Improve context deadline (#381)

* Safe time for context

* Add comment

* update doc

docs/changelog.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - Set NoWait to true for tor listen config ([#368](https://github.com/wabarc/wayback/pull/368))
+- Improve context deadline ([#381](https://github.com/wabarc/wayback/pull/381))
 
 ## [0.19.1] - 2023-03-21
 

wayback.go

@@ -181,6 +181,8 @@ func Wayback(ctx context.Context, rdx reduxer.Reduxer, cfg *config.Options, urls
 		ctx, cancel = context.WithTimeout(ctx, cfg.WaybackTimeout())
 		defer cancel()
 	}
+	ctx, cancel := context.WithTimeout(ctx, duration(ctx))
+	defer cancel()
 
 	mu := sync.Mutex{}
 	cols := []Collect{}
@@ -232,7 +234,12 @@ func Wayback(ctx context.Context, rdx reduxer.Reduxer, cfg *config.Options, urls
 func Playback(ctx context.Context, cfg *config.Options, urls ...*url.URL) (cols []Collect, err error) {
 	logger.Debug("start...")
 
-	ctx, cancel := context.WithTimeout(ctx, cfg.WaybackTimeout())
+	if _, ok := ctx.Deadline(); !ok {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithTimeout(ctx, cfg.WaybackTimeout())
+		defer cancel()
+	}
+	ctx, cancel := context.WithTimeout(ctx, duration(ctx))
 	defer cancel()
 
 	mu := sync.Mutex{}
@@ -278,3 +285,13 @@ func Playback(ctx context.Context, cfg *config.Options, urls ...*url.URL) (cols
 
 	return cols, nil
 }
+
+// duration reduce the context deadline time for downstream and reserve
+// extra time for the caller.
+func duration(ctx context.Context) time.Duration {
+	deadline, _ := ctx.Deadline()
+	elapsed := deadline.Unix() - time.Now().Unix()
+	safeTime := elapsed * 90 / 100
+
+	return time.Duration(safeTime) * time.Second
+}