lib/repo: Factor out GPG verifier preparation

In order to use the GPG verifier, it needs to be seeded with GPG keys
after instantation. Currently this is only used for verifying data, but
it will also be used for getting a list of trusted GPG keys in a
subsequent commit.

src/libostree/ostree-repo.c

@@ -5338,28 +5338,25 @@ find_keyring (OstreeRepo          *self,
   return TRUE;
 }
 
-static OstreeGpgVerifyResult *
+static gboolean
-_ostree_repo_gpg_verify_data_internal (OstreeRepo    *self,
+_ostree_repo_gpg_prepare_verifier (OstreeRepo         *self,
-                                       const gchar   *remote_name,
+                                   const gchar        *remote_name,
-                                       GBytes        *data,
+                                   GFile              *keyringdir,
-                                       GBytes        *signatures,
+                                   GFile              *extra_keyring,
-                                       GFile         *keyringdir,
+                                   OstreeGpgVerifier **out_verifier,
-                                       GFile         *extra_keyring,
+                                   GCancellable       *cancellable,
-                                       GCancellable  *cancellable,
+                                   GError            **error)
-                                       GError       **error)
 {
-  g_autoptr(OstreeGpgVerifier) verifier = NULL;
+  g_autoptr(OstreeGpgVerifier) verifier = _ostree_gpg_verifier_new ();
   gboolean add_global_keyring_dir = TRUE;
 
-  verifier = _ostree_gpg_verifier_new ();
-
   if (remote_name == OSTREE_ALL_REMOTES)
     {
       /* Add all available remote keyring files. */
 
       if (!_ostree_gpg_verifier_add_keyring_dir_at (verifier, self->repo_dir_fd, ".",
                                                     cancellable, error))
-        return NULL;
+        return FALSE;
     }
   else if (remote_name != NULL)
     {
@@ -5369,11 +5366,11 @@ _ostree_repo_gpg_verify_data_internal (OstreeRepo    *self,
 
       remote = _ostree_repo_get_remote_inherited (self, remote_name, error);
       if (remote == NULL)
-        return NULL;
+        return FALSE;
 
       g_autoptr(GBytes) keyring_data = NULL;
       if (!find_keyring (self, remote, &keyring_data, cancellable, error))
-        return NULL;
+        return FALSE;
 
       if (keyring_data != NULL)
         {
@@ -5389,14 +5386,14 @@ _ostree_repo_gpg_verify_data_internal (OstreeRepo    *self,
                                                              ";,",
                                                              &gpgkeypath_list,
                                                              error))
-        return NULL;
+        return FALSE;
 
       if (gpgkeypath_list)
         {
           for (char **iter = gpgkeypath_list; *iter != NULL; ++iter)
             if (!_ostree_gpg_verifier_add_keyfile_path (verifier, *iter,
                                                         cancellable, error))
-              return NULL;
+              return FALSE;
         }
     }
 
@@ -5404,20 +5401,46 @@ _ostree_repo_gpg_verify_data_internal (OstreeRepo    *self,
     {
       /* Use the deprecated global keyring directory. */
       if (!_ostree_gpg_verifier_add_global_keyring_dir (verifier, cancellable, error))
-        return NULL;
+        return FALSE;
     }
 
   if (keyringdir)
     {
       if (!_ostree_gpg_verifier_add_keyring_dir (verifier, keyringdir,
                                                  cancellable, error))
-        return NULL;
+        return FALSE;
     }
   if (extra_keyring != NULL)
     {
       _ostree_gpg_verifier_add_keyring_file (verifier, extra_keyring);
     }
 
+  if (out_verifier != NULL)
+    *out_verifier = g_steal_pointer (&verifier);
+
+  return TRUE;
+}
+
+static OstreeGpgVerifyResult *
+_ostree_repo_gpg_verify_data_internal (OstreeRepo    *self,
+                                       const gchar   *remote_name,
+                                       GBytes        *data,
+                                       GBytes        *signatures,
+                                       GFile         *keyringdir,
+                                       GFile         *extra_keyring,
+                                       GCancellable  *cancellable,
+                                       GError       **error)
+{
+  g_autoptr(OstreeGpgVerifier) verifier = NULL;
+  if (!_ostree_repo_gpg_prepare_verifier (self,
+                                          remote_name,
+                                          keyringdir,
+                                          extra_keyring,
+                                          &verifier,
+                                          cancellable,
+                                          error))
+    return NULL;
+
   return _ostree_gpg_verifier_check_signature (verifier,
                                                data,
                                                signatures,