From b6a5bb484d90c6705bd1b010efcc2c1c18be1f34 Mon Sep 17 00:00:00 2001
From: Kevin Israel <pleasestand@live.com>
Date: Tue, 8 Oct 2013 17:23:06 -0400
Subject: [PATCH] FormatJson: Remove whitespace from empty arrays and objects

As noted in c370ad21d7f8, the pretty output can differ between
Zend PHP and HHVM. This change adds some post-processing to make
the output consistent across implementations and with JavaScript
JSON.stringify() and Python json.dumps(); all whitespace between
the opening and closing brackets/braces is removed.

Change-Id: I490e0ff1fac3d6c3fb44ab127e432872c0301a9d
---
 includes/json/FormatJson.php                  | 20 ++++++++++++++++++-
 .../phpunit/includes/json/FormatJsonTest.php  | 14 +++++++------
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/includes/json/FormatJson.php b/includes/json/FormatJson.php
index bc2fff10c5..d61165120e 100644
--- a/includes/json/FormatJson.php
+++ b/includes/json/FormatJson.php
@@ -55,6 +55,17 @@ class FormatJson {
 	 */
 	const ALL_OK = 3;
 
+	/**
+	 * Regex that matches whitespace inside empty arrays and objects.
+	 *
+	 * This doesn't affect regular strings inside the JSON because those can't
+	 * have a real line break (\n) in them, at this point they are already escaped
+	 * as the string "\n" which this doesn't match.
+	 *
+	 * @private
+	 */
+	const WS_CLEANUP_REGEX = '/(?<=[\[{])\n\s*+(?=[\]}])/';
+
 	/**
 	 * Characters problematic in JavaScript.
 	 *
@@ -130,6 +141,12 @@ class FormatJson {
 		if ( $json === false ) {
 			return false;
 		}
+
+		if ( $pretty ) {
+			// Remove whitespace inside empty arrays/objects; different JSON encoders
+			// vary on this, and we want our output to be consistent across implementations.
+			$json = preg_replace( self::WS_CLEANUP_REGEX, '', $json );
+		}
 		if ( $escaping & self::UTF8_OK ) {
 			$json = str_replace( self::$badChars, self::$badCharsEscaped, $json );
 		}
@@ -213,6 +230,7 @@ class FormatJson {
 					$buf .= substr( $json, $i, $skip );
 			}
 		}
-		return str_replace( "\x01", '\"', preg_replace( '/ +$/m', '', $buf ) );
+		$buf = preg_replace( self::WS_CLEANUP_REGEX, '', $buf );
+		return str_replace( "\x01", '\"', $buf );
 	}
 }
diff --git a/tests/phpunit/includes/json/FormatJsonTest.php b/tests/phpunit/includes/json/FormatJsonTest.php
index eb024aba2a..149be05b47 100644
--- a/tests/phpunit/includes/json/FormatJsonTest.php
+++ b/tests/phpunit/includes/json/FormatJsonTest.php
@@ -12,28 +12,30 @@ class FormatJsonTest extends MediaWikiTestCase {
 					123,
 					456,
 				),
+				// Nested json works without problems
 				'"7":["8",{"9":"10"}]',
+				// Whitespace clean up doesn't touch strings that look alike
+				"{\n\t\"emptyObject\": {\n\t},\n\t\"emptyArray\": [ ]\n}",
 			),
 		);
 
 		// 4 space indent, no trailing whitespace, no trailing linefeed
 		$json = '{
-    "emptyObject": {
-    },
-    "emptyArray": [
-    ],
+    "emptyObject": {},
+    "emptyArray": [],
     "string": "foobar\\\\",
     "filledArray": [
         [
             123,
             456
         ],
-        "\"7\":[\"8\",{\"9\":\"10\"}]"
+        "\"7\":[\"8\",{\"9\":\"10\"}]",
+        "{\n\t\"emptyObject\": {\n\t},\n\t\"emptyArray\": [ ]\n}"
     ]
 }';
 
 		$json = str_replace( "\r", '', $json ); // Windows compat
-		$this->assertSame( $json, str_replace("\n\n", "\n", FormatJson::encode( $obj, true ) ));
+		$this->assertSame( $json, FormatJson::encode( $obj, true ) );
 	}
 
 	public static function provideEncodeDefault() {
-- 
2.20.1