Avoid allocating memory in Type() method.

varint.go

@@ -0,0 +1,34 @@
+package cid
+
+// Version of varint function that work with a string rather than
+// []byte to avoid unnecessary allocation
+
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license as given at https://golang.org/LICENSE
+
+// uvarint decodes a uint64 from buf and returns that value and the
+// number of characters read (> 0). If an error occurred, the value is 0
+// and the number of bytes n is <= 0 meaning:
+//
+// 	n == 0: buf too small
+// 	n  < 0: value larger than 64 bits (overflow)
+// 	        and -n is the number of bytes read
+//
+func uvarint(buf string) (uint64, int) {
+	var x uint64
+	var s uint
+	// we have a binary string so we can't use a range loope
+	for i := 0; i < len(buf); i++ {
+		b := buf[i]
+		if b < 0x80 {
+			if i > 9 || i == 9 && b > 1 {
+				return 0, -(i + 1) // overflow
+			}
+			return x | uint64(b)<<s, i + 1
+		}
+		x |= uint64(b&0x7f) << s
+		s += 7
+	}
+	return 0, 0
+}