Implement the http.CloseNotifier interface

[jpillora]

I've got a chain of middleware and the outer layer is doing w.(http.CloserNotifier).CloseNotify() - basically assuming a stdlib http.ResponseWriter. I was thinking about making it return nil if !ok though I think a panic is more appropriate here.

[adammck]

Thanks for the patch! I'm not familiar with the CloseNotifier interface-- can you clarify for me how/why you're using this?

[jpillora]

No worries, I'm using https://github.com/donovanhide/eventsource (SSE/EventSource) which inturn uses https://golang.org/pkg/net/http/#CloseNotifier. The eventsource package requires it to monitor the state of the underlying TCP connection.

[jpillora]

I just realised, in rare situations, this could break existing programs. There are three options I can see:

1. Close the PR, don't support.
2. If underlying response writer isn't a CloseNotifier, return a new channel that never returns.
3. If underlying response writer isn't a CloseNotifier, return a new channel that we close after we've closed off the gzip writer.

[chuyeow]

If underlying response writer isn't a CloseNotifier, return a new channel that never returns.

I think returning a channel that never returns is closest to the "default" behavior. http.Handlers that do not use the http.CloseNotifier interface are effectively saying that they do not care when the client disconnects early, so a channel that never returns models that behavior.

[jpillora]

This can now be closed in favour of ctx.Done() (https://golang.org/pkg/context/#Context)