REST API: Introduce _pretty query parameter to opt in to JSON_PRETTY_PRINT.

Add support for a "_pretty" meta-parameter on all REST controllers which instructs WordPress to return pretty-printed JSON, for better readability when inspecting endpoint responses in curl output or certain developer tools.

Introduce the "rest_json_encode_options" filter to permit site owners to control this behavior globally.

Props Viper007Bond, TimothyBlynJacobs, chrisguitarguy, johnbillion, swissspidy, adamsilverstein, danielbachhuber, rmccue.
Fixes #41998.


git-svn-id: https://develop.svn.wordpress.org/trunk@54127 602fd350-edb4-49c9-b593-d223f7449a82

Author: kadamwhite

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -230,6 +230,33 @@ protected function json_error( $code, $message, $status = null ) {
 		return wp_json_encode( $error );
 	}
 
+	/**
+	 * Gets the encoding options passed to {@see wp_json_encode}.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @param \WP_REST_Request $request The current request object.
+	 *
+	 * @return int The JSON encode options.
+	 */
+	protected function get_json_encode_options( WP_REST_Request $request ) {
+		$options = 0;
+
+		if ( $request->has_param( '_pretty' ) ) {
+			$options |= JSON_PRETTY_PRINT;
+		}
+
+		/**
+		 * Filters the JSON encoding options used to send the REST API response.
+		 *
+		 * @since 6.1.0
+		 *
+		 * @param int $options             JSON encoding options {@see json_encode()}.
+		 * @param WP_REST_Request $request Current request object.
+		 */
+		return apply_filters( 'rest_json_encode_options', $options, $request );
+	}
+
 	/**
 	 * Handles serving a REST API request.
 	 *
@@ -493,7 +520,7 @@ public function serve_request( $path = null ) {
 				return null;
 			}
 
-			$result = wp_json_encode( $result );
+			$result = wp_json_encode( $result, $this->get_json_encode_options( $request ) );
 
 			$json_error_message = $this->get_json_last_error();
 
@@ -506,7 +533,7 @@ public function serve_request( $path = null ) {
 				);
 
 				$result = $this->error_to_response( $json_error_obj );
-				$result = wp_json_encode( $result->data );
+				$result = wp_json_encode( $result->data, $this->get_json_encode_options( $request ) );
 			}
 
 			if ( $jsonp_callback ) {