examples: Add a hostname resolution example

Prints the IPv4, followed by the IPv6 address for the requested
hostname, and exits.

Closes: #41

examples/host-lookup.c

@@ -0,0 +1,114 @@
+/*
+ * Copyright © 2014-2015 VideoLabs SAS
+ * Copyright © 2021 Red Hat Inc
+ *
+ * Authors: Jonathan Calmels <[email protected]>
+ *          Bastien Nocera <[email protected]>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <compat.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <time.h>
+
+#include <microdns/microdns.h>
+
+#include "compat.h"
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+#define TIMEOUT 1
+
+static bool stopflag = false;
+static time_t start_time;
+
+static double get_elapsed(void)
+{
+        time_t t;
+
+        t = time(NULL);
+        return difftime(t, start_time);
+}
+
+static bool stop(void *p_cookie)
+{
+        double elapsed;
+        if (stopflag)
+                return stopflag;
+        elapsed = get_elapsed();
+        return elapsed >= (double) TIMEOUT;
+}
+
+static void callback(void *p_cookie, int status, const struct rr_entry *entries)
+{
+        struct rr_entry *entry;
+        char *hostname = p_cookie;
+        char err[128];
+
+        if (status < 0) {
+                mdns_strerror(status, err, sizeof(err));
+                fprintf(stderr, "error: %s\n", err);
+                return;
+        }
+        entry = (struct rr_entry *) entries;
+        while (entry) {
+                if (entry->type == RR_A)
+                        printf("%s resolves to IPv4 address %s\n", hostname, entry->data.A.addr_str);
+                if (entry->type == RR_AAAA)
+                        printf("%s resolves to IPv6 address %s\n", hostname, entry->data.AAAA.addr_str);
+                entry = entry->next;
+        }
+        stopflag = true;
+}
+
+int main(int i_argc, char *ppsz_argv[])
+{
+        int r = 0;
+        char err[128];
+        struct mdns_ctx *ctx;
+        const char **ppsz_names;
+        int i_nb_names;
+
+        if (i_argc <= 1)
+        {
+                fprintf(stderr, "Usage: %s [HOSTNAME]\n", ppsz_argv[0]);
+                return (1);
+        }
+
+        ppsz_names = (const char **) &ppsz_argv[1];
+        i_nb_names = i_argc - 1;
+
+        if ((r = mdns_init(&ctx, NULL, MDNS_PORT)) < 0)
+                goto err;
+        start_time = time(NULL);
+        if ((r = mdns_listen(ctx, ppsz_names, i_nb_names, RR_A, TIMEOUT, stop,
+                             callback, ppsz_argv[1])) < 0)
+                goto err;
+        stopflag = false;
+        start_time = time(NULL);
+        if ((r = mdns_listen(ctx, ppsz_names, i_nb_names, RR_AAAA, TIMEOUT, stop,
+                             callback, ppsz_argv[1])) < 0)
+                goto err;
+err:
+        if (r < 0) {
+                mdns_strerror(r, err, sizeof(err));
+                fprintf(stderr, "fatal: %s\n", err);
+        }
+        mdns_destroy(ctx);
+        return (0);
+}

examples/meson.build

@@ -11,4 +11,5 @@ examples_kwargs = {
 
 executable('listen', 'main.c', kwargs: examples_kwargs)
 executable('announce', 'announce.c', kwargs: examples_kwargs)
+executable('host-lookup', 'host-lookup.c', kwargs: examples_kwargs)