_usec += current_time.tv_usec;
            uptime = (current_usec - usec) / 1000000.0;
        }
    }
    else uptime = 0.0;
}

extern float battery_level;
void enable_battery_monitoring();


int main()
{
    //enable_battery_monitoring();

    if (daemon(0, 0) < 0)
        return 1;

    set_up_udp_sock();

    while (1)
    {
        if (process_udp(250) < 0)
            break;

        update();
    }

    if (udp >= 0)
        close(udp);

    return 0;
}