khenaidoo | 106c61a | 2021-08-11 18:05:46 -0400 | [diff] [blame] | 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 | // +build !purego,!appengine |
| 6 | |
| 7 | package strs |
| 8 | |
| 9 | import ( |
| 10 | "unsafe" |
| 11 | |
| 12 | pref "google.golang.org/protobuf/reflect/protoreflect" |
| 13 | ) |
| 14 | |
| 15 | type ( |
| 16 | stringHeader struct { |
| 17 | Data unsafe.Pointer |
| 18 | Len int |
| 19 | } |
| 20 | sliceHeader struct { |
| 21 | Data unsafe.Pointer |
| 22 | Len int |
| 23 | Cap int |
| 24 | } |
| 25 | ) |
| 26 | |
| 27 | // UnsafeString returns an unsafe string reference of b. |
| 28 | // The caller must treat the input slice as immutable. |
| 29 | // |
| 30 | // WARNING: Use carefully. The returned result must not leak to the end user |
| 31 | // unless the input slice is provably immutable. |
| 32 | func UnsafeString(b []byte) (s string) { |
| 33 | src := (*sliceHeader)(unsafe.Pointer(&b)) |
| 34 | dst := (*stringHeader)(unsafe.Pointer(&s)) |
| 35 | dst.Data = src.Data |
| 36 | dst.Len = src.Len |
| 37 | return s |
| 38 | } |
| 39 | |
| 40 | // UnsafeBytes returns an unsafe bytes slice reference of s. |
| 41 | // The caller must treat returned slice as immutable. |
| 42 | // |
| 43 | // WARNING: Use carefully. The returned result must not leak to the end user. |
| 44 | func UnsafeBytes(s string) (b []byte) { |
| 45 | src := (*stringHeader)(unsafe.Pointer(&s)) |
| 46 | dst := (*sliceHeader)(unsafe.Pointer(&b)) |
| 47 | dst.Data = src.Data |
| 48 | dst.Len = src.Len |
| 49 | dst.Cap = src.Len |
| 50 | return b |
| 51 | } |
| 52 | |
| 53 | // Builder builds a set of strings with shared lifetime. |
| 54 | // This differs from strings.Builder, which is for building a single string. |
| 55 | type Builder struct { |
| 56 | buf []byte |
| 57 | } |
| 58 | |
| 59 | // AppendFullName is equivalent to protoreflect.FullName.Append, |
| 60 | // but optimized for large batches where each name has a shared lifetime. |
| 61 | func (sb *Builder) AppendFullName(prefix pref.FullName, name pref.Name) pref.FullName { |
| 62 | n := len(prefix) + len(".") + len(name) |
| 63 | if len(prefix) == 0 { |
| 64 | n -= len(".") |
| 65 | } |
| 66 | sb.grow(n) |
| 67 | sb.buf = append(sb.buf, prefix...) |
| 68 | sb.buf = append(sb.buf, '.') |
| 69 | sb.buf = append(sb.buf, name...) |
| 70 | return pref.FullName(sb.last(n)) |
| 71 | } |
| 72 | |
| 73 | // MakeString is equivalent to string(b), but optimized for large batches |
| 74 | // with a shared lifetime. |
| 75 | func (sb *Builder) MakeString(b []byte) string { |
| 76 | sb.grow(len(b)) |
| 77 | sb.buf = append(sb.buf, b...) |
| 78 | return sb.last(len(b)) |
| 79 | } |
| 80 | |
| 81 | func (sb *Builder) grow(n int) { |
| 82 | if cap(sb.buf)-len(sb.buf) >= n { |
| 83 | return |
| 84 | } |
| 85 | |
| 86 | // Unlike strings.Builder, we do not need to copy over the contents |
| 87 | // of the old buffer since our builder provides no API for |
| 88 | // retrieving previously created strings. |
| 89 | sb.buf = make([]byte, 2*(cap(sb.buf)+n)) |
| 90 | } |
| 91 | |
| 92 | func (sb *Builder) last(n int) string { |
| 93 | return UnsafeString(sb.buf[len(sb.buf)-n:]) |
| 94 | } |