implement default outbound handler

proxy/context.go

@@ -7,8 +7,9 @@ import (
 type key int
 
 const (
-	inboundMetaKey  = key(0)
-	outboundMetaKey = key(1)
+	inboundMetaKey key = iota
+	outboundMetaKey
+	dialerKey
 )
 
 func ContextWithInboundMeta(ctx context.Context, meta *InboundHandlerMeta) context.Context {
@@ -34,3 +35,15 @@ func OutboundMetaFromContext(ctx context.Context) *OutboundHandlerMeta {
 	}
 	return v.(*OutboundHandlerMeta)
 }
+
+func ContextWithDialer(ctx context.Context, dialer Dialer) context.Context {
+	return context.WithValue(ctx, dialerKey, dialer)
+}
+
+func DialerFromContext(ctx context.Context) Dialer {
+	v := ctx.Value(dialerKey)
+	if v == nil {
+		return nil
+	}
+	return v.(Dialer)
+}