Handle general form posts

amp.php

@@ -106,7 +106,6 @@ function amp_after_setup_theme() {
  * @global string $pagenow
  */
 function amp_init() {
-	global $pagenow;
 
 	/**
 	 * Triggers on init when AMP plugin is active.
@@ -128,9 +127,7 @@ function amp_init() {
 	if ( class_exists( 'Jetpack' ) && ! ( defined( 'IS_WPCOM' ) && IS_WPCOM ) ) {
 		require_once AMP__DIR__ . '/jetpack-helper.php';
 	}
-	if ( isset( $pagenow ) && 'wp-comments-post.php' === $pagenow ) {
-		amp_prepare_comment_post();
-	}
+	amp_prepare_xhr_post();
 }
 
 // Make sure the `amp` query var has an explicit value.

includes/amp-helper-functions.php

@@ -406,17 +406,33 @@ function amp_print_schemaorg_metadata() {
  *
  * @since 0.7.0
  */
-function amp_prepare_comment_post() {
-	if ( ! isset( $_GET['__amp_source_origin'] ) ) { // WPCS: CSRF ok. Beware of AMP_Theme_Support::purge_amp_query_vars().
+function amp_prepare_xhr_post() {
+	global $pagenow;
+	if ( ! isset( $_GET['__amp_source_origin'] ) || ! isset( $pagenow ) ) { // WPCS: CSRF ok. Beware of AMP_Theme_Support::purge_amp_query_vars().
 		return;
 	}
 
-	// Add amp comment hooks.
-	add_filter( 'comment_post_redirect', function() {
-		// We don't need any data, so just send a success.
-		wp_send_json_success();
-	}, PHP_INT_MAX, 2 );
-
+	if ( 'wp-comments-post.php' === $pagenow ) {
+		// This only runs on wp-comments-post.php.
+		add_filter( 'comment_post_redirect', function() {
+			// We don't need any data, so just send a success.
+			wp_send_json_success();
+		}, PHP_INT_MAX, 2 );
+	} elseif ( ! isset( $_GET['_wp_amp_action_xhr_converted'] ) ) { // WPCS: CSRF ok.
+		// submission was from a set action-xhr, implying it's being handled already.
+		return;
+	} else {
+		// Add amp redirect hooks.
+		add_filter( 'wp_redirect', 'amp_handle_general_post', PHP_INT_MAX, 2 );
+		add_action( 'template_redirect', function() {
+			/*
+			 * Buffering starts here, so unlikely the form has a redirect,
+			 * so force a redirect to the same page.
+			 */
+			$location = esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) ); // WPCS: CSRF ok, input var ok.
+			amp_handle_general_post( $location );
+		}, 0 );
+	}
 	// Add die handler for AMP error display.
 	add_filter( 'wp_die_handler', function() {
 		/**
@@ -438,3 +454,18 @@ function amp_prepare_comment_post() {
 	$origin = esc_url_raw( wp_unslash( $_GET['__amp_source_origin'] ) ); // WPCS: CSRF ok.
 	header( 'AMP-Access-Control-Allow-Source-Origin: ' . $origin, true );
 }
+
+/**
+ * Handle a general, non comment AMP XHR post.
+ *
+ * @since 0.7.0
+ * @param string $location The location to redirect to.
+ */
+function amp_handle_general_post( $location ) {
+
+	$url = site_url( $location );
+	header( 'AMP-Redirect-To: ' . $url );
+	header( 'Access-Control-Expose-Headers: AMP-Redirect-To;' );
+	// Send json success as no data is required.
+	wp_send_json_success();
+}

includes/class-amp-theme-support.php

@@ -102,7 +102,7 @@ public static function init() {
 			self::register_paired_hooks();
 		}
 
-		self::purge_amp_query_vars(); // Note that amp_prepare_comment_post() still looks at $_GET['__amp_source_origin'].
+		self::purge_amp_query_vars(); // Note that amp_prepare_xhr_post() still looks at $_GET['__amp_source_origin'].
 		self::register_hooks();
 		self::$embed_handlers    = self::register_content_embed_handlers();
 		self::$sanitizer_classes = amp_get_content_sanitizers();
@@ -214,6 +214,7 @@ public static function register_hooks() {
 	public static function purge_amp_query_vars() {
 		$query_vars = array(
 			'__amp_source_origin',
+			'_wp_amp_action_xhr_converted',
 			'amp_latest_update_time',
 		);
 

includes/sanitizers/class-amp-form-sanitizer.php

@@ -87,7 +87,11 @@ public function sanitize() {
 			} elseif ( 'post' === $method ) {
 				$node->removeAttribute( 'action' );
 				if ( ! $xhr_action ) {
+					// record that action was converted tp action-xhr.
+					$action_url = add_query_arg( '_wp_amp_action_xhr_converted', 1, $action_url );
 					$node->setAttribute( 'action-xhr', $action_url );
+					// Append error handler if not found.
+					$this->error_handler( $node );
 				} elseif ( 'http://' === substr( $xhr_action, 0, 7 ) ) {
 					$node->setAttribute( 'action-xhr', substr( $xhr_action, 5 ) );
 				}
@@ -108,4 +112,43 @@ public function sanitize() {
 			}
 		}
 	}
+
+	/**
+	 * Checks if the form has an error handler else create one if not.
+	 *
+	 * @link https://www.ampproject.org/docs/reference/components/amp-form
+	 * @since 0.7
+	 * @param DOMElement $node The form node to check.
+	 */
+	public function error_handler( $node ) {
+		$templates = $node->getElementsByTagName( 'template' );
+		if ( $templates->length ) {
+			for ( $i = $templates->length - 1; $i >= 0; $i-- ) {
+				if ( $templates->item( $i )->parentNode->hasAttribute( 'submit-error' ) ) {
+					return; // Found error template, do nothing.
+				}
+			}
+		}
+		$node->appendChild( $this->create_error_template() );
+	}
+
+	/**
+	 * Creates a error handler element node.
+	 *
+	 * @link https://www.ampproject.org/docs/reference/components/amp-form
+	 * @since 0.7
+	 *
+	 * return DOMElement
+	 */
+	public function create_error_template() {
+		$node     = $this->dom->createElement( 'div' );
+		$template = $this->dom->createElement( 'template' );
+		$mustache = $this->dom->createTextNode( '{{{error}}}' );
+		$node->setAttribute( 'submit-error', '' );
+		$template->setAttribute( 'type', 'amp-mustache' );
+		$template->appendChild( $mustache );
+		$node->appendChild( $template );
+
+		return $node;
+	}
 }

tests/test-amp-form-sanitizer.php

@@ -46,7 +46,7 @@ public function get_data() {
 			),
 			'form_with_post_method_http_action_and_no_target' => array(
 				'<form method="post" action="http://example.org/example-page/"></form>',
-				'<form method="post" action-xhr="//example.org/example-page/" target="_top"></form>',
+				'<form method="post" action-xhr="//example.org/example-page/?_wp_amp_action_xhr_converted=1" target="_top"><div submit-error=""><template type="amp-mustache">{{{error}}}</template></div></form>',
 			),
 			'form_with_post_method_http_action_and_blank_target' => array(
 				'<form method="post" action-xhr="http://example.org/example-page/" target="_blank"></form>',
@@ -58,7 +58,7 @@ public function get_data() {
 			),
 			'form_with_post_method_https_action_and_custom_target' => array(
 				'<form method="post" action="https://example.org/" target="some_other_target"></form>',
-				'<form method="post" target="_blank" action-xhr="https://example.org/"></form>',
+				'<form method="post" target="_blank" action-xhr="https://example.org/?_wp_amp_action_xhr_converted=1"><div submit-error=""><template type="amp-mustache">{{{error}}}</template></div></form>',
 			),
 		);
 	}