Web.Fn

This package provides a simple framework for routing and responses. The two primary goals are:

1. All web handler functions are just plain IO. There is no Fn monad, or monad transformer. This has a lot of nice properties, foremost among them is that it is easier to call handlers from other contexts (like GHCi, when testing, in other threads, etc). As a result, these functions take a single extra parameter that has the context that they need (like database connection pools, the request, etc).
2. Web handlers are functions with typed parameters. When routing, we specify many parameters (most commonly, numeric ids, but can be many things), so the handlers should be functions that take those as parameters.

Application setup

type FnRequest = (Request, PostMVar)

A normal WAI Request and the parsed post body (if present). We can only parse the body once, so we need to have our request (which we pass around) to be able to have the parsed body.

defaultFnRequest :: FnRequest

A default request, which is a WAI defaultRequest and a place for an MVar where post info will be placed (if you parse the post body).

Warning: If you try to parse the post body (with !=>) without replacing the Nothing placeholder with an actual MVar, it will blow up!

class RequestContext ctxt where

Specify the way that Fn can get the FnRequest out of your context.

The easiest way to instantiate this is to use the lens, but if you don't want to use lenses, define getRequest and setRequest.

Note that requestLens is defined in terms of getRequest and setRequest and vice-versa, so you need to define _one_ of these.

Methods

requestLens :: Functor f => (FnRequest -> f FnRequest) -> ctxt -> f ctxt

getRequest :: ctxt -> FnRequest

setRequest :: ctxt -> FnRequest -> ctxt

Instances

RequestContext FnRequest

Methods

requestLens :: Functor f => (FnRequest -> f FnRequest) -> FnRequest -> f FnRequest

getRequest :: FnRequest -> FnRequest

setRequest :: FnRequest -> FnRequest -> FnRequest

toWAI :: RequestContext ctxt => ctxt -> (ctxt -> IO Response) -> Application

Convert an Fn application (provide a context, a context to response function and we'll create a WAI application by updating the FnRequest value for each call).

Routing

type Req = (Request, [Text], Query, StdMethod, PostMVar)

The parts of the path, when split on /, and the query.

type Route ctxt = ctxt -> Req -> IO (Maybe (IO (Maybe Response)))

The type of a route, constructed with 'pattern ==> handler'.

route :: RequestContext ctxt => ctxt -> [Route ctxt] -> IO (Maybe Response)

The main construct for Fn, route takes a context (which it will pass to all handlers) and a list of potential matches (which, once they match, may still end up deciding not to handle the request - hence the double Maybe). It can be nested.

 app c = route c [ end ==> index
                 , path "foo" // path "bar" // segment /? param "id ==> h]
   where index :: Ctxt -> IO (Maybe Response)
         index _ = okText "This is the index."
         h :: Ctxt -> Text -> Text -> IO (Maybe Response)
         h _ s i = okText ("got path /foo/" <> s <> ", with id=" <> i)

fallthrough :: IO (Maybe Response) -> IO Response -> IO Response

The route function (and all your handlers) return 'IO (Maybe Response)', because each can elect to not respond (in which case we will continue to match on routes). But to construct an application, we need a response in the case that nothing matched - this is what fallthrough allows you to specify. In particular, notFoundText and notFoundHtml may be useful.

(==>) :: RequestContext ctxt => (Req -> IO (Maybe (Req, k -> a))) -> (ctxt -> k) -> ctxt -> Req -> IO (Maybe a)

The non-body parsing connective between route patterns and the handler that will be called if the pattern matches. The type is not particularly illuminating, as it uses polymorphism to be able to match route patterns with varying numbers (and types) of parts with functions of the corresponding number of arguments and types.

(!=>) :: RequestContext ctxt => (Req -> IO (Maybe (Req, k -> a))) -> (ctxt -> k) -> ctxt -> Req -> IO (Maybe a)

The connective between route patterns and the handler that parses the body, which allows post params to be extracted with param and allows file to work (otherwise, it will trigger a runtime error).

(//) :: (r -> IO (Maybe (r, k -> k'))) -> (r -> IO (Maybe (r, k' -> a))) -> r -> IO (Maybe (r, k -> a))

Connects two path segments. Note that when normally used, the type parameter r is Req. It is more general here to facilitate testing.

(/?) :: (r -> IO (Maybe (r, k -> k'))) -> (r -> IO (Maybe (r, k' -> a))) -> r -> IO (Maybe (r, k -> a))

Deprecated: Use the identical // instead.

A synonym for //. To be removed

path :: Text -> Req -> IO (Maybe (Req, a -> a))

Matches a literal part of the path. If there is no path part left, or the next part does not match, the whole match fails.

end :: Req -> IO (Maybe (Req, a -> a))

Matches there being no parts of the path left. This is useful when matching index routes.

anything :: Req -> IO (Maybe (Req, a -> a))

Matches anything.

segment :: FromParam p => Req -> IO (Maybe (Req, (p -> a) -> a))

Captures a part of the path. It will parse the part into the type specified by the handler it is matched to. If there is no segment, or if the segment cannot be parsed as such, it won't match.

method :: StdMethod -> Req -> IO (Maybe (Req, a -> a))

Matches on a particular HTTP method.

class FromParam a where

A class that is used for parsing for param and paramOpt. and segment.

Minimal complete definition

fromParam

Methods

fromParam :: [Text] -> Either ParamError a

Instances

FromParam Double

Methods

fromParam :: [Text] -> Either ParamError Double

FromParam Int

Methods

fromParam :: [Text] -> Either ParamError Int

FromParam Text

Methods

fromParam :: [Text] -> Either ParamError Text

FromParam a => FromParam [a]

Methods

fromParam :: [Text] -> Either ParamError [a]

FromParam a => FromParam (Maybe a)

Methods

fromParam :: [Text] -> Either ParamError (Maybe a)

data ParamError

Constructors

ParamMissing

ParamTooMany

ParamUnparsable

ParamOtherError Text

Instances

Eq ParamError

Methods

(==) :: ParamError -> ParamError -> Bool

(/=) :: ParamError -> ParamError -> Bool

Show ParamError

Methods

showsPrec :: Int -> ParamError -> ShowS

show :: ParamError -> String

showList :: [ParamError] -> ShowS

param :: FromParam p => Text -> Req -> IO (Maybe (Req, (p -> a) -> a))

Matches on a query parameter of the given name. It is parsed into the type needed by the handler, which can be a Maybe type if the parameter is optional, or a list type if there can be many. If the parameters cannot be parsed into the type needed by the handler, it won't match.

Note: If you have used the !=> connective, so that the request body has been parsed, this will also match post parameters (and will combine the two together). If you haven't used that connective (so the pattern is matched to handler with ==>), it will only match query parameters.

paramMany :: FromParam p => Text -> Req -> IO (Maybe (Req, ([p] -> a) -> a))

Deprecated: Use param with a list type, or define param parsing for non-empty list.

Matches on query parameters of the given name. If there are no parameters, or they cannot be parsed into the type needed by the handler, it won't match.

paramOpt :: FromParam p => Text -> Req -> IO (Maybe (Req, (Either ParamError p -> a) -> a))

If the specified parameters are present, they will be parsed into the type needed by the handler, but if they aren't present or cannot be parsed, the handler will still be called.

Note: If you have used the !=> connective, so that the request body has been parsed, this will also match post parameters (and will combine the two together). If you haven't used that connective (so the pattern is matched to handler with ==>), it will only match query parameters.

data File

An uploaded file.

Constructors

File

Fields

• fileName :: Text
• fileContentType :: Text
• filePath :: FilePath

file :: Text -> Req -> IO (Maybe (Req, (File -> a) -> a))

Matches an uploaded file with the given parameter name.

files :: Req -> IO (Maybe (Req, ([(Text, File)] -> a) -> a))

Matches all uploaded files, passing their parameter names and contents.

Responses

staticServe :: RequestContext ctxt => Text -> ctxt -> IO (Maybe Response)

Serves static files out of the specified path according to the request path. Note that if you have matched parts of the path, those will not be included in the path used to find the static file. For example, if you have a file static/img/a.png, and do:

path "img" ==> staticServe "static"

It will match img/img/a.png, not img/a.png. If you wanted that, you could:

anything ==> staticServe "static"

If no file is found, or if the path has .. or starts with /, this will continue routing.

sendFile :: FilePath -> IO (Maybe Response)

Sends a specific file specified by path. It will specify the content-type if it can figure it out by the file extension.

If no file exists at the given path, it will keep routing.

okText :: Text -> IO (Maybe Response)

Returns Text as a response.

okJson :: Text -> IO (Maybe Response)

Returns Text as a JSON response with appropriate header.

okHtml :: Text -> IO (Maybe Response)

Returns Html (in Text) as a response.

errText :: Text -> IO (Maybe Response)

Returns Text as a response with a 500 status code.

errHtml :: Text -> IO (Maybe Response)

Returns Html (in Text) as a response with a 500 status code.

notFoundText :: Text -> IO Response

Returns a 404 with the given Text as a body. Note that this returns a 'IO Response' not an 'IO (Maybe Response)' because the expectaiton is that you are calling this with fallthrough.

notFoundHtml :: Text -> IO Response

Returns a 404 with the given html as a body. Note that this returns a 'IO Response' not an 'IO (Maybe Response)' because the expectaiton is that you are calling this with fallthrough.

redirect :: Text -> IO (Maybe Response)

Redirects to the given url. Note that the target is not validated, so it should be an absolute path/url.

redirectReferer :: RequestContext ctxt => ctxt -> IO (Maybe Response)

Redirects to the referrer, if present in headers, else to "/".

Helpers

tempFileBackEnd' :: InternalState -> ignored1 -> FileInfo () -> IO ByteString -> IO FilePath

Internal helper - uses the name of the file as the pattern.