Minimal WPE launcher, with user message handler to poweroff/reboot a device

minicog.c

/*
 * SPDX-License-Identifier: MIT
 *
 * cc -o minicog minicog.c $(pkg-config wpe-webkit-1.1 cogcore --cflags --libs)
 */

#include <cog/cog.h>
#include <sys/reboot.h>

static const char *s_starturl = NULL;

static void
handle_power_control_message(WebKitUserContentManager *content_manager,
                             WebKitJavascriptResult *js_result, void *userdata)
{
    JSCValue *value = webkit_javascript_result_get_js_value(js_result);
    if (!jsc_value_is_string(value)) {
        g_warning("Invalid powerControl message: argument is not a string");
        return;
    }

    g_autofree char *value_as_string = jsc_value_to_string(value);
    int action;
    if (strcmp(value_as_string, "poweroff") == 0) {
        action = RB_POWER_OFF;
    } else if (strcmp(value_as_string, "reboot") == 0) {
        action = RB_AUTOBOOT;
    } else {
        g_warning("Invalid powerControl message: '%s'", value_as_string);
        return;
    }

    g_message("Device will %s now!", value_as_string);

    /*
     * This fails unless the process is run as "root" (not recommended!)
     * or has been granted the CAP_SYS_BOOT capability. In reality, this
     * should probably call the org.freedesktop.systemd1.Reboot() method
     * and friends using D-Bus instead.
     */
    sync();
    reboot(action);
}

static WebKitUserContentManager*
create_content_manager(void)
{
    g_autoptr(WebKitUserContentManager) content_manager = webkit_user_content_manager_new();
    webkit_user_content_manager_register_script_message_handler(content_manager, "powerControl");
    g_signal_connect(content_manager, "script-message-received::powerControl",
                     G_CALLBACK(handle_power_control_message), NULL);
    return g_steal_pointer(&content_manager);
}

static WebKitWebView*
on_create_view(CogShell *shell, CogPlatform *platform)
{
    g_autoptr(GError) error = NULL;
    WebKitWebViewBackend *view_backend = cog_platform_get_view_backend(platform, NULL, &error);
    if (!view_backend)
        g_error("Cannot obtain view backend: %s", error->message);

    g_autoptr(WebKitUserContentManager) content_manager = create_content_manager();

    WebKitSettings *settings = cog_shell_get_web_settings(shell);
    webkit_settings_set_enable_write_console_messages_to_stdout(settings, TRUE);

    g_autoptr(WebKitWebView) web_view =
        g_object_new(WEBKIT_TYPE_WEB_VIEW,
                     "user-content-manager", content_manager,
                     "settings", settings,
                     "web-context", cog_shell_get_web_context(shell),
                     "backend", view_backend,
                     NULL);

    cog_platform_init_web_view(platform, web_view);

    webkit_web_view_load_uri(web_view, s_starturl);
    return g_steal_pointer(&web_view);
}

int
main(int argc, char *argv[])
{
    g_set_application_name("minicog");

    if (argc != 2 && argc != 3) {
        g_printerr("Usage: %s [URL [platform]]\n", argv[0]);
        return EXIT_FAILURE;
    }

    g_autoptr(GError) error = NULL;
    if (!(s_starturl = cog_uri_guess_from_user_input(argv[1], TRUE, &error)))
        g_error("Invalid URL '%s': %s", argv[1], error->message);

    cog_modules_add_directory(COG_MODULEDIR);

    g_autoptr(GApplication) app = g_application_new(NULL, G_APPLICATION_DEFAULT_FLAGS);
    g_autoptr(CogShell) shell = cog_shell_new("minicog", FALSE);

    g_autoptr(CogPlatform) platform =
        cog_platform_new((argc == 3) ? argv[2] : g_getenv("COG_PLATFORM"), &error);
    if (!platform)
        g_error("Cannot create platform: %s", error->message);

    if (!cog_platform_setup(platform, shell, "", &error))
        g_error("Cannot setup platform: %s\n", error->message);

    g_signal_connect(shell, "create-view", G_CALLBACK(on_create_view), platform);
    g_signal_connect_swapped(app, "shutdown", G_CALLBACK(cog_shell_shutdown), shell);
    g_signal_connect_swapped(app, "startup", G_CALLBACK(cog_shell_startup), shell);
    g_signal_connect(app, "activate", G_CALLBACK(g_application_hold), NULL);

    return g_application_run(app, 1, argv);
}

powercontrol.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Device Power Control</title>
  </head>
  <body>
    <button id="reboot">Reboot</button>
    <button id="poweroff">Power Off</button>
    <script type="text/javascript">
      function addHandler(name) {
        document.getElementById(name).addEventListener("click", (event) => {
          window.webkit.messageHandlers.powerControl.postMessage(name);
	  return false;
        });
      }
      addHandler("reboot");
      addHandler("poweroff");
    </script>
  </body>
</html>