Add page reloading in offline.php templates

tests/test-template.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * Tests for template.php
+ *
+ * @package PWA
+ */
+
+use Yoast\WPTestUtils\WPIntegration\TestCase;
+
+/**
+ * Tests for template.php
+ */
+class Test_Template extends TestCase {
+	/**
+	 * Test if function adding script on GET method, is_offline() or is_500 is true
+	 *
+	 * @covers ::wp_service_worker_offline_page_reload()
+	 */
+	public function test_wp_service_worker_offline_page_reload() {
+		$this->assertEquals( 10, has_action( 'wp_footer', 'wp_service_worker_offline_page_reload' ) );
+		$this->assertEquals( 10, has_action( 'error_footer', 'wp_service_worker_offline_page_reload' ) );
+
+		// Check when method is GET but not offline or 500.
+		$actual_script = wp_service_worker_offline_page_reload();
+		$this->assertEquals( $_SERVER['REQUEST_METHOD'], 'GET' );
+		$this->assertFalse( is_offline() );
+		$this->assertFalse( is_500() );
+		$this->assertEmpty( $actual_script );
+
+		// Check if script is added when offline.
+		$error_template_url = add_query_arg( 'wp_error_template', 'offline', home_url( '/', 'relative' ) );
+		$this->go_to( $error_template_url );
+
+		ob_start();
+		wp_service_worker_offline_page_reload();
+		$actual_script = ob_get_clean();
+		$this->assertEquals( $_SERVER['REQUEST_METHOD'], 'GET' );
+		$this->assertTrue( is_offline() );
+		$this->assertFalse( is_500() );
+		$this->assertStringContainsString( '<script type="module">', $actual_script );
+		$this->assertStringContainsString( 'await fetch(location.href, {method: \'HEAD\'})', $actual_script );
+
+		// Check if script is added when 500.
+		$error_template_url = add_query_arg( 'wp_error_template', '500', home_url( '/', 'relative' ) );
+		$this->go_to( $error_template_url );
+
+		ob_start();
+		wp_service_worker_offline_page_reload();
+		$actual_script = ob_get_clean();
+		$this->assertEquals( $_SERVER['REQUEST_METHOD'], 'GET' );
+		$this->assertFalse( is_offline() );
+		$this->assertTrue( is_500() );
+		$this->assertStringContainsString( '<script type="module">', $actual_script );
+		$this->assertStringContainsString( 'await fetch(location.href, {method: \'HEAD\'})', $actual_script );
+
+		$this->go_to( home_url( '/', 'relative' ) );
+
+		// Check when method is not GET.
+		$_SERVER['REQUEST_METHOD'] = 'POST';
+		$actual_script             = wp_service_worker_offline_page_reload();
+		$this->assertEquals( $_SERVER['REQUEST_METHOD'], 'POST' );
+		$this->assertFalse( is_offline() );
+		$this->assertFalse( is_500() );
+		$this->assertEmpty( $actual_script );
+	}
+}

wp-includes/template.php

@@ -171,3 +171,55 @@ function wp_service_worker_error_details_template( $output = '' ) {
 function wp_service_worker_error_message_placeholder() {
 	echo '<p><!--WP_SERVICE_WORKER_ERROR_MESSAGE--></p>';
 }
+
+/**
+ * Reload the offline page and check if user comes online.
+ *
+ * @since 0.7
+ */
+function wp_service_worker_offline_page_reload() {
+	if ( isset( $_SERVER['REQUEST_METHOD'] ) && 'GET' !== $_SERVER['REQUEST_METHOD'] ) {
+		return;
+	}
+
+	if ( ! is_offline() && ! is_500() ) {
+		return;
+	}
+
+	?>
+	<script type="module">
+		/**
+		 * Listen to changes in the network state, reload when online.
+		 * This handles the case when the device is completely offline.
+		 */
+		window.addEventListener('online', () => {
+			window.location.reload();
+		});
+
+		// Create a counter to implement exponential backoff.
+		let count = 0;
+
+		/**
+		 * Check if the server is responding and reload the page if it is.
+		 * This handles the case when the device is online, but the server is offline or misbehaving.
+		 */
+		async function checkNetworkAndReload() {
+			try {
+				const response = await fetch(location.href, {method: 'HEAD'});
+				// Verify we get a valid response from the server
+				if (response.status >= 200 && response.status < 500) {
+					window.location.reload();
+					return;
+				}
+			} catch {
+				// Unable to connect so do nothing.
+			}
+			window.setTimeout(checkNetworkAndReload, Math.pow(2, count++) * 2500);
+		}
+		checkNetworkAndReload();
+	</script>
+	<?php
+}
+
+add_action( 'wp_footer', 'wp_service_worker_offline_page_reload' );
+add_action( 'error_footer', 'wp_service_worker_offline_page_reload' );