Regenerate Elixir modules from protobuf schema at the specified URL. Depends on nix package manager.

protobuf_regenerate.sh

#! /usr/bin/env nix-shell
#! nix-shell -i bash -p elixir_1_8 erlang protobuf curl
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-19.03.tar.gz

## Adapted from directions at https://github.com/tony612/protobuf-elixir

# lives at ./script/protobuf_regenerate.sh

set -ex

TARGET_DIR="$(dirname "$0")/../lib"
SCHEMA_URL="$1"
SCHEMA_FILE="${TARGET_DIR}/schema.proto"

# install protoc-gen-elixir plugin to ~/.mix/escripts/
mix escript.install --force hex protobuf

# download protobuf schema
curl "$SCHEMA_URL" > "$SCHEMA_FILE"

# generate elixir modules
protoc --proto_path="$TARGET_DIR" \
       --elixir_out="$TARGET_DIR" \
       --plugin="protoc-gen-elixir=$HOME/.mix/escripts/protoc-gen-elixir" \
       "$SCHEMA_FILE"

regenerate.ex

# lives at ./lib/mix/tasks/protobuf/regenerate.ex

defmodule Mix.Tasks.Protobuf.Regenerate do
  use Mix.Task

  @default_schema_url "FIXME"

  @moduledoc """
  Fetches a protobuf schema and regenerates modules.

      mix protobuf.regenerate [URL]

  The protobuf schema URL is downloaded to ./lib/schema.proto. Then Elixir
  modules are generated to ./lib/schema.pb.ex.

  When URL is omitted it defaults to #{@default_schema_url}.

  *Notice*: This task assumes the [nix package
  manager](https://nixos.org/nix/) is installed.
  """

  @shortdoc "Fetches protobuf schema and regenerates modules."
  def run([url]) do
    script_path = Path.join([File.cwd!(), "script", "protobuf_regenerate.sh"])
    System.cmd(script_path, [url], into: IO.stream(:stdio, :line), stderr_to_stdout: true)
  end

  def run([]), do: run([@default_schema_url])
end