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i3blocks/weather/weather_signaler.c

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+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <time.h>
+#include <stdio.h>
+
+// Sleep time between daemon updates.
+#define SLEEP_TIME_S    300
+
+// Test for internet connection. Returns true if connection is established.
+static int test_internet_connection()
+{
+    const char *cmd = "nc -zw1 google.com 443 1> /dev/null 2>&1";
+    return !system(cmd);
+}
+
+// Signal handler for signaling the weather applet.
+static void timer_handler(int sig, siginfo_t *si, void *uc)
+{
+    (void) sig; // Ignore parameter.
+    (void) si;  // Ignore parameter.
+    (void) uc;  // Ignore parameter.
+
+    // Test for internet connection till found or 20 times.
+    for (int i = 0; i < 20; ++i)
+    {
+        if (test_internet_connection())
+        {
+            // Connection established. Break out.
+            break;
+        }
+        else
+        {
+            // Retry every second.
+            sleep(1);
+        }
+    }
+
+    // Signal the weather applet.
+    const char *cmd = "pkill -RTMIN+2 i3blocks";
+    if ( system(cmd) )
+    {
+        // Error message should be printed to stdout since stdout is the way to
+        // interface with a user in i3blocks.
+        puts("WEATHER_SIGNALER ERROR\n");
+    }
+}
+
+int timer_init_launch(
+        timer_t *timer,
+        struct sigevent *sev,
+        struct sigaction *sa,
+        struct itimerspec *tspec)
+{
+    // Event initialization.
+    sev->sigev_notify = SIGEV_SIGNAL;
+    sev->sigev_signo = SIGRTMIN;
+    sev->sigev_value.sival_ptr = timer;
+
+    // Signal action type initializaion.
+    sa->sa_flags = SA_SIGINFO;
+    sa->sa_sigaction = timer_handler;
+    sigemptyset(&sa->sa_mask);
+    if (sigaction(SIGRTMIN, sa, NULL) == -1)
+        return -1;
+
+    // Initialze timer.
+    if (timer_create(CLOCK_BOOTTIME, sev, timer) == -1)
+        return -1;
+
+    // Start the timer.
+    tspec->it_value.tv_sec = SLEEP_TIME_S;
+    tspec->it_value.tv_nsec = 0;
+    tspec->it_interval.tv_sec = SLEEP_TIME_S;
+    tspec->it_interval.tv_nsec = 0;
+    if (timer_settime(*timer, 0, tspec, NULL) == -1)
+        return -1;
+
+    // Initialization successful.
+    return 0;
+}
+
+int main()
+{
+    timer_t timer;
+    struct sigevent sev;
+    struct sigaction sa;
+    struct itimerspec tspec;
+
+    // Initialize signaler
+    if (timer_init_launch(&timer, &sev, &sa, &tspec))
+        exit(EXIT_FAILURE);
+
+    // Signal on daemon launch.
+    sleep(1);
+    timer_handler(0, NULL, NULL);
+
+    while(1)
+    {
+        sleep(100);
+    }
+}