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protoc_plugin

README.md

Dart plugin for the protoc compiler

pub package

This repository provides a plugin for the protoc compiler. It generates Dart files for working with data in protocol buffers format.

Requirements

To compile a .proto file, you must use the 'protoc' command which is installed separately. Protobuf 3.0.0 or above is required.

The generated files are pure Dart code that run in either in the Dart VM or in a browser (using dart2js). They depend the protobuf Dart package. A Dart project that includes generated files should add "protobuf" to its pubspec.yaml file.

How to build and use

Note: currently the workflow is POSIX-oriented.

To build standalone protoc plugin:

  • run pub install to install all dependencies
  • Now you can use the plugin either by adding the bin directory to your PATH, or passing it directly with protoc's --plugin option.

Please, remember that the plugin is pure Dart script and requires the presence of dart executable in your PATH.

When both the dart executable and bin/protoc-gen-dart are in the PATH the protocol buffer compiler can be invoked to generate like this:

$ protoc --dart_out=. test.proto

Optionally using pub global

$ pub global activate protoc_plugin

And then add .pub-cache/bin in your home dir to your PATH if you haven't already.

This will activate the latest published version of the plugin. If you wish to use a local working copy, use

$ pub global activate -s path <path/to/your/dart-protoc-plugin>

Options to control the generated Dart code

The protocol buffer compiler accepts options for each plugin. For the Dart plugin, these options are passed together with the --dart_out option. The individial options are separated using comma, and the final output directive is separated from the options using colon. Pass options <option 1> and <option 2> like this:

--dart_out="<option 1>,<option 2>:."

Generating Code Info

The plugin includes the generate_kythe_info option, which, if passed at run time, will make the plugin generate metadata files alongside the .dart files generated for the proto messages and their enums. Pass this along with the other dart_out options:

--dart_out="generate_kythe_info,<other options>:."

Using protocol buffer libraries to build new libraries

The protocol buffer compiler produces several files for each .proto file it compiles. In some cases this is not exactly what is needed, e.g one would like to create new libraries which exposes the objects in these libraries or create new librares combining object definitions from several .proto libraries into one.

The best way to aproach this is to create the new libraries needed and re-export the relevant protocol buffer classes.

Say we have the file m1.proto with the following content

message M1 {
  optional string a;
}

and m2.proto containing

message M2 {
  optional string b;
}

Compiling these to Dart will produce two libraries in m1.pb.dart and m2.pb.dart. The following code shows a library M which combines these two protocol buffer libraries, exposes the classes M1 and M2 and adds som additional methods.

library M;

import "m1.pb.dart";
import "m2.pb.dart";

export "m1.pb.dart" show M1;
export "m2.pb.dart" show M2;

M1 createM1() => new M1();
M2 createM2() => new M2();

Hacking

Here are some ways to get protoc:

  • Linux: apt-get install protobuf-compiler
  • Mac homebrew: brew install protobuf

If the version installed this way doesn't work, an alternative is to compile protoc from source.

Remember to run the tests. That is as easy as make run-tests.

Useful references