Happstack.Server.Response

Functions and classes related to generating a Response and setting the response code. For detailed instruction see the Happstack Crash Course: http://happstack.com/docs/crashcourse/HelloWorld.html#response_code

Converting values to a Response

class ToMessage a where

toResponse will convert a value into a Response body, set the content-type, and set the default response code for that type.

happstack-server Example:

 main = simpleHTTP nullConf $ toResponse "hello, world!"

will generate a Response with the content-type text/plain, the response code 200 OK, and the body: hello, world!.

simpleHTTP will call toResponse automatically, so the above can be shortened to:

 main = simpleHTTP nullConf $ "hello, world!"

happstack-lite Example:

 main = serve Nothing $ toResponse "hello, world!"

Minimal definition: toMessage (and usually toContentType).

Methods

toContentType :: a -> ByteString

toMessage :: a -> ByteString

toResponse :: a -> Response

Instances

ToMessage Integer

ToMessage String

ToMessage ()

ToMessage Text

ToMessage Text

ToMessage ByteString

ToMessage ByteString

ToMessage Html

ToMessage Html

ToMessage Html

ToMessage Response

ToMessage a => ToMessage (Maybe a)

flatten :: (ToMessage a, Functor f) => f a -> f Response

alias for: fmap toResponse

turns m a into m Response using toResponse.

 main = simpleHTTP nullConf $ flatten $ do return "flatten me."

toResponseBS

Arguments

:: ByteString

content-type

-> ByteString

response body

-> Response

A low-level function to build a Response from a content-type and a ByteString.

Creates a Response in a manner similar to the ToMessage class, but without requiring an instance declaration.

example:

 import Data.ByteString.Char8 as C
 import Data.ByteString.Lazy.Char8 as L
 import Happstack.Server

 main = simpleHTTP nullConf $ ok $ toResponseBS (C.pack "text/plain") (L.pack "hello, world")

(note: pack and pack only work for ascii. For unicode strings you would need to use utf8-string, text, or something similar to create a valid ByteString).

Setting the Response Code

ok :: FilterMonad Response m => a -> m a

Respond with 200 OK.

 main = simpleHTTP nullConf $ ok "Everything is OK"

noContent :: FilterMonad Response m => a -> m a

Respond with 204 No Content

A 204 No Content response may not contain a message-body. If you try to supply one, it will be dutifully ignored.

 main = simpleHTTP nullConf $ noContent "This will be ignored."

internalServerError :: FilterMonad Response m => a -> m a

Respond with 500 Internal Server Error.

 main = simpleHTTP nullConf $ internalServerError "Sorry, there was an internal server error."

badGateway :: FilterMonad Response m => a -> m a

Responds with 502 Bad Gateway.

 main = simpleHTTP nullConf $ badGateway "Bad Gateway."

badRequest :: FilterMonad Response m => a -> m a

Respond with 400 Bad Request.

 main = simpleHTTP nullConf $ badRequest "Bad Request."

unauthorized :: FilterMonad Response m => a -> m a

Respond with 401 Unauthorized.

 main = simpleHTTP nullConf $ unauthorized "You are not authorized."

forbidden :: FilterMonad Response m => a -> m a

Respond with 403 Forbidden.

 main = simpleHTTP nullConf $ forbidden "Sorry, it is forbidden."

notFound :: FilterMonad Response m => a -> m a

Respond with 404 Not Found.

 main = simpleHTTP nullConf $ notFound "What you are looking for has not been found."

prettyResponse :: Response -> String

A nicely formatted rendering of a Response

requestEntityTooLarge :: FilterMonad Response m => a -> m a

Respond with 413 Request Entity Too Large.

 main = simpleHTTP nullConf $ requestEntityTooLarge "That's too big for me to handle."

seeOther :: (FilterMonad Response m, ToSURI uri) => uri -> res -> m res

Respond with 303 See Other.

 main = simpleHTTP nullConf $ seeOther "http://example.org/" "What you are looking for is now at http://example.org/"

NOTE: The second argument of seeOther is the message body which will sent to the browser. According to the HTTP 1.1 spec,

the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).

This is because pre-HTTP/1.1 user agents do not support 303. However, in practice you can probably just use "" as the second argument.

found :: (FilterMonad Response m, ToSURI uri) => uri -> res -> m res

Respond with 302 Found.

You probably want seeOther. This method is not in popular use anymore, and is generally treated like 303 by most user-agents anyway.

movedPermanently :: (FilterMonad Response m, ToSURI a) => a -> res -> m res

Respond with 301 Moved Permanently.

 main = simpleHTTP nullConf $ movedPermanently "http://example.org/" "What you are looking for is now at http://example.org/"

tempRedirect :: (FilterMonad Response m, ToSURI a) => a -> res -> m res

Respond with 307 Temporary Redirect.

 main = simpleHTTP nullConf $ tempRedirect "http://example.org/" "What you are looking for is temporarily at http://example.org/"

setResponseCode

Arguments

:: FilterMonad Response m

=> Int

response code

-> m ()

Set an arbitrary return code in your response.

A filter for setting the response code. Generally you will use a helper function like ok or seeOther.

 main = simpleHTTP nullConf $ do setResponseCode 200
                                 return "Everything is OK"

see also: resp

resp

Arguments

:: FilterMonad Response m

=> Int

response code

-> b

value to return

-> m b

Same as setResponseCode status >> return val.

Use this if you want to set a response code that does not already have a helper function.

 main = simpleHTTP nullConf $ resp 200 "Everything is OK"

Handling if-modified-since

ifModifiedSince

Arguments

:: UTCTime

mod-time for the Response (MUST NOT be later than server's time of message origination)

-> Request

incoming request (used to check for if-modified-since)

-> Response

Response to send if there are modifications

-> Response

Honor an if-modified-since header in a Request. If the Request includes the if-modified-since header and the Response has not been modified, then return 304 (Not Modified), otherwise return the Response.