# Protox
[](https://travis-ci.org/ahamez/protox) [](https://coveralls.io/github/ahamez/protox?branch=master) [](https://hex.pm/packages/protox) [](https://inch-ci.org/github/ahamez/protox)
Protox is a native Elixir library to work with Google's Protocol Buffers (aka protobuf), versions 2 and 3.
This library passes all the tests of the conformance checker provided by Google. See the Conformance section for more information.
# Prerequisites
Protox uses Google's `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 will generate 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's 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
Here's how to create a new message:
```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 iolist, not a binary. Such iolists 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
Here's how to 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/ahamez/protox#unknown-fields).
# Unknown Fields
If any unknown fields are encountered when decoding, they are kept in the decoded message.
It's possible to access them with the function `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.unknown_fields()
[{5, 2, <<121, 97, 121, 101>>}]
```
You must always use `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`.
You can use the generated `default/1` function to get the default value:
```elixir
use Protox,
schema: """
syntax = "proto2";
message Foo {
optional int32 a = 1 [default = 42];
}
"""
iex> Foo.default(:a)
{:ok, 42}
```
* For Protobuf 3, unset optional fields are mapped to their default values, as mandated by
the [Protobuf spec](https://developers.google.com/protocol-buffers/docs/proto3#default).
* 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's 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() \| integer()
message | struct()
# Conformance
The protox library has been tested using the conformance checker provided by Google. Note that only the binary part is tested as protox supports only this format. For instance, JSON tests are skipped.
Here's how to launch the conformance test:
* Get conformance-test-runner [sources](https://github.com/google/protobuf/archive/v3.12.1.tar.gz).
* Compile conformance-test-runner:
`tar xf protobuf-3.12.1.tar.gz && cd protobuf-3.12.1 && ./autogen.sh && ./configure && make -j && cd conformance && make -j`
* `mix protox.conformance --runner=/path/to/protobuf-3.12.1/conformance/conformance-test-runner`.
A report will be generated in a directory `conformance_report`.
If everything's fine, the following text should be displayed:
```
CONFORMANCE TEST BEGIN ====================================
CONFORMANCE SUITE PASSED: 1302 successes, 705 skipped, 0 expected failures, 0 unexpected failures.
CONFORMANCE TEST BEGIN ====================================
CONFORMANCE SUITE PASSED: 0 successes, 69 skipped, 0 expected failures, 0 unexpected failures.
```
You can alternatively launch these conformance tests with `mix test` by setting the `PROTOBUF_CONFORMANCE_RUNNER` environment variable and including the `conformance` tag:
```
PROTOBUF_CONFORMANCE_RUNNER=./protobuf-3.12.1/conformance/conformance-test-runner MIX_ENV=test mix test --include conformance
```
# Benchmark
```
MIX_ENV=benchmarks mix run benchmarks/run.exs
```
# 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.
