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How to handle json object that was stringified in Python

I have a question about JSON.stringify() and how to parse it. I have a frontend code and a backend in python (Django).
My fetch function looks like this in frontend.
const response = await fetch('some-url', {
method: "POST",
headers: {
"Content-Type": "application/json",
},
body: JSON.stringify({
payload: payload
})
});
When i do console.log on JSON.stringify({payload: payload}), its type is string. Then in my backend code, when i print out request.data['payload']), its type is <class 'dict'>. I am confused why the type changed when i sent the request to the backed. I was going to use json.loads() to parse the payload but since it is already dictionary it returns an error and i can just do request.data['payload'] to access its data.
Can someone explain this behavior?

So I guess you are using Django Rest framework.
request.data
Will in Django Rest provide you with a parsed version of the request body. Because you are using the content-type: json it will try and parse it as .. json.
See docs here: https://www.django-rest-framework.org/api-guide/requests/#data
In regular Django for parsing a JSON request it would require the use of json.loads like:
parsed_json = json.loads(request.body)

Javascript fetch api payload not delivered

console.log("data ", data); // returns an object in JSON format {propertyName: propertyValue}
dataString = JSON.stringify(dataString); //correctly stringified json
let response = await fetch('updateRecevingEntry.php',
{
method:'POST',
headers: {'Content-Type':'application/json'},
body: dataString
}).then(response=>response.json());
however I get back an undefined index on the php side.
where the php is:
$matkey = $_POST['materialKey'];
returns
<b>Notice</b>: Undefined index: materialKey in <b>path/updateRecevingEntry.php</b> on line <b>3</b><br />
for all the data... none of it is getting caught.
so why is the _POST['propertyName'] not catching the stringData from the body?
I've tried a few variations, such as sending the data instead of the string data messing with the header, but I can't seem to figure out how to send the payload such that _POST['propertyName'] catches the data in the body.
I was using $.ajax from jquery before, and it was working: but I'm in the process of refactoring that out.
the Fetch api is new to me. where am I going wrong. I also don't want to parse a json object on the php side.
after reading one of the answers, I got it to work in one case,
but
let response = await fetch('updateRecevingEntry.php',
{
method:'POST',
headers: {'Content-Type':'application/json'},
body: sendData
}).then(response=>response.json());
and the php
$postData = json_decode(file_get_contents("php://input"), true);
var_dump($postData);
just returns a big fat NULL.
Edit two: turns out it just needs to actually be encoded via JSON.stringify(sendData). Since the. It works as expected.

The first thing I've noticed is that you're not using the right variable (you're using stringData instead of dataString):
dataString = JSON.stringify(dataString); //correctly stringified json
let response = await fetch('updateRecevingEntry.php', {
method:'POST',
headers: {'Content-Type':'application/json'},
body: dataString
}).then(response=>response.json());
Though you shouldn't need to stringify it as you're sending it with json headers.
Additionally, have you tried instead of $_POST, using php://input?
From PHP.net:
php://input is a read-only stream that allows you to read raw data from the request body. In the case of POST requests, it is preferable to use php://input instead of $HTTP_RAW_POST_DATA as it does not depend on special php.ini directives. Moreover, for those cases where $HTTP_RAW_POST_DATA is not populated by default, it is a potentially less memory intensive alternative to activating always_populate_raw_post_data. php://input is not available with enctype="multipart/form-data".
So you would use it like so:
$postData = json_decode(file_get_contents("php://input"), true);
$matkey = $postData['materialKey'];
This reads the body of the POST request as a JSON string then converts it to a PHP array.

IE11 inteprets AJAX POST reply as string, despite being JSON array

From an JQuery AJAX post request the server sends me an reply that just says Hello, and I want to get that Hello as a string.
I wrote this code to get the text value:
var posting = $.post(
"https://server/bla",
{
input: theinput
}
);
posting.done(function( reply ) {
console.log(reply);
console.log(typeof reply);
console.log(reply[0]);
}
It works perfectly on Firefox 55:
Array [ "Hello" ]
object
Hello
... but IE11 seems to believe it is a string (same code):
["Hello"]
string
"[\"Hello\"]"
I wrote a hackish workaround that just uses substring to remove the brackets and quotes at the beginning and end if the variable is a string, but it does not handle well quotes within the reply (Hell"o becomes Hell\"o).
Is there a cleaner solution?
By the way, here is the server side Java code:
JSONArray jsonArray = JSONFactoryUtil.createJSONArray();
jsonArray.put("Hello");

As tipped by Rory, the datatype parameter helps here.
dataType Type: String The type of data expected from the server.
Default: Intelligent Guess (xml, json, script, text, html).
I rewrote the query part to this:
var posting = $.ajax({
type: "POST",
url: "<%=addResUrl%>",
data: {
input: theinput
},
dataType: "json"
});
Note the dataType: "json".
And now it works in IE11 the same way as in Firefox: The JSON is recognized as JSON.

How to receive Non-primitive data in WebMethod?

I am trying to pass an array of bytes to my WebMethod through JavaScript.
The problem is that my WebMethod returns with the message "The test form is only available for primitive methods as parameters."
When I change data type to string or any other kind of primitive variables the WebMethod accepts it goes on.
I'm transforming an object into a byte[], named msgpackEnvio using MessagePack(The transformation itself occurs well), and then sending to WebService.
Here's my request to WebService using jquery
$.ajax({
beforeSend: function (request) {
request.setRequestHeader("Content-Type", "application/json");
},
processData: false,
dataType: "json",
url: url,
data: msgpackEnvio,
type: "POST",
error: function (data) {
$('#upload-load').hide();
$('.bt-enviar-excel').removeAttr('disabled', 'disabled');
var msg = document.getElementsByClassName('msg')[0];
msg.style.color = 'red';
msg.innerHTML = 'Erro interno servidor!';
},
success: //some code
In fact, the code above doesn't matters at all, my problem is in the webService, and how to make it receive an array or perhaps an object.
And here's my WebMethod that should be able to receive a byte[]
[WebMethod]
public string TestMessagePack(byte[] name)
{
//my code
return "Finish";
}

You can use base64 encoding and decoding to send byte arrays as strings. Anything more than that and you might want to use post requests and JSON serialization/deserialization instead. There's not going to be a generic one size fits all conversion between complex C# objects and javascript objects which is why only primitive parameters are allowed, so for nonprimitive things you'll need a translation layer. That's normally going to mean some form of string serialization and deserialization.

Javascript json parsing of php response

I'm working on a project and use ajax to update some informations in forms.
Here is my ajax function :
function update_ad() {
var project_name = document.getElementById("mol_project").value;
if (project_name !== '') {
$.ajax({
type: 'POST',
url: "controllers/get_project.php",
data: {project_name: project_name},
dataType: 'text',
success: function (data) {
var result = JSON.parse(data);
}
});
}
}
On my development environement everything works fine. The function get the json text from php server and parse it so I can use data after that.
But on my production environement, I receive a parsing error :
SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
Here is the received Json :
{"project_name":"Jaguar","project_ORB_code":null,"project_manager":null,"project_abbr":"JR","project_mol_index":"2","project_comment":null}
Jquery, apache and php version are the same on both environements. I guess it's a server configuration issue but I can't figure out where it is.

replace dataType: 'text' to dataType: json,
Look at the spec for JSON (easily understood version here: http://json.org/). There is nowhere that says that parenthesis are valid. ({"foo": true}), for example will never parse. It may be evaled as it is valid javascript, but javascript is not JSON.

Okay, in your JSON, there's a UTF-8 BOM in the front. Can you find the difference between:
{"project_name":"Jaguar","project_ORB_code":null,"project_manager":null,"project_abbr":"JR","project_mol_index":"2","project_comment":null}
And:
{"project_name":"Jaguar","project_ORB_code":null,"project_manager":null,"project_abbr":"JR","project_mol_index":"2","project_comment":null}
Where the latter is a valid JSON. Check it out with JSONLint. You need to make sure that the output you are receiving is free of UTF-8 BOM.
When I tried using the encodeURI() function on the JSON, it gave me this output:
encodeURI(' {"pr'); // "%20%EF%BB%BF%7B%22pr" - Wrong one!
encodeURI(' {"pr'); // "%20%7B%22pr" - Correct one!
We can make use of encodeURI to detect the anamolies and fix it in the client side. I am working on a solution.
The unicode signature, if you see, is EF BB BF, which is explained in this article. We can make use of this signature and try to correct it.
If you have the access to the PHP source, try setting the right headers:
header("Content-type: application/json; charset=utf-8");