Forcing 4 decimal places on a number without changing its type to string

user_5796284 0
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I receive some data including a decimal number from an api in post request with content-type:json

among the posted data , is a Amount parameters with 4 decimal places

{
  "Amount": 500.0000  ,
  "param1" : "value1" ,
  "param2" : "value2" 
}

after parsing the json

$data = json_decode(file_get_contents('php://input'), true);
var_dump($data);

here is my output

array(3) {
  ["Amount"]=>
  float(500)
  ["param1"]=>
  string(6) "value1"
  ["param2"]=>
  string(6) "value2"
}

the problem is I’m losing the decimal places on the Amount if they are zero

so instead of 500.0000 I get 500 , I know they are the same numbers mathematically but I need to generate a hash from these posted parameters which requires me to have Amount as a float number with 4 decimal places exactly as posted in the first place

I can do something like

$data['Amount'] = sprintf('%0.4f',   $data['Amount'] );

but than it would convert the Amount into an string , which results in a invalid hash

array(3) {
  ["Amount"]=>
  string(8) "500.0000"
  ["param1"]=>
  string(6) "value1"
  ["param2"]=>
  string(6) "value2"
}

I need my $data output to be

  ["Amount"]=>
  float(500.0000)

tried to run it throw floatval , lost the decimal zeros again ! I’m losing my mind over something so simple , any idea how to solve this ?

--------------- edit --------------------

purpose of this hash is to verify the origin of request (making sure its my provider who is sending me this data )

they send me publicKey with the request , I should generate the hash with some of the params and compare it against that public key

In order to create the hash , I need to json_encode some of the received parameters and run them throw sha256 , at the end I need to compare them to a received public_key

so if I receive

{
  "Amount": 5000.0000,
  "Token": "6789",
  "OperatorId": 7799,
  "TransactionId": 110883669553,
  "PublicKey": "f7bb8448c5701b9530fbecc8f9d6296b2ce0600118c402213709bcf19f533c1b"
}

this is how I calculate the hash

$shared_key  =  'someKey';
$hash_params = [
   'Amount'       => $data['Amount'] , 
   'TransactionId' => $data['TransactionId'] , 
];
$hash_string = json_encode($hash_params) . $shared_key ;
$hash =  hash('sha256',    $hash_string  );    
if($hash != $data['PublicKey'] )
{
    die( "hash check failed");
}

In this scenario I need to sha256 this $hash_string

{"WithdrawAmount":5000.0000,"TransactionId":12345 }someKey

if it turns to

{"WithdrawAmount":"5000.0000","TransactionId":12345 }someKey

it'll give me a wrong hash

php json
4 Answers

I don't think there's an easy and simple way to perform a json_encode, of a Float value forcing 4 decimal places when the decimal part of the number is "0000", without manipulating the json string.

The json_enconde method has 2 predefined constants which helps us "almost" achieve the desired result, and these are the JSON_NUMERIC_CHECK and JSON_PRESERVE_ZERO_FRACTION but normally the 0 are removed.

echo json_encode(["amount" => "5.0000"], JSON_NUMERIC_CHECK | JSON_PRESERVE_ZERO_FRACTION);

Outputs: {"amount":5.0}

My solution, would be to perform the encoding using a unique string as amount value and then replace it using str_replace for the formatted amount like this:

$amount_needle = "###amount###";
$hash_params = [
   'Amount'       => $amount_needle, 
   'TransactionId' => $data['TransactionId'], 
];
$encoded_json = json_encode($hash_params);
$hash_string = str_replace("\"{$amount_needle}\"", sprintf('%0.4f', $data['Amount']), $encoded_json) . $shared_key ;
user_22178590

As already mentioned, there is no direct way to format the float value in the JSON string.

As an alternative to the replacement technique shown in Claudio's answer, here is a simple utility class that helps build the JSON string with the desired formatting:

class JSONBuilder
{
    private $params = [];

    public function add($name, $value, $format='')
    {
        if($format)
            $encoded = sprintf($format, $value);
        else
            $encoded = json_encode($value);
        $this->params[] = sprintf('"%s":%s', $name, $encoded);
    }

    public function get()
    {
        return '{' . join(',', $this->params) . '}';
    }
}

Example:

$b = new JSONBuilder();
$b->add('Amount', 5000.0, '%0.4f');
$b->add('Token', '6789');
$b->add('TransactionId', 12345);
echo $b->get();

Output:

{"Amount":5000.0000,"Token":"6789","TransactionId":12345}
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