capnproto_dart

Reads and writes Cap'n Proto messages in Dart.
If you're building an app with Capn' Proto RPC, you usually don't need to depend on this package directly — see capnproto_dart_rpc.
Use capnproto_dart directly when you're reading or writing Cap'n Proto messages without RPC.

How the pieces fit together

• capnpc_dart
  a compiler plugin that turns your .capnp schema into Dart classes.
• capnproto_dart (this package)
  the runtime generated classes use to serialize and deserialize.
• capnproto_dart_rpc
  adds networked RPC (calling methods on a remote object) on top of both.

Install

Add this package and the code-generation builder to pubspec.yaml:

dependencies:
  capnproto_dart: ^0.1.0

dev_dependencies:
  build_runner: ^2.4.13
  capnpc_dart_builder: ^0.1.0

dart pub get

The official capnp compiler must also be installed and on PATH — capnpc_dart_builder shells out to it to parse your schemas.

Build and read a message

build_runner only looks under lib/, so put your schema at, say, lib/schema/hello.capnp, then run dart run build_runner build to generate lib/schema/hello.capnp.dart:

import 'package:capnproto_dart/capnproto_dart.dart';
import 'schema/hello.capnp.dart';

void main() {
  final builder = MessageBuilder();
  final greeting = builder.initRoot(greetingFactory);
  greeting.name = 'World';

  final bytes = builder.serialize();

  final reader = MessageReader.deserialize(bytes);
  final decoded = reader.getRoot(greetingFactory);
  print(decoded.name); // World
}

That's the core workflow: build a message, serialize it to bytes, and read it back.
The generated factory is always named <StructName>Factory (lower camelCase), one per struct in your schema.

Also available

You likely won't need these on day one, but they're here when you do:

• Packed encoding (serializePacked/deserializePacked)
  a smaller wire format for the same messages.
• Message streams (MessageStream)
  read or write several messages back-to-back over a socket or file.
• Text format (encodeText/decodeText)
  human-readable output, handy for debugging or test fixtures.
• Dynamic access
  inspect a message without knowing its schema type at compile time.

See the serialization guide and API documentation for details on all of the above.