accurate error messages during writing

go/storage/store.go

@@ -174,6 +174,9 @@ func (s *Store) Close() {
 }
 func (s *Store) Write(i VolumeId, n *Needle) (size uint32, err error) {
 	if v := s.volumes[i]; v != nil && !v.readOnly {
+		if v.readOnly {
+		  err = errors.New("Volume " + i + " is read only!")
+		} else {
 			size, err = v.write(n)
 			if err != nil && s.volumeSizeLimit < v.ContentSize()+uint64(size) && s.volumeSizeLimit >= v.ContentSize() {
 				log.Println("volume", i, "size is", v.ContentSize(), "close to", s.volumeSizeLimit)
@@ -181,9 +184,11 @@ func (s *Store) Write(i VolumeId, n *Needle) (size uint32, err error) {
 					log.Printf("error with Join: %s", err)
 				}
 			}
+		}
 		return
 	}
 	log.Println("volume", i, "not found!")
+  err = errors.New("Volume " + i + " not found!")
 	return
 }
 func (s *Store) Delete(i VolumeId, n *Needle) (uint32, error) {