Fix slow call to scandir() when uploading files

inc/class-stream-wrapper.php

@@ -589,6 +589,32 @@ public function dir_opendir( $path, $options ) {
 
 		$this->openedBucketPrefix = $params['Key'];
 
+		// WordPress attempts to scan whole directories via wp_unique_filename(), which can be very slow
+		// when there are thousands of files in a single uploads sub directory. This is due to behaviour
+		// introduced in https://core.trac.wordpress.org/changeset/46822/. Essentially when a file is uploaded,
+		// it's not enough to make sure no filename already exists (and append a `-1` to the end), because
+		// image sizes of that image could also conflict with already existing files too. Because image sizes
+		// (in the form of -800x600.jpg) can be arbitrary integers, it's not possible to iterate the filesystem
+		// for all possible matching / colliding file names. WordPress core uses a preg-match on all files that
+		// might conflict with the given filename.
+		//
+		// Fortunately, we can make use of S3 arbitrary prefixes to optimize this query. The WordPress regex
+		// done via _wp_check_existing_file_names() is essentially `^$filename-...`, so we can modify the prefix
+		// to include the filename, therefore only return a subset of files from S3 that are more likely to match
+		// the preg_match() call.
+		//
+		// Essentially, wp_unique_filename( my-file.jpg ) doing a `scandir( s3://bucket/2019/04/ )` will actually result in an s3
+		// listObject query for `s3://bucket/2019/04/my-file` which means even if there are millions of files in `2019/04/` we only
+		// return a much smaller subset.
+		//
+		// Anyone reading this far, brace yourselves for a mighty horrible hack.
+		$backtrace = debug_backtrace( 0, 3 );
+		if ( isset( $backtrace[1]['function'] ) && $backtrace[1]['function'] === 'scandir' && isset( $backtrace[2]['function'] ) && $backtrace[2]['function'] === 'wp_unique_filename' ) {
+			$filename = $backtrace[2]['args'][1];
+			$name = pathinfo( $filename, PATHINFO_FILENAME );
+			$op['Prefix'] .= $name;
+		}
+
 		// Filter our "/" keys added by the console as directories, and ensure
 		// that if a filter function is provided that it passes the filter.
 		$this->objectIterator = \Aws\flatmap(

tests/test-s3-uploads.php

@@ -171,4 +171,16 @@ function test_get_s3_bucket() {
 		$this->assertEquals( 'hmn-uploads', $uploads->get_s3_bucket() );
 	}
 
+	function test_wp_unique_filename() {
+		S3_Uploads\Plugin::get_instance()->setup();
+		$upload_dir = wp_upload_dir();
+
+		file_put_contents( $upload_dir['path'] . '/my-file-scaled.jpg', '' );
+		$filename = wp_unique_filename( $upload_dir['path'], 'my-file.jpg' );
+		$this->assertEquals( 'my-file-1.jpg', $filename );
+
+		$filename = wp_unique_filename( $upload_dir['path'], 'my-new-file.jpg' );
+		$this->assertEquals( 'my-new-file.jpg', $filename );
+	}
+
 }