Codegen

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Use protoc with protobuf elixir plugin or using protobuf_generate hex package to generate the necessary files.

Write your protobuf file

syntax = "proto3";

package helloworld;

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greeting
message HelloReply {
  string message = 1;
}

// The greeting service definition.
service GreetingServer {
  rpc SayUnaryHello (HelloRequest) returns (HelloReply) {}
  rpc SayServerHello (HelloRequest) returns (stream HelloReply) {}
  rpc SayBidStreamHello (stream HelloRequest) returns (stream HelloReply) {}
}

Compile protos (protoc + elixir plugin)

The most basic way to compile protobuf files is by using the elixir plugin for the protoc compiler:

protoc --elixir_out=plugins=grpc:./lib -I./priv/protos helloworld.proto

See more detailed explanation here.

But you can also benefit from more advanced options if you use the protobuf_generator. This is especially useful for use with HTTP Transcoding:

mix protobuf.generate  \ 
  --include-path=priv/proto \ 
  --include-path=deps/googleapis  \ 
  --generate-descriptors=true \ 
  --output-path=./lib \ 
  --plugins=ProtobufGenerate.Plugins.GRPCWithOptions \ 
  google/api/annotations.proto google/api/http.proto helloworld.proto

See more detailed explanation here.