Question

I’m currently running into a massive wall due to a problem i cannot seem to solve.

The problem is that, when you issue a payment through the Facebook payment platform (facebook javascript sdk), it sends data to your callback page, which should handle the payment on the background.

This all works decent, but there is 1 problem: The order ID that facebook uses is a 64bit ID, and my server is a 32bits server, thus it loses precision on the ID when it gets saved to a variable in the callback page. This ultimately results in not being able to get a proper order_ID in the end, because it cannot save the ID.

The issue has been described on several pages on this forum, for example:

facebook credit callback, order_id changes format changes after moving to a new server

and

PHP: Converting a 64bit integer to string

Yet, on both pages there is no solution to the problem, and i cannot seem to fix this myself.
I have tried to convert the json data that facebook sends to my callback page into string data instead of an array with integers (this happens in the basic code provided by facebook), but i just cannot get this to work.

Seeing that others have overcome this problem (without having to migrate everything to a 64bits server), i am wondering how.

Is anyone able to shine a light on this subject?

Edit:
I have tried converting to string, the standard facebook code that gets called to decode the json data (code provided by facebook):

$request = parse_signed_request($_POST['signed_request'], $app_secret);

This calls the function parse_signed_request, which does:

function parse_signed_request($signed_request, $secret) {
list($encoded_sig, $payload) = explode('.', $signed_request, 2);

$sig = base64_url_decode($encoded_sig);

$data = json_decode(base64_url_decode($payload), true);

  if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
    error_log('Unknown algorithm. Expected HMAC-SHA256');
    return null;
  }

  // check sig
  $expected_sig = hash_hmac('sha256', $payload, $secret, $raw = true);
  if ($sig !== $expected_sig) {
    error_log('Bad Signed JSON signature!');
    return null;
  }
  return $data;
}

This function decodes the encrypted json data from facebook (using the app secret) and should decode the json data to a PHP array.

That function uses the following function (the exact:

function base64_url_decode($input) {
  return base64_decode(strtr($input, '-_', '+/'));
}

Now, the above code results in the order ID not being saved properly, and it loses its precision, resulting in an id like: 4.8567130814993E+14

I have tried to use the following function to somehow decode the json data into a string (so the 64bit integer ID does not lose its precision), but to no avail:

  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);
    }
}

Edit (Eugenes answer):

If i were to try modifying the JSON data before i use json_decode to make it a php variable, i should be using the preg_replace function?
Below is an example of the initial JSON data that gets sent to the callback page to initiate the payment process.
Here you can already see what the problem is (this is after using json_decode, the id and other data lose their precision). The ID’s are modified to not reflect any real data.
If you compare the buyer ID on the top and user id on the bottom, you can see precision is lost.

Array
(
[algorithm] => HMAC-SHA256
[credits] => Array
    (
        [buyer] => 1.0055555551318E+14
        [receiver] => 1.0055555551318E+14
        [order_id] => 5.2555555501665E+14
        [order_info] => {"item_id":"77"}
        [test_mode] => 1
    )

[expires] => 1358456400
[issued_at] => 1358452270
[oauth_token] => AAAH4s2ZCCEMkBAPiGSNsmj98HNdTandalotmoredata
[user] => Array
    (
        [country] => nl
        [locale] => nl_NL
        [age] => Array
            (
                [min] => 21
            )

    )

[user_id] => 100555555513181
)

Edit #3:

I have tried the following to make all the integers in the JSON data seen as strings, but that results in an error from the facebook platform. It does however change the integers to a string, so i do not lose precision (too bad nothing else works now xD)

preg_replace('/([^\\\])":([0-9]{10,})(,|})/', '$1":"$2"$3', $a)

Answer 1

Which version of PHP are you running?

If you are running a version of PHP that supports the JSON “JSON_BIGINT_AS_STRING” option, that may be your answer. You may have to modify their library wherever json_decode is being used to add that option. See http://php.net/manual/en/function.json-decode.php

If your PHP version does not support JSON_BIGINT_AS_STRING, then your options are limited to:

The hacky option: Do some kind of regex operation on the JSON string as it comes back from the FB API and wrap that big ints in double-quotes, so that they decode as a string and not a big int.

The ideal option: Bite the bullet and migrate to a 64 bit environment. It will save you from a lot of headaches in the long run.