better_protoc_plugin

An opinionated, "new and improved" protobuf protoc compiler plugin used to generate Dart code with real Dart enums, message interfaces, automatic DateTime/Duration conversion, etc.

TLDR: Usage

Simplest way, If activated globally:

dart pub global activate better_protoc_plugin

# => Activated better_protoc_plugin 1.2.2

cd $HOME/myproject

# Notice the `better_protos` option in addition to `gprc:path...`.
# Assumes .proto files raae in `$HOME/myproject/proto`.
# You must explicitly include any google/protobuf/.proto files
# because unfortunately `protoc` doesn't understand wildcards on those.
protoc --dart_out=better_protos,grpc:path/to/generated \
    -Iproto \
    proto/* \
    -I$HOME/myproject/proto \
    $HOME/myproject/proto/* \
    google/protobuf/timestamp.proto \
    google/protobuf/duration.proto

From source, if cloned from GitHub into $HOME/better_protoc_plugin:

cd $HOME/better_protoc_plugin

make

cd $HOME/myproject

# Notice the `better_protos` option in addition to `gprc:path...`.
# Assumes .proto files raae in `$HOME/myproject/proto`.
# You must explicitly include any google/protobuf/.proto files
# because unfortunately `protoc` doesn't understand wildcards on those.
protoc --plugin=$HOME/better_protoc_plugin/bin/protoc-gen-dart \
    --dart_out=better_protos,grpc:path/to/generated \
    --proto_path=$HOME/better_protoc_plugin/protos \
    -Iproto \
    proto/* \
    -I$HOME/myproject/proto \
    $HOME/myproject/proto/* \
    google/protobuf/timestamp.proto \
    google/protobuf/duration.proto

Latest merged google/protobuf.dart upstream commit:

LATEST_UPSTREAM_COMMIT=96d9522

To compare:

$ make compare-upstream

After merging in changes, update LATEST_UPSTREAM_COMMIT variable in Makefile and this README to the latest commit. NOTE: we only care about the protoc_plugin subdirectory of the upstream repo (which is added as a git submodule to this project for easy comparison).

Forked from Google's protoc_plugin v22.0.0-dev @96d9522

Premise: The reason I created this fork is to make it easier to use protobuf with Dart backends/database ORMs by generating interfaces, because having to create separate database model definitions without the type safety of interfaces is extra work and error prone. Heck, protoc_plugin generates your backend services and client stubs for you! Why not go all the way?

This fork improves the generators by adding interface classes, additional convenience wrappers/converters, and addressing several other open issues, without changing the underlying protocols.

• additional abstract interface class with typed getters generated for each message:
  • interface name prefixed with I;
  • useful for implementing strongly-typed ORM classes;
• dart:core.DateTime and dart:core.Duration setters/getters and conversion for protobuf.Timestamp and protobuf.Duration fields (google/protobuf.dart#792):
  • DateTime uses built-in protobuf TimeStampMixin converters;
• Dart null safety (nullable optionals) for non-required/presence fields, with getter/setter wrappers (google/protobuf.dart#493):
  • getters use has{Field}() to check for presence;
  • setting a field to null calls clearField();
  • not used for required/non-presence, repeated, or map fields;
• real Dart enums instead of classes with static constants (google/protobuf.dart#862):
  • generates proper Dart camelCased enum values with conversion to/from CONSTANT_CASE protobuf values (google/protobuf.dart#372);

Bugfixes / PRs welcomed.

Please, Google Dart/Flutter Team, it would be great to see some of these features in the official dart protoc generator.

I will try to pull in any generator changes/improvements from google/protobuf.dart. Hopefully eventually we will see better support for Dart interfaces, optionals, enums, and native type conversions so it's easier to use protobuf with Dart backends & ORMs.

I intend to keep this updated and use in my production projects in the meantime.

Testing

$ dart pub get
$ make run-tests

Original protoc_plugin README:

This repository provides a Dart 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. protoc 3.0.0 or above is required.

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

How to build

Make sure you have dart executable in your PATH. See the Dart installation instructions for details.

If you encounter any issues while following the instructions below, please make sure you have the latest version of Dart installed.

The recommended way is to activate the latest published version of the plugin:

$ dart pub global activate better_protoc_plugin

Make sure you have ~/.pub-cache/bin in your PATH.

This method installs a Dart script and requires presence of dart executable in your PATH.

To build from the source:

• Run dart pub get in better_protoc_plugin directory
• Add better_protoc_plugin/bin to your PATH, or pass the path to better_protoc_plugin/bin/protoc-gen-dart to protoc's --plugin option.

The protoc-gen-dart executable is a Dart script and requires presence of dart executable in your PATH.

To build a standalone executable from the source:

• Run dart pub get in better_protoc_plugin
• Build standalone executable with dart compile exe bin/better_protoc_plugin.dart in better_protoc_plugin

The generated executable does not require a dart executable to run. You should copy the generated executable better_protoc_plugin/bin/better_protoc_plugin.exe to your PATH with name protoc-gen-dart, or pass the path to it to protoc's --plugin option when invoking protoc.

How to use

Once you have protoc-gen-dart in the PATH the protocol buffer compiler can be invoked like this to generate Dart for the proto file test.proto:

$ protoc --dart_out=. test.proto

If you don't want to add protoc-gen-dart to PATH, you can specify the path to it like this:

$ protoc --dart_out=. test.proto --plugin=<path to plugin executable>

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 individual 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 grpc Headers

To generate code for grpc, you will need to pass in the grpc option:

--dart_out="grpc:."

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 libraries combining object definitions from several .proto libraries into one.

The best way to approach 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

syntax = "proto3";

message M1 {
  string a = 1;
}

and m2.proto containing

syntax = "proto3";

message M2 {
  string b = 1;
}

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 some 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 dart pub get and then make run-tests.

Useful references

• Main Dart site
• Main protobuf site
• Protobuf runtime support project