Add proto marshal helper for bytes

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

util/proto/marshal.go

@@ -0,0 +1,44 @@
+/*
+This package contains help functions for stable marshaller. Their usage is
+totally optional. One can implement fast stable marshaller without these
+runtime function calls.
+*/
+
+package proto
+
+import (
+	"encoding/binary"
+	"math/bits"
+)
+
+func BytesMarshal(field int, buf, v []byte) (int, error) {
+	if len(v) == 0 {
+		return 0, nil
+	}
+
+	// buf length check can prevent panic at PutUvarint, but it will make
+	// marshaller a bit slower.
+
+	prefix := field<<3 | 0x2
+	i := binary.PutUvarint(buf, uint64(prefix))
+	i += binary.PutUvarint(buf[i:], uint64(len(v)))
+	i += copy(buf[i:], v)
+
+	return i, nil
+}
+
+func BytesSize(field int, v []byte) int {
+	ln := len(v)
+	if ln == 0 {
+		return 0
+	}
+
+	prefix := field<<3 | 0x2
+
+	return VarUIntSize(uint64(prefix)) + VarUIntSize(uint64(ln)) + ln
+}
+
+// varUIntSize returns length of varint byte sequence for uint64 value 'x'.
+func VarUIntSize(x uint64) int {
+	return (bits.Len64(x|1) + 6) / 7
+}