Facebook Credits, the Order ID, and dealing with large integers in 32 bit PHP

So, currently at work I’ve been rewriting all our Payment Gateways for Your Members. Making them more better Class based an abstracting out the common functions to a base class, to save memory footprint and code etc.

And came across a problem when rewriting the Facebook Credits handler.

The order ID that gets passed around, as well as the Application ID is too long for a 32 Bit PHP installation to handle when treating it as an Integer.

So a number like “239724439419867” was ending up as “1.7592246582797E+14” when stored/processed, or converted to a string.
Now the obvious way to process this is to convert it to a string another way, which is somewhat difficult since before you even start it is in a format that you can’t handle.

The saving grace here is the fact that data is passed to you as a JSON packet (aside from the fact the Order ID is in the $_POST variable and thus a string, so I could of used it from there).

This led to me to look at the JSON packet, which starts as a string but when decoded the large integers are still a larger integer than can be processed (whether you json_decode to a Array or to an Object, the problem persists). So I thought about how to process the raw JSON packet and make sure the order ID, and other large integers are treated as strings.

If you look at a Raw JSON packet you can easily spot whats a string, integer, object or array.

Take this example Facebook Credits JSON Packet, (wrapped for readability):

{"order_id":239724439419867,"buyer":197803678,"app":148748711865470,
"receiver":197803678,"amount":5,"update_time":1320075413,
"time_placed":1320075408,"data":"","items":[{"item_id":"<item_id>","title":"Post",
"description":"A New Purchasable Post",
"image_url":"<some url>","product_url":"<some other url>",
"price":5,"data":"<data>"}],"status":"<status>"}
  • order_id is an integer as it has no ” around it
  • status is a string as its surrounded by “
  • Items is an array as its surrounded by [, in this case containing a single object, entries/items are comma separated.

So after thinking about this I decided the best way to sort this out was to convert the integers in the raw JSON packet to strings before decoding.

In pseudo code.

Lop off the { and } from the start and end
Explode around ,
array walk each item
split on :
check if there are no " in the second bit
if none wrap in "
glue back together

Something alone the lines of:

function largeint($rawjson) {
  $rawjson = substr($rawjson, 1, -1);
  $rawjson = explode(',' , $rawjson);
  array_walk($rawjson, 'strfun');
  $rawjson = implode(',', $rawjson);
  $rawjson = '{', . $rawjson . '}';
  $json = json_decode($rawjson);
  return $json;
}

function strfun(&$entry, $key) {
  $data = explode(':', $entry);
  if (FALSE === strpos($data[1], '"')) {
    $data[1] = '"' . $data[1] . '"';
    $entry = implode(':', $data);
  }
}

I’m not sure in terms of memory footprint if its cheaper to do a substr of $data[1] and check if its a ” or not.
I suppose it could test the string length of the detected integer to see if its invalid/unable to process, but then you would be performing a string function on an integer and again the problem would arise.

But as a block of code is does the job, its obviously not ideal for all situations, since in this case I want the integer as a string, I’m not using it for math, but if I did, we probably need to do some bizarre unpack-ing or something.

Any opinions or improvements give us a comment below 😀

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