HaskellのServantとPersistentでデータの簡易配信

README.md

HaskellのウェブフレームワークらしきServantで、 SQLiteのデータを配信できるようにする。

「ウェブフレームワークらしき」というのは、 JSONでやりとりするマイクロサービスを作るのはカンタンだが、 HTMLを返すのに一手間かかるという、 ウェブフレームワークらしからぬ仕様なので。 あと、Servantはウェブサーバだけでなく、 クライアント側の開発もサポートしている。 フルスタックではないし、これからもどこか不思議な方向を目指している感じ。
Haskell界隈で微妙に名前を聞いて、 シンプルで快速らしいのでやってみた。

Application、ServerやProxyなど、 普通とは違った意味で使われていて、最初戸惑う。 また、言語拡張されて、型の考え方もかなり特殊。 とはいえ、まずAPIを定義（ルーティングを定義）して、 後でそれを実装するようなServerを書くと考えれば、 一応一貫性があってわかりやすいかもしれない。
ただ、importや言語拡張の山で、 何も見ずに始めるのはほぼムリ （今回Persistentと合わせたので、余計ひどい）。 テンプレートから始めて、書き換えていくのが自然。

References

• Servantチュートリアル
• Persistent

Main.hs

import Data.Time
import Data.Aeson
import Control.Monad.Logger
import Control.Monad.IO.Class
import Control.Monad.Trans.Resource (runResourceT)
import GHC.Generics
import Network.Wai
import Network.Wai.Handler.Warp

import Servant
import Database.Persist
import Database.Persist.Quasi
import Database.Persist.TH
import Database.Persist.Sqlite

share [mkPersist sqlSettings, mkMigrate "migrateAll"]
  $(persistFileWith lowerCaseSettings "models")

instance ToJSON SensorData

-- routing
type CombinedAPI = HomeAPI 
              :<|> "data" :> DataAPI
type HomeAPI = Get '[JSON] ()
type DataAPI = Get '[JSON] [SensorData]

main :: IO ()
main = runStderrLoggingT $ 
  withSqlitePool "log.sqlite" 5 $ \pool -> liftIO $ do
    doMigrate pool
    run 8080 (app1 pool)

app1 :: ConnectionPool -> Application
app1 pool = serve api $ combinedServer pool

api :: Proxy CombinedAPI
api = Proxy

-- Server **APIs
combinedServer :: ConnectionPool -> Server CombinedAPI
combinedServer pool = homeServer 
                 :<|> dataServer pool

homeServer :: Server HomeAPI
homeServer = throwError err302'
  where err302' = err302 {errHeaders = [("Location", "http://localhost:8080/data")]}

dataServer :: ConnectionPool -> Server DataAPI
dataServer pool = do
  let select = selectList [] [Desc SensorDataCreated, LimitTo 50]
  items <- runSqlPool select pool
  return [value | Entity _ value <- items]

-- misc
doMigrate :: ConnectionPool -> IO ()
doMigrate pool = runResourceT $ 
  runSqlPool (runMigration migrateAll) pool

models

SensorData
  created UTCTime
  val1 Int
  val2 Int
  val3 Int
  val4 Int
  deriving Show Read Eq Ord Generic

persistent-data.cabal

name:           persistent-data
version:        0.1
category:       Web
build-type:     Simple
cabal-version:  >= 1.20

executable persistent-data-server
  main-is: Main.hs
  ghc-options: -Wall
  default-language: Haskell2010
  build-depends:
      base
    , aeson
    , containers
    , servant-server
    , wai
    , warp
    , time
    , monad-logger
    , resourcet
    , persistent
    , persistent-template
    , persistent-sqlite

  default-extensions:
      OverloadedStrings
    , GADTs                      
    , GeneralizedNewtypeDeriving 
    , MultiParamTypeClasses      
    , QuasiQuotes                
    , TemplateHaskell            
    , TypeFamilies 
    , DataKinds
    , DeriveGeneric
    , TypeOperators

sample.sql

PRAGMA foreign_keys=OFF;
BEGIN TRANSACTION;
CREATE TABLE "sensor_data"("id" INTEGER PRIMARY KEY,"created" TIMESTAMP NOT NULL,"val1" INTEGER NOT NULL,"val2" INTEGER NOT NULL,"val3" INTEGER NOT NULL,"val4" INTEGER NOT NULL);
INSERT INTO "sensor_data" VALUES(1,'2017-01-03T02:30:02.457641',226,1,18,241);
INSERT INTO "sensor_data" VALUES(2,'2017-01-03T02:30:02.574624',111,214,142,110);
INSERT INTO "sensor_data" VALUES(3,'2017-01-03T02:30:02.677518',97,195,116,65);
INSERT INTO "sensor_data" VALUES(4,'2017-01-03T02:30:02.778752',47,32,78,79);
INSERT INTO "sensor_data" VALUES(5,'2017-01-03T02:30:02.889444',65,177,89,128);
INSERT INTO "sensor_data" VALUES(6,'2017-01-03T02:30:02.994967',159,17,129,227);
INSERT INTO "sensor_data" VALUES(7,'2017-01-03T02:30:03.097499',143,252,162,134);
INSERT INTO "sensor_data" VALUES(8,'2017-01-03T02:30:03.202987',102,67,215,59);
INSERT INTO "sensor_data" VALUES(9,'2017-01-03T02:30:03.307562',89,240,183,241);
INSERT INTO "sensor_data" VALUES(10,'2017-01-03T02:30:03.41304',16,38,169,150);
INSERT INTO "sensor_data" VALUES(11,'2017-01-03T02:30:03.517555',70,127,18,29);
INSERT INTO "sensor_data" VALUES(12,'2017-01-03T02:30:03.623054',169,118,37,225);
INSERT INTO "sensor_data" VALUES(13,'2017-01-03T02:30:03.743016',164,21,65,201);
INSERT INTO "sensor_data" VALUES(14,'2017-01-03T02:30:03.847569',21,59,117,101);
INSERT INTO "sensor_data" VALUES(15,'2017-01-03T02:30:03.953031',235,212,67,9);
INSERT INTO "sensor_data" VALUES(16,'2017-01-03T02:30:04.057545',246,237,177,144);
INSERT INTO "sensor_data" VALUES(17,'2017-01-03T02:30:04.163005',170,149,171,239);
INSERT INTO "sensor_data" VALUES(18,'2017-01-03T02:30:04.267547',45,107,221,229);
INSERT INTO "sensor_data" VALUES(19,'2017-01-03T02:30:04.373084',40,111,42,207);
INSERT INTO "sensor_data" VALUES(20,'2017-01-03T02:30:04.477527',33,90,16,157);
INSERT INTO "sensor_data" VALUES(21,'2017-01-03T02:30:04.583116',67,94,185,22);
INSERT INTO "sensor_data" VALUES(22,'2017-01-03T02:30:04.687612',155,33,43,207);
INSERT INTO "sensor_data" VALUES(23,'2017-01-03T02:30:04.788784',143,77,243,116);
INSERT INTO "sensor_data" VALUES(24,'2017-01-03T02:30:04.890848',231,27,155,243);
INSERT INTO "sensor_data" VALUES(25,'2017-01-03T02:30:04.996366',86,77,26,64);
INSERT INTO "sensor_data" VALUES(26,'2017-01-03T02:30:05.097581',12,160,62,26);
INSERT INTO "sensor_data" VALUES(27,'2017-01-03T02:30:05.203052',210,150,237,164);
INSERT INTO "sensor_data" VALUES(28,'2017-01-03T02:30:05.30758',215,47,152,210);
INSERT INTO "sensor_data" VALUES(29,'2017-01-03T02:30:05.413122',3,28,156,97);
INSERT INTO "sensor_data" VALUES(30,'2017-01-03T02:30:05.517673',206,233,123,173);
INSERT INTO "sensor_data" VALUES(31,'2017-01-03T02:30:05.62314',59,158,158,28);
INSERT INTO "sensor_data" VALUES(32,'2017-01-03T02:30:05.72761',77,236,29,166);
INSERT INTO "sensor_data" VALUES(33,'2017-01-03T02:30:05.833085',176,17,67,152);
INSERT INTO "sensor_data" VALUES(34,'2017-01-03T02:30:05.937641',248,174,157,231);
INSERT INTO "sensor_data" VALUES(35,'2017-01-03T02:30:06.043115',7,206,52,109);
INSERT INTO "sensor_data" VALUES(36,'2017-01-03T02:30:06.147595',83,121,124,98);
INSERT INTO "sensor_data" VALUES(37,'2017-01-03T02:30:06.253078',254,95,142,229);
INSERT INTO "sensor_data" VALUES(38,'2017-01-03T02:30:06.357602',116,94,70,170);
INSERT INTO "sensor_data" VALUES(39,'2017-01-03T02:30:06.463102',170,62,100,82);
INSERT INTO "sensor_data" VALUES(40,'2017-01-03T02:30:06.56773',56,126,175,127);
INSERT INTO "sensor_data" VALUES(41,'2017-01-03T02:30:06.668793',151,152,133,113);
INSERT INTO "sensor_data" VALUES(42,'2017-01-03T02:30:06.774283',147,56,137,212);
INSERT INTO "sensor_data" VALUES(43,'2017-01-03T02:30:06.874662',58,20,84,106);
INSERT INTO "sensor_data" VALUES(44,'2017-01-03T02:30:06.977668',155,16,234,243);
INSERT INTO "sensor_data" VALUES(45,'2017-01-03T02:30:07.078944',228,197,200,119);
INSERT INTO "sensor_data" VALUES(46,'2017-01-03T02:30:07.18442',103,70,199,209);
INSERT INTO "sensor_data" VALUES(47,'2017-01-03T02:30:07.287652',92,55,118,61);
INSERT INTO "sensor_data" VALUES(48,'2017-01-03T02:30:07.388988',53,119,186,181);
INSERT INTO "sensor_data" VALUES(49,'2017-01-03T02:30:07.494522',196,88,138,111);
INSERT INTO "sensor_data" VALUES(50,'2017-01-03T02:30:07.597694',23,75,240,190);
INSERT INTO "sensor_data" VALUES(51,'2017-01-03T02:30:07.708408',61,238,194,250);
INSERT INTO "sensor_data" VALUES(52,'2017-01-03T02:30:07.813902',196,8,62,140);
INSERT INTO "sensor_data" VALUES(53,'2017-01-03T02:30:07.917687',10,133,82,85);
INSERT INTO "sensor_data" VALUES(54,'2017-01-03T02:30:08.023168',4,117,79,42);
INSERT INTO "sensor_data" VALUES(55,'2017-01-03T02:30:08.127706',61,56,200,131);
INSERT INTO "sensor_data" VALUES(56,'2017-01-03T02:30:08.233189',92,34,229,206);
INSERT INTO "sensor_data" VALUES(57,'2017-01-03T02:30:08.337706',252,254,196,106);
INSERT INTO "sensor_data" VALUES(58,'2017-01-03T02:30:08.438824',65,93,206,175);
INSERT INTO "sensor_data" VALUES(59,'2017-01-03T02:30:08.544444',244,223,145,22);
INSERT INTO "sensor_data" VALUES(60,'2017-01-03T02:30:08.647798',70,75,71,209);
INSERT INTO "sensor_data" VALUES(61,'2017-01-03T02:30:08.753279',206,250,55,155);
INSERT INTO "sensor_data" VALUES(62,'2017-01-03T02:30:08.857783',101,62,125,205);
INSERT INTO "sensor_data" VALUES(63,'2017-01-03T02:30:08.96326',249,1,239,96);
INSERT INTO "sensor_data" VALUES(64,'2017-01-03T02:30:09.067798',244,116,127,29);
INSERT INTO "sensor_data" VALUES(65,'2017-01-03T02:30:09.173252',56,187,45,114);
INSERT INTO "sensor_data" VALUES(66,'2017-01-03T02:30:09.277765',60,51,112,17);
INSERT INTO "sensor_data" VALUES(67,'2017-01-03T02:30:09.383229',130,153,187,170);
INSERT INTO "sensor_data" VALUES(68,'2017-01-03T02:30:09.487748',222,170,107,88);
INSERT INTO "sensor_data" VALUES(69,'2017-01-03T02:30:09.59327',73,150,23,17);
INSERT INTO "sensor_data" VALUES(70,'2017-01-03T02:30:09.697762',203,196,128,11);
INSERT INTO "sensor_data" VALUES(71,'2017-01-03T02:30:09.803245',83,215,154,66);
INSERT INTO "sensor_data" VALUES(72,'2017-01-03T02:30:09.905638',7,195,232,155);
INSERT INTO "sensor_data" VALUES(73,'2017-01-03T02:30:10.007774',117,245,235,197);
INSERT INTO "sensor_data" VALUES(74,'2017-01-03T02:30:10.11333',108,107,37,144);
INSERT INTO "sensor_data" VALUES(75,'2017-01-03T02:30:10.217787',23,216,141,161);
INSERT INTO "sensor_data" VALUES(76,'2017-01-03T02:30:10.318941',165,248,164,208);
INSERT INTO "sensor_data" VALUES(77,'2017-01-03T02:30:10.424454',134,17,117,149);
INSERT INTO "sensor_data" VALUES(78,'2017-01-03T02:30:10.527784',154,19,43,245);
INSERT INTO "sensor_data" VALUES(79,'2017-01-03T02:30:10.633306',208,148,165,221);
INSERT INTO "sensor_data" VALUES(80,'2017-01-03T02:30:10.737805',102,16,120,0);
INSERT INTO "sensor_data" VALUES(81,'2017-01-03T02:30:10.839962',162,18,106,117);
INSERT INTO "sensor_data" VALUES(82,'2017-01-03T02:30:10.945544',139,75,109,111);
INSERT INTO "sensor_data" VALUES(83,'2017-01-03T02:30:11.047848',74,76,23,53);
INSERT INTO "sensor_data" VALUES(84,'2017-01-03T02:30:11.15331',199,213,133,6);
INSERT INTO "sensor_data" VALUES(85,'2017-01-03T02:30:11.257807',106,243,197,83);
INSERT INTO "sensor_data" VALUES(86,'2017-01-03T02:30:11.36329',112,15,48,178);
INSERT INTO "sensor_data" VALUES(87,'2017-01-03T02:30:11.467819',220,81,179,76);
INSERT INTO "sensor_data" VALUES(88,'2017-01-03T02:30:11.573304',178,231,130,33);
INSERT INTO "sensor_data" VALUES(89,'2017-01-03T02:30:11.677855',20,241,142,28);
INSERT INTO "sensor_data" VALUES(90,'2017-01-03T02:30:11.783354',55,234,204,173);
INSERT INTO "sensor_data" VALUES(91,'2017-01-03T02:30:11.887872',164,2,10,77);
INSERT INTO "sensor_data" VALUES(92,'2017-01-03T02:30:11.993339',223,186,103,36);
INSERT INTO "sensor_data" VALUES(93,'2017-01-03T02:30:12.09789',14,194,246,137);
INSERT INTO "sensor_data" VALUES(94,'2017-01-03T02:30:12.198987',245,200,104,70);
INSERT INTO "sensor_data" VALUES(95,'2017-01-03T02:30:12.304473',33,68,92,90);
INSERT INTO "sensor_data" VALUES(96,'2017-01-03T02:30:12.405712',180,134,26,224);
INSERT INTO "sensor_data" VALUES(97,'2017-01-03T02:30:12.507851',45,28,168,142);
INSERT INTO "sensor_data" VALUES(98,'2017-01-03T02:30:12.613334',136,178,252,97);
INSERT INTO "sensor_data" VALUES(99,'2017-01-03T02:30:12.717894',106,120,107,79);
INSERT INTO "sensor_data" VALUES(100,'2017-01-03T02:30:12.823357',44,239,35,195);
COMMIT;

stack.yaml

resolver: lts-7.14
packages:
- '.'
extra-deps: []
flags: {}
extra-package-dbs: []