# Protox
[](https://travis-ci.org/EasyMile/protox) [](https://coveralls.io/github/EasyMile/protox?branch=master) [](https://hex.pm/packages/protox) [](http://inch-ci.org/github/EasyMile/protox)
Protox is a native Elixir library to work with Google's Protocol Buffers (version 2 and 3).
# Conformance
This library has been tested using the conformance checker provided by Google. More information at https://github.com/EasyMile/protox-conformance.
# Prerequisites
Protox uses Google `protoc` (>= 3.0) to parse `.proto` files. It must be available in `$PATH`. This dependency is only required at compile time.
You can get it [here](https://github.com/google/protobuf).
# Usage
## From a Textual Description
```elixir
defmodule Bar do
use Protox, schema: """
syntax = "proto3";
package fiz;
message Baz {
}
message Foo {
int32 a = 1;
map<int32, Baz> b = 2;
}
"""
end
```
The previous example generates two modules: `Fiz.Baz` and `Fiz.Foo`.
Note that the module in which the `Protox` macro is called is completely ignored.
## From Files
```elixir
defmodule Foo do
@external_resource "./defs/foo.proto"
@external_resource "./defs/bar.proto"
@external_resource "./defs/baz/fiz.proto"
use Protox, files: [
"./defs/foo.proto",
"./defs/bar.proto",
"./defs/baz/fiz.proto",
]
end
```
## Working With Namespaces
It is possible to prepend a namespace to all generated modules:
```elixir
defmodule Bar do
use Protox, schema: """
syntax = "proto3";
enum Enum {
FOO = 0;
BAR = 1;
}
""",
namespace: Namespace
end
```
In this case, the module `Namespace.Enum` is generated.
## Specify import path
An import path can be specified using the `path:` option:
```elixir
defmodule Baz do
@external_resource "./defs/prefix/foo.proto"
@external_resource "./defs/prefix/bar/bar.proto"
use Protox,
files: [
"./defs/prefix/foo.proto",
"./defs/prefix/bar/bar.proto",
],
path: "./defs"
end
```
It corresponds to the `-I` option of `protoc`.
## Encode
```elixir
iex> %Fiz.Foo{a: 3, b: %{1 => %Fiz.Baz{}}} |> Protox.Encode.encode()
[[[], "\b", <<3>>], <<18>>, <<4>>, "\b", <<1>>, <<18>>, <<0>>]
```
Note that `Protox.Encode.encode/1` returns an IO list, not a binary. Such IO lists can be used
directly with files or sockets write operations.
However, you can use `:binary.list_to_bin/1` to get a binary:
```elixir
iex> %Fiz.Foo{a: 3, b: %{1 => %Fiz.Baz{}}} |> Protox.Encode.encode() |> :binary.list_to_bin()
<<8, 3, 18, 4, 8, 1, 18, 0>>
```
## Decode
```elixir
iex> <<8, 3, 18, 4, 8, 1, 18, 0>> |> Fiz.Foo.decode()
{:ok,
%Fiz.Foo{__uf__: [], a: 3,
b: %{1 => %Fiz.Baz{__uf__: []}}}}
```
The `__uf__` field is explained in the section [Unknown fields](https://github.com/EasyMile/protox#unknown-fields).
# Unknown Fields
If any unknown field is encountered when decoding, it is kept in the decoded message.
It is possible to access them with the function `get_unknown_fields/1` defined with the message.
```elixir
iex> msg = <<8, 42, 42, 4, 121, 97, 121, 101, 136, 241, 4, 83>> |> Msg.decode!()
%Msg{a: 42, b: "", z: -42, __uf__: [{5, 2, <<121, 97, 121, 101>>}]}
iex> msg |> Msg.get_unknown_fields()
[{5, 2, <<121, 97, 121, 101>>}]
```
You must always use `get_unknown_fields/1` as the name of the field
(e.g. `__uf__`) is generated at compile time to avoid collision with the actual
fields of the Protobuf message.
This function returns a list of tuples `{tag, wire_type, bytes}`.
# Unsupported Features
* Protobuf 3 JSON mapping
* groups
* rpc
Furthermore, all options other than `packed` and `default` are ignored.
# Implementation Choices
* Required fields (Protobuf 2): an error is raised when decoding a message with a missing required
field.
* When decoding enum aliases, the last encountered constant is used.
For instance, in the following example, `:BAR` is always used if the value `1` is read
on the wire.
```protobuf
enum E {
option allow_alias = true;
FOO = 0;
BAZ = 1;
BAR = 1;
}
```
* Unset optionals
* For Protobuf 2, unset optional fields are mapped to `nil`.
* For Protobuf 3, unset optional fields are mapped to their default values, as mandated by
the Protobuf spec.
* Messages and enums names: non camel case names are converted using the
[`Macro.camelize/1`](https://hexdocs.pm/elixir/Macro.html#camelize/1) function.
Thus, in the following example, `non_camel` becomes `NonCamel`.
```protobuf
syntax = "proto3";
message non_camel {
}
message Camel {
non_camel x = 1;
}
```
# Types Mapping
The following table shows how Protobuf types are mapped to Elixir ones.
Protobuf | Elixir
-----------|--------------
int32 | integer()
int64 | integer()
uint32 | integer()
uint64 | integer()
sint32 | integer()
sint64 | integer()
fixed32 | integer()
fixed64 | integer()
sfixed32 | integer()
sfixed64 | integer()
float | float(), :infinity, :'-infinity', :nan
double | float(), :infinity, :'-infinity', :nan
bool | boolean()
string | String.t
bytes | binary()
map | %{}
oneof | {:field, value}
enum | atom()
message | struct()
# Credits
Both [gpb](https://github.com/tomas-abrahamsson/gpb) and
[exprotobuf](https://github.com/bitwalker/exprotobuf) were very useful in
understanding how to implement Protocol Buffers.
