fix($httpBackend): fix HTTP PATCH requests in IE8

[jeffsmohan]

In Internet Explorer 8, the native XMLHttpRequest object does not allow the HTTP PATCH method. In order to accomplish a PATCH, you need to use the ActiveX object. Update the default XHR to use the ActiveX object when doing a PATCH in IE8. See the following for documentation:

• http://blogs.msdn.com/b/ieinternals/archive/2009/07/23/the-ie8-native-xmlhttprequest-object.aspx
• http://bugs.jquery.com/ticket/13240
• http://codepen.io/jeffschenck/full/yjczt (to quickly replicate the issue in IE8)

Discussed previously in #2518. I wanted to put together an example of how we could fix this, and Travis reports a green light on this branch. I'm not too familiar with the structure and internals of the project yet, though, so if you point me in the direction of how to add tests for HttpBackend (which appears to be mocked in testing) and any cleanup needed, I'm happy to work on it.

[petebacondarwin]

@jeffschenck - thanks for the PR. Have you signed the CLA? Also we need to be able to test this change. Can you knock up a unit test that highlights the problem in IE8 before your change fixes it?

[jeffsmohan]

@petebacondarwin I have signed the CLA.

As I mentioned, I'm happy to work up some tests for this, but I'm not too familiar with the test suite setup yet. And this seems like a particularly special-case sort of situation — testing HttpBackend, a service that's mocked in most of the test suite; and testing it particularly in one browser, IE8. Can you point me in the right direction? What file would this test be added in? How do I look to see tests first failing and then passing in IE8?

Let me know and I'll work up the test(s). Thanks!

[petebacondarwin]

@jeffschenck - Thanks for this. Regarding writing a test. This file would be a good place to start: https://github.com/angular/angular.js/blob/master/test/ng/httpBackendSpec.js

Then you should look at running the tests locally, grunt test.

[jeffsmohan]

@petebacondarwin Thanks — forgive me if I've missed something obvious, but I've had the tests passing locally and looked through httpBackendSpec.js. The problem is that all the calls to createHttpBackend in that file use mocked versions of XHR, which won't expose the IE8 quirk that causes this bug. As far as I can figure, in order to reproduce the error in IE8 on Travis, we need to actually use the real XHR object and really attempt to make a request.

Is there somewhere outside of the httpBackendSpec.js unit tests (e2e testing?) where the actual XHR object is used and actual requests are attempted? Would this be a better place for this test? Or, alternatively, am I missing some way to reproduce the bug in IE8's version of the XMLHttpRequest object?

Thanks for the help!

[petebacondarwin]

We do run our tests on IE8. I haven't look in detail right now but I assume that you are going to write a test that checks that if the test is on IE8 then the ActiveX object is being used instead of XHR...

[jeffsmohan]

Updated the pull request with additionally a test for using ActiveXObject in IE8 PATCH requests. Let me know if there's anything else needed here, thanks!

[IgorMinar]

none of this is needed. just use msie variable that we expose internally

[jeffsmohan]

Good to know. I had assumed it was only exposed in the test environment.

[IgorMinar]

I created an alternative fix as #5390.

thanks for the PR