Add base128 encoding library.

common/data/base128/base128_test.go

Index: common/data/base128/base128_test.go
diff --git a/common/data/base128/base128_test.go b/common/data/base128/base128_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..74d387857ca6e5add88c556e23cec20ad2c76fc9
--- /dev/null
+++ b/common/data/base128/base128_test.go
@@ -0,0 +1,91 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package base128
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestBase128(t *testing.T) {
+	t.Parallel()
+
+	Convey("base128", t, func() {
+		Convey("lengths", func() {
+			cases := []struct {
+				dec, enc int
+			}{
+				{0, 0},
+				{1, 2},
+				{6, 7},
+				{7, 8},
+				{8, 10},
+				{9, 11},
+			}
+			for _, c := range cases {
+				Convey(fmt.Sprintf("enc:%d dec:%d", c.enc, c.dec), func() {
+					So(DecodedLen(c.enc), ShouldEqual, c.dec)
+					So(EncodedLen(c.dec), ShouldEqual, c.enc)
+					So(EncodedLen(DecodedLen(c.enc)), ShouldEqual, c.enc)
+					So(DecodedLen(EncodedLen(c.dec)), ShouldEqual, c.dec)
+				})
+			}
+		})
+
+		Convey("errors", func() {
+			Convey("bad length", func() {
+				_, err := Decode(nil, []byte{0xff})
+				So(err, ShouldEqual, ErrLength)
+
+				_, err = Decode(nil, bytes.Repeat([]byte{0xff}, 9))
+				So(err, ShouldEqual, ErrLength)
+
+				So(func() { Decode(nil, []byte{0xff, 0xff}) }, ShouldPanic)
+			})
+
+			Convey("bad byte", func() {
+				_, err := Decode([]byte{0}, []byte{0x7f, 0xff})
+				So(err, ShouldEqual, ErrBit)
+			})
+		})
+
+		Convey("bytes", func() {
+			cases := []struct {
+				dec, enc []byte
+			}{
+				{[]byte{}, []byte{}},
+				{[]byte{0xff}, []byte{0x7f, 0x40}},
+				{
+					bytes.Repeat([]byte{0xff}, 6),
+					append(bytes.Repeat([]byte{0x7f}, 6), 0x7e),
+				},
+				{
+					bytes.Repeat([]byte{0xff}, 7),
+					bytes.Repeat([]byte{0x7f}, 8),
+				},
+				{
+					bytes.Repeat([]byte{0xff}, 8),
+					append(bytes.Repeat([]byte{0x7f}, 9), 0x40),
+				},
+			}
+			for _, c := range cases {
+				Convey(fmt.Sprintf("%q -> %q", c.dec, c.enc), func() {
+					buf := make([]byte, len(c.enc))
+					So(Encode(buf, c.dec), ShouldEqual, len(buf))
+					So(buf, ShouldResemble, c.enc)
+
+					buf = make([]byte, len(c.dec))
+					n, err := Decode(buf, c.enc)
+					So(err, ShouldBeNil)
+					So(n, ShouldEqual, len(buf))
+					So(buf, ShouldResemble, c.dec)
+				})
+			}
+		})
+	})
+}