volume: support http status 304 for the same file id

weed/server/volume_grpc_tail.go

@@ -111,7 +111,7 @@ func (vs *VolumeServer) VolumeTailReceiver(ctx context.Context, req *volume_serv
 	defer glog.V(1).Infof("receive tailing volume %d finished", v.Id)
 
 	return resp, operation.TailVolumeFromSource(req.SourceVolumeServer, vs.grpcDialOption, v.Id, req.SinceNs, int(req.IdleTimeoutSeconds), func(n *needle.Needle) error {
-		_, err := vs.store.Write(v.Id, n)
+		_, _, err := vs.store.Write(v.Id, n)
 		return err
 	})
 

weed/server/volume_server_handlers_write.go

@@ -41,11 +41,14 @@ func (vs *VolumeServer) PostHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	ret := operation.UploadResult{}
-	_, errorStatus := topology.ReplicatedWrite(vs.GetMaster(), vs.store, volumeId, needle, r)
+	_, isUnchanged, writeError := topology.ReplicatedWrite(vs.GetMaster(), vs.store, volumeId, needle, r)
 	httpStatus := http.StatusCreated
-	if errorStatus != "" {
+	if isUnchanged {
+		httpStatus = http.StatusNotModified
+	}
+	if writeError != nil {
 		httpStatus = http.StatusInternalServerError
-		ret.Error = errorStatus
+		ret.Error = writeError.Error()
 	}
 	if needle.HasName() {
 		ret.Name = string(needle.Name)