responseHeaders not available until readyState 4 (expected 2)

[Rob--W]

In XMLHttpRequest, there are multiple readyStates of interest: 2 (response headers received)and 4 (load finished).

I created a script that checks responseHeaders at readyState 2, and if it indicates support for range requests, I abort the request and restart the request with a much smaller range.
In theory, this works. However, it does not work in GreaseMonkey because it only sets the headers when the request has fully finished:

greasemonkey/modules/xmlhttprequester.js

Lines 253 to 254 in 3f462ac

	if (4 != req.readyState) break;
	responseState.responseHeaders = req.getAllResponseHeaders();

git blame shows that this logic was already in place in the initial commit of the repo, so I did not discover why the implementation is like this.

This, and the fact that HTTP cookies are not included in the request is the reason why I switched to a full WebExtension for the script. It would still be good to fix the issue in GM though.

[janekptacijarabaci]

git blame shows that this logic was already in place in the initial commit of the repo, so I did not discover why the implementation is like this.

AFAIK not:
https://addons.mozilla.org/cs/firefox/files/browse/3733/file/chrome/greasemonkey/content/xmlhttprequester.js#L123

But if there isn't a serious reason for not:
#2461

the fact that HTTP cookies are not included in the request

See also #2236

But AFAIK, you can use:
"headers": {
"cookie": document.cookie
},

See also #1802

[Rob--W]

"AFAIK not" = "there is no reason for the limitation"?

That cookie suggestion does not work for http-only cookies, and neither for redirects.

[janekptacijarabaci]

I edited it, I'm sorry.

There is no reason for the limitation?

I think it's for no reason. AFAIK.