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
 5package strs
 6
 7import (
 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.
18func 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.
26func 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.
32type 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.
38func (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.
52func (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
58func (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
69func (sb *Builder) last(n int) string {
70	return UnsafeString(sb.buf[len(sb.buf)-n:])
71}