feat($http): Added method to abort a pending request. (2nd attempt)

[dbinit]

Fixes issue #1159. Was pull request #1623.

Addressed issues brought up by Miško:

1. After calling .abort(), the promise is guaranteed to be resolved with a rejection (unless it has already been resolved).
2. The .abort() method now returns a boolean:
   • True - if successfully aborted (or already aborted).
   • False - if abort failed because the promise is already resolved.
3. Updated $httpBackend mock to support aborting.

[rickkln]

I am currently trying to use this solution and at first it seemed to be working but now I'm getting a strange problem that I can't seem to solve.

I am watching three drop downs on a dashboard: Year, Month and Day. Each time the value in the drop down changes I want to query for the new dashboard for that new date. However sometimes the user changes the month and then the day in quick succession. I therefore want to abort the query for the first date and only send the query for the final date.

I am currently trying to implement the solution like this:

 $scope.$watch('dash_year', function() {
if($scope.current_request != undefined) {
$scope.current_request.abort();
}
$scope.dashboard_loading = true;
getDashboard();
});
$scope.$watch('dash_month', function() {
if($scope.current_request != undefined) {
console.log($scope.current_request);
$scope.current_request.abort();
}
$scope.dashboard_loading = true;
getDashboard();
});
$scope.$watch('dash_day', function() {
if($scope.current_request != undefined) {
$scope.current_request.abort();
}
$scope.dashboard_loading = true;
getDashboard();
});

If I make some quick changes to the month I get this in the console:
First the console.log($scope.current_request); to see if it is trying to abort an actual request, that returns this:

So yes it seems $scope.current_request has the correct value.

But then the console says this:

For me it does this every time I try to abort a request, always "$digest already in progress".

What would be the correct way to implement this abort request solution in conjunction with a $watch?

[fredrikbonander]

@Rick-KLN, there's an quick fick for that. Edit http.js (done method) to check if digest is already running.

if(!$rootScope.$$phase){$rootScope.$apply();}

I forked it (https://github.com/The-Amazing-Society/angular.js/commit/623e12aea0a4fefa5d4225e72181b75bcec0dd5a) to implement this, had the same problem.

[dbinit]

Thanks guys. It looks like I incorrectly assumed that abort would fire the onreadystatechange event separately. I'll push a fix + test in a little bit here.

[fredrikbonander]

@dbinit Great work, I borrowed code from you fork. I would be real nice to get this merged in.

[rickkln]

Thanks a lot guys!

[TomKaltz]

Will this ever get merged into a production release?

[steinerj]

+1 on the merge :)

[g00fy-]

+1

[bracketdash]

+1 for merging this. Also looking forward to something similar for $resource.

[svileng]

+1

[knalli]

👍 (Probably needs to be merged again).

Okay, I was surprised at the lack of http's abort... so: What does this PR hold back? How we can help?

[damrbaby]

How would you abort a pending request if you are using $resource?

[g00fy-]

@damrbaby add a $abort method to the resource, that would fallback to $http's abort ?

[dbinit]

Unfortunately I don't think this is going to be accepted as is. There is still ongoing discussion as to what the best approach is.

Using a $q progress callback might be more suitable (see #2223). If returning a rejection from a progress callback could abort the XHR, it would be almost equivalent to this.

[dbinit]

I did a bit more research and found several implementations of Deferred/Promise that have an optional "canceler" feature.

I've submitted #2452 to implement that feature. If it's accepted, adding $http cancellation would be fairly trivial.

[aminariana]

+1,
need a cancel feature to avoid querying race condition.