Protoc compiler Dart plugin
This application provides a plugin for protoc compiler which generates pure Dart library to deal with protobufs.
Please, do not forget that generated libraries depend on runtime support library which can be found here.
How to build and use
Note: currently the workflow is POSIX-oriented.
To build standalone protoc
plugin:
- run
pub get
to install all dependecies - run
make build-plugin
. That will create a fileout/protoc-gen-dart
which is a plugin - Now you can use it either by adding into
PATH
or passing directly withprotoc
'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 out/protoc-gen-dart
are in the
PATH
the protocol buffer compiler can be invoked to generate like this:
$ protoc --dart_out=. test.proto
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>:."
Option for setting the name of field accessors
The following message definition has the field name has_field
.
message MyMessage {
optional string has_field = 1;
}
This poses the problem, that the Dart class will have a getter and a
setter called hasField
. This conflicts with the method hasField
which is already defined on the superclass GeneratedMessage
.
To work around this problem the option field_name
can be
used. Option field_name
takes two values separated by the vertical
bar. The first value is the full name of the field and the second
value is the name of the field in the generated Dart code. Passing the
following option:
--dart_out="field_name=MyMessage.has_field|HasFld:."
Will generate the following message field accessors:
String get hasFld => getField(1);
void set hasFld(String v) { setField(1, v); }
bool hasHasFld() => hasField(1);
void clearHasFld() => clearField(1);
Using protocol buffer libraries to build new libraries
The protocol buffer compiler produces one library 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
Remember to run the tests. That is as easy as make run-tests
.
The default way of running the Dart protoc plugin is through the
generated out/protoc-gen-dart
script. However when run this way the
Dart code is assembled into one large Dart file using dart2dart. To
run with the actual source in the repository create an executable
script called protoc-gen-dart
with the following content:
#! /bin/bash
dart bin/protoc_plugin.dart
When running protoc just ensure that this script is first when PATH is
searched. If the script is in the current directory run protoc
like
this:
$ PATH=.:$PATH protoc --dart_out=. test.proto
It is also possible to call the script something else than
protoc-gen-dart
and then refer directly to it using the --plugin
option. If the script is called dart-plugin
run protoc
like this:
$ protoc --plugin=protoc-gen-dart=./plugin --dart_out=. test.proto