defaulting file ttl to volume ttl

fix https://github.com/chrislusf/seaweedfs/issues/992

weed/storage/needle/volume_ttl.go

@@ -48,6 +48,9 @@ func ReadTTL(ttlString string) (*TTL, error) {
 
 // read stored bytes to a ttl
 func LoadTTLFromBytes(input []byte) (t *TTL) {
+	if input[0] == 0 && input[1] == 0 {
+		return EMPTY_TTL
+	}
 	return &TTL{Count: input[0], Unit: input[1]}
 }
 

weed/storage/volume_read_write.go

@@ -91,6 +91,11 @@ func (v *Volume) writeNeedle(n *needle.Needle) (offset uint64, size uint32, isUn
 		return
 	}
 
+	if n.Ttl == needle.EMPTY_TTL && v.Ttl != needle.EMPTY_TTL {
+		n.SetHasTtl()
+		n.Ttl = v.Ttl
+	}
+
 	n.AppendAtNs = uint64(time.Now().UnixNano())
 	if offset, size, _, err = n.Append(v.dataFile, v.Version()); err != nil {
 		return