Submitting JSON data via JQuery ajax.post to PHP

Question

Im submitting Data to a php file via AJAX using POST. It worked fine with just submitting strings, but now I wanted to submit my JS Object with JSON and decode it on PHP side.

In the console I can see, that my data is submitted correctly but on PHP side json_decode returns NULL.

I've tried the following:

this.getAbsence = function()
{
    alert(JSON.stringify(this));
    jQuery.ajax({
        type: "POST",
        contentType: "application/json; charset=utf-8",
        url: "ajax/selectSingle.php?m=getAbsence",
        data: JSON.stringify(this),
        success : function(data){
            alert(data);
        }
    });
}

PHP:

echo $_POST['data'];
echo json_decode($_POST['data']);
echo var_dump(json_decode($_POST['data']));

And:

this.getAbsence = function()
{
    alert(JSON.stringify(this));
    jQuery.ajax({
        type: "POST",
        contentType: "application/json; charset=utf-8",
        url: "ajax/selectSingle.php?m=getAbsence",
        data: {'Absence' : JSON.stringify(this)},
        success : function(data){
            alert(data);
        }
    });
}

PHP:

echo $_POST['Absence'];
echo json_decode($_POST['Absence']);
echo var_dump(json_decode($_POST['Absence']));

The alert was just to check everything is alright...

And yea usual string were echoed correctly :-)

Answer 1

Where you went wrong in your code in the first code is that you must have used this:

var_dump(json_decode(file_get_contents("php://input"))); //and not $_POST['data']

Quoting from PHP Manual

php://input is a read-only stream that allows you to read raw data from the request body.

Since in your case, you are submitting a JSON in the body, you have to read it from this stream. Usual method of $_POST['field_name'] wont work, because the post body is not in an URLencoded format.

In the second part, you must have used this:

contentType: "application/json; charset=utf-8",
url: "ajax/selectSingle.php?m=getAbsence",
data: JSON.stringify({'Absence' : JSON.stringify(this)}),

UPDATE:

When request has a content type application/json, PHP wont parse the request and give you the JSON object in $_POST, you must parse it yourself from the raw HTTP body. The JSON string is retrieved using file_get_contents("php://input");.

If you must get that using $_POSTyou would make it:

data: {"data":JSON.stringify({'Absence' : JSON.stringify(this)})},

And then in PHP do:

$json = json_decode($_POST['data']);