Script Loader: Refactor Etag generation for concatenated assets.

Move Etag HTTP header generation in `load-scripts.php` and `load-styles.php` to `WP_Dependencies`.

Introduces the method `WP_Dependencies::get_etag()` and associated unit tests.

Follow up to [57943].

Props vrajadas, martinkrcho, mukesh27.
Fixes #61485.

Built from https://develop.svn.wordpress.org/trunk@58935


git-svn-id: http://core.svn.wordpress.org/trunk@58331 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/load-scripts.php

@@ -52,24 +52,7 @@ wp_default_scripts( $wp_scripts );
 wp_default_packages_vendor( $wp_scripts );
 wp_default_packages_scripts( $wp_scripts );
 
-$etag = "WP:{$wp_version};";
+$etag = $wp_scripts->get_etag( $load );
-
-foreach ( $load as $handle ) {
-	if ( ! array_key_exists( $handle, $wp_scripts->registered ) ) {
-		continue;
-	}
-
-	$ver   = $wp_scripts->registered[ $handle ]->ver ? $wp_scripts->registered[ $handle ]->ver : $wp_version;
-	$etag .= "{$handle}:{$ver};";
-}
-
-/*
- * This is not intended to be cryptographically secure, just a fast way to get
- * a fixed length string based on the script versions. As this file does not
- * load the full WordPress environment, it is not possible to use the salted
- * wp_hash() function.
- */
-$etag = 'W/"' . md5( $etag ) . '"';
 
 if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) && stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) === $etag ) {
 	header( "$protocol 304 Not Modified" );

wp-admin/load-styles.php

@@ -55,24 +55,7 @@ $out            = '';
 $wp_styles = new WP_Styles();
 wp_default_styles( $wp_styles );
 
-$etag = "WP:{$wp_version};";
+$etag = $wp_styles->get_etag( $wp_version, $load );
-
-foreach ( $load as $handle ) {
-	if ( ! array_key_exists( $handle, $wp_styles->registered ) ) {
-		continue;
-	}
-
-	$ver   = $wp_styles->registered[ $handle ]->ver ? $wp_styles->registered[ $handle ]->ver : $wp_version;
-	$etag .= "{$handle}:{$ver};";
-}
-
-/*
- * This is not intended to be cryptographically secure, just a fast way to get
- * a fixed length string based on the script versions. As this file does not
- * load the full WordPress environment, it is not possible to use the salted
- * wp_hash() function.
- */
-$etag = 'W/"' . md5( $etag ) . '"';
 
 if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) && stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) === $etag ) {
 	header( "$protocol 304 Not Modified" );

wp-includes/class-wp-dependencies.php

@@ -490,4 +490,42 @@ class WP_Dependencies {
 
 		return true;
 	}
+
+	/**
+	 * Get etag header for cache validation.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @global string $wp_version The WordPress version string.
+	 *
+	 * @param string[] $load Array of script or style handles to load.
+	 * @return string Etag header.
+	 */
+	public function get_etag( $load ) {
+		/*
+		 * Note: wp_get_wp_version() is not used here, as this file can be included
+		 * via wp-admin/load-scripts.php or wp-admin/load-styles.php, in which case
+		 * wp-includes/functions.php is not loaded.
+		 */
+		global $wp_version;
+
+		$etag = "WP:{$wp_version};";
+
+		foreach ( $load as $handle ) {
+			if ( ! array_key_exists( $handle, $this->registered ) ) {
+				continue;
+			}
+
+			$ver   = $this->registered[ $handle ]->ver ?? $wp_version;
+			$etag .= "{$handle}:{$ver};";
+		}
+
+		/*
+		 * This is not intended to be cryptographically secure, just a fast way to get
+		 * a fixed length string based on the script versions. As this file does not
+		 * load the full WordPress environment, it is not possible to use the salted
+		 * wp_hash() function.
+		 */
+		return 'W/"' . md5( $etag ) . '"';
+	}
 }

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-alpha-58934';
+$wp_version = '6.7-alpha-58935';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.