Media: Generate identically-dimensioned sub-sizes only once

src/wp-admin/includes/image.php

@@ -484,24 +484,73 @@ function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id ) {
 		}
 	}
 
+	/*
+	 * Group the sizes that would produce an identical file so each is generated
+	 * only once and then shared by every size name that requested it.
+	 *
+	 * Sub-sizes are stored on disk by their dimensions, so two registered sizes
+	 * with the same width, height, and crop resolve to the same file. Without
+	 * grouping, that file is re-encoded and re-written once per size name, which
+	 * slows uploads and is a common cause of timeouts when many sizes are
+	 * registered (for example a plugin size equal to a core size).
+	 */
+	$size_groups = array();
+
+	foreach ( $new_sizes as $new_size_name => $new_size_data ) {
+		$signature = wp_json_encode(
+			array(
+				'width'  => isset( $new_size_data['width'] ) ? $new_size_data['width'] : null,
+				'height' => isset( $new_size_data['height'] ) ? $new_size_data['height'] : null,
+				'crop'   => isset( $new_size_data['crop'] ) ? $new_size_data['crop'] : false,
+			)
+		);
+
+		if ( ! isset( $size_groups[ $signature ] ) ) {
+			$size_groups[ $signature ] = array(
+				'data'  => $new_size_data,
+				'names' => array(),
+			);
+		}
+
+		$size_groups[ $signature ]['names'][] = $new_size_name;
+	}
+
 	if ( method_exists( $editor, 'make_subsize' ) ) {
-		foreach ( $new_sizes as $new_size_name => $new_size_data ) {
-			$new_size_meta = $editor->make_subsize( $new_size_data );
+		foreach ( $size_groups as $group ) {
+			$new_size_meta = $editor->make_subsize( $group['data'] );
 
 			if ( is_wp_error( $new_size_meta ) ) {
 				// TODO: Log errors.
 			} else {
-				// Save the size meta value.
-				$image_meta['sizes'][ $new_size_name ] = $new_size_meta;
+				// Save the size meta value for every size name with these dimensions.
+				foreach ( $group['names'] as $new_size_name ) {
+					$image_meta['sizes'][ $new_size_name ] = $new_size_meta;
+				}
+
 				wp_update_attachment_metadata( $attachment_id, $image_meta );
 			}
 		}
 	} else {
-		// Fall back to `$editor->multi_resize()`.
-		$created_sizes = $editor->multi_resize( $new_sizes );
+		// Fall back to `$editor->multi_resize()`, generating one file per unique size.
+		$unique_sizes = array();
+
+		foreach ( $size_groups as $signature => $group ) {
+			$unique_sizes[ $signature ] = $group['data'];
+		}
+
+		$created_sizes = $editor->multi_resize( $unique_sizes );
 
 		if ( ! empty( $created_sizes ) ) {
-			$image_meta['sizes'] = array_merge( $image_meta['sizes'], $created_sizes );
+			foreach ( $size_groups as $signature => $group ) {
+				if ( ! isset( $created_sizes[ $signature ] ) ) {
+					continue;
+				}
+
+				foreach ( $group['names'] as $new_size_name ) {
+					$image_meta['sizes'][ $new_size_name ] = $created_sizes[ $signature ];
+				}
+			}
+
 			wp_update_attachment_metadata( $attachment_id, $image_meta );
 		}
 	}

tests/phpunit/tests/image/makeSubsizes.php

@@ -0,0 +1,118 @@
+<?php
+
+require_once ABSPATH . WPINC . '/class-wp-image-editor.php';
+require_once ABSPATH . WPINC . '/class-wp-image-editor-gd.php';
+
+/**
+ * Tests for the `_wp_make_subsizes()` function.
+ *
+ * @group image
+ * @group media
+ * @group upload
+ *
+ * @covers ::_wp_make_subsizes
+ */
+class Tests_Image_MakeSubsizes extends WP_UnitTestCase {
+
+	public function set_up() {
+		parent::set_up();
+
+		require_once ABSPATH . 'wp-admin/includes/image.php';
+
+		if ( ! call_user_func( array( 'WP_Image_Editor_GD', 'test' ) ) ) {
+			$this->markTestSkipped( 'The GD image editor is not available.' );
+		}
+	}
+
+	public function tear_down() {
+		remove_all_filters( 'wp_image_editors' );
+		$this->remove_added_uploads();
+
+		parent::tear_down();
+	}
+
+	/**
+	 * Ensures registered sizes that resolve to the same file are generated once.
+	 *
+	 * Sub-sizes are stored on disk by their dimensions, so two sizes registered
+	 * with matching width, height, and crop produce an identical file. They
+	 * should be generated a single time and shared by every size name, rather
+	 * than re-encoded once per name.
+	 *
+	 * @ticket 61925
+	 *
+	 * @covers ::_wp_make_subsizes
+	 */
+	public function test_identical_sizes_are_generated_once_and_shared() {
+		Spy_Make_Subsize_Image_Editor::$make_subsize_count = 0;
+
+		add_filter(
+			'wp_image_editors',
+			static function () {
+				return array( 'Spy_Make_Subsize_Image_Editor' );
+			}
+		);
+
+		$attachment_id = self::factory()->attachment->create_upload_object( DIR_TESTDATA . '/images/canola.jpg' );
+
+		$file       = get_attached_file( $attachment_id );
+		$image_meta = wp_get_attachment_metadata( $attachment_id );
+
+		// Count only the sub-sizes generated by the call under test.
+		Spy_Make_Subsize_Image_Editor::$make_subsize_count = 0;
+
+		// Two size names requesting an identical file, plus one distinct size.
+		$new_sizes = array(
+			'test_dedup_a'  => array(
+				'width'  => 40,
+				'height' => 40,
+				'crop'   => true,
+			),
+			'test_dedup_b'  => array(
+				'width'  => 40,
+				'height' => 40,
+				'crop'   => true,
+			),
+			'test_distinct' => array(
+				'width'  => 80,
+				'height' => 80,
+				'crop'   => true,
+			),
+		);
+
+		$result = _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id );
+
+		$this->assertSame(
+			2,
+			Spy_Make_Subsize_Image_Editor::$make_subsize_count,
+			'Two identical sizes and one distinct size should generate two files, not three.'
+		);
+
+		$this->assertArrayHasKey( 'test_dedup_a', $result['sizes'], 'The first identical size should be recorded.' );
+		$this->assertArrayHasKey( 'test_dedup_b', $result['sizes'], 'The second identical size should be recorded.' );
+		$this->assertSame(
+			$result['sizes']['test_dedup_a'],
+			$result['sizes']['test_dedup_b'],
+			'Both identical size names should reference the same generated file.'
+		);
+	}
+}
+
+/**
+ * A GD image editor that counts calls to make_subsize() for the dedup test.
+ */
+class Spy_Make_Subsize_Image_Editor extends WP_Image_Editor_GD {
+
+	/**
+	 * Number of times make_subsize() has been called.
+	 *
+	 * @var int
+	 */
+	public static $make_subsize_count = 0;
+
+	public function make_subsize( $size_data ) {
+		++self::$make_subsize_count;
+
+		return parent::make_subsize( $size_data );
+	}
+}