lib/repo-finder: Add Avahi based OstreeRepoFinder implementation

This is a more complex implementation of OstreeRepoFinder which resolves
ref names to remote URIs by looking for refs advertised by peers on the
local network using DNS-SD records and mDNS (Avahi). The idea is to
allow OS and app updates to be propagated over local networks, without
the internet.

It requires an OSTree server and code to generate the DNS-SD adverts in
order to be fully functional — support for this will be added
separately.

Unit tests are included.

Includes fixes by Krzesimir Nowak <krzesimir@kinvolk.io>.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #924
Approved by: cgwalters

src/libostree/ostree-repo-pull.c

@@ -43,6 +43,9 @@
 #include "ostree-repo-finder.h"
 #include "ostree-repo-finder-config.h"
 #include "ostree-repo-finder-mount.h"
+#ifdef HAVE_AVAHI
+#include "ostree-repo-finder-avahi.h"
+#endif  /* HAVE_AVAHI */
 #endif /* OSTREE_ENABLE_EXPERIMENTAL_API */
 
 #include <gio/gunixinputstream.h>
@@ -3961,11 +3964,13 @@ typedef struct
   OstreeCollectionRef **refs;
   GVariant *options;
   OstreeAsyncProgress *progress;
+  OstreeRepoFinder *default_finder_avahi;
 } FindRemotesData;
 
 static void
 find_remotes_data_free (FindRemotesData *data)
 {
+  g_clear_object (&data->default_finder_avahi);
   g_clear_object (&data->progress);
   g_clear_pointer (&data->options, g_variant_unref);
   ostree_collection_ref_freev (data->refs);
@@ -3978,7 +3983,8 @@ G_DEFINE_AUTOPTR_CLEANUP_FUNC (FindRemotesData, find_remotes_data_free)
 static FindRemotesData *
 find_remotes_data_new (const OstreeCollectionRef * const *refs,
                        GVariant                      *options,
-                       OstreeAsyncProgress           *progress)
+                       OstreeAsyncProgress           *progress,
+                       OstreeRepoFinder              *default_finder_avahi)
 {
   g_autoptr(FindRemotesData) data = NULL;
 
@@ -3986,6 +3992,7 @@ find_remotes_data_new (const OstreeCollectionRef * const *refs,
   data->refs = ostree_collection_ref_dupv (refs);
   data->options = (options != NULL) ? g_variant_ref (options) : NULL;
   data->progress = (progress != NULL) ? g_object_ref (progress) : NULL;
+  data->default_finder_avahi = (default_finder_avahi != NULL) ? g_object_ref (default_finder_avahi) : NULL;
 
   return g_steal_pointer (&data);
 }
@@ -4085,10 +4092,10 @@ ostree_repo_find_remotes_async (OstreeRepo                     *self,
 {
   g_autoptr(GTask) task = NULL;
   g_autoptr(FindRemotesData) data = NULL;
-  GMainContext *context;
   OstreeRepoFinder *default_finders[4] = { NULL, };
   g_autoptr(OstreeRepoFinder) finder_config = NULL;
   g_autoptr(OstreeRepoFinder) finder_mount = NULL;
+  g_autoptr(OstreeRepoFinder) finder_avahi = NULL;
 
   g_return_if_fail (OSTREE_IS_REPO (self));
   g_return_if_fail (is_valid_collection_ref_array (refs));
@@ -4102,21 +4109,43 @@ ostree_repo_find_remotes_async (OstreeRepo                     *self,
   task = g_task_new (self, cancellable, callback, user_data);
   g_task_set_source_tag (task, ostree_repo_find_remotes_async);
 
-  context = g_main_context_get_thread_default ();
-
   /* Are we using #OstreeRepoFinders provided by the user, or the defaults? */
   if (finders == NULL)
     {
+#ifdef HAVE_AVAHI
+      GMainContext *context = g_main_context_get_thread_default ();
+      g_autoptr(GError) local_error = NULL;
+#endif  /* HAVE_AVAHI */
+
       finder_config = OSTREE_REPO_FINDER (ostree_repo_finder_config_new ());
       finder_mount = OSTREE_REPO_FINDER (ostree_repo_finder_mount_new (NULL));
+#ifdef HAVE_AVAHI
+      finder_avahi = OSTREE_REPO_FINDER (ostree_repo_finder_avahi_new (context));
+#endif  /* HAVE_AVAHI */
 
       default_finders[0] = finder_config;
       default_finders[1] = finder_mount;
+      default_finders[2] = finder_avahi;
 
       finders = default_finders;
+
+#ifdef HAVE_AVAHI
+      ostree_repo_finder_avahi_start (OSTREE_REPO_FINDER_AVAHI (finder_avahi),
+                                      &local_error);
+
+      if (local_error != NULL)
+        {
+          g_warning ("Avahi finder failed; removing it: %s", local_error->message);
+          default_finders[2] = NULL;
+          g_clear_object (&finder_avahi);
+        }
+#endif  /* HAVE_AVAHI */
     }
 
-  data = find_remotes_data_new (refs, options, progress);
+  /* We need to keep a pointer to the default Avahi finder so we can stop it
+   * again after the operation, which happens implicitly by dropping the final
+   * ref. */
+  data = find_remotes_data_new (refs, options, progress, finder_avahi);
   g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) find_remotes_data_free);
 
   /* Asynchronously resolve all possible remotes for the given refs. */