add options for components

hosts/hosts.go

@@ -5,7 +5,11 @@ import (
 	"net"
 )
 
+type Options struct{}
+
+type Option func(opts *Options)
+
 // HostMapper is a mapping from hostname to IP.
 type HostMapper interface {
-	Lookup(ctx context.Context, network, host string) ([]net.IP, bool)
+	Lookup(ctx context.Context, network, host string, opts ...Option) ([]net.IP, bool)
 }