Flutter高性能数据序列化插件capnproto的使用

在本教程中，我们将详细介绍如何在Flutter项目中使用高性能的数据序列化插件capnproto。capnproto-dart 是一个纯Dart实现的库，用于处理Cap’n Proto协议。

安装capnproto-dart

首先，在你的pubspec.yaml文件中添加capnproto-dart依赖：

dependencies:
  capnproto: ^0.1.0

然后运行以下命令以安装依赖：

flutter pub get

示例代码

接下来，我们来看一下如何在Flutter项目中使用capnproto-dart来序列化和反序列化数据。我们通过一个简单的例子来说明。

示例结构定义

假设你有一个名为main.capnp的文件，其中定义了两个结构体TestStruct和Foo。这个文件可以通过以下命令生成对应的Dart代码：

capnp compile -ocapnp main.capnp > main-compiled.capnp

Dart代码实现

以下是完整的示例代码，展示了如何读取编译后的消息并进行反序列化：

import 'dart:io';
import 'dart:typed_data';

import 'package:capnproto/capnproto.dart';

void main(List<String> args) {
  // 读取编译后的消息文件
  final compiledFile = File('example/message.bin');
  print(compiledFile.absolute.path);
  final data = compiledFile.readAsBytesSync();
  final message = Message.fromBuffer(data.buffer);

  // 反序列化消息
  final testStruct = message.getRoot(TestStruct.from);
  print(testStruct);
}

// 对于每个在Cap'n Proto定义中的结构体，创建一个类似的类
class TestStruct {
  // 创建一个构造函数
  const TestStruct(this.segmentView, this.dataSectionLengthInWords);

  // 创建一个静态方法`from`，该方法委托给上述构造函数
  static TestStruct from(
    SegmentView segmentView,
    int dataSectionLengthInWords,
  ) =>
      TestStruct(segmentView, dataSectionLengthInWords);

  final SegmentView segmentView;
  final int dataSectionLengthInWords;

  // 为每个成员写一个getter，这些getter委托给`segmentView`（底层缓冲区的一个视图）
  void get unit => segmentView.getVoid(0);
  bool get boolean => segmentView.getBool(0);
  UnmodifiableBoolListView get booleanList =>
      segmentView.getBoolList(dataSectionLengthInWords + 0);
  int get int8 => segmentView.getInt8(8 ~/ CapnpConstants.bitsPerByte);
  int get int16 => segmentView.getInt16(16 ~/ CapnpConstants.bitsPerByte);
  int get int32 => segmentView.getInt32(32 ~/ CapnpConstants.bitsPerByte);
  int get int64 => segmentView.getInt64(64 ~/ CapnpConstants.bitsPerByte);
  int get uint8 => segmentView.getUInt8(128 ~/ CapnpConstants.bitsPerByte);
  int get uint16 => segmentView.getUInt16(144 ~/ CapnpConstants.bitsPerByte);
  UnmodifiableUint16ListView get uint16List =>
      segmentView.getUInt16List(dataSectionLengthInWords + 1);
  int get uint32 => segmentView.getUInt32(160 ~/ CapnpConstants.bitsPerByte);
  int get uint64 => segmentView.getUInt64(192 ~/ CapnpConstants.bitsPerByte);
  double get float32 =>
      segmentView.getFloat32(256 ~/ CapnpConstants.bitsPerByte);
  UnmodifiableFloat32ListView get float32List =>
      segmentView.getFloat32List(dataSectionLengthInWords + 2);
  double get float64 =>
      segmentView.getFloat64(320 ~/ CapnpConstants.bitsPerByte);
  String get text => segmentView.getText(dataSectionLengthInWords + 3);
  UnmodifiableUint8ListView get data =>
      segmentView.getData(dataSectionLengthInWords + 4);
  Foo get foo => segmentView.getStruct(dataSectionLengthInWords + 5, Foo.from);
  UnmodifiableCompositeListView<Foo> get fooList =>
      segmentView.getCompositeList(dataSectionLengthInWords + 6, Foo.from);

  // 这是可选的
  [@override](/user/override)
  String toString() =>
      'TestStruct(unit: <void>, boolean: $boolean, booleanList: $booleanList, int8: $int8, int16: $int16, int32: $int32, int64: $int64, uint8: $uint8, uint16: $uint16, uint16List: $uint16List, uint32: $uint32, uint64: $uint64, float32: $float32, float32List: $float32List, float64: $float64, text: $text, data: $data, foo: $foo, fooList: $fooList';
}

class Foo {
  const Foo(this.segmentView, this.dataSectionLengthInWords);

  // 创建一个静态方法`from`，该方法委托给上述构造函数
  static Foo from(SegmentView segmentView, int dataSectionLengthInWords) =>
      Foo(segmentView, dataSectionLengthInWords);

  final SegmentView segmentView;
  final int dataSectionLengthInWords;

  int get bar => segmentView.getUInt8(0);

  [@override](/user/override)
  String toString() => 'Foo(bar: $bar)';
}