example: rework "vpn-import-libnm" example

- add more error handling and free/unref data.

- split code in 3 functions: vpn_connection_import(),
  connection_add() and main(). These steps are mostly
  independent, and having them in separate functions
  makes their separation clearer.

- handle error from nm_client_add_connection_async() to
  exit program with non zero exit code.

examples/C/glib/vpn-import-libnm.c

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 /*
  * The example shows how to import VPN connection from a file.
+ *
  * @author: Jagadeesh Kotra <jagadeesh@stdin.top>
  *
  * Compile with:
@@ -9,66 +10,154 @@
 
 #include <glib.h>
 #include <NetworkManager.h>
-#include <stdlib.h>
+
+/*****************************************************************************/
+
+static NMConnection *
+vpn_connection_import(const char *filename)
+{
+    NMConnection *conn = NULL;
+    GSList *      plugins;
+    GSList *      iter;
+
+    g_print("Try to import file \"%s\"...\n", filename);
+
+    plugins = nm_vpn_plugin_info_list_load();
+
+    for (iter = plugins; iter; iter = iter->next) {
+        GError *           error  = NULL;
+        NMVpnPluginInfo *  plugin = iter->data;
+        NMVpnEditorPlugin *editor;
+        const char *       plugin_name = nm_vpn_plugin_info_get_name(plugin);
+
+        g_print("plugin[%s]: trying import...\n", plugin_name);
+
+        editor = nm_vpn_plugin_info_load_editor_plugin(plugin, &error);
+        if (error) {
+            g_print("plugin[%s]: error loading plugin: %s\n", plugin_name, error->message);
+            g_clear_error(&error);
+            continue;
+        }
+
+        conn = nm_vpn_editor_plugin_import(editor, filename, &error);
+        if (error) {
+            g_print("plugin[%s]: error importing file: %s\n", plugin_name, error->message);
+            g_clear_error(&error);
+            continue;
+        }
+
+        if (!nm_connection_normalize(conn, NULL, NULL, &error)) {
+            g_print("plugin[%s]: imported connection invalid: %s\n", plugin_name, error->message);
+            g_clear_error(&error);
+            g_clear_object(&conn);
+            continue;
+        }
+
+        g_print("plugin[%s]: imported connection \"%s\" (%s)\n",
+                plugin_name,
+                nm_connection_get_id(conn),
+                nm_connection_get_uuid(conn));
+        break;
+    }
+    g_slist_free_full(plugins, g_object_unref);
+
+    if (!conn) {
+        g_print("Failure to import the file with any plugin\n");
+        return NULL;
+    }
+
+    return conn;
+}
+
+/*****************************************************************************/
+
+typedef struct {
+    GMainLoop *         loop;
+    GError *            error;
+    NMRemoteConnection *rconn;
+} RequestData;
 
 static void
-add_cb(NMClient *client, GAsyncResult *result, GMainLoop *loop)
+add_cb(GObject *source, GAsyncResult *result, gpointer user_data)
 {
-    GError *err = NULL;
-    nm_client_add_connection_finish(client, result, &err);
-    if (err != NULL) {
-        g_print("Error: %s\n", err->message);
-    } else {
-        g_print("Connection Added.\n");
+    RequestData *rdata = user_data;
+
+    rdata->rconn = nm_client_add_connection_finish(NM_CLIENT(source), result, &rdata->error);
+    g_main_loop_quit(rdata->loop);
 }
 
-    g_main_loop_quit(loop);
+static NMRemoteConnection *
+connection_add(NMConnection *conn)
+{
+    GError *    error = NULL;
+    NMClient *  client;
+    RequestData rdata;
+
+    g_print("Adding connection \"%s\" (%s)\n",
+            nm_connection_get_id(conn),
+            nm_connection_get_uuid(conn));
+
+    client = nm_client_new(NULL, &error);
+    if (!client) {
+        g_print("Failure to connect with NetworkManager: %s\n", error->message);
+        return NULL;
     }
 
+    g_print("Adding connection \"%s\" (%s)\n",
+            nm_connection_get_id(conn),
+            nm_connection_get_uuid(conn));
+
+    rdata = (RequestData){
+        .loop  = g_main_loop_new(NULL, FALSE),
+        .rconn = NULL,
+        .error = NULL,
+    };
+
+    nm_client_add_connection_async(client, conn, TRUE, NULL, add_cb, &rdata);
+
+    g_main_loop_run(rdata.loop);
+
+    g_clear_pointer(&rdata.loop, g_main_loop_unref);
+
+    if (rdata.error != NULL) {
+        g_print("Error: %s\n", rdata.error->message);
+        g_clear_error(&rdata.error);
+    } else {
+        g_print("Connection successfully added: %s\n", nm_object_get_path(NM_OBJECT(rdata.rconn)));
+    }
+
+    g_clear_object(&client);
+
+    return rdata.rconn;
+}
+
+/*****************************************************************************/
+
 int
 main(int argc, char **argv)
 {
-    GMainLoop *        loop = g_main_loop_new(NULL, FALSE);
-    GSList *           plugins;
-    GSList *           iter;
-    NMVpnEditorPlugin *editor;
-    NMClient *         client;
-    GError *           err  = NULL;
-    NMConnection *     conn = NULL;
+    NMRemoteConnection *rconn;
+    NMConnection *      conn;
+    const char *        filename;
+    gboolean            success;
 
     if (argc < 2) {
         g_print("program takes exactly one(1) argument.\n");
-        exit(1);
+        return 1;
     }
 
-    plugins = nm_vpn_plugin_info_list_load();
-    g_assert(plugins != NULL);
+    filename = argv[1];
 
-    for (iter = plugins; iter; iter = iter->next) {
-        const char *plugin_name = nm_vpn_plugin_info_get_name(iter->data);
-        g_print("Trying Plugin: %s\n", plugin_name);
+    conn = vpn_connection_import(filename);
+    if (!conn)
+        return 1;
 
-        //try to load plugin
-        editor = nm_vpn_plugin_info_load_editor_plugin(iter->data, NULL);
+    rconn = connection_add(conn);
 
-        conn = nm_vpn_editor_plugin_import(editor, argv[1], &err);
-        if (err != NULL) {
-            g_print("Error: %s\n", err->message);
-            g_error_free(err);
-            err = NULL;
-        } else {
-            g_print("%s imported with %s plugin.\n", argv[1], plugin_name);
-            break;
-        }
-    }
-
-    g_slist_free_full(plugins, g_object_unref);
-    g_assert(conn != NULL);
-
-    client = nm_client_new(NULL, NULL);
-
-    nm_client_add_connection_async(client, conn, TRUE, NULL, (GAsyncReadyCallback) add_cb, loop);
-    g_main_loop_run(loop);
-
-    return 0;
+    success = (rconn != NULL);
+
+    g_clear_object(&conn);
+    g_clear_object(&rconn);
+
+    return success ? 0 : 1;
 }