Generating Responses

WebGear has a number of middlewares and functions to generate responses. We'll explore them in this chapter.

Basic Response Generation

The easiest way to generate responses is using the respondA arrow. For example, to generate a plain text response with HTTP status 200:

import qualified Network.HTTP.Types as HTTP

respondA HTTP.ok200 "text/plain" -< "A response body"

The respondA arrow generates a Linked res Response. You can compose it with unlinkA to convert it to a Response.

For generating JSON responses, you can use respondJsonA:

data Person = Person { name :: Text, email :: Text }
  deriving (Generic, ToJSON)

let person :: Person
    person = Person "John Smith" "john@smith.com"

unlinkA <<< respondJsonA HTTP.ok200 -< person

Advanced Response Generation

You can get finer control over the response using a few additional middlewares and arrows.

The mkResponse arrow generates a response with a specific HTTP status code.

-- resp :: Linked '[Status] Response
resp <- mkResponse HTTP.ok200 -< ()

There are helper arrows in the WebGear.Core.Trait.Status module that generates responses for all standard HTTP status codes.

The setBody and setJSONBody middlewares can add a body to a response. For example:

setBody "text/plain" ok200 -< ("Hello, World!", ())

let person :: Person
    person = Person "John Smith" "john@smith.com"

setJSONBody ok200 -< (person, ())

The setHeader middleware adds a header value to a response:

setHeader @"Cache-Control" @Text ok200 -< ("no-cache", ())