Add direct serving of package content (#25543)

Fixes #24723

Direct serving of content aka HTTP redirect is not mentioned in any of
the package registry specs but lots of official registries do that so it
should be supported by the usual clients.

routers/api/packages/generic/generic.go

@@ -30,7 +30,7 @@ func apiError(ctx *context.Context, status int, obj interface{}) {
 
 // DownloadPackageFile serves the specific generic package.
 func DownloadPackageFile(ctx *context.Context) {
-	s, pf, err := packages_service.GetFileStreamByPackageNameAndVersion(
+	s, u, pf, err := packages_service.GetFileStreamByPackageNameAndVersion(
 		ctx,
 		&packages_service.PackageInfo{
 			Owner:       ctx.Package.Owner,
@@ -50,12 +50,8 @@ func DownloadPackageFile(ctx *context.Context) {
 		apiError(ctx, http.StatusInternalServerError, err)
 		return
 	}
-	defer s.Close()
 
-	ctx.ServeContent(s, &context.ServeHeaderOptions{
-		Filename:     pf.Name,
-		LastModified: pf.CreatedUnix.AsLocalTime(),
-	})
+	helper.ServePackageFile(ctx, s, u, pf)
 }
 
 // UploadPackage uploads the specific generic package.