gRPC Elixir

gRPC Elixir is a full-featured Elixir implementation of the gRPC protocol, supporting unary and streaming RPCs, interceptors, HTTP transcoding, and TLS. This version adopts a unified stream-based model for all types of calls.

Table of contents

• Installation
• Protobuf Code Generation
• Server Implementation
  • Unary RPC using Stream API
  • Server-Side Streaming
  • Bidirectional Streaming
• Application Startup
• Client Usage
  • Basic Connection and RPC
  • Using Interceptors
  • Target Schemes and Resolvers
    • Supported formats
    • Example (DNS)
    • Example (Unix socket)
  • Compression and Metadata
  • Client Adapters
    • Using Mint Adapter
• HTTP Transcoding
• CORS
• Features
• Benchmark
• Contributing

Installation

The package can be installed as:

def deps do
  [
    {:grpc, "~> 0.11"},
    {:protobuf, "~> 0.14"}, # optional for import wellknown google types
    {:grpc_reflection, "~> 0.2"} # optional enable grpc reflection
  ]
end

Protobuf Code Generation

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

1. 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) {}
}

2. Compile protos (protoc + elixir plugin):

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

Server Implementation

All RPC calls must be implemented using the stream-based API, even for unary requests.

NOTE: The old API was deprecated based on GRPC.Server.send_reply/2 and direct struct returns was deprecated as of version 0.10.x.

Unary RPC using Stream API

defmodule HelloworldStreams.Server do
  use GRPC.Server, service: Helloworld.GreetingServer.Service

  alias GRPC.Stream

  alias Helloworld.HelloRequest
  alias Helloworld.HelloReply

  @spec say_unary_hello(HelloRequest.t(), GRPC.Server.Stream.t()) :: any()
  def say_unary_hello(request, _materializer) do
    GRPC.Stream.unary(request)
    |> GRPC.Stream.map(fn %HelloReply{} = reply ->
      %HelloReply{message: "[Reply] #{reply.message}"}
    end)
    |> GRPC.Stream.run()
  end
end

Server-Side Streaming

def say_server_hello(request, materializer) do
  Stream.repeatedly(fn ->
    index = :rand.uniform(10)
    %HelloReply{message: "[#{index}] Hello #{request.name}"}
  end)
  |> Stream.take(10)
  |> GRPC.Stream.from()
  |> GRPC.Stream.run_with(materializer)
end

Bidirectional Streaming

@spec say_bid_stream_hello(Enumerable.t(), GRPC.Server.Stream.t()) :: any()
def say_bid_stream_hello(request, materializer) do
  output_stream =
    Stream.repeatedly(fn ->
      index = :rand.uniform(10)
      %HelloReply{message: "[#{index}] Server response"}
    end)

  GRPC.Stream.from(request, join_with: output_stream)
  |> GRPC.Stream.map(fn
    %HelloRequest{name: name} -> %HelloReply{message: "Welcome #{name}"}
    other -> other
  end)
  |> GRPC.Stream.run_with(materializer)
end

The Stream API supports composable stream transformations via ask, map, run and other functions, enabling clean and declarative stream pipelines. For a complete list of available operators and detailed documentation, see GRPC.Stream.

---

Application Startup

Add the server supervisor to your application's supervision tree:

defmodule Helloworld.Application do
  @ false
  use Application

  @impl true
  def start(_type, _args) do
    children = [
      GrpcReflection,
      {
        GRPC.Server.Supervisor, [
          endpoint: Helloworld.Endpoint,
          port: 50051,
          start_server: true,
          # adapter_opts: [# any adapter-specific options like tls configuration....]
        ]
      }
    ]

    opts = [strategy: :one_for_one, name: Helloworld.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

Client Usage

This section demonstrates how to establish client connections and perform RPC calls using the Elixir gRPC client.

---

Basic Connection and RPC

iex> {:ok, channel} = GRPC.Stub.connect("localhost:50051")
iex> request = Helloworld.HelloRequest.new(name: "grpc-elixir")
iex> {:ok, reply} = channel |> Helloworld.GreetingServer.Stub.say_unary_hello(request)

---

Using Interceptors

Client interceptors allow you to add logic to the request/response lifecycle, such as logging, tracing, or authentication.

iex> {:ok, channel} =
...>   GRPC.Stub.connect("localhost:50051",
...>     interceptors: [GRPC.Client.Interceptors.Logger]
...>   )
iex> request = Helloworld.HelloRequest.new(name: "Alice")
iex> {:ok, reply} = channel |> Helloworld.GreetingServer.Stub.say_unary_hello(request)

---

Target Schemes and Resolvers

The connect/2 function supports URI-like targets that are resolved via the internal gRPC Resolver. You can connect using DNS, Unix Domain sockets, IPv4/IPv6, or even xDS-based endpoints.

Supported formats:

Scheme	Example	Description
dns://	"dns://example.com:50051"	Resolves via DNS A/AAAA records
ipv4:	"ipv4:10.0.0.5:50051"	Connects directly to an IPv4 address
unix:	"unix:/tmp/service.sock"	Connects via a Unix domain socket
xds:///	"xds:///my-service"	Resolves via xDS control plane (Envoy/Istio)
none	"127.0.0.1:50051"	Implicit DNS (default port 50051)

Example (DNS):

iex> {:ok, channel} = GRPC.Stub.connect("dns://orders.prod.svc.cluster.local:50051")
iex> request = Orders.GetOrderRequest.new(id: "123")
iex> {:ok, reply} = channel |> Orders.OrderService.Stub.get_order(request)

Example (Unix socket):

iex> {:ok, channel} = GRPC.Stub.connect("unix:/tmp/my.sock")

NOTE: When using DNS or xDS targets, the connection layer periodically refreshes endpoints.

---

Compression and Metadata

You can specify message compression and attach default headers to all requests.

iex> {:ok, channel} =
...>   GRPC.Stub.connect("localhost:50051",
...>     compressor: GRPC.Compressor.Gzip,
...>     headers: [{"authorization", "Bearer my-token"}]
...>   )

---

Client Adapters

By default, GRPC.Stub.connect/2 uses the Gun adapter. You can switch to Mint (pure Elixir HTTP/2) or other adapters as needed.

Using Mint Adapter

iex> GRPC.Stub.connect("localhost:50051",
...>   adapter: GRPC.Client.Adapters.Mint
...> )

You can configure adapter options globally via your application’s config:

# File: config/config.exs
config :grpc, GRPC.Client.Adapters.Mint,
  timeout: 10_000,
  transport_opts: [cacertfile: "/etc/ssl/certs/ca-certificates.crt"]

The accepted options are the same as Mint.HTTP.connect/4.

---

HTTP Transcoding

1. Adding grpc-gateway annotations to your protobuf file definition:

import "google/api/annotations.proto";
import "google/protobuf/timestamp.proto";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {
    option (google.api.http) = {
      get: "/v1/greeter/{name}"
    };
  }

  rpc SayHelloFrom (HelloRequestFrom) returns (HelloReply) {
    option (google.api.http) = {
      post: "/v1/greeter"
      body: "*"
    };
  }
}

2. Add protoc plugin dependency and compile your protos using protobuf_generate hex package:

In mix.exs:

def deps do
  [
    {:grpc, "~> 0.11"},
    {:protobuf_generate, "~> 0.1.3"}
  ]
end

And in your terminal:

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

3. Enable http_transcode option in your Server module

defmodule Helloworld.Greeter.Server do
  use GRPC.Server,
    service: Helloworld.Greeter.Service,
    http_transcode: true

  # callback implementations...
end

See full application code in helloworld_transcoding example.

CORS

When accessing gRPC from a browser via HTTP transcoding or gRPC-Web, CORS headers may be required for the browser to allow access to the gRPC endpoint. Adding CORS headers can be done by using GRPC.Server.Interceptors.CORS as an interceptor in your GRPC.Endpoint module, configuring it as described in the module documentation:

Example:

# Define your endpoint
defmodule Helloworld.Endpoint do
  use GRPC.Endpoint

  intercept GRPC.Server.Interceptors.Logger
  intercept GRPC.Server.Interceptors.CORS, allow_origin: "mydomain.io"
  run Helloworld.Greeter.Server
end

Features

• Various kinds of RPC:
  • Unary
  • Server-streaming
  • Client-streaming
  • Bidirectional-streaming
• HTTP Transcoding
• TLS Authentication
• Error Handling
• Interceptors
• Connection Backoff
• Data Compression
• gRPC Reflection

Benchmark

1. Simple benchmark by using ghz

2. Benchmark followed by official spec

Contributing

Your contributions are welcome!

Please open issues if you have questions, problems and ideas. You can create pull requests directly if you want to fix little bugs, add small features and so on. But you'd better use issues first if you want to add a big feature or change a lot of code.