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Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
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Very, very alpha implementation of Twirp service generation for Haskell.

This project provides a number of things:

  1. A protoc plugin for generating a Haskell Twirp service (based on Servant) for Services defined in a proto file.
  2. A haskell library, twirp for quickly serving up the generated application.

It requires the use of proto-lens to generate haskell datatypes from proto messages.

An example, end-to-end application is included in app.


  1. Install protoc (e.g., brew install protoc)
  2. Install the required protoc plugins:
    • cabal install proto-lens-protoc
    • go get github.com/tclem/twirp-haskell/protoc-gen-twirp_haskell
    • go get github.com/tclem/proto-lens-jsonpb/protoc-gen-jsonpb_haskell


Use the protoc plugin to generate a twirp service and associated protobuf types from a proto file.

protoc -I=. --proto_path=./proto \
  --plugin=protoc-gen-haskell=`which proto-lens-protoc` --haskell_out=./app \
  --jsonpb_haskell_out=./app \
  --plugin=protoc-gen-twirp_haskell=./script/run-twirp_haskell --twirp_haskell_out=./app/Twirp/Example/Haberdasher \

The result is a couple of files that describe your service. First, here are the types that define a Servant API:

-- Code generated by protoc-gen-twirp_haskell 0.1.0, DO NOT EDIT.
{-# LANGUAGE TypeOperators #-}
module Twirp.Example.Haberdasher.Haberdasher where

import Servant
import Twirp

import Proto.Haberdasher

--  This is an example set of twirp services.

type HaberdasherAPI
  =    "twirp" :> "twirp.example.haberdasher.Haberdasher" :> HaberdasherService
  :<|> "twirp" :> "twirp.example.haberdasher.Health" :> HealthService

--  Haberdasher service makes hats for clients.
type HaberdasherService
  --  MakeHat produces a hat of mysterious, randomly-selected color!
  =    "MakeHat" :> ReqBody [Protobuf, JSON] Size :> Post '[Protobuf, JSON] Hat
  --  Get paid
  :<|> "GetBill" :> ReqBody [Protobuf, JSON] Hat :> Post '[Protobuf, JSON] Bill

--  Health check service
type HealthService
  =    "Check" :> ReqBody [Protobuf, JSON] Ping :> Post '[Protobuf, JSON] Pong

The datatypes are defined in [Proto.Haberdasher](app/Proto/Haberdasher.hs).

Plugging this into an existing warp/wai server is straightforward. See [app/Main.hs](app/Main.hs) for the full details:

type RequestID = String

type API
  = Header "X-Request-Id" RequestID
  :> HaberdasherAPI

main :: IO ()
main = run 8003 app

app :: Application
app = twirpErrorResponses apiApp

apiApp :: Application
apiApp = serve (Proxy :: Proxy API) server

server :: Server API
server _requestID = (makeHat :<|> getBill) :<|> checkHealth