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Javascript XMLHTTPRequest send with protocol undefined in header

I am trying to debug a functionality that runs from a plain old Javascript Web Page and requests to a server.
This perfectly works on my computer but fails on another (the real target)
When it fails, i get an empty string response from the server.
Here is the code that build the request
// Send request to web server
var url = "/start?f="+filesDesc[iFile].name+"&ft="+ft+"&t="+time0ms;
var req = new XMLHttpRequest();
if (req) {
req.open("POST", url, true);
// Hack to pass bytes through unprocessed.
req.overrideMimeType('text/plain; charset=x-user-defined');
req.timeout = 2000;
req.onreadystatechange = function(e) {
// In local files, status is 0 upon success in Mozilla Firefox
if(req.readyState === XMLHttpRequest.DONE) {
var status = req.status;
if (status === 0 || (status >= 200 && status < 400)) {
// The request has been completed successfully
console.debug(req.responseText);
} else {
console.debug("startPlaying : error while sending rqst" );
}
}
};
req.send();
}
I noticed that on my computer (working) the output header of the request looks like this :
POST /start?f=2021-02-09_14;05;40&ft=1612880820756.4346&t=1614243685530 HTTP/1.1
On the target computer (FAIL) it looks like :
POST /start?f=2021-02-09_14;05;40&ft=1612879543815&t=1614183852864 undefined
Notice the "undefined" protocol information
I wonder what can produce such a difference knowing that :
The computer are the same 'Asus ZenBook'
Navigator are the same : Mozilla Firefox 85.0.2 (32 bits)
Network drivers are the same
Client and Server code are the same.
This is very strange behaviour.
Many thanks for any precious piece of information !

We find out that this behaviour was a side effect of a DOM exception caused by registering activeX filters. Our application also tried to load video with calls to :
navigator.mediaDevices.getUserMedia({video: { deviceId: device.deviceId }})
This was ending in an :
Uncaught DOMException: A network error occured.
Believe me or not, removing activeX filters removes the network error !
We felt into a problem similar to :
NotReadableError: Failed to allocate videosource

IE11 XMLHttpRequest do not receive full data from server

I am currently working on a web application and I came across with a strange problem. The request that I send to my flask app from Google Chrome and Firefox with XMLHttpRequest works as intended but in IE11 and possibly older versions it looks like IE closes the connection before the data is fully transferred. I send post request like this:
function getData() {
var req = new XMLHttpRequest();
req.open("POST", "http://"+window.host+"/text", true);
req.responseType = "json";
req.addEventListener("readystatechange", function(e){
if (e.target.readyState == 4 && e.target.status == 200){
display(e.target.response.data);
}
});
req.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
req.send(JSON.stringify({"text": "some text"}));
}
and receive from flask app like this:
#app.route('/text', methods=["POST"])
def data():
if request.is_json:
if "text" in request.get_json():
for i in request.get_json()["text"]:
if not re.search(textIntegrity, i):
return jsonify({"status": "Unrecognized characters: {}.".format(i)})
break
data = reData(request.get_json()["text"])
return jsonify({"status": 200, "data": data})
else:
return jsonify({"status": "Key 'text' not found."})
else:
return jsonify({"status": "Request type is not in json format."})
In mozilla and firefox I get the full data and the XMLHttpRequest object states that the response type is json: Mozilla Response but in IE there is no response type and the reponse is cut if it is too long:
IE Response
I don't know whether it's the flask problem or the way that IE handles the request, maybe I need to add some headers to flask project but I don't know.

Use ActiveXObject objects instead of XMLHttpRequest for older IE:
if (window.XMLHttpRequest) {
// code for modern browsers
xmlhttp = new XMLHttpRequest();
} else {
// code for old IE browsers
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
I am not sure the above will solve the issue because you already have IE11 (newer version). Why don't you try AJAX call using JS frameworks and see if you get same issue.
I would say, instead of using XMLHttpRequest(), use any JS framework/library to make AJAX calls to your flask REST endpoint, because JS frameworks/libraries will take care of these kind of issues with IE. For example JQuery, AngularJS.

I ended up changing server side code and client side code a little and made the server to send json data as string and parsing it on the client side.
function getData() {
var req = new XMLHttpRequest();
req.open("POST", "http://"+window.host+"/text", true);
req.addEventListener("readystatechange", function(e){
if (e.target.readyState == 4 && e.target.status == 200){
display(JSON.parse(e.target.response));
}
});
req.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
req.send(JSON.stringify({"text": "some text"}));
}
#app.route('/text', methods=["POST"])
def data():
if request.is_json:
if "text" in request.get_json():
for i in request.get_json()["text"]:
if not re.search(textIntegrity, i):
return jsonify({"status": "Unrecognized characters: {}.".format(i)})
break
data = reData(request.get_json()["text"])
return json.dumps(data);
else:
return json.dumps({"status": "Key 'text' not found."})
else:
return json.dumps({"status": "Request type is not in json format."})
It maybe is just an issue about flask jsonify, the way flask handles the responses or the way IE handles the requests, I don't know, I had the opportunity to edit the server so I went with that way.

Native ajax call does not redirect on 302

I have been googling for hours now. I've read a dozen "answers" on Stackoverflow, all of them using jQuery.
This is the common answer...
The ajax-request will follow that redirect afaik
Well, it doesn't.
I am trying to send a PUT from a form via native JS AJAX
[Please I beg you, don't tell me to use jQuery. I found a bug in jQuery via PUT
(1) so I'm going around it]
This is my code snippet...
var xhr = new XMLHttpRequest();
xhr.open(method, url);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.send(data);
xhr.onload = function (e) {
if (xhr.readyState === 4) {
if (xhr.status === 200) {
console.log(xhr.responseText);
} else {
console.error(xhr.statusText);
}
}
};
xhr.onerror = function (e) {
console.error(xhr.statusText);
};
This block works great, I can POST, PUT and DELETE without issues. The server receives the data and updates the DB according to the sent METHOD just fine.
My (SLIM based) PHP, upon successful completion, returns a 302 and a URL to go to.
This process works using POSTMAN hitting the PHP, and it goes to the right page.
Opening Chrome Tools/Network, it shows that the PHP is returning a 302 and than a 200
My response object contains the full HTML for a page in the responseText property.
Funny thing is, if I hard code a bad URL,the browser goes to my 404 page fine.
Your thoughts? (Please don't ask me or tell me to use jQuery)
EDIT/ADDENDUM -----------------------
I have discovered that the redirect is using the same METHOD of the original call.
I'm doing
PUT /user/1
the Redirect is doing
PUT http://myserver.test/
This is the right place to go. Now I understand the 405.
I don't have a PUT route defined, therefore the 405.
I create a PUT route and it works in POSTMAN but still gives me a 405 in Chrome and Firefox.
I have 2 issues to solve:
1) change the METHOD on the redirect
2) figure out why the browser doesn't like the 307

I found "a" solution. I'm not sure I like it, but...
var xhr = new XMLHttpRequest();
xhr.open(method, url);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.send(data);
xhr.onload = function (e) {
if (xhr.readyState === 4) {
window.location.replace(xhr.responseURL); // <---- solution
}
};

How to get only response headers from XMLHttpRequest

Is it possible to get only response headers from XMLHttpRequest without downloading file data?

If the server you are making the request to supports the method, it sounds like what you want is to make an HTTP HEAD request. See the HTTP spec.
For example compare the output from curl -v -X GET https://github.com and curl -v -X HEAD https://github.com.
Also see HTTP HEAD Request in Javascript/Ajax?

Using JavaScript (as specified in the question) simply use a head request via AJAX:
var xhr = new XMLHttpRequest();
var method = 'head';
var url = 'https://www.example.com/';
xhr.open(method,url,true);
xhr.send(null);
xhr.onreadystatechange = function()
{
if (xhr.readyState === 4)
{
console.log(xhr.getAllResponseHeaders())
}
}

Firstly, the answer from John fixes this issue but it got downvoted because it didn't have enough of an explanation.
So here is the fix with an explanation as well as an extra bit that you can add as well.
Client side solution is as follows (I am using the status code as the example):
function checkStatus(url) {
return new Promise((resolve, reject) => {
const request = new XMLHttpRequest();
request.open('HEAD', url, true)
request.onreadystatechange = () => {
if (request.readyState >= 2) {
resolve(request.status)
request.abort()
}
}
request.onerror = (e) => {
reject(e)
}
request.send()
})
}
The reason why this works is for two reasons.
Firstly we are passing HEAD in as the method instead of GET this should be enough on its own, but if you want to do more, you can move onto the second reason.
The second reason this works is because of the readyState states.
0 = UNSENT
1 = OPENED
2 = HEADERS_RECEIVED
3 = LOADING
4 = DONE
At state 2 the headers are ready to be viewed. This means you can then return whatever you need and/or abort the rest of the request preventing any further data being downloaded.
Worth noting you can also do this with request.onprogress at stage 3.
See https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/readyState and https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods for more details.

XMLHttpRequest receiving no data or just "undefined"

i try to make a Firefox Addon which runs a XMLHttp Request in Javascript. I want to get the data from this request and send it to *.body.innerhtml.
That's my code so far...
var xhr = new XMLHttpRequest();
xhr.open("GET", "http://xx.xxxxx.com", true);
xhr.send();
setTimeout(function() { set_body(xhr.responseHtml); }, 6000);
Instead of receiving the data, I get "undefined". If I change xhr.responseHtml to responseText I get nothing. I don't know why I'm getting nothing. I'm working on Ubuntu 12.04 LTS with Firefox 12.0.
If you need any more details on the script please ask!
Update:
set_body Function
document.body.innerHTML = '';
document.body.innerHTML = body;
document.close();

Update SOLVED:
I had to determine the RequestHeaders (right after xhr.open):
xhr.setRequestHeader("Host", "xxx");
For following Items: Host, Origin and Referer. So it seems there was really a problem with the same origin policy.
But now it works! Thanks to all!

when you set the last param of open to true you are asking for an async event. So you need to add a callback to xhr like so:
xhr.onReadyStateChange = function(){
// define what you want to happen when server returns
}
that is invoked when the server responds. To test this without async set the third param to false. Then send() will block and wait there until the response comes back. Setting an arbitrary timeout of 6 seconds is not the right way to handle this.

This code should work:
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
set_body(xhr.responseText);
}
};
xhr.open("GET", "http://xx.xxxxx.com", true);
xhr.send();
Make sure that you are getting a correct response from URL http://xx.xxxxx.com. You may have a problem with cross-domain calls. If you have a page at domain http://first.com and you try to do XMLHttpRequest from domain http://second.com, Firefox will fail silently (there will be no error message, no response, nothing). This is a security measure to prevent XSS (Cross-site scripting).
Anyway, if you do XMLHttpRequest from a chrome:// protocol, it is considered secure and it will work. So make sure you use this code and make the requests from your addon, not from your localhost or something like that.