# protobuf-elixir
[](https://hex.pm/packages/protobuf)
[](https://travis-ci.org/tony612/protobuf-elixir)
A pure Elixir implementation of [Google Protobuf](https://developers.google.com/protocol-buffers/)
## Why this instead of exprotobuf(gpb)?
It has some must-have and other cool features like:
1. A protoc [plugin](https://developers.google.com/protocol-buffers/docs/cpptutorial#compiling-your-protocol-buffers) 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](https://github.com/tony612/protobuf-elixir/blob/master/test/support/test_msg.ex))
3. Plugins support. Only [grpc](https://github.com/tony612/grpc-elixir) 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`:
```elixir
def deps do
[
{:protobuf, "~> 0.5.3"},
# Only for files generated from Google's protos.
# Can be ignored if you don't use Google's protos.
{:google_protos, "~> 0.1"}
]
end
```
## Features
* [x] Define messages with DSL
* [x] Decode basic messages
* [x] Skip unknown fields
* [x] Decode embedded messages
* [x] Decode packed and repeated fields
* [x] Encode messages
* [x] protoc plugin
* [x] map
* [x] Support default values
* [x] Validate values
* [x] Generate typespecs
* [x] oneof
## Usage
### Generate Elixir code
1. Install `protoc`(cpp) [here](https://github.com/google/protobuf/blob/master/src/README.md) 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:
```elixir
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
```elixir
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.
- Default values will be set by default in `decode`, which can be changed by `:use_default` option.
- Validation is done in `encode`. An error will be raised if the struct is invalid(like type is not matched).
### gRPC Support
If you write [services](https://developers.google.com/protocol-buffers/docs/proto#services) in protobuf, you can generate [gRPC](https://github.com/tony612/grpc-elixir) 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
```
## Sponsors
This project is being sponsored by [Tubi](https://tubitv.com/). Thank you!
<img src="https://user-images.githubusercontent.com/1253659/37473536-4db44048-28a9-11e8-90d5-f8a2f5a8d53c.jpg" height="80">
## Acknowledgements
Many thanks to [gpb](https://github.com/tomas-abrahamsson/gpb) and
[golang/protobuf](https://github.com/golang/protobuf) as good examples of
writing Protobuf decoder/encoder.
