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protobuf-elixir

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A pure Elixir implementation of Google Protobuf.

Why this instead of exprotobuf(gpb)?

It has some must-have and other cool features like:

  1. A protoc plugin to generate Elixir code just like what other official libs do, which is powerful and reliable.
  2. Generate simple and explicit code with the power of Macro. See test/support/test_msg.ex.
  3. Plugins support. Only grpc is supported now.
  4. Use structs for messages instead of Erlang records.
  5. Support Typespec in generated code.

Installation

The package can be installed by adding :protobuf to your list of dependencies in mix.exs:

def deps do
  [
    {:protobuf, "~> 0.7.1"},
    # Only for files generated from Google's protos.
    # Can be ignored if you don't use Google's protos.
    # Or you can generate the code by yourself.
    {:google_protos, "~> 0.1"}
  ]
end

Features

  • Define messages with DSL
  • Decode basic messages
  • Skip unknown fields
  • Decode embedded messages
  • Decode packed and repeated fields
  • Encode messages
  • protoc plugin
  • map
  • Support default values
  • Validate values
  • Generate typespecs
  • oneof
  • (proto2) Extension (Experiment, see Protobuf.Extension)

Usage

Generate Elixir code

  1. Install protoc(cpp) here or brew install protobuf on MacOS.

  2. Install protoc plugin protoc-gen-elixir for Elixir . NOTE: You have to make sure protoc-gen-elixir(this name is important) is in your PATH.

    $ mix escript.install hex protobuf
  3. Generate Elixir code using protoc

    $ protoc --elixir_out=./lib helloworld.proto
  4. Files helloworld.pb.ex will be generated, like:

    defmodule Helloworld.HelloRequest do
      use Protobuf, syntax: :proto3
    
      @type t :: %__MODULE__{
        name: String.t
      }
      defstruct [:name]
    
      field :name, 1, type: :string
    end
    
    defmodule Helloworld.HelloReply do
      use Protobuf, syntax: :proto3
    
      @type t :: %__MODULE__{
        message: String.t
      }
      defstruct [:message]
    
      field :message, 1, type: :string
    end

Encode and decode in your code

struct = Foo.new(a: 3.2, c: Foo.Bar.new())
encoded = Foo.encode(struct)
struct = Foo.decode(encoded)

Note:

  • You should use YourModule.new instead of using the struct directly because default values will be set for all fields.
  • Validation is done in encode. An error will be raised if the struct is invalid(like type is not matched).

Descriptor support

If you use any custom options in your protobufs then to gain access to them you'll need to include the raw descriptors in the generated modules. You can generate the descriptors by passing gen_descriptors=true in --elixir_out.

The descriptors will be available on each module from the descriptor/0 function.

$ protoc --elixir_out=gen_descriptors=true:./lib/ *.proto
$ protoc --elixir_out=gen_descriptors=true,plugins=grpc:./lib/ *.proto

gRPC Support

If you write services in protobuf, you can generate gRPC code by passing plugins=grpc in --elixir_out:

$ protoc --elixir_out=plugins=grpc:./lib/ *.proto

Tips for protoc

Custom protoc-gen-elixir name or path using --plugin:

$ protoc --elixir_out=./lib --plugin=./protoc-gen-elixir *.proto

Pass -I argument if you import other protobuf files:

$ protoc -I protos --elixir_out=./lib protos/hello.proto

Custom options

Since extensions(Protobuf.Extension) is supported now, some options are defined, like custom module_prefix.

  1. Copy src/elixirpb.proto to your protos path.

  2. Import elixirpb.proto and use the options.

    syntax = "proto2";
    
    package your.pkg;
    
    import "elixirpb.proto";
    
    option (elixirpb.file).module_prefix = "Foo.Bar";
  3. Generate code as before

More options will be added in the future, see elixirpb.proto comments for details.

Tests

mix test

Sponsors

Acknowledgements

Many thanks to gpb and golang/protobuf as good examples of writing Protobuf decoder/encoder.