TypeError from fetch module due to no headers received

This is part bug report, and part question.

Bug report
I don't know if you would classify this as a bug, but when a request done via the fetch module returns no headers, it will throw an error here:

https://github.com/NativeScript/NativeScript/blob/master/xhr/xhr.ts#L119

Due to the returnvalue here:
https://github.com/NativeScript/NativeScript/blob/master/xhr/xhr.ts#L184
(toLowerCase on null)

Which eventually calls the xhr.onerror handler which is set to always throw:

reject(new TypeError('Network request failed'))

Headers should be set, but when they're not, this is what happens. Which leads me to my question...

Question
I'm completely stumped by this and am by no means implying that this is caused by the fetch/xhr modules, but I'm completely lost on where to look right now. When my remote API endpoint returns with a 401 - Unathorized, the xhr response does not pick up any response headers. If I return a 403 instead, response headers are present.

I've verified that it's not the API server doing something wrong, because the response headers are picked up by numerous other Clients such as Postman, Webbrowser, etc, when I return a 401. Any ideas?

Running all this on Android.

JS: Response {
JS:   "content": {
JS:    .......
JS:   },
JS:   "statusCode": 401,
JS:   "headers": {}
JS: }

JS: Response {
JS:   "content": {
JS:    .......
JS:   },
JS:   "statusCode": 403,
JS:   "headers": {
JS:     "Date": "Thu, 10 Mar 2016 14:32:10 GMT",
JS:     "Content-Type": "application/json; charset=utf-8",
JS:     "Content-Length": "286",
JS:     "Keep-Alive": "timeout=15, max=100",
JS:     "Connection": "Keep-Alive",
JS:     "X-Android-Sent-Millis": "1457620330281",
JS:     "X-Android-Received-Millis": "1457620330364"
JS:   }
JS: }

@wubzz

Hey @wubzz,

The null ref exception was fixed immediately (check my pull request) and here is an example how to get the headers:

    fetch("http://httpbin.org/status/401").then(function(r){
        console.log("STATUS: " + r.status);

        r.headers.forEach(function(key, value){
            console.log(key + ":" + value);
        });

        return r.text();
    }, function(e){
        console.log("ERROR: " + e)
    }).then(function(r){
        console.log("CONTENT: " + r)
    });

@enchev

@enchev Thanks!

Debugging this on my own by logging the output of the xhr module, I still find no explanation why the headers object was empty to begin with. It makes no sense at all. Even here:
https://github.com/NativeScript/NativeScript/blob/master/xhr/xhr.ts#L85
There are no headers set in the response. I got stuck after that and couldn't dig deeper (http.request(..)), so I'll just add this info here in case someone else has any idea.

@wubzz

Hey @wubzz,

After I've fixed the exception I was able to get headers using http://httpbin.org/status/401 url from the echo service we use for testing.

I'm getting similar error when trying to make post request with fetch module
CLI error prints
TypeError: Network request failed: unexpected expected token < in JSON at position 3

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.

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TypeError from fetch module due to no headers received #1737

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TypeError from fetch module due to no headers received #1737

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enchev commented on Mar 11, 2016

wubzz commented on Mar 11, 2016

enchev commented on Mar 12, 2016

bismert commented on Jun 23, 2017

lock commented on Aug 28, 2019

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