1 // Copyright 2018 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 package strs
6 7 import (
8 "unsafe"
9 10 "google.golang.org/protobuf/reflect/protoreflect"
11 )
12 13 // UnsafeString returns an unsafe string reference of b.
14 // The caller must treat the input slice as immutable.
15 //
16 // WARNING: Use carefully. The returned result must not leak to the end user
17 // unless the input slice is provably immutable.
18 func UnsafeString(b []byte) string {
19 return unsafe.String(unsafe.SliceData(b), len(b))
20 }
21 22 // UnsafeBytes returns an unsafe bytes slice reference of s.
23 // The caller must treat returned slice as immutable.
24 //
25 // WARNING: Use carefully. The returned result must not leak to the end user.
26 func UnsafeBytes(s string) []byte {
27 return unsafe.Slice(unsafe.StringData(s), len(s))
28 }
29 30 // Builder builds a set of strings with shared lifetime.
31 // This differs from strings.Builder, which is for building a single string.
32 type Builder struct {
33 buf []byte
34 }
35 36 // AppendFullName is equivalent to protoreflect.FullName.Append,
37 // but optimized for large batches where each name has a shared lifetime.
38 func (sb *Builder) AppendFullName(prefix protoreflect.FullName, name protoreflect.Name) protoreflect.FullName {
39 n := len(prefix) + len(".") + len(name)
40 if len(prefix) == 0 {
41 n -= len(".")
42 }
43 sb.grow(n)
44 sb.buf = append(sb.buf, prefix...)
45 sb.buf = append(sb.buf, '.')
46 sb.buf = append(sb.buf, name...)
47 return protoreflect.FullName(sb.last(n))
48 }
49 50 // MakeString is equivalent to string(b), but optimized for large batches
51 // with a shared lifetime.
52 func (sb *Builder) MakeString(b []byte) string {
53 sb.grow(len(b))
54 sb.buf = append(sb.buf, b...)
55 return sb.last(len(b))
56 }
57 58 func (sb *Builder) grow(n int) {
59 if cap(sb.buf)-len(sb.buf) >= n {
60 return
61 }
62 63 // Unlike strings.Builder, we do not need to copy over the contents
64 // of the old buffer since our builder provides no API for
65 // retrieving previously created strings.
66 sb.buf = make([]byte, 0, 2*(cap(sb.buf)+n))
67 }
68 69 func (sb *Builder) last(n int) string {
70 return UnsafeString(sb.buf[len(sb.buf)-n:])
71 }
72