Happstack.Server.RqData

Functions for extracting values from the query string, form data, cookies, etc.

For in-depth documentation see the following section of the Happstack Crash Course:

http://happstack.com/docs/crashcourse/RqData.html

Looking up keys

Form Values and Query Parameters

look :: (Functor m, Monad m, HasRqData m) => String -> m String

Gets the first matching named input parameter as a String

Searches the QUERY_STRING followed by the Request body.

This function assumes the underlying octets are UTF-8 encoded.

Example:

 handler :: ServerPart Response
 handler =
      do foo <- look "foo"
         ok $ toResponse $ "foo = " ++ foo

see also: looks, lookBS, and lookBSs

looks :: (Functor m, Monad m, HasRqData m) => String -> m [String]

Gets all matches for the named input parameter as Strings

Searches the QUERY_STRING followed by the Request body.

This function assumes the underlying octets are UTF-8 encoded.

see also: look and lookBSs

lookBS :: (Functor m, Monad m, HasRqData m) => String -> m ByteString

Gets the first matching named input parameter as a lazy ByteString

Searches the QUERY_STRING followed by the Request body.

see also: lookBSs

lookBSs :: (Functor m, Monad m, HasRqData m) => String -> m [ByteString]

Gets all matches for the named input parameter as lazy ByteStrings

Searches the QUERY_STRING followed by the Request body.

see also: lookBS

lookRead :: (Functor m, Monad m, HasRqData m, Read a) => String -> m a

Gets the first matching named input parameter and decodes it using Read

Searches the QUERY_STRING followed by the Request body.

This function assumes the underlying octets are UTF-8 encoded.

see also: lookReads

lookReads :: (Functor m, Monad m, HasRqData m, Read a) => String -> m [a]

Gets all matches for the named input parameter and decodes them using Read

Searches the QUERY_STRING followed by the Request body.

This function assumes the underlying octets are UTF-8 encoded.

see also: lookReads

lookFile

Arguments

:: (Monad m, HasRqData m)

=> String

name of input field to search for

-> m (FilePath, FilePath, ContentType)

(temporary file location, uploaded file name, content-type)

Gets the first matching named file

Files can only appear in the request body. Additionally, the form must set enctype="multipart/form-data".

This function returns a tuple consisting of:

1. The temporary location of the uploaded file
2. The local filename supplied by the browser
3. The content-type supplied by the browser

NOTE: You must move the file from the temporary location before the Response is sent. The temporary files are automatically removed after the Response is sent.

lookPairs :: (Monad m, HasRqData m) => m [(String, Either FilePath String)]

gets all the input parameters, and converts them to a String

The results will contain the QUERY_STRING followed by the Request body.

This function assumes the underlying octets are UTF-8 encoded.

see also: lookPairsBS

lookPairsBS :: (Monad m, HasRqData m) => m [(String, Either FilePath ByteString)]

gets all the input parameters

The results will contain the QUERY_STRING followed by the Request body.

see also: lookPairs

Cookies

lookCookie :: (Monad m, HasRqData m) => String -> m Cookie

Gets the named cookie the cookie name is case insensitive

lookCookieValue :: (Functor m, Monad m, HasRqData m) => String -> m String

gets the named cookie as a string

readCookieValue :: (Functor m, Monad m, HasRqData m, Read a) => String -> m a

gets the named cookie as the requested Read type

low-level

lookInput :: (Monad m, HasRqData m) => String -> m Input

Gets the first matching named input parameter

Searches the QUERY_STRING followed by the Request body.

see also: lookInputs

lookInputs :: (Monad m, HasRqData m) => String -> m [Input]

Gets all matches for the named input parameter

Searches the QUERY_STRING followed by the Request body.

see also: lookInput

Filters

body :: HasRqData m => m a -> m a

limit the scope to the Request body

 handler :: ServerPart Response
 handler =
     do foo <- body $ look "foo"
        ok $ toResponse $ "foo = " ++ foo

queryString :: HasRqData m => m a -> m a

limit the scope to the QUERY_STRING

 handler :: ServerPart Response
 handler =
     do foo <- queryString $ look "foo"
        ok $ toResponse $ "foo = " ++ foo

Validation and Parsing

checkRq :: (Monad m, HasRqData m) => m a -> (a -> Either String b) -> m b

convert or validate a value

This is similar to fmap except that the function can fail by returning Left and an error message. The error will be propagated by calling rqDataError.

This function is useful for a number of things including:

1. Parsing a String into another type
2. Checking that a value meets some requirements (for example, that is an Int between 1 and 10).

Example usage at:

http://happstack.com/docs/crashcourse/RqData.html#rqdatacheckrq

checkRqM :: (Monad m, HasRqData m) => m a -> (a -> m (Either String b)) -> m b

like checkRq but the check function can be monadic

readRq

Arguments

:: Read a

=> String

name of key (only used for error reporting)

-> String

String to read

-> Either String a

Left on error, Right on success

use read to convert a String to a value of type a

 look "key" `checkRq` (readRq "key")

use with checkRq

Handling POST/PUT Requests

decodeBody :: (ServerMonad m, MonadPlus m, MonadIO m) => BodyPolicy -> m ()

The POST/PUT body of a Request is not received or decoded unless this function is invoked.

It is an error to try to use the look functions for a POST/PUT request with out first calling this function.

It is ok to call decodeBody at the beginning of every request:

 main = simpleHTTP nullConf $ 
           do decodeBody (defaultBodyPolicy "/tmp/" 4096 4096 4096)
              handlers

You can achieve finer granularity quotas by calling decodeBody with different values in different handlers.

Only the first call to decodeBody will have any effect. Calling it a second time, even with different quota values, will do nothing.

Body Policy

data BodyPolicy

see defaultBodyPolicy

Constructors

BodyPolicy

Fields

inputWorker :: Int64 -> Int64 -> Int64 -> InputWorker

maxDisk :: Int64

maximum bytes for files uploaded in this Request

maxRAM :: Int64

maximum bytes for all non-file values in the Request body

maxHeader :: Int64

maximum bytes of overhead for headers in multipart/form-data

defaultBodyPolicy

Arguments

:: FilePath

temporary directory for file uploads

-> Int64

maximum bytes for files uploaded in this Request

-> Int64

maximum bytes for all non-file values in the Request body

-> Int64

maximum bytes of overhead for headers in multipart/form-data

-> BodyPolicy

create a BodyPolicy for use with decodeBody

RqData Monad & Error Reporting

data RqData a

An applicative functor and monad for looking up key/value pairs in the QUERY_STRING, Request body, and cookies.

Instances

Monad RqData

Functor RqData

MonadPlus RqData

Applicative RqData

Alternative RqData

HasRqData RqData

MonadReader RqEnv RqData

mapRqData :: (Either (Errors String) a -> Either (Errors String) b) -> RqData a -> RqData b

transform the result of 'RqData a'.

This is similar to fmap except it also allows you to modify the Errors not just a.

newtype Errors a

a list of errors

Constructors

Errors

Fields

unErrors :: [a]

Instances

Typeable1 Errors

Eq a => Eq (Errors a)

Data a => Data (Errors a)

Ord a => Ord (Errors a)

Read a => Read (Errors a)

Show a => Show (Errors a)

Monoid (Errors a)

Error (Errors String)

Using RqData with ServerMonad

getDataFn

Arguments

:: (HasRqData m, ServerMonad m, MonadIO m)

=> RqData a

RqData monad to evaluate

-> m (Either [String] a)

return Left errors or Right a

run RqData in a ServerMonad.

Example: a simple GET or POST variable based authentication guard. It handles the request with errorHandler if authentication fails.

  data AuthCredentials = AuthCredentials { username :: String,  password :: String }

  isValid :: AuthCredentials -> Bool
  isValid = const True

  myRqData :: RqData AuthCredentials
  myRqData = do
     username <- look "username"
     password <- look "password"
     return (AuthCredentials username password)

  checkAuth :: (String -> ServerPart Response) -> ServerPart Response
  checkAuth errorHandler = do
     d <- getDataFn myRqData
     case d of
         (Left e) -> errorHandler (unlines e)
         (Right a) | isValid a -> mzero
         (Right a) | otherwise -> errorHandler "invalid"

NOTE: you must call decodeBody prior to calling this function if the request method is POST or PUT.

withDataFn :: (HasRqData m, MonadIO m, MonadPlus m, ServerMonad m) => RqData a -> (a -> m r) -> m r

similar to getDataFn, except it calls a sub-handler on success or mzero on failure.

NOTE: you must call decodeBody prior to calling this function if the request method is POST or PUT.

class FromData a where

Used by withData and getData. Make your preferred data type an instance of FromData to use those functions.

Methods

fromData :: RqData a

Instances

FromData a => FromData (Maybe a)

(FromData a, FromData b) => FromData (a, b)

(FromData a, FromData b, FromData c) => FromData (a, b, c)

(FromData a, FromData b, FromData c, FromData d) => FromData (a, b, c, d)

getData :: (HasRqData m, MonadIO m, ServerMonad m, FromData a) => m (Either [String] a)

A variant of getDataFn that uses FromData to chose your RqData for you. The example from getData becomes:

  data AuthCredentials = AuthCredentials { username :: String,  password :: String }

  isValid :: AuthCredentials -> Bool
  isValid = const True

  myRqData :: RqData AuthCredentials
  myRqData = do
     username <- look "username"
     password <- look "password"
     return (AuthCredentials username password)

  instance FromData AuthCredentials where
     fromData = myRqData

  checkAuth :: (String -> ServerPart Response) -> ServerPart Response
  checkAuth errorHandler = do
     d <- getData
     case d of
         (Left e) -> errorHandler (unlines e)
         (Right a) | isValid a -> mzero
         (Right a) | otherwise -> errorHandler "invalid"

NOTE: you must call decodeBody prior to calling this function if the request method is POST or PUT.

withData :: (HasRqData m, MonadIO m, FromData a, MonadPlus m, ServerMonad m) => (a -> m r) -> m r

similar to getData except it calls a subhandler on success or mzero on failure.

NOTE: you must call decodeBody prior to calling this function if the request method is POST or PUT.

HasRqData class

type RqEnv = ([(String, Input)], [(String, Input)], [(String, Cookie)])

the environment used to lookup query parameters. It consists of the triple: (query string inputs, body inputs, cookie inputs)

class HasRqData m where

A class for monads which contain a RqEnv

Methods

askRqEnv :: m RqEnv

localRqEnv :: (RqEnv -> RqEnv) -> m a -> m a

rqDataError :: Errors String -> m a

lift some Errors into RqData

Instances

HasRqData RqData

MonadIO m => HasRqData (ServerPartT m)