Add abort (or similar) to HttpClientRequest

[kevmoo]

HttpRequest (in dart:html) has an abort() method

There is a request to add a feature to the http package to support timeout.

This can be done with dart:html, but not dart:io

[kevmoo]

Marked this as blocking #19831.

[kevmoo]

Added C11 label.

[sgjesse]

When creating a HTTP request in dart:io we have the following steps:

HttpClient client = new HttpClient();
client.getUrl(Uri.parse("http://www.example.com/"))
   .then((HttpClientRequest request) {
     // Optionally set up headers...
     // Optionally write to the request object...
     // Then call close.
     ...
     return request.close();
   })
   .then((HttpClientResponse response) {
     // Process the response.
     ...
   });

The call to getUrl completes when the connection has been established. This can take time, so it should be possible to cancel that part. Currently there is no object to hook up any abort call to. A Future is returned, but futures cannot be canceled/aborted.

Then the future completes with a HttpClientRequest. That is closed to send the request and wait for the response. This can take time. In this step there is an object (the HttpClientRequest) on which you can actually call something (e.g. abort). However is seems wrong to call abort after calling close.

Finally the HttpClientResponse comes along and the response can be processed. Here there is also an object where an abort method can be added.

Having to add abort to both HttpClientRequest and HttpClientResponse seems wrong.

One option could be to add an additional argument to getUrl (and friends) where the called can pass an object where getUrl can place a callback for aborting the HTTP transaction, e.g.:

var c = new HttpClientConnectionController();
new Timer(new Duration(seconds: 2), () {
  c.cancel();
});
client.getUrl(Uri.parse("http://www.example.com/"), controller: c)
   .then((HttpClientRequest request) {
   ...
   .catchError((e) => ..., test: (e) => e is CancledException);

Straight-line code here ensures that the cancel member of HttpClientConnectionController has been set by getUrl before the timer callback can be called.

This is also related to issue #19120.

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cc @lrhn.

[kasperl]

Added this to the 1.10 milestone.

[DartBot]

This comment was originally written by @kaendfinger

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In all honesty, it would be nice to have some sort of Cancelable Future. In fact, in theory, it would be easy to add cancellation to futures, since it's built upon the Timer, you could either do an if statement to check if it was canceled, but it's unclear how this would propagate to the other futures.

[lrhn]

There are definitely cases where it would be nice to have some sort of channel to tell an asynchronous computation that its result is no longer needed.

I don't think adding a function to Future is the best way to do that. Futures can be safely shared with other code. If the future could also be used to cancel the computation for everybody, then sharing it would no longer be safe.
I'd rather have something like a CancelableComputation class with a future and a cancel method (and a shorter name) - since we can't just return a tuple of a future and cancel function.

[sgjesse]

Removed this from the 1.10 milestone.
Added this to the 1.11 milestone.