Description:
------------
PHP's json_decode() function accepts an empty string as JSON data and returns NULL without setting json_last_error(). An empty string is not valid JSON; see productions in RFC 4627 <https://tools.ietf.org/html/rfc4627> and RFC 7159 <https://tools.ietf.org/html/rfc7159>, or try decoding an empty string using builtin JSON parsers in Python, Go, or V8: all of them raise syntax errors.

To be consistent with other errors, trying to decode an empty string should return NULL but set json_last_error() to indicate a syntax error. For example, this is what happens when json_decode(" ") is called.

This affects PHP 5.4.32 on RHEL 5, PHP 5.6.5 built from the Git tag on Mac OS X 10.9, and probably any other configuration with the JSON extension.

It looks like this behavior was discovered during the course of bug #54484 <https://bugs.php.net/bug.php?id=54484> but never fixed. I've included a patch that fixes it, a regression test, and an update to the test for bug #54484.

Test script:
---------------
--TEST--
Bug #XXXXX (json_decode() decodes empty string without indicating error)
--SKIPIF--
<?php if (!extension_loaded("json")) print "skip"; ?>
--FILE--
<?php
json_decode("");
var_dump(json_last_error());
?>
--EXPECT--
int(4)


Actual result:
--------------
int(0)