internal/catmsg: added varint implementation
the catmsg package contains functionality local to
x/text internal related to the catalog package.
Change-Id: Iba503cf7dd67ad82973727bc096e4732d4dcf56b
Reviewed-on: https://go-review.googlesource.com/41330
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
diff --git a/internal/catmsg/varint.go b/internal/catmsg/varint.go
new file mode 100644
index 0000000..a2cee2c
--- /dev/null
+++ b/internal/catmsg/varint.go
@@ -0,0 +1,62 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package catmsg
+
+// This file implements varint encoding analogous to the one in encoding/binary.
+// We need a string version of this function, so we add that here and then add
+// the rest for consistency.
+
+import "errors"
+
+var (
+ errIllegalVarint = errors.New("catmsg: illegal varint")
+ errVarintTooLarge = errors.New("catmsg: varint too large for uint64")
+)
+
+const maxVarintBytes = 10 // maximum length of a varint
+
+// encodeUint encodes x as a variable-sized integer into buf and returns the
+// number of bytes written. buf must be at least maxVarintBytes long
+func encodeUint(buf []byte, x uint64) (n int) {
+ for ; x > 127; n++ {
+ buf[n] = 0x80 | uint8(x&0x7F)
+ x >>= 7
+ }
+ buf[n] = uint8(x)
+ n++
+ return n
+}
+
+func decodeUintString(s string) (x uint64, size int, err error) {
+ i := 0
+ for shift := uint(0); shift < 64; shift += 7 {
+ if i >= len(s) {
+ return 0, i, errIllegalVarint
+ }
+ b := uint64(s[i])
+ i++
+ x |= (b & 0x7F) << shift
+ if b&0x80 == 0 {
+ return x, i, nil
+ }
+ }
+ return 0, i, errVarintTooLarge
+}
+
+func decodeUint(b []byte) (x uint64, size int, err error) {
+ i := 0
+ for shift := uint(0); shift < 64; shift += 7 {
+ if i >= len(b) {
+ return 0, i, errIllegalVarint
+ }
+ c := uint64(b[i])
+ i++
+ x |= (c & 0x7F) << shift
+ if c&0x80 == 0 {
+ return x, i, nil
+ }
+ }
+ return 0, i, errVarintTooLarge
+}
diff --git a/internal/catmsg/varint_test.go b/internal/catmsg/varint_test.go
new file mode 100644
index 0000000..a079c77
--- /dev/null
+++ b/internal/catmsg/varint_test.go
@@ -0,0 +1,123 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package catmsg
+
+import (
+ "fmt"
+ "testing"
+)
+
+func TestEncodeUint(t *testing.T) {
+ testCases := []struct {
+ x uint64
+ enc string
+ }{
+ {0, "\x00"},
+ {1, "\x01"},
+ {2, "\x02"},
+ {0x7f, "\x7f"},
+ {0x80, "\x80\x01"},
+ {1 << 14, "\x80\x80\x01"},
+ {0xffffffff, "\xff\xff\xff\xff\x0f"},
+ {0xffffffffffffffff, "\xff\xff\xff\xff\xff\xff\xff\xff\xff\x01"},
+ }
+ for _, tc := range testCases {
+ buf := [maxVarintBytes]byte{}
+ got := string(buf[:encodeUint(buf[:], tc.x)])
+ if got != tc.enc {
+ t.Errorf("EncodeUint(%#x) = %q; want %q", tc.x, got, tc.enc)
+ }
+ }
+}
+
+func TestDecodeUint(t *testing.T) {
+ testCases := []struct {
+ x uint64
+ size int
+ enc string
+ err error
+ }{{
+ x: 0,
+ size: 0,
+ enc: "",
+ err: errIllegalVarint,
+ }, {
+ x: 0,
+ size: 1,
+ enc: "\x80",
+ err: errIllegalVarint,
+ }, {
+ x: 0,
+ size: 3,
+ enc: "\x80\x80\x80",
+ err: errIllegalVarint,
+ }, {
+ x: 0,
+ size: 1,
+ enc: "\x00",
+ }, {
+ x: 1,
+ size: 1,
+ enc: "\x01",
+ }, {
+ x: 2,
+ size: 1,
+ enc: "\x02",
+ }, {
+ x: 0x7f,
+ size: 1,
+ enc: "\x7f",
+ }, {
+ x: 0x80,
+ size: 2,
+ enc: "\x80\x01",
+ }, {
+ x: 1 << 14,
+ size: 3,
+ enc: "\x80\x80\x01",
+ }, {
+ x: 0xffffffff,
+ size: 5,
+ enc: "\xff\xff\xff\xff\x0f",
+ }, {
+ x: 0xffffffffffffffff,
+ size: 10,
+ enc: "\xff\xff\xff\xff\xff\xff\xff\xff\xff\x01",
+ }, {
+ x: 0xffffffffffffffff,
+ size: 10,
+ enc: "\xff\xff\xff\xff\xff\xff\xff\xff\xff\x01\x00",
+ }, {
+ x: 0,
+ size: 10,
+ enc: "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\x01",
+ err: errVarintTooLarge,
+ }}
+ forms := []struct {
+ name string
+ decode func(s string) (x uint64, size int, err error)
+ }{
+ {"decode", func(s string) (x uint64, size int, err error) {
+ return decodeUint([]byte(s))
+ }},
+ {"decodeString", decodeUintString},
+ }
+ for _, f := range forms {
+ for _, tc := range testCases {
+ t.Run(fmt.Sprintf("%s:%q", f.name, tc.enc), func(t *testing.T) {
+ x, size, err := f.decode(tc.enc)
+ if err != tc.err {
+ t.Error("err = %q; want %q", err, tc.err)
+ }
+ if size != tc.size {
+ t.Errorf("size = %d; want %d", size, tc.size)
+ }
+ if x != tc.x {
+ t.Errorf("decode = %#x; want %#x", x, tc.x)
+ }
+ })
+ }
+ }
+}
