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 //go:build !purego && !appengine && go1.21 6 // +build !purego,!appengine,go1.21 7 8 package strs 9 10 import ( 11 "unsafe" 12 13 "google.golang.org/protobuf/reflect/protoreflect" 14 ) 15 16 // UnsafeString returns an unsafe string reference of b. 17 // The caller must treat the input slice as immutable. 18 // 19 // WARNING: Use carefully. The returned result must not leak to the end user 20 // unless the input slice is provably immutable. 21 func UnsafeString(b []byte) string { 22 return unsafe.String(unsafe.SliceData(b), len(b)) 23 } 24 25 // UnsafeBytes returns an unsafe bytes slice reference of s. 26 // The caller must treat returned slice as immutable. 27 // 28 // WARNING: Use carefully. The returned result must not leak to the end user. 29 func UnsafeBytes(s string) []byte { 30 return unsafe.Slice(unsafe.StringData(s), len(s)) 31 } 32 33 // Builder builds a set of strings with shared lifetime. 34 // This differs from strings.Builder, which is for building a single string. 35 type Builder struct { 36 buf []byte 37 } 38 39 // AppendFullName is equivalent to protoreflect.FullName.Append, 40 // but optimized for large batches where each name has a shared lifetime. 41 func (sb *Builder) AppendFullName(prefix protoreflect.FullName, name protoreflect.Name) protoreflect.FullName { 42 n := len(prefix) + len(".") + len(name) 43 if len(prefix) == 0 { 44 n -= len(".") 45 } 46 sb.grow(n) 47 sb.buf = append(sb.buf, prefix...) 48 sb.buf = append(sb.buf, '.') 49 sb.buf = append(sb.buf, name...) 50 return protoreflect.FullName(sb.last(n)) 51 } 52 53 // MakeString is equivalent to string(b), but optimized for large batches 54 // with a shared lifetime. 55 func (sb *Builder) MakeString(b []byte) string { 56 sb.grow(len(b)) 57 sb.buf = append(sb.buf, b...) 58 return sb.last(len(b)) 59 } 60 61 func (sb *Builder) grow(n int) { 62 if cap(sb.buf)-len(sb.buf) >= n { 63 return 64 } 65 66 // Unlike strings.Builder, we do not need to copy over the contents 67 // of the old buffer since our builder provides no API for 68 // retrieving previously created strings. 69 sb.buf = make([]byte, 0, 2*(cap(sb.buf)+n)) 70 } 71 72 func (sb *Builder) last(n int) string { 73 return UnsafeString(sb.buf[len(sb.buf)-n:]) 74 } 75