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 PlainText -< "A response body" :: Text

For generating JSON responses:

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

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

respondA HTTP.ok200 JSON -< person

Advanced Response Generation

You can get finer control over the response using a few additional control structures.

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

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

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

setBody can add a body to a response. For example:

(ok200 -< ())
  >-> (\resp -> setBody PlainText -< (response, "Hello, World!" :: Text))

setHeader adds a header value to a response:

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