archiver: allow to override the archive type via query parameter

internal/http/services/archiver/handler.go

@@ -229,13 +229,21 @@ func (s *svc) Handler() http.Handler {
 			return
 		}
 
-		userAgent := ua.Parse(r.Header.Get("User-Agent"))
-
 		archName := s.config.Name
-		if userAgent.OS == ua.Windows {
-			archName += ".zip"
-		} else {
-			archName += ".tar"
+		archTypeParam, ok := v["arch_type"] // optional, either "tar" or "zip"
+		var archType string
+		if ok {
+			archType = archTypeParam[0]
+		}
+		if !ok || archTypeParam[0] != "tar" && archTypeParam[0] != "zip" {
+			// in case of missing or bogus arch_type, detect it via user-agent
+			userAgent := ua.Parse(r.Header.Get("User-Agent"))
+			if userAgent.OS == ua.Windows {
+				archType = "zip"
+			} else {
+				archType = "tar"
+			}
+			archName += "." + archType
 		}
 
 		log.Debug().Msg("Requested the following files/folders to archive: " + render.Render(files))
@@ -244,7 +252,7 @@ func (s *svc) Handler() http.Handler {
 		rw.Header().Set("Content-Transfer-Encoding", "binary")
 
 		// create the archive
-		if userAgent.OS == ua.Windows {
+		if archType == "zip" {
 			err = arch.CreateZip(ctx, rw)
 		} else {
 			err = arch.CreateTar(ctx, rw)