MessageLite

背景

之前在逆向YouTube期间遇到过：

__const:0000000004F7BF60 ; public video_streaming::OnesieRequestProto :
__const:0000000004F7BF60 ;   public /* offset 0x0 */ proto2::MessageLite

结论

• Protobuf的C++的类是：Message和MessageLite
  • MessageLite是轻量级=lite版的Message
    • Lite版==编译为LITE_RUNTIME版本=runtime是lite版
      • 只有：Encoding=编码 和 serializing=序列化
        • 没有：reflection和descriptors
  • MessageLite类的继承关系图
    • 

LITE_RUNTIME

LITE_RUNTIME的定义

https://github.com/alexeyxo/protobuf-objc.git

中有定义：

• src/compiler/google/protobuf/descriptor.proto

  // Generated classes can be optimized for speed or code size.
  enum OptimizeMode {
    SPEED = 1;        // Generate complete code for parsing, serialization,
                      // etc.
    CODE_SIZE = 2;    // Use ReflectionOps to implement these methods.
    LITE_RUNTIME = 3; // Generate code using MessageLite and the lite runtime.
  }
  optional OptimizeMode optimize_for = 9 [default=SPEED];

以及相关部分：

• src/compiler/google/protobuf/descriptor.pb.h

  // nested types ----------------------------------------------------

  typedef FileOptions_OptimizeMode OptimizeMode;
  static const OptimizeMode SPEED = FileOptions_OptimizeMode_SPEED;
  static const OptimizeMode CODE_SIZE = FileOptions_OptimizeMode_CODE_SIZE;
  static const OptimizeMode LITE_RUNTIME = FileOptions_OptimizeMode_LITE_RUNTIME;
  static inline bool OptimizeMode_IsValid(int value) {
    return FileOptions_OptimizeMode_IsValid(value);
  }
  static const OptimizeMode OptimizeMode_MIN =
    FileOptions_OptimizeMode_OptimizeMode_MIN;
  static const OptimizeMode OptimizeMode_MAX =
    FileOptions_OptimizeMode_OptimizeMode_MAX;
  static const int OptimizeMode_ARRAYSIZE =
    FileOptions_OptimizeMode_OptimizeMode_ARRAYSIZE;
  static inline const ::google::protobuf::EnumDescriptor*
  OptimizeMode_descriptor() {
    return FileOptions_OptimizeMode_descriptor();
  }
  static inline const ::std::string& OptimizeMode_Name(OptimizeMode value) {
    return FileOptions_OptimizeMode_Name(value);
  }
  static inline bool OptimizeMode_Parse(const ::std::string& name,
      OptimizeMode* value) {
    return FileOptions_OptimizeMode_Parse(name, value);
  }

• src/compiler/google/protobuf/descriptor.pb.cc

bool FileOptions::MergePartialFromCodedStream(
    ::google::protobuf::io::CodedInputStream* input) {
#define DO_(EXPRESSION) if (!(EXPRESSION)) goto failure
  ::google::protobuf::uint32 tag;
  // @@protoc_insertion_point(parse_start:google.protobuf.FileOptions)
  for (;;) {
    ::std::pair< ::google::protobuf::uint32, bool> p = input->ReadTagWithCutoff(16383);
    tag = p.first;
    if (!p.second) goto handle_unusual;
    switch (::google::protobuf::internal::WireFormatLite::GetTagFieldNumber(tag)) {
      // optional string java_package = 1;
      case 1: {
        if (tag == 10) {
          DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                input, this->mutable_java_package()));
          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
            this->java_package().data(), this->java_package().length(),
            ::google::protobuf::internal::WireFormat::PARSE,
            "java_package");
        } else {
          goto handle_unusual;
        }
        if (input->ExpectTag(66)) goto parse_java_outer_classname;
        break;
      }
。。。
      // optional .google.protobuf.FileOptions.OptimizeMode optimize_for = 9 [default = SPEED];
      case 9: {
        if (tag == 72) {
         parse_optimize_for:
          int value;
          DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<
                   int, ::google::protobuf::internal::WireFormatLite::TYPE_ENUM>(
                 input, &value)));
          if (::google::protobuf::FileOptions_OptimizeMode_IsValid(value)) {
            set_optimize_for(static_cast< ::google::protobuf::FileOptions_OptimizeMode >(value));
          } else {
            mutable_unknown_fields()->AddVarint(9, value);
          }
        } else {
          goto handle_unusual;
        }
        if (input->ExpectTag(80)) goto parse_java_multiple_files;
        break;
      }

LITE_RUNTIME的用法

在.proto文件中加上定义：

option optimize_for = LITE_RUNTIME;

就表示：

• 底层实现是用：MessageLite
  • 而不是普通的：Message
• 且不会用到任何有关于descriptors或reflection
• 适用于场景：资源受限
  • 此处YouTube估计是故意的，以便于你很难逆向找到protobuf的定义
  • 注：如果只是想要省空间，则应该改用：
    • optimize_for = CODE_SIZE

Proto2MessageLite

另外，之前下载的

google/protobuf/protobuf-refs_heads_master/java/lite.md

中也有很多：Proto3MessageLite

以及可以搜到很多相关的：

  java/core/src/test/java/com/google/protobuf/Proto2ExtensionLookupSchemaTest.java \
  java/core/src/test/java/com/google/protobuf/Proto2LiteSchemaTest.java            \
  java/core/src/test/java/com/google/protobuf/Proto2MessageFactory.java            \
  java/core/src/test/java/com/google/protobuf/Proto2MessageInfoFactory.java        \
  java/core/src/test/java/com/google/protobuf/Proto2MessageLiteFactory.java        \
  java/core/src/test/java/com/google/protobuf/Proto2SchemaTest.java                \
  java/core/src/test/java/com/google/protobuf/Proto2UnknownEnumValueTest.java      \
  java/core/src/test/java/com/google/protobuf/Proto3LiteSchemaTest.java            \
  java/core/src/test/java/com/google/protobuf/Proto3MessageFactory.java            \
  java/core/src/test/java/com/google/protobuf/Proto3MessageInfoFactory.java        \
  java/core/src/test/java/com/google/protobuf/Proto3MessageLiteFactory.java        \
  java/core/src/test/java/com/google/protobuf/Proto3MessageLiteInfoFactory.java    \
  java/core/src/test/java/com/google/protobuf/Proto3SchemaTest.java                \