add If-None-Match and If-Modified-Since

fix https://github.com/chrislusf/seaweedfs/issues/1269

weed/filer2/entry_codec.go

@@ -52,6 +52,7 @@ func EntryAttributeToPb(entry *Entry) *filer_pb.FuseAttributes {
 		UserName:      entry.Attr.UserName,
 		GroupName:     entry.Attr.GroupNames,
 		SymlinkTarget: entry.Attr.SymlinkTarget,
+		Md5:           entry.Attr.Md5,
 	}
 }
 
@@ -71,6 +72,7 @@ func PbToEntryAttribute(attr *filer_pb.FuseAttributes) Attr {
 	t.UserName = attr.UserName
 	t.GroupNames = attr.GroupName
 	t.SymlinkTarget = attr.SymlinkTarget
+	t.Md5 = attr.Md5
 
 	return t
 }
@@ -93,6 +95,10 @@ func EqualEntry(a, b *Entry) bool {
 		return false
 	}
 
+	if !bytes.Equal(a.Md5, b.Md5) {
+		return false
+	}
+
 	for i := 0; i < len(a.Chunks); i++ {
 		if !proto.Equal(a.Chunks[i], b.Chunks[i]) {
 			return false