The ultimate method for ensuring top-notch security in JavaScript JSON Inline practices

Question

The ultimate method for ensuring top-notch security in JavaScript JSON Inline practices

Utilizing varnish+esi, I am able to retrieve external json content from a RESTFul API. This approach allows for efficient request management and data refreshing without burdening the webserver with each individual request.

For example:

<head>
.... 
<script> 
 var data = <esi:include src='apiurl/data'>;
</script>
...

Upon including the ESI, Varnish will return:

 var data = {attr:1, attr2:'martin'};

While this method works well, it may encounter parsing errors if the API responds with an error message.

var data = <html><head><script>...api js here...</script></head><body><h1 ... api html ....

To resolve this issue, I implemented a hidden div to manage and capture any potential errors:

...
<b id=esi-data style=display:none;><esi:include src='apiurl/data'></b>
<script>
  try{
    var data = $.parseJSON($('#esi-data').html());
  }catch{ alert('manage the error here');}
....

I also experimented with using a script type text/esi, but encountered issues where the browser would render the HTML within the script tag (strange behavior), as seen here:

<script id=esi-data type='text/esi'><esi:include src='apiurl/data'></script>

Question:

Is there a way to encapsulate the esi:include tag to prevent the browser from parsing it?

javascript json parsing varnish esi

Answer 1

Answer №1

Allow me to elaborate on the suggestion I mentioned regarding using an iframe in my previous comment—it's not as straightforward as you may think!

The concept is quite similar to what you're already doing, but instead of utilizing a regular HTML element like a div, you incorporate an iframe.

<iframe id="esi-data" src="about:blank"><esi:include src="apiurl/data"></iframe>

var $iframe = $('#esi-data');

try {
    var data = $.parseJSON($iframe.html());
} catch (e) { ... }

$iframe.remove();

#esi-data { display: none; }

How does this differ from your solution? There are two key distinctions:

Your visitors truly cannot see the data/error page. An iframe follows an embedded content model, which means any content within the <iframe>…</iframe> tags gets entirely replaced in the DOM—but you can still access the original content using innerHTML.
It adheres to HTML5 standards... somewhat. In HTML5, content inside iframe elements is treated as text. While it should technically be parseable as a fragment and only contain phrasing content (with no script elements!), it is essentially interpreted as text by both validators and browsers.
Scripts within the error page will not execute. The content is parsed as text and replaced in the DOM with another document—eliminating any possibility for script elements to run.

Check it out live here. If you disable the line where I remove the iframe element and inspect the DOM, you'll observe that the HTML content is substituted with a blank document. Additionally, note that the embedded script tag remains inactive.

Important: while improbable, this approach could potentially fail if the third party introduces an iframe into their error page for any reason. To enhance this method's resilience, consider combining your method with another: encase the iframe in a hidden div that you delete once parsing is complete.

Answer 2

Allow me to elaborate on the suggestion I mentioned regarding using an iframe in my previous comment—it's not as straightforward as you may think!

The concept is quite similar to what you're already doing, but instead of utilizing a regular HTML element like a div, you incorporate an iframe.

<iframe id="esi-data" src="about:blank"><esi:include src="apiurl/data"></iframe>

var $iframe = $('#esi-data');

try {
    var data = $.parseJSON($iframe.html());
} catch (e) { ... }

$iframe.remove();

#esi-data { display: none; }

How does this differ from your solution? There are two key distinctions:

Your visitors truly cannot see the data/error page. An iframe follows an embedded content model, which means any content within the <iframe>…</iframe> tags gets entirely replaced in the DOM—but you can still access the original content using innerHTML.
It adheres to HTML5 standards... somewhat. In HTML5, content inside iframe elements is treated as text. While it should technically be parseable as a fragment and only contain phrasing content (with no script elements!), it is essentially interpreted as text by both validators and browsers.
Scripts within the error page will not execute. The content is parsed as text and replaced in the DOM with another document—eliminating any possibility for script elements to run.

Check it out live here. If you disable the line where I remove the iframe element and inspect the DOM, you'll observe that the HTML content is substituted with a blank document. Additionally, note that the embedded script tag remains inactive.

Important: while improbable, this approach could potentially fail if the third party introduces an iframe into their error page for any reason. To enhance this method's resilience, consider combining your method with another: encase the iframe in a hidden div that you delete once parsing is complete.

Answer 3

Answer №2

Here's another approach I can suggest.

While the solution you currently have may be the best option, one alternative method could involve using a less efficient way of calling esi:insert in a separate HTML window, then fetching the contents similar to how AJAX works on the server side. This process might resemble something like what is described in this article. You could then examine the retrieved contents, possibly using json_decode, and return an error JSON string upon success.

The main drawback I foresee with this approach is that it could be resource-intensive and potentially slow down requests since the separate page would need to be fetched as if your server was acting as a client, parsed, and then returned.

In my opinion, it might be best to stick with your current solution.

Answer 4

Here's another approach I can suggest.

While the solution you currently have may be the best option, one alternative method could involve using a less efficient way of calling esi:insert in a separate HTML window, then fetching the contents similar to how AJAX works on the server side. This process might resemble something like what is described in this article. You could then examine the retrieved contents, possibly using json_decode, and return an error JSON string upon success.

The main drawback I foresee with this approach is that it could be resource-intensive and potentially slow down requests since the separate page would need to be fetched as if your server was acting as a client, parsed, and then returned.

In my opinion, it might be best to stick with your current solution.

Answer 5

Answer №3

This particular issue presents a complex challenge with no straightforward solution, and in some cases, no solution at all.

I inquired about whether the document was HTML(5) or XHTML(5) because in the latter scenario, using a CDATA section to encapsulate the content could alter your approach slightly. The revised solution might look something like this:

...
<b id='esi-data' style='display:none;'>
    <![CDATA[ <esi:include src='apiurl/data'> ]]>
</b>
<script>
    try{
        var data = $.parseJSON($('#esi-data').html());
    }catch{ alert('manage the error here');}
....

This solution is effective if:

You are utilizing XHTML5
The error does not contain a CDATA section (as nesting CDATA sections is not possible).

I am uncertain if transitioning from one serialization to another is feasible, but I wanted to clarify the intention behind my question. Hopefully, this clarification will assist you in resolving the issue :).

Answer 6

This particular issue presents a complex challenge with no straightforward solution, and in some cases, no solution at all.

I inquired about whether the document was HTML(5) or XHTML(5) because in the latter scenario, using a CDATA section to encapsulate the content could alter your approach slightly. The revised solution might look something like this:

...
<b id='esi-data' style='display:none;'>
    <![CDATA[ <esi:include src='apiurl/data'> ]]>
</b>
<script>
    try{
        var data = $.parseJSON($('#esi-data').html());
    }catch{ alert('manage the error here');}
....

This solution is effective if:

You are utilizing XHTML5
The error does not contain a CDATA section (as nesting CDATA sections is not possible).

I am uncertain if transitioning from one serialization to another is feasible, but I wanted to clarify the intention behind my question. Hopefully, this clarification will assist you in resolving the issue :).

Answer 7

Answer №4

Have you considered updating your API so that it returns JSON { "error":"error_code_or_text" } in case of an error? By doing this, you could enhance user experience by providing alerts for errors directly in the interface.

Answer 8

Have you considered updating your API so that it returns JSON { "error":"error_code_or_text" } in case of an error? By doing this, you could enhance user experience by providing alerts for errors directly in the interface.

Answer 9

Answer №5

<script>var info = 555;</script>

<script>
info = <esi:include src='apiurl/info'>;
</script>

<script>
if(info == 555) alert("Oops, something went wrong");
</script>

If an error occurs and "info" is not in JSON format, a javascript error will be triggered. The following script block will handle this situation.

Answer 10

<script>var info = 555;</script>

<script>
info = <esi:include src='apiurl/info'>;
</script>

<script>
if(info == 555) alert("Oops, something went wrong");
</script>

If an error occurs and "info" is not in JSON format, a javascript error will be triggered. The following script block will handle this situation.

The ultimate method for ensuring top-notch security in JavaScript JSON Inline practices

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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