HttpClient should honor the system configured proxy

[brianquinlan]

This bug corresponds to this Flutter issue:
flutter/flutter#26359

And the reason that this is important is discussed here:
#48056

[fr-markyan]

It would be very helpful if HttpClient can respect system configured proxy, especially for enterprise app

[brianquinlan]

I've been experimenting with moving Flutter to use package:http.

That would allow the user to use package:cronet_http on Android and package:cupertino_http on iOS, which do honor the system-configured proxy.

We could also solve this issue in HttpClient. This would actually be fairly easy on iOS but harder on Android (AFAIK, the only way would be to make JNI calls to get the proxy configuration).

[brianquinlan]

I started a discussing on this in the hackers-framework-🔩 Discussion. So far the feedback is that depending on package:http seems like a bad idea.

[brianquinlan]

It looks like there is only one common use case in Flutter where dart:io HttpClient is used: image display through Image.network.

It is very easy to replace this with package:cached_network_image, which uses package:http and can, therefore, be configured to use a native http client.

[brianquinlan]

I've updated the examples in cupertino_http and cronet_http to use package:cached_network_image.

At this point it should be possible to use those packages to deal with the proxy issue.

[brianquinlan]

I wrote a design doc suggesting that we recommend package:http as an HTTP client. Feedback welcome!

[brianquinlan]

I presented this at the Dash forum. It's basically asking for feedback for the design doc. There seemed to be consensus so I'm moving forward on it.