Wait at most 1s for the banner fetch, finish it in the background

Author: u9g

cmd/lk/banner.go

@@ -35,10 +35,12 @@ import (
 // file is the whole release process: no build or tag involved.
 const bannerURL = "https://raw.githubusercontent.com/livekit/livekit-cli/main/banner.json"
 
-// The banner prints before the command, so the fetch is awaited. To keep that off
-// most runs, the fetched file is cached and reused for bannerTTL.
+// The banner prints before the command, so the fetch is awaited, but only for
+// bannerWait: a slower fetch keeps running in the background to refresh the cache
+// for the next run. The fetched file is cached and reused for bannerTTL.
 const (
-	bannerTimeout = time.Second
+	bannerWait    = time.Second
+	bannerTimeout = 10 * time.Second
 	bannerTTL     = time.Hour
 )
 
@@ -58,7 +60,7 @@ type banner struct {
 }
 
 // loadBanner returns banner.json from the cache when it is fresh, otherwise from
-// the network, falling back to a stale cache when the fetch fails.
+// the network when it answers within bannerWait, falling back to the stale cache.
 func loadBanner(ctx context.Context) []byte {
 	path, err := bannerCachePath()
 	if err != nil {
@@ -68,14 +70,25 @@ func loadBanner(ctx context.Context) []byte {
 		raw, _ := os.ReadFile(path)
 		return raw
 	}
-	raw := fetchBanner(ctx)
-	if raw == nil {
-		raw, _ = os.ReadFile(path)
-		return raw
-	}
-	if os.MkdirAll(filepath.Dir(path), 0700) == nil {
-		_ = os.WriteFile(path, raw, 0600)
+	// The fetch is detached from ctx so it outlives the wait and can still write the
+	// cache after the command has moved on.
+	fetched := make(chan []byte, 1)
+	go func() {
+		raw := fetchBanner(context.Background())
+		if raw != nil && os.MkdirAll(filepath.Dir(path), 0700) == nil {
+			_ = os.WriteFile(path, raw, 0600)
+		}
+		fetched <- raw
+	}()
+	select {
+	case raw := <-fetched:
+		if raw != nil {
+			return raw
+		}
+	case <-time.After(bannerWait):
+	case <-ctx.Done():
 	}
+	raw, _ := os.ReadFile(path)
 	return raw
 }