Fix: Return immutable Cache-Control headers for UnixFS directories

CHANGELOG.md

@@ -20,6 +20,7 @@ The following emojis are used to highlight certain changes:
 
 - `bitswap/server` minor memory use and performance improvements
 - `bitswap` unify logger names to use uniform format bitswap/path/pkgname
+- `gateway` now returns immutable cache-control headers for unixfs directories
 
 ### Removed
 

gateway/handler_unixfs_dir.go

@@ -136,10 +136,8 @@ func (i *handler) serveDirectory(ctx context.Context, w http.ResponseWriter, r *
 	dirEtag := getDirListingEtag(resolvedPath.RootCid())
 	w.Header().Set("Etag", dirEtag)
 
-	// Add TTL if known.
-	if rq.ttl > 0 {
-		w.Header().Set("Cache-Control", fmt.Sprintf("public, max-age=%d", int(rq.ttl.Seconds())))
-	}
+	// Set Cache-Control
+	w.Header().Set("Cache-Control", immutableCacheControl)
 
 	if r.Method == http.MethodHead {
 		rq.logger.Debug("return as request's HTTP method is HEAD")