# Elixir Protocol Buffer 

**Warning:** only protocol buffers 3 is supported. Use [protobuf-elixir](https://github.com/tony612/protobuf-elixir) if you need support for version 2 (protobuf-elixir was a major inspiration for this project).

This is a protocol buffer encoder and decoder. Its goal is to be fast at the cost of larger generated files. This is achieved by generate a significant part of the encoding and decoding logic at generation time with the protoc plugin.

Encoding and decoding performance is ~3-4x times faster yhan protobuf-elixir. For example, if we take our test `%Everything` structure, which has all field types, including all array types (with 2 values per array) and a few maps, `pbuf` takes ~14µs to encode and ~24µs to decode, versus 66µs and 67µs. However, the .beam file is 19K vs 7K.

## Installation
Assuming you already have protoc installed, you'll want to run:

    $ mix escript.install hex pbuf

to install the pbuf elixir generator. This will place `protoc-gen-fast-elixir` in your `~/.mix/escript/` folder. This must be on your $PATH.

You can then generate elixir files using the `protoc` command with the `-fast-elixir_out=PATH` flag:

    protoc --fast-elixir_out=generated/ myschema.proto 

Note the name `fast-elixir_out`. This allows you to also have [protobuf](https://github.com/tony612/protobuf-elixir) installed in order to support proto2 syntax.

## Encoding
The generated code is normal Elixir modules with a `defstruct`. Use `new/1` to create new instances:

    user = Models.User.new(name: "leto", age: 2000)

And `Pbuf.encode!/1` and `Pbuf.encode_to_iodata!/1` to encode them:

    data = Pbuf.encode!(user)

Only structures generated by `protoc` can be passed to `encode!/1` and `encode_to_iodata!/1`; you cannot pass maps or other structures.

These functions will raise a `Pbuf.Encoder.Error` on invalid data (such as assigning a `float` to a `bool` field). There are currently no non-raising functions.

## Decoding
Decoding is done via `Pbuf.decode!/2`:
    
    user = Pbuf.decode!(Models.User, data)

As an alternative, you can also use: `Models.User.decode!(data)`.

Unlike encoding, there **are** non-raising versions of `decode!`:
  
    # or use Models.user.decode(data)
    case Pbuf.decode(Models.User, data) do
      {:ok, user} -> ...
      {:error, err} -> # err is a %Pbuf.Decode.Error{}
    end

Decoding truly invalid data (as opposed to simply unexpected types) can raise.

### Enumerations
A field declared as an `enum` should be set to the atom representation of the protocol buffer name, or the integer value. For example, a message defined as:

    message User {
      UserType type = 1;
    }

    enum UserType {
      USER_TYPE_UNKNOWN = 0;
      USER_TYPE_PENDING = 1;
      USER_TYPE_NORMAL = 2;
      USER_TYPE_DELETED = 3;
    }

Should be used as:

    user = User.new(type: :USER_TYPE_PENDING)
    # OR
    user = User.new(type: 1)

(casing is preserved from the proto file)

### Oneofs
The value of a oneof field must be set to a tuple where the first element is the name of the field and the second is the value. Given:

    message Event {
      oneof event_oneof {
        Commit commit = 1;
        Wiki wiki = 2;
      }
    }

Then valid values for `event_oneof` are: nil, `{:commit, Commit.t}` or `{:wiki, Wiki.t}`.


## What's Ugly?
There are two distinctly ugly parts of the code. The first is pretty much anything to do with `oneof` fields. The second is the decoding of maps.