1// Protocol Buffers - Google's data interchange format
2// Copyright 2008 Google Inc. All rights reserved.
3// https://developers.google.com/protocol-buffers/
4//
5// Redistribution and use in source and binary forms, with or without
6// modification, are permitted provided that the following conditions are
7// met:
8//
9// * Redistributions of source code must retain the above copyright
10// notice, this list of conditions and the following disclaimer.
11// * Redistributions in binary form must reproduce the above
12// copyright notice, this list of conditions and the following disclaimer
13// in the documentation and/or other materials provided with the
14// distribution.
15// * Neither the name of Google Inc. nor the names of its
16// contributors may be used to endorse or promote products derived from
17// this software without specific prior written permission.
18//
19// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31#ifndef GOOGLE_PROTOBUF_METADATA_LITE_H__
32#define GOOGLE_PROTOBUF_METADATA_LITE_H__
33
34#include <string>
35#include <google/protobuf/stubs/common.h>
36#include <google/protobuf/arena.h>
37#include <google/protobuf/port.h>
38
39#include <google/protobuf/port_def.inc>
40
41#ifdef SWIG
42#error "You cannot SWIG proto headers"
43#endif
44
45namespace google {
46namespace protobuf {
47namespace internal {
48
49// This is the representation for messages that support arena allocation. It
50// uses a tagged pointer to either store the Arena pointer, if there are no
51// unknown fields, or a pointer to a block of memory with both the Arena pointer
52// and the UnknownFieldSet, if there are unknown fields. This optimization
53// allows for "zero-overhead" storage of the Arena pointer, relative to the
54// above baseline implementation.
55//
56// The tagged pointer uses the LSB to disambiguate cases, and uses bit 0 == 0 to
57// indicate an arena pointer and bit 0 == 1 to indicate a UFS+Arena-container
58// pointer.
59class InternalMetadata {
60 public:
61 InternalMetadata() : ptr_(nullptr) {}
62 explicit InternalMetadata(Arena* arena) : ptr_(arena) {}
63
64 template <typename T>
65 void Delete() {
66 // Note that Delete<> should be called not more than once.
67 if (have_unknown_fields() && arena() == NULL) {
68 delete PtrValue<Container<T>>();
69 }
70 }
71
72 PROTOBUF_ALWAYS_INLINE Arena* arena() const {
73 if (PROTOBUF_PREDICT_FALSE(have_unknown_fields())) {
74 return PtrValue<ContainerBase>()->arena;
75 } else {
76 return PtrValue<Arena>();
77 }
78 }
79
80 PROTOBUF_ALWAYS_INLINE bool have_unknown_fields() const {
81 return PtrTag() == kTagContainer;
82 }
83
84 PROTOBUF_ALWAYS_INLINE void* raw_arena_ptr() const { return ptr_; }
85
86 template <typename T>
87 PROTOBUF_ALWAYS_INLINE const T& unknown_fields(
88 const T& (*default_instance)()) const {
89 if (PROTOBUF_PREDICT_FALSE(have_unknown_fields())) {
90 return PtrValue<Container<T>>()->unknown_fields;
91 } else {
92 return default_instance();
93 }
94 }
95
96 template <typename T>
97 PROTOBUF_ALWAYS_INLINE T* mutable_unknown_fields() {
98 if (PROTOBUF_PREDICT_TRUE(have_unknown_fields())) {
99 return &PtrValue<Container<T>>()->unknown_fields;
100 } else {
101 return mutable_unknown_fields_slow<T>();
102 }
103 }
104
105 template <typename T>
106 PROTOBUF_ALWAYS_INLINE void Swap(InternalMetadata* other) {
107 // Semantics here are that we swap only the unknown fields, not the arena
108 // pointer. We cannot simply swap ptr_ with other->ptr_ because we need to
109 // maintain our own arena ptr. Also, our ptr_ and other's ptr_ may be in
110 // different states (direct arena pointer vs. container with UFS) so we
111 // cannot simply swap ptr_ and then restore the arena pointers. We reuse
112 // UFS's swap implementation instead.
113 if (have_unknown_fields() || other->have_unknown_fields()) {
114 DoSwap<T>(other->mutable_unknown_fields<T>());
115 }
116 }
117
118 template <typename T>
119 PROTOBUF_ALWAYS_INLINE void MergeFrom(const InternalMetadata& other) {
120 if (other.have_unknown_fields()) {
121 DoMergeFrom<T>(other.unknown_fields<T>(nullptr));
122 }
123 }
124
125 template <typename T>
126 PROTOBUF_ALWAYS_INLINE void Clear() {
127 if (have_unknown_fields()) {
128 DoClear<T>();
129 }
130 }
131
132 private:
133 void* ptr_;
134
135 // Tagged pointer implementation.
136 enum {
137 // ptr_ is an Arena*.
138 kTagArena = 0,
139 // ptr_ is a Container*.
140 kTagContainer = 1,
141 };
142 static constexpr intptr_t kPtrTagMask = 1;
143 static constexpr intptr_t kPtrValueMask = ~kPtrTagMask;
144
145 // Accessors for pointer tag and pointer value.
146 PROTOBUF_ALWAYS_INLINE int PtrTag() const {
147 return reinterpret_cast<intptr_t>(ptr_) & kPtrTagMask;
148 }
149
150 template <typename U>
151 U* PtrValue() const {
152 return reinterpret_cast<U*>(reinterpret_cast<intptr_t>(ptr_) &
153 kPtrValueMask);
154 }
155
156 // If ptr_'s tag is kTagContainer, it points to an instance of this struct.
157 struct ContainerBase {
158 Arena* arena;
159 };
160
161 template <typename T>
162 struct Container : public ContainerBase {
163 T unknown_fields;
164 };
165
166 template <typename T>
167 PROTOBUF_NOINLINE T* mutable_unknown_fields_slow() {
168 Arena* my_arena = arena();
169 Container<T>* container = Arena::Create<Container<T>>(my_arena);
170 // Two-step assignment works around a bug in clang's static analyzer:
171 // https://bugs.llvm.org/show_bug.cgi?id=34198.
172 ptr_ = container;
173 ptr_ = reinterpret_cast<void*>(reinterpret_cast<intptr_t>(ptr_) |
174 kTagContainer);
175 container->arena = my_arena;
176 return &(container->unknown_fields);
177 }
178
179 // Templated functions.
180
181 template <typename T>
182 void DoClear() {
183 mutable_unknown_fields<T>()->Clear();
184 }
185
186 template <typename T>
187 void DoMergeFrom(const T& other) {
188 mutable_unknown_fields<T>()->MergeFrom(other);
189 }
190
191 template <typename T>
192 void DoSwap(T* other) {
193 mutable_unknown_fields<T>()->Swap(other);
194 }
195};
196
197// String Template specializations.
198
199template <>
200inline void InternalMetadata::DoClear<std::string>() {
201 mutable_unknown_fields<std::string>()->clear();
202}
203
204template <>
205inline void InternalMetadata::DoMergeFrom<std::string>(
206 const std::string& other) {
207 mutable_unknown_fields<std::string>()->append(other);
208}
209
210template <>
211inline void InternalMetadata::DoSwap<std::string>(std::string* other) {
212 mutable_unknown_fields<std::string>()->swap(*other);
213}
214
215// This helper RAII class is needed to efficiently parse unknown fields. We
216// should only call mutable_unknown_fields if there are actual unknown fields.
217// The obvious thing to just use a stack string and swap it at the end of
218// the parse won't work, because the destructor of StringOutputStream needs to
219// be called before we can modify the string (it check-fails). Using
220// LiteUnknownFieldSetter setter(&_internal_metadata_);
221// StringOutputStream stream(setter.buffer());
222// guarantees that the string is only swapped after stream is destroyed.
223class PROTOBUF_EXPORT LiteUnknownFieldSetter {
224 public:
225 explicit LiteUnknownFieldSetter(InternalMetadata* metadata)
226 : metadata_(metadata) {
227 if (metadata->have_unknown_fields()) {
228 buffer_.swap(*metadata->mutable_unknown_fields<std::string>());
229 }
230 }
231 ~LiteUnknownFieldSetter() {
232 if (!buffer_.empty())
233 metadata_->mutable_unknown_fields<std::string>()->swap(buffer_);
234 }
235 std::string* buffer() { return &buffer_; }
236
237 private:
238 InternalMetadata* metadata_;
239 std::string buffer_;
240};
241
242} // namespace internal
243} // namespace protobuf
244} // namespace google
245
246#include <google/protobuf/port_undef.inc>
247
248#endif // GOOGLE_PROTOBUF_METADATA_LITE_H__
249