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// Copyright 2018 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.
//go:build !purego && !appengine
// +build !purego,!appengine
package strs
import (
"unsafe"
pref "google.golang.org/protobuf/reflect/protoreflect"
)
type (
stringHeader struct {
Data unsafe.Pointer
Len int
}
sliceHeader struct {
Data unsafe.Pointer
Len int
Cap int
}
)
// UnsafeString returns an unsafe string reference of b.
// The caller must treat the input slice as immutable.
//
// WARNING: Use carefully. The returned result must not leak to the end user
// unless the input slice is provably immutable.
func UnsafeString(b []byte) (s string) {
src := (*sliceHeader)(unsafe.Pointer(&b))
dst := (*stringHeader)(unsafe.Pointer(&s))
dst.Data = src.Data
dst.Len = src.Len
return s
}
// UnsafeBytes returns an unsafe bytes slice reference of s.
// The caller must treat returned slice as immutable.
//
// WARNING: Use carefully. The returned result must not leak to the end user.
func UnsafeBytes(s string) (b []byte) {
src := (*stringHeader)(unsafe.Pointer(&s))
dst := (*sliceHeader)(unsafe.Pointer(&b))
dst.Data = src.Data
dst.Len = src.Len
dst.Cap = src.Len
return b
}
// Builder builds a set of strings with shared lifetime.
// This differs from strings.Builder, which is for building a single string.
type Builder struct {
buf []byte
}
// AppendFullName is equivalent to protoreflect.FullName.Append,
// but optimized for large batches where each name has a shared lifetime.
func (sb *Builder) AppendFullName(prefix pref.FullName, name pref.Name) pref.FullName {
n := len(prefix) + len(".") + len(name)
if len(prefix) == 0 {
n -= len(".")
}
sb.grow(n)
sb.buf = append(sb.buf, prefix...)
sb.buf = append(sb.buf, '.')
sb.buf = append(sb.buf, name...)
return pref.FullName(sb.last(n))
}
// MakeString is equivalent to string(b), but optimized for large batches
// with a shared lifetime.
func (sb *Builder) MakeString(b []byte) string {
sb.grow(len(b))
sb.buf = append(sb.buf, b...)
return sb.last(len(b))
}
func (sb *Builder) grow(n int) {
if cap(sb.buf)-len(sb.buf) >= n {
return
}
// Unlike strings.Builder, we do not need to copy over the contents
// of the old buffer since our builder provides no API for
// retrieving previously created strings.
sb.buf = make([]byte, 2*(cap(sb.buf)+n))
}
func (sb *Builder) last(n int) string {
return UnsafeString(sb.buf[len(sb.buf)-n:])
}
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