Feature: add custom DNS support (#56)

common/picker/picker.go

@@ -0,0 +1,22 @@
+package picker
+
+import "context"
+
+func SelectFast(ctx context.Context, in <-chan interface{}) <-chan interface{} {
+	out := make(chan interface{})
+	go func() {
+		select {
+		case p, open := <-in:
+			if open {
+				out <- p
+			}
+		case <-ctx.Done():
+		}
+
+		close(out)
+		for range in {
+		}
+	}()
+
+	return out
+}

common/picker/picker_test.go

@@ -0,0 +1,44 @@
+package picker
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func sleepAndSend(delay int, in chan<- interface{}, input interface{}) {
+	time.Sleep(time.Millisecond * time.Duration(delay))
+	in <- input
+}
+
+func sleepAndClose(delay int, in chan interface{}) {
+	time.Sleep(time.Millisecond * time.Duration(delay))
+	close(in)
+}
+
+func TestPicker_Basic(t *testing.T) {
+	in := make(chan interface{})
+	fast := SelectFast(context.Background(), in)
+	go sleepAndSend(20, in, 1)
+	go sleepAndSend(30, in, 2)
+	go sleepAndClose(40, in)
+
+	number, exist := <-fast
+	if !exist || number != 1 {
+		t.Error("should recv 1", exist, number)
+	}
+}
+
+func TestPicker_Timeout(t *testing.T) {
+	in := make(chan interface{})
+	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*5)
+	defer cancel()
+	fast := SelectFast(ctx, in)
+	go sleepAndSend(20, in, 1)
+	go sleepAndClose(30, in)
+
+	_, exist := <-fast
+	if exist {
+		t.Error("should recv false")
+	}
+}