What version of Go are you using (go version)?

$ go version
go version go1.10 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env

What did you do?

func httpDo(ctx context.Context, req *http.Request, f func(*http.Response, error) error) error {
    // Run the HTTP request in a goroutine and pass the response to f.
    tr := &http.Transport{}
    client := &http.Client{Transport: tr}
    c := make(chan error, 1)
    go func() { c <- f(client.Do(req)) }()
    select {
    case <-ctx.Done():
        tr.CancelRequest(req)
        <-c // Wait for f to return.
        return ctx.Err()
    case err := <-c:
        return err
    }
}

What did you expect to see?

The CancelRequest() method of type *http.Transport is deprecated now. As https://golang.org/pkg/net/http/#Transport.CancelRequest suggested Use Request.WithContext to create a request with a cancelable context instead. Could we just update the httpDo like this:

func httpDo(ctx context.Context, req *http.Request, f func(*http.Response, error) error) error {
	client := http.Client{}
	c := make(chan error)
	subCtx, subCancel := context.WithCancel(ctx)
	newReq := req.WithContext(subCtx)
	go func() { c <- f(client.Do(newReq)) }()
	select {
	case <-ctx.Done():
                subCancel()
		<-c
		return ctx.Err()
	case err := <-c:
		return err
	}
	return nil
}

What did you see instead?