Tweaks to decode interface

internal/decompress/lz4.go

@@ -12,9 +12,16 @@ func (l Lz4) Reader(r io.Reader) (io.ReadCloser, error) {
 	return io.NopCloser(lz4.NewReader(r)), nil
 }
 
-func (l Lz4) Resetable() bool { return true }
-
 func (l Lz4) Reset(old, src io.Reader) error {
 	old.(*lz4.Reader).Reset(src)
 	return nil
 }
+
+func (l Lz4) Decode(in []byte, outSize int) (out []byte, err error) {
+	out = make([]byte, outSize)
+	outLen, err := lz4.UncompressBlock(in, out)
+	if outLen < outSize {
+		out = out[:outLen]
+	}
+	return
+}