refactor: fetcher接口调整，返回channel来通知任务成功和失败

download/base/fetcher.go

@@ -2,7 +2,7 @@ package base
 
 // 对应协议的下载支持
 type Fetcher interface {
-	Init(ctl Controller)
+	Setup(ctl Controller) (err <-chan error)
 	// 解析请求
 	Resolve(req *Request) (res *Resource, err error)
 	// 创建任务
@@ -13,9 +13,12 @@ type Fetcher interface {
 }
 
 type DefaultFetcher struct {
-	Ctl Controller
+	Ctl    Controller
+	DoneCh chan error
 }
 
-func (f *DefaultFetcher) Init(ctl Controller) {
+func (f *DefaultFetcher) Setup(ctl Controller) (doneCh <-chan error) {
 	f.Ctl = ctl
+	f.DoneCh = make(chan error, 1)
+	return f.DoneCh
 }