Why does curl turn null post arguments into empty strings?

Question

When making a curl post to another script, sometimes I may want to send null as the value for certain keys:

$postdata = array(
        'userID'        => 0,
        'questionText'  => "Can you answer this question?",
        'time'          => null);

$req = curl_init($url);
curl_setopt($req, CURLOPT_POST, true);
curl_setopt($req, CURLOPT_POSTFIELDS, $postdata);
curl_setopt($req, CURLOPT_RETURNTRANSFER, false);
curl_setopt($req, CURLOPT_VERBOSE, true); 
$data = curl_exec($req);
curl_close();

However, the data seems to have changed by the time it is received. Doing a vardump on $_POST reveals that the 'time' value is now an empty string:

array(3) {
    ["userID"]=>
    string(1) "0"
    ["questionText"]=>
    string(29) "Can you answer this question?"
    ["time"]=>
    string(0) ""
}

What's going on here? Why is everything a string? How can I perserve the typing?

What happens when you don't set the attribute at all in the request array? — Subir Kumar Sao
– Subir Kumar Sao, Commented Nov 27, 2017 at 5:49
AFAIK any query to a website will be converted to text and there's no way to represent null in a text so in the end your post data might look like this: userID=0&questionText=Can you answer this question?&time= — Pratansyah
– Pratansyah, Commented Nov 27, 2017 at 5:52
HTTP transfers text only. Therefore a null value cannot be accurately represented. Why is it causing a problem for you? Do you need to differentiate between empty string and NULL on the receiving end? — marekful
– marekful, Commented Nov 27, 2017 at 6:03
In an HTTP request you will only ever receive strings. You have to map value types to database fields on the server side. I recommend to use an ORM framework. — marekful
– marekful, Commented Nov 28, 2017 at 0:24

GoldenJoe · Accepted Answer · 2017-11-29 03:58:08Z

1

As comments to the original question state, HTTP requests will only ever provide strings.

answered Nov 29, 2017 at 3:58

GoldenJoe

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