yesod-rest

A Yesod scaffolding site with Postgres backend. It provides a JSON API backend as a separate subsite. The primary purpose of this repository is to use Yesod as a API server backend and do the frontend development using a tool like React or Angular. The current code includes a basic hello world using React and Babel which is bundled finally by webpack and added in the handler getHomeR in a type safe manner.

Features

1. Provides an API server.
2. Boilerplate for writing frontend code using React Javascript ecosystem is provided. (can be easily adapted to other tools like Angular, etc.)
3. Brings all the advantage of Yesod - type safe urls, simple DSL for routes etc.

Setup and Execution steps

1. Install Stack.
2. sudo apt-get install libpq-dev postgresql postgresql-contrib (For Debian based systems)
3. cd yesod-rest
4. stack build yesod-bin cabal-install --install-ghc
5. cd static && npm install
6. npm run webpack
7. stack build
8. stack exec -- yesod devel (Runs development server)
9. (Or) stack exec yesod-rest

Adding a API Route

Add the route to config/apiRoutes file and define your corresponding handler function in API.hs.

Demo:

GET Request

curl --header "Accept: application/json" http://localhost:3000/api/v1/user

{
  "name": "Sibi",
  "age": 26
}

POST Request

curl -i --header "Accept: application/json" -X POST -d '{"ident":"Sibi Prabakaran","password":"strongPassword"}' http://localhost:3000/api/v1/user

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Date: Fri, 09 Sep 2016 17:57:40 GMT
Server: Warp/3.2.8
Content-Type: application/json; charset=utf-8
Set-Cookie: _SESSION=Ch3WRY8GM9nVwwsjYU7SmfHloAneNgflzNuOUyyaXw5aEj5M+Ok/6qrtq5cLT5HR0htufC2ZdE7K0LvWFPoAEt7+lNdgYYnz+WwTnkXIGxCyEQj2LXhvaxdqf5OUGGuRPrvqlWbKBwE=; Path=/; Expires=Fri, 09-Sep-2016 19:57:40 GMT; HttpOnly
Vary: Accept, Accept-Language

{
  "ident": "Sibi Prabakaran",
  "password": "strongPassword"
}

Passing the same request again will give an 500 status code because it will violate the uniqueness constraint of the DB Schema.

curl -i --header "Accept: application/json" -X POST -d '{"ident":"Sibi Prabakaran","password":"strongPassword"}' http://localhost:3000/api/v1/user

HTTP/1.1 500 Internal Server Error
Transfer-Encoding: chunked
Date: Fri, 09 Sep 2016 18:14:45 GMT
Server: Warp/3.2.8
Content-Type: application/json; charset=utf-8
Set-Cookie: _SESSION=Eumei1PVc9GOFWVRKw+jzQuk+ijlarUMueuYm5mvN2gnOhAG9VQHvceOdLXVWjFAjDZcJ4rj0cZrPFbcqQIb0R55bhGDtuSJhQlOQoIKPeclfMh6I4kol0Pkv8xcInJQ0s0zH9XTCR8=; Path=/; Expires=Fri, 09-Sep-2016 20:14:45 GMT; HttpOnly
Vary: Accept, Accept-Language

{"error":"SqlError {sqlState = \"23505\", sqlExecStatus = FatalError,
sqlErrorMsg = \"duplicate key value violates unique constraint
\\\"unique_user\\\"\", sqlErrorDetail = \"Key (ident)=(Sibi
Prabakaran) already exists.\", sqlErrorHint =
\"\"}","message":"Internal Server Error"}

PATCH Request

curl -i --header "Accept: application/json" -X PATCH http://localhost:3000/api/v1/user/sibi

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Date: Fri, 09 Sep 2016 22:53:06 GMT
Server: Warp/3.2.8
Content-Type: application/json; charset=utf-8
Set-Cookie: _SESSION=Yvx90pnkmvDybys5+2dS4O6wwupCM+k46bWHHxxD29MO7KU9kPPzxP44ZT0pVN4YBwT8LjsLja8eVsg055HXWnnN6ot4/BFwkJcarIQ20COroeoJ+mxzNQ1AL+324n1a/gnCZWCCupI=; Path=/; Expires=Sat, 10-Sep-2016 00:53:06 GMT; HttpOnly
Vary: Accept, Accept-Language

{
  "id": 1,
  "ident": "sibi",
  "password": null
}

Also demonstrating the custom error handling in PATCH method:

curl -i --header "Accept: application/json" --request PATCH http://localhost:3000/api/v1/user/sibi_invalid_request

HTTP/1.1 400 Bad Request
Transfer-Encoding: chunked
Date: Fri, 09 Sep 2016 22:57:28 GMT
Server: Warp/3.2.8
Content-Type: application/json; charset=utf-8
Set-Cookie: _SESSION=6JraQjDLpGRyZ0/f14zVMvcHQBGY+pIuBVriVal0uMRsadj6ZJA5xirafSAham1q9w2Us0h7AsUfE/Me/aIkZkx3C4jnHXxMR9Wc+zTXCQWPAiSTH3PtZF3dvDkedfSB+aSc+nvJGCU=; Path=/; Expires=Sat, 10-Sep-2016 00:57:28 GMT; HttpOnly
Vary: Accept, Accept-Language

{
  "errors": [
    "User id is invalid"
  ],
  "message": "Invalid Arguments"
}

FAQ

• I see this error on stack exec yesod-rest:

yesod-rest: libpq: failed (could not connect to server: Connection refused
        Is the server running on host "localhost" (127.0.0.1) and accepting
        TCP/IP connections on port 5432?)

You most likely haven't installed the postgres server. For Ubuntu systems, it can be done by:

sudo apt-get install postgresql postgresql-contrib

• I see this error on stack exec yesod-rest:

yesod-rest: libpq: failed (FATAL:  password authentication failed for user "postgres"
FATAL:  password authentication failed for user "postgres")

See this.

• I see this error on stack exec yesod-rest:

yesod-rest: libpq: failed (FATAL:  database "test" does not exist)

Create a database named test on your postgres server.

• The webpack program is automatically getting closed.

Try running this command:

echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p