common: Properly handle empty arrays of P2P results

ostree_repo_find_remotes_finish() can return an empty array of
OstreeRepoFinderResults without setting @error and expects the caller to
check for this before doing a pull. Currently in a few different places
Flatpak does not check if the array is empty after calling
ostree_repo_find_remotes_finish() which leads to a critical warning in
ostree_repo_pull_from_remotes_async() which expects a non-empty results
array. This is causing one of the unit tests to fail.

So properly handle the case of an empty results array in each place it
can occur. In most places it's an error condition so the error pointer
is set appropriately. In list_remotes_for_configured_remote() it's not
an error because there may legitimately be no LAN/USB remotes available,
so in that case just properly handle the case of (results == NULL).

Also, add a debug statement in flatpak_dir_do_resolve_p2p_refs() since
we're now building a string of the refs being resolved.

Closes: #2705
Approved by: alexlarsson

common/flatpak-dir.c

@@ -3686,6 +3686,7 @@ flatpak_dir_do_resolve_p2p_refs (FlatpakDir             *self,
   g_auto(GLnxLockFile) child_repo_lock = { 0, };
   g_autoptr(GFile) user_cache_dir = NULL;
   g_autoptr(FlatpakTempDir) child_repo_tmp_dir = NULL;
+  g_autoptr(GString) refs_str = NULL;
   int i;
 
   main_context = flatpak_main_context_new_default ();
@@ -3693,11 +3694,18 @@ flatpak_dir_do_resolve_p2p_refs (FlatpakDir             *self,
   if (with_commit_ids)
     commit_ids_to_fetch = g_ptr_array_new ();
 
+  refs_str = g_string_new ("");
   for (i = 0; datas[i] != NULL; i++)
     {
       FlatpakDirResolveData *data = datas[i];
       FlatpakDirResolve *resolve = data->resolve;
 
+      if (i != 0)
+        g_string_append (refs_str, ", ");
+      g_string_append_printf (refs_str, "(%s, %s)",
+                              data->collection_ref.collection_id,
+                              data->collection_ref.ref_name);
+
       g_ptr_array_add (collection_refs_to_fetch, &data->collection_ref);
       if (commit_ids_to_fetch)
         {
@@ -3708,6 +3716,8 @@ flatpak_dir_do_resolve_p2p_refs (FlatpakDir             *self,
 
   g_ptr_array_add (collection_refs_to_fetch, NULL);
 
+  g_debug ("Resolving these collection-refs: [%s]", refs_str->str);
+
   g_variant_builder_init (&find_builder, G_VARIANT_TYPE ("a{sv}"));
   if (commit_ids_to_fetch)
     g_variant_builder_add (&find_builder, "{s@v}", "override-commit-ids",
@@ -3743,6 +3753,9 @@ flatpak_dir_do_resolve_p2p_refs (FlatpakDir             *self,
   if (results == NULL)
     return FALSE;
 
+  if (results[0] == NULL)
+    return flatpak_fail (error, _("No remotes found which provide these refs: [%s]"), refs_str->str);
+
   /* Drop from the results all ops that are no-op updates */
   for (i = 0; datas[i] != NULL; i++)
     {
@@ -4477,7 +4490,13 @@ repo_pull (OstreeRepo                           *self,
           results_to_fetch = (const OstreeRepoFinderResult * const *) results;
         }
 
-      if (results_to_fetch != NULL)
+      if (results_to_fetch != NULL && results_to_fetch[0] == NULL)
+        {
+          flatpak_fail (error, _("No remotes found which provide the ref (%s, %s)"),
+                        collection_ref.collection_id, collection_ref.ref_name);
+          res = FALSE;
+        }
+      else if (results_to_fetch != NULL)
         {
           GVariantBuilder pull_builder, ref_keyring_map_builder;
           g_autoptr(GVariant) pull_options = NULL;
@@ -5257,24 +5276,25 @@ flatpak_dir_pull (FlatpakDir                           *self,
            * below won't need to fetch the metadata. For an explanation of the
            * attack we're protecting against see
            * https://github.com/flatpak/flatpak/issues/1447#issuecomment-445347590 */
-          {
-            OstreeRepoPullFlags metadata_pull_flags = flags | OSTREE_REPO_PULL_FLAGS_COMMIT_ONLY;
-            /*TODO: Use OSTREE_REPO_PULL_FLAGS_MIRROR for all collection-ref pulls */
-            metadata_pull_flags |= OSTREE_REPO_PULL_FLAGS_MIRROR;
-            if (!repo_pull (repo, state->remote_name,
-                            NULL, ref, NULL, results,
-                            flatpak_flags, metadata_pull_flags,
-                            progress, cancellable, error))
-              {
-                g_prefix_error (error, _("While pulling %s from remote %s: "), ref, state->remote_name);
-                goto out;
-              }
+          if (results[0] != NULL)
+            {
+              OstreeRepoPullFlags metadata_pull_flags = flags | OSTREE_REPO_PULL_FLAGS_COMMIT_ONLY;
+              /*TODO: Use OSTREE_REPO_PULL_FLAGS_MIRROR for all collection-ref pulls */
+              metadata_pull_flags |= OSTREE_REPO_PULL_FLAGS_MIRROR;
+              if (!repo_pull (repo, state->remote_name,
+                              NULL, ref, NULL, results,
+                              flatpak_flags, metadata_pull_flags,
+                              progress, cancellable, error))
+                {
+                  g_prefix_error (error, _("While pulling %s from remote %s: "), ref, state->remote_name);
+                  goto out;
+                }
 
-            if (!flatpak_repo_resolve_rev (repo, collection_ref.collection_id,
-                                           state->remote_name, ref, TRUE, &rev,
-                                           cancellable, error))
-              goto out;
-          }
+              if (!flatpak_repo_resolve_rev (repo, collection_ref.collection_id,
+                                             state->remote_name, ref, TRUE, &rev,
+                                             cancellable, error))
+                goto out;
+            }
 #else
           gsize i;
           for (i = 0, rev = NULL; results[i] != NULL && rev == NULL; i++)

common/flatpak-installation.c

@@ -1004,6 +1004,7 @@ flatpak_installation_list_installed_refs_for_update (FlatpakInstallation *self,
   g_auto(OstreeRepoFinderResultv) results = NULL;
   g_autoptr(GAsyncResult) result = NULL;
   g_autoptr(GPtrArray) collection_refs = NULL; /* (element-type OstreeCollectionRef) */
+  g_autoptr(GString) refs_str = NULL;
 
   remote_commits = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, g_free);
 
@@ -1078,6 +1079,7 @@ flatpak_installation_list_installed_refs_for_update (FlatpakInstallation *self,
 
   collection_refs = g_ptr_array_new ();
 
+  refs_str = g_string_new ("");
   for (i = 0; i < installed->len; i++)
     {
       FlatpakInstalledRef *installed_ref = g_ptr_array_index (installed, i);
@@ -1090,6 +1092,10 @@ flatpak_installation_list_installed_refs_for_update (FlatpakInstallation *self,
           g_autofree char *ref = flatpak_ref_format_ref (FLATPAK_REF (installed_ref));
           OstreeCollectionRef *c_r = ostree_collection_ref_new (collection_id, ref);
           g_ptr_array_add (collection_refs, c_r);
+
+          if (i != 0)
+            g_string_append (refs_str, ", ");
+          g_string_append_printf (refs_str, "(%s, %s)", collection_id, ref);
         }
     }
 
@@ -1121,6 +1127,12 @@ flatpak_installation_list_installed_refs_for_update (FlatpakInstallation *self,
 
       if (results == NULL)
         return NULL;
+
+      if (results[0] == NULL)
+        {
+          flatpak_fail (error, _("No remotes found which provide these refs: [%s]"), refs_str->str);
+          return NULL;
+        }
     }
 
   for (i = 0; i < installed->len; i++)
@@ -1277,7 +1289,10 @@ list_remotes_for_configured_remote (FlatpakInstallation *self,
   if (types_filter[FLATPAK_REMOTE_TYPE_LAN])
     ostree_repo_finder_avahi_stop (OSTREE_REPO_FINDER_AVAHI (finder_avahi));
 
-  for (i = 0; results != NULL && results[i] != NULL; i++)
+  if (results == NULL)
+    return FALSE;
+
+  for (i = 0; results[i] != NULL; i++)
     {
       g_ptr_array_add (remotes,
                        flatpak_remote_new_from_ostree (results[i]->remote,