Web.Scotty

It should be noted that most of the code snippets below depend on the OverloadedStrings language pragma.

Scotty is set up by default for development mode. For production servers, you will likely want to modify settings and the defaultHandler. See the comments on each of these functions for more information.

Please refer to the examples directory and the spec test suite for concrete use cases, e.g. constructing responses, exception handling and useful implementation details.

Running scotty servers

scotty :: Port -> ScottyM () -> IO ()

Run a scotty application using the warp server.

scottyOpts :: Options -> ScottyM () -> IO ()

Run a scotty application using the warp server, passing extra options.

scottySocket :: Options -> Socket -> ScottyM () -> IO ()

Run a scotty application using the warp server, passing extra options, and listening on the provided socket. This allows the user to provide, for example, a Unix named socket, which can be used when reverse HTTP proxying into your application.

data Options

Constructors

Options

Fields

• verbose :: Int

  0 = silent, 1(def) = startup banner

• settings :: Settings

  Warp Settings Note: to work around an issue in warp, the default FD cache duration is set to 0 so changes to static files are always picked up. This likely has performance implications, so you may want to modify this for production servers using setFdCacheDuration.

Instances

Default Options

Defined in Web.Scotty.Internal.Types

Methods

def :: Options

defaultOptions :: Options

scotty-to-WAI

scottyApp :: ScottyM () -> IO Application

Turn a scotty application into a WAI Application, which can be run with any WAI handler.

Defining Middleware and Routes

Middleware and routes are run in the order in which they are defined. All middleware is run first, followed by the first route that matches. If no route matches, a 404 response is given.

middleware :: Middleware -> ScottyM ()

Use given middleware. Middleware is nested such that the first declared is the outermost middleware (it has first dibs on the request and last action on the response). Every middleware is run on each request.

get :: RoutePattern -> ActionM () -> ScottyM ()

get = addroute GET

post :: RoutePattern -> ActionM () -> ScottyM ()

post = addroute POST

put :: RoutePattern -> ActionM () -> ScottyM ()

put = addroute PUT

delete :: RoutePattern -> ActionM () -> ScottyM ()

delete = addroute DELETE

patch :: RoutePattern -> ActionM () -> ScottyM ()

patch = addroute PATCH

options :: RoutePattern -> ActionM () -> ScottyM ()

options = addroute OPTIONS

addroute :: StdMethod -> RoutePattern -> ActionM () -> ScottyM ()

Define a route with a StdMethod, a route pattern representing the path spec, and an Action which may modify the response.

get "/" $ text "beam me up!"

The path spec can include values starting with a colon, which are interpreted as captures. These are parameters that can be looked up with pathParam.

>>> :{
let server = S.get "/foo/:bar" (S.pathParam "bar" >>= S.text)
 in do
      withScotty server $ curl "http://localhost:3000/foo/something"
:}
"something"

matchAny :: RoutePattern -> ActionM () -> ScottyM ()

Add a route that matches regardless of the HTTP verb.

notFound :: ActionM () -> ScottyM ()

Specify an action to take if nothing else is found. Note: this _always_ matches, so should generally be the last route specified.

nested :: Application -> ActionM ()

Nest a whole WAI application inside a Scotty handler. Note: You will want to ensure that this route fully handles the response, as there is no easy delegation as per normal Scotty actions. Also, you will have to carefully ensure that you are expecting the correct routes, this could require stripping the current prefix, or adding the prefix to your application's handlers if it depends on them. One potential use-case for this is hosting a web-socket handler under a specific route.

setMaxRequestBodySize :: Kilobytes -> ScottyM ()

Set global size limit for the request body. Requests with body size exceeding the limit will not be processed and an HTTP response 413 will be returned to the client. Size limit needs to be greater than 0, otherwise the application will terminate on start.

Route Patterns

capture :: String -> RoutePattern

Standard Sinatra-style route. Named captures are prepended with colons. This is the default route type generated by OverloadedString routes. i.e.

get (capture "/foo/:bar") $ ...

and

{-# LANGUAGE OverloadedStrings #-}
...
get "/foo/:bar" $ ...

are equivalent.

regex :: String -> RoutePattern

Match requests using a regular expression. Named captures are not yet supported.

>>> :{
let server = S.get (S.regex "^/f(.*)r$") $ do
                cap <- S.pathParam "1"
                S.text cap
 in do
      withScotty server $ curl "http://localhost:3000/foo/bar"
:}
"oo/ba"

function :: (Request -> Maybe [Param]) -> RoutePattern

Build a route based on a function which can match using the entire Request object. Nothing indicates the route does not match. A Just value indicates a successful match, optionally returning a list of key-value pairs accessible by param.

>>> :{
let server = S.get (function $ \req -> Just [("version", T.pack $ show $ W.httpVersion req)]) $ do
                v <- S.pathParam "version"
                S.text v
 in do
      withScotty server $ curl "http://localhost:3000/"
:}
"HTTP/1.1"

literal :: String -> RoutePattern

Build a route that requires the requested path match exactly, without captures.

Accessing the Request and its fields

request :: ActionM Request

Get the Request object.

header :: Text -> ActionM (Maybe Text)

Get a request header. Header name is case-insensitive.

headers :: ActionM [(Text, Text)]

Get all the request headers. Header names are case-insensitive.

body :: ActionM ByteString

Get the request body.

NB: loads the entire request body in memory

bodyReader :: ActionM (IO ByteString)

Get an IO action that reads body chunks

• This is incompatible with body since body consumes all chunks.

jsonData :: FromJSON a => ActionM a

Parse the request body as a JSON object and return it. Raises an exception if parse is unsuccessful.

NB: uses body internally

Accessing Path, Form and Query Parameters

param :: Parsable a => Text -> ActionM a

Deprecated: (#204) Not a good idea to treat all parameters identically. Use pathParam, formParam and queryParam instead.

Get a parameter. First looks in captures, then form data, then query parameters.

• Raises an exception which can be caught by catch if parameter is not found.
• If parameter is found, but parseParam fails to parse to the correct type, next is called. This means captures are somewhat typed, in that a route won't match if a correctly typed capture cannot be parsed.

params :: ActionM [Param]

Deprecated: (#204) Not a good idea to treat all parameters identically. Use pathParams, formParams and queryParams instead.

Get all parameters from path, form and query (in that order).

pathParam :: Parsable a => Text -> ActionM a

Get a path parameter.

• Raises an exception which can be caught by catch if parameter is not found. If the exception is not caught, scotty will return a HTTP error code 500 ("Internal Server Error") to the client.
• If the parameter is found, but parseParam fails to parse to the correct type, next is called.

Since: 0.21

captureParam :: Parsable a => Text -> ActionM a

Synonym for pathParam

Since: 0.20

formParam :: Parsable a => Text -> ActionM a

Get a form parameter.

• Raises an exception which can be caught by catch if parameter is not found. If the exception is not caught, scotty will return a HTTP error code 400 ("Bad Request") to the client.
• This function raises a code 400 also if the parameter is found, but parseParam fails to parse to the correct type.

Since: 0.20

queryParam :: Parsable a => Text -> ActionM a

Get a query parameter.

• Raises an exception which can be caught by catch if parameter is not found. If the exception is not caught, scotty will return a HTTP error code 400 ("Bad Request") to the client.
• This function raises a code 400 also if the parameter is found, but parseParam fails to parse to the correct type.

Since: 0.20

pathParamMaybe :: Parsable a => Text -> ActionM (Maybe a)

Look up a path parameter. Returns Nothing if the parameter is not found or cannot be parsed at the right type.

NB : Doesn't throw exceptions. In particular, route pattern matching will not continue, so developers must raiseStatus or throw to signal something went wrong.

Since: 0.21

captureParamMaybe :: Parsable a => Text -> ActionM (Maybe a)

Synonym for pathParamMaybe

Since: 0.21

formParamMaybe :: Parsable a => Text -> ActionM (Maybe a)

Look up a form parameter. Returns Nothing if the parameter is not found or cannot be parsed at the right type.

NB : Doesn't throw exceptions, so developers must raiseStatus or throw to signal something went wrong.

Since: 0.21

queryParamMaybe :: Parsable a => Text -> ActionM (Maybe a)

Look up a query parameter. Returns Nothing if the parameter is not found or cannot be parsed at the right type.

NB : Doesn't throw exceptions, so developers must raiseStatus or throw to signal something went wrong.

Since: 0.21

pathParams :: ActionM [Param]

Get path parameters

captureParams :: ActionM [Param]

Synonym for pathParams

formParams :: ActionM [Param]

Get form parameters

queryParams :: ActionM [Param]

Get query parameters

Files

files :: ActionM [File ByteString]

Get list of uploaded files.

NB: Loads all file contents in memory with options defaultParseRequestBodyOptions

filesOpts

Arguments

:: ParseRequestBodyOptions

-> ([Param] -> [File FilePath] -> ActionM a)

temp files validation, storage etc

-> ActionM a

Get list of temp files and form parameters decoded from multipart payloads.

NB the temp files are deleted when the continuation exits

data ParseRequestBodyOptions

A data structure that describes the behavior of the parseRequestBodyEx function.

Since: wai-extra-3.0.16.0

Modifying the Response and Redirecting

status :: Status -> ActionM ()

Set the HTTP response status. Default is 200.

addHeader :: Text -> Text -> ActionM ()

Add to the response headers. Header names are case-insensitive.

setHeader :: Text -> Text -> ActionM ()

Set one of the response headers. Will override any previously set value for that header. Header names are case-insensitive.

redirect :: Text -> ActionM a

Redirect to given URL. Like throwing an uncatchable exception. Any code after the call to redirect will not be run.

redirect "http://www.google.com"

OR

redirect "/foo/bar"

Setting Response Body

Note: only one of these should be present in any given route definition, as they completely replace the current Response body.

text :: Text -> ActionM ()

Set the body of the response to the given Text value. Also sets "Content-Type" header to "text/plain; charset=utf-8" if it has not already been set.

html :: Text -> ActionM ()

Set the body of the response to the given Text value. Also sets "Content-Type" header to "text/html; charset=utf-8" if it has not already been set.

file :: FilePath -> ActionM ()

Send a file as the response. Doesn't set the "Content-Type" header, so you probably want to do that on your own with setHeader.

json :: ToJSON a => a -> ActionM ()

Set the body of the response to the JSON encoding of the given value. Also sets "Content-Type" header to "application/json; charset=utf-8" if it has not already been set.

stream :: StreamingBody -> ActionM ()

Set the body of the response to a StreamingBody. Doesn't set the "Content-Type" header, so you probably want to do that on your own with setHeader.

raw :: ByteString -> ActionM ()

Set the body of the response to the given ByteString value. Doesn't set the "Content-Type" header, so you probably want to do that on your own with setHeader.

Accessing the fields of the Response

getResponseHeaders :: ActionM ResponseHeaders

Access the HTTP headers of the Response

Since: 0.21

getResponseStatus :: ActionM Status

Access the HTTP Status of the Response

Since: 0.21

getResponseContent :: ActionM Content

Access the content of the Response

Since: 0.21

Exceptions

raise :: Text -> ActionM a

Deprecated: Throw an exception instead

Throw a "500 Server Error" StatusError, which can be caught with catch.

Uncaught exceptions turn into HTTP 500 responses.

raiseStatus :: Status -> Text -> ActionM a

Deprecated: Use status, text, and finish instead

Throw a StatusError exception that has an associated HTTP error code and can be caught with catch.

Uncaught exceptions turn into HTTP responses corresponding to the given status.

throw :: Exception e => e -> ActionM a

Throw an exception which can be caught within the scope of the current Action with catch.

If the exception is not caught locally, another option is to implement a global Handler (with defaultHandler) that defines its interpretation and a translation to HTTP error codes.

Uncaught exceptions turn into HTTP 500 responses.

rescue :: Exception e => ActionM a -> (e -> ActionM a) -> ActionM a

Deprecated: Use catch instead

Catch an exception e.g. a StatusError or a user-defined exception.

raise JustKidding `catch` (\msg -> text msg)

next :: ActionM ()

Abort execution of this action and continue pattern matching routes. Like an exception, any code after next is not executed.

NB : Internally, this is implemented with an exception that can only be caught by the library, but not by the user.

As an example, these two routes overlap. The only way the second one will ever run is if the first one calls next.

get "/foo/:bar" $ do
  w :: Text <- pathParam "bar"
  unless (w == "special") next
  text "You made a request to /foo/special"

get "/foo/:baz" $ do
  w <- pathParam "baz"
  text $ "You made a request to: " <> w

finish :: ActionM a

Abort execution of this action. Like an exception, any code after finish is not executed.

As an example only requests to /foo/special will include in the response content the text message.

get "/foo/:bar" $ do
  w :: Text <- pathParam "bar"
  unless (w == "special") finish
  text "You made a request to /foo/special"

Since: 0.10.3

defaultHandler :: ErrorHandler IO -> ScottyM ()

Global handler for user-defined exceptions.

liftAndCatchIO :: IO a -> ActionM a

Deprecated: Use liftIO instead

Like liftIO, but catch any IO exceptions and turn them into Scotty exceptions.

liftIO :: MonadIO m => IO a -> m a

Lift a computation from the IO monad. This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations (i.e. IO is the base monad for the stack).

Example

import Control.Monad.Trans.State -- from the "transformers" library

printState :: Show s => StateT s IO ()
printState = do
  state <- get
  liftIO $ print state

Had we omitted liftIO, we would have ended up with this error:

• Couldn't match type ‘IO’ with ‘StateT s IO’
 Expected type: StateT s IO ()
   Actual type: IO ()

The important part here is the mismatch between StateT s IO () and IO ().

Luckily, we know of a function that takes an IO a and returns an (m a): liftIO, enabling us to run the program and see the expected results:

> evalStateT printState "hello"
"hello"

> evalStateT printState 3
3

catch

Arguments

:: (MonadUnliftIO m, Exception e)

=> m a

action

-> (e -> m a)

handler

-> m a

Catch a synchronous (but not asynchronous) exception and recover from it.

This is parameterized on the exception type. To catch all synchronous exceptions, use catchAny.

Since: unliftio-0.1.0.0

data StatusError

Deprecated: If it is supposed to be caught, a proper exception type should be defined

E.g. when a parameter is not found in a query string (400 Bad Request) or when parsing a JSON body fails (422 Unprocessable Entity)

Constructors

StatusError Status Text

Deprecated: If it is supposed to be caught, a proper exception type should be defined

Instances

Exception StatusError

Defined in Web.Scotty.Internal.Types

Methods

toException :: StatusError -> SomeException

fromException :: SomeException -> Maybe StatusError

displayException :: StatusError -> String

Show StatusError

Defined in Web.Scotty.Internal.Types

Methods

showsPrec :: Int -> StatusError -> ShowS

show :: StatusError -> String

showList :: [StatusError] -> ShowS

MonadUnliftIO m => MonadError StatusError (ActionT m)

Models the invariant that only StatusErrors can be thrown and caught.

Defined in Web.Scotty.Internal.Types

Methods

throwError :: StatusError -> ActionT m a

catchError :: ActionT m a -> (StatusError -> ActionT m a) -> ActionT m a

data ScottyException

Thrown e.g. when a request is too large

Constructors

RequestTooLarge

MalformedJSON ByteString Text

FailedToParseJSON ByteString Text

PathParameterNotFound Text

QueryParameterNotFound Text

FormFieldNotFound Text

FailedToParseParameter Text Text Text

WarpRequestException InvalidRequest

WaiRequestParseException RequestParseException

ResourceTException InvalidAccess

Instances

Exception ScottyException

Defined in Web.Scotty.Internal.Types

Methods

toException :: ScottyException -> SomeException

fromException :: SomeException -> Maybe ScottyException

displayException :: ScottyException -> String

Show ScottyException

Defined in Web.Scotty.Internal.Types

Methods

showsPrec :: Int -> ScottyException -> ShowS

show :: ScottyException -> String

showList :: [ScottyException] -> ShowS

Parsing Parameters

type Param = (Text, Text)

class Parsable a where

Minimum implemention: parseParam

Minimal complete definition

parseParam

Methods

parseParam :: Text -> Either Text a

Take a Text value and parse it as a, or fail with a message.

parseParamList :: Text -> Either Text [a]

Default implementation parses comma-delimited lists.

parseParamList t = mapM parseParam (T.split (== ',') t)

Instances

Parsable Int16

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Int16

parseParamList :: Text -> Either Text [Int16]

Parsable Int32

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Int32

parseParamList :: Text -> Either Text [Int32]

Parsable Int64

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Int64

parseParamList :: Text -> Either Text [Int64]

Parsable Int8

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Int8

parseParamList :: Text -> Either Text [Int8]

Parsable Word16

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Word16

parseParamList :: Text -> Either Text [Word16]

Parsable Word32

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Word32

parseParamList :: Text -> Either Text [Word32]

Parsable Word64

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Word64

parseParamList :: Text -> Either Text [Word64]

Parsable Word8

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Word8

parseParamList :: Text -> Either Text [Word8]

Parsable ByteString

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text ByteString

parseParamList :: Text -> Either Text [ByteString]

Parsable ByteString

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text ByteString

parseParamList :: Text -> Either Text [ByteString]

Parsable Text

Defined in Web.Scotty.Action

Methods

parseParam :: Text0 -> Either Text0 Text

parseParamList :: Text0 -> Either Text0 [Text]

Parsable Text

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Text

parseParamList :: Text -> Either Text [Text]

Parsable UTCTime

parse a UTCTime timestamp formatted as a ISO 8601 timestamp:

yyyy-mm-ddThh:mm:ssZ , where the seconds can have a decimal part with up to 12 digits and no trailing zeros.

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text UTCTime

parseParamList :: Text -> Either Text [UTCTime]

Parsable Integer

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Integer

parseParamList :: Text -> Either Text [Integer]

Parsable Natural

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Natural

parseParamList :: Text -> Either Text [Natural]

Parsable ()

Checks if parameter is present and is null-valued, not a literal (). If the URI requested is: '/foo?bar=()&baz' then baz will parse as (), where bar will not.

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text ()

parseParamList :: Text -> Either Text [()]

Parsable Bool

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Bool

parseParamList :: Text -> Either Text [Bool]

Parsable Char

Overrides default parseParamList to parse String.

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Char

parseParamList :: Text -> Either Text [Char]

Parsable Double

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Double

parseParamList :: Text -> Either Text [Double]

Parsable Float

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Float

parseParamList :: Text -> Either Text [Float]

Parsable Int

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Int

parseParamList :: Text -> Either Text [Int]

Parsable Word

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text Word

parseParamList :: Text -> Either Text [Word]

Parsable a => Parsable [a]

Defined in Web.Scotty.Action

Methods

parseParam :: Text -> Either Text [a]

parseParamList :: Text -> Either Text [[a]]

readEither :: Read a => Text -> Either Text a

Useful for creating Parsable instances for things that already implement Read. Ex:

instance Parsable Int where parseParam = readEither

Types

type ScottyM = ScottyT IO

type ActionM = ActionT IO

data RoutePattern

Instances

IsString RoutePattern

Defined in Web.Scotty.Internal.Types

Methods

fromString :: String -> RoutePattern

type File t = (Text, FileInfo t)

Type parameter t is the file content. Could be () when not needed or a FilePath for temp files instead.

data Content

Constructors

ContentBuilder Builder

ContentFile FilePath

ContentStream StreamingBody

ContentResponse Response

type Kilobytes = Int

type ErrorHandler m = Handler (ActionT m) ()

Specializes a Handler to the ActionT monad

data Handler (m :: Type -> Type) a

Generalized version of Handler

Constructors

Exception e => Handler (e -> m a)

Instances

Monad m => Functor (Handler m)

Defined in Control.Monad.Catch

Methods

fmap :: (a -> b) -> Handler m a -> Handler m b

(<$) :: a -> Handler m b -> Handler m a

data ScottyState m

defaultScottyState :: ScottyState m