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charlesmc..

validating json unnecessarily is killing firefox

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in Developing jQuery Core • 1 years ago

I'm trying to parse a json string that's just over 2MB long, and when I get to line 507 of jquery 1.4.2 (inside parseJSON commented with: "Make sure the incoming data is actual JSON") I'm getting an internal Firefox error: "script stack space quota is exhausted".

When I hack the code to skip that if statement, everything returns hunky-dory. My question/suggestion is that we skip that test, at least where window.JSON.parse is set. If using either a browser compiled version or the json.org version an error will be thrown if invalid JSON is encountered, therefore, we could rewrite the code thus:

// Try to use the native JSON parser first
if (window.JSON && window.JSON.parse) {
try {
return window.JSON.parse( data );
} catch (err) {
jQuery.error( "Invalid JSON: " + data );
}
} else {
if ( /^[\],:{}\s]*$/.test(data.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, "@")
.replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, "]")
.replace(/(?:^|:|,)(?:\s*\[)+/g, "")) ) {
return (new Function("return " + data))();
} else {
jQuery.error( "Invalid JSON: " + data );
}

This way it only runs the valid json script if it's forced to use the relatively unsafe "eval" code, as opposed to running it each time, even if it's just going to go out and immediately validate it again with the compiled JSON parse.

Replies(5)

jeresig

Re: validating json unnecessarily is killing firefox

1 years ago

Unfortunately the browsers aren't consistent in what JSON they are willing to parse with their JSON.parse code. For example, Chrome accepts a number of invalid strings that we need to reject. Additionally, we need to be consistent about what strings we accept and reject (and using a regular expression to double-check that makes that happen).

I'm slightly confused though: If you're having problems on this particular regular expression (copied from JSON2.js) surely you're also having problems in Internet Explorer?

charlesmc..

Re: validating json unnecessarily is killing firefox

1 years ago

A very reasonable assumption, but no, IE is fine. It looks like I'm somehow hitting this:

https://bugzilla.mozilla.org/show_bug.cgi?id=547967
edit: or this:
https://bugzilla.mozilla.org/show_bug.cgi?id=502836

Which, I realize makes it unlikely that jquery would or should "fix" it, unless a whole lot of people also start hitting it with large json sets. I'm also not sure if it's something unique to my json other than the sheer size. If I get a chance I'll create some big but simple json to try it against. Alternatively I could just warn my users against running any of these new-fangled browsers!

For the record the json set that breaks it is 2,377,160 bytes, give or take a couple of bytes.

charlesmc..

Re: validating json unnecessarily is killing firefox

1 years ago

In case this is something that needs to be addressed for some reason, here's some code that reproduces the issue pretty cleanly (at least on my system). Code works fine in IE8. breaks FF3.6, untested otherwise. Perhaps a regex wizard could rewrite the regex to take it into consideration.

<?
if(isset($_REQUEST['action'])) {
   // >= 862316 breaks Firefox 3.6
   // <= 862315 works for Firefox 3.6

   $contents = '';
   if($_REQUEST['action']=='hi') {
       for($i=0;$i<862316; $i++) {
           $contents .= "x";
       }
   } else {
       for($i=0;$i<862315; $i++) {
           $contents .= "x";
       }

   }

   $string = json_encode($contents);
   header('Content-Type: text/javascript');
   echo $string;
   exit;
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.4.2.js"></script>
<script type="text/javascript" >

   $(document).ready(function(){

       $(':button').click(function(){
           $.ajax({
               url: 'test.php',
               data: {action:this.id},
               success: on_success,
               error: on_fail,
               dataType: 'json'
           });
       })

   });

   function on_success(results) {
       alert(results.length);
   }

   function on_fail(XMLHttpRequest, textStatus, errorThrown) {
       alert(errorThrown);
   }

</script>

</head>
<body>
<input type="button" id="hi" value="hi"/>
<input type="button" id="lo" value="lo"/>
</body>
</html>

speedpack..

Re: validating json unnecessarily is killing firefox

1 year ago

Just for the record - I'm running into this issue when searching for elements in an ajax returned chunck of html... I guess we'll need to wait for Mozilla to fix :)

ask732

Re: validating json unnecessarily is killing firefox

1 year ago

FWIW, I'm using FF 3.6.8 and having the same problem. Happens where I'm requesting data in for what turns out to be an overly-large select (i.e. drop-down list). Having such a large, monolithic, drop-down list is bad UI, so I'm changing it to something more dynamic. But others may have more unavoidable reasons to pull large amounts of JSON data across and will hit the same problem.

Not sure Mozilla should/will change their limitation. So it might be up to the library to work around it, no?