Web.FormUrlEncoded

Convert a value into Form.

An example type and instance:

{-# LANGUAGE OverloadedLists #-}

data Person = Person
  { name :: String
  , age  :: Int }

instance ToForm Person where
  toForm person =
    [ ("name", toQueryParam (name person))
    , ("age", toQueryParam (age person)) ]

Instead of manually writing ToForm instances you can use a default generic implementation of toForm.

To do that, simply add deriving Generic clause to your datatype and declare a ToForm instance for your datatype without giving definition for toForm.

For instance, the previous example can be simplified into this:

data Person = Person
  { name :: String
  , age  :: Int
  } deriving (Generic)

instance ToForm Person

The default implementation of toForm is genericToForm.

Parse Form into a value.

An example type and instance:

data Person = Person
  { name :: String
  , age  :: Int }

instance FromForm Person where
  fromForm f = Person
    <$> parseUnique "name" f
    <*> parseUnique "age"  f

Instead of manually writing FromForm instances you can use a default generic implementation of fromForm.

To do that, simply add deriving Generic clause to your datatype and declare a FromForm instance for your datatype without giving definition for fromForm.

For instance, the previous example can be simplified into this:

data Person = Person
  { name :: String
  , age  :: Int
  } deriving (Generic)

instance FromForm Person

The default implementation of fromForm is genericFromForm. It only works for records and it will use parseQueryParam for each field's value.

The contents of a form, not yet URL-encoded.

Form can be URL-encoded with urlEncodeForm and URL-decoded with urlDecodeForm.

This is a convenience function for encoding a datatype that has instance of ToForm directly to a application/x-www-form-urlencoded ByteString.

This is effectively urlEncodeForm . toForm.

_NOTE:_ this encoding is unstable and may result in different key order (but not values). For a stable encoding see urlEncodeAsFormStable.

This is a convenience function for encoding a datatype that has instance of ToForm directly to a application/x-www-form-urlencoded ByteString.

This is effectively urlEncodeFormStable . toForm.

>>> urlEncodeAsFormStable Person {name = "Dennis", age = 22}"age=22&name=Dennis"

This is a convenience function for decoding a application/x-www-form-urlencoded ByteString directly to a datatype that has an instance of FromForm.

This is effectively fromForm <=< urlDecodeForm.

>>> urlDecodeAsForm "name=Dennis&age=22" :: Either Text PersonRight (Person {name = "Dennis", age = 22})

Encode a Form to an application/x-www-form-urlencoded ByteString.

_NOTE:_ this encoding is unstable and may result in different key order (but not values). For a stable encoding see urlEncodeFormStable.

Encode a Form to an application/x-www-form-urlencoded ByteString.

For an unstable (but faster) encoding see urlEncodeForm.

Key-value pairs get encoded to key=value and separated by &:

>>> urlEncodeFormStable [("name", "Julian"), ("lastname", "Arni")]"lastname=Arni&name=Julian"

Keys with empty values get encoded to just key (without the = sign):

>>> urlEncodeFormStable [("is_test", "")]"is_test"

Empty keys are allowed too:

>>> urlEncodeFormStable [("", "foobar")]"=foobar"

However, if both key and value are empty, the key-value pair is ignored. (This prevents urlDecodeForm . urlEncodeFormStable from being a true isomorphism).

>>> urlEncodeFormStable [("", "")]""

Everything is escaped with escapeURIString isUnreserved:

>>> urlEncodeFormStable [("fullname", "Andres Löh")]"fullname=Andres%20L%C3%B6h"

Decode an application/x-www-form-urlencoded ByteString to a Form.

Key-value pairs get decoded normally:

>>> urlDecodeForm "name=Greg&lastname=Weber"Right (fromList [("lastname","Weber"),("name","Greg")])

Keys with no values get decoded to pairs with empty values.

>>> urlDecodeForm "is_test"Right (fromList [("is_test","")])

Empty keys are allowed:

>>> urlDecodeForm "=foobar"Right (fromList [("","foobar")])

The empty string gets decoded into an empty Form:

>>> urlDecodeForm ""Right (fromList [])

Everything is un-escaped with unEscapeString:

>>> urlDecodeForm "fullname=Andres%20L%C3%B6h"Right (fromList [("fullname","Andres L\246h")])

Improperly formed strings result in an error:

>>> urlDecodeForm "this=has=too=many=equals"Left "not a valid pair: this=has=too=many=equals"

A Generic-based implementation of toForm. This is used as a default implementation in ToForm.

Note that this only works for records (i.e. product data types with named fields):

data Person = Person
  { name :: String
  , age  :: Int
  } deriving (Generic)

In this implementation each field's value gets encoded using toQueryParam. Two field types are exceptions:

• for values of type Maybe a an entry is added to the Form only when it is Just x and the encoded value is toQueryParam x; Nothing values are omitted from the Form;

• for values of type [a] (except [Char]) an entry is added for every item in the list; if the list is empty no entries are added to the Form;

Here's an example:

data Post = Post
  { title    :: String
  , subtitle :: Maybe String
  , comments :: [String]
  } deriving (Generic, Show)

instance ToForm Post

>>> urlEncodeAsFormStable Post { title = "Test", subtitle = Nothing, comments = ["Nice post!", "+1"] }"comments=Nice%20post%21&comments=%2B1&title=Test"

A Generic-based implementation of fromForm. This is used as a default implementation in FromForm.

Note that this only works for records (i.e. product data types with named fields):

data Person = Person
  { name :: String
  , age  :: Int
  } deriving (Generic)

In this implementation each field's value gets decoded using parseQueryParam. Two field types are exceptions:

• for values of type Maybe a an entry is parsed if present in the Form and the is decoded with parseQueryParam; if no entry is present result is Nothing;

• for values of type [a] (except [Char]) all entries are parsed to produce a list of parsed values;

Here's an example:

data Post = Post
  { title    :: String
  , subtitle :: Maybe String
  , comments :: [String]
  } deriving (Generic, Show)

instance FromForm Post

>>> urlDecodeAsForm "comments=Nice%20post%21&comments=%2B1&title=Test" :: Either Text PostRight (Post {title = "Test", subtitle = Nothing, comments = ["Nice post!","+1"]})

A stable version of toList.

Parse a Form into a list of entries groupped by key.

_NOTE:_ this conversion is unstable and may result in different key order (but not values). For a stable encoding see toEntriesByKeyStable.

Parse a Form into a list of entries groupped by key.

>>> toEntriesByKeyStable [("name", "Nick"), ("color", "red"), ("color", "white")] :: Either Text [(Text, [Text])]Right [("color",["red","white"]),("name",["Nick"])]

For an unstable (but faster) conversion see toEntriesByKey.

Convert a list of entries groupped by key into a Form.

>>> fromEntriesByKey [("name",["Nick"]),("color",["red","blue"])]fromList [("color","red"),("color","blue"),("name","Nick")]

Find all values corresponding to a given key in a Form.

>>> lookupAll "name" [][]>>> lookupAll "name" [("name", "Oleg")]["Oleg"]>>> lookupAll "name" [("name", "Oleg"), ("name", "David")]["Oleg","David"]

Lookup an optional value for a key. Fail if there is more than one value.

>>> lookupMaybe "name" []Right Nothing>>> lookupMaybe "name" [("name", "Oleg")]Right (Just "Oleg")>>> lookupMaybe "name" [("name", "Oleg"), ("name", "David")]Left "Duplicate key \"name\""

Lookup a unique value for a key. Fail if there is zero or more than one value.

>>> lookupUnique "name" []Left "Could not find key \"name\"">>> lookupUnique "name" [("name", "Oleg")]Right "Oleg">>> lookupUnique "name" [("name", "Oleg"), ("name", "David")]Left "Duplicate key \"name\""

Lookup all values for a given key in a Form and parse them with parseQueryParams.

>>> parseAll "age" [] :: Either Text [Word8]Right []>>> parseAll "age" [("age", "8"), ("age", "seven")] :: Either Text [Word8]Left "could not parse: `seven' (input does not start with a digit)">>> parseAll "age" [("age", "8"), ("age", "777")] :: Either Text [Word8]Left "out of bounds: `777' (should be between 0 and 255)">>> parseAll "age" [("age", "12"), ("age", "25")] :: Either Text [Word8]Right [12,25]

Lookup an optional value for a given key and parse it with parseQueryParam. Fail if there is more than one value for the key.

>>> parseMaybe "age" [] :: Either Text (Maybe Word8)Right Nothing>>> parseMaybe "age" [("age", "12"), ("age", "25")] :: Either Text (Maybe Word8)Left "Duplicate key \"age\"">>> parseMaybe "age" [("age", "seven")] :: Either Text (Maybe Word8)Left "could not parse: `seven' (input does not start with a digit)">>> parseMaybe "age" [("age", "777")] :: Either Text (Maybe Word8)Left "out of bounds: `777' (should be between 0 and 255)">>> parseMaybe "age" [("age", "7")] :: Either Text (Maybe Word8)Right (Just 7)

Lookup a unique value for a given key and parse it with parseQueryParam. Fail if there is zero or more than one value for the key.

>>> parseUnique "age" [] :: Either Text Word8Left "Could not find key \"age\"">>> parseUnique "age" [("age", "12"), ("age", "25")] :: Either Text Word8Left "Duplicate key \"age\"">>> parseUnique "age" [("age", "seven")] :: Either Text Word8Left "could not parse: `seven' (input does not start with a digit)">>> parseUnique "age" [("age", "777")] :: Either Text Word8Left "out of bounds: `777' (should be between 0 and 255)">>> parseUnique "age" [("age", "7")] :: Either Text Word8Right 7

Encode a list of key-value pairs to an application/x-www-form-urlencoded ByteString.

See also urlEncodeFormStable.

Decode an application/x-www-form-urlencoded ByteString to a list of key-value pairs.

See also urlDecodeForm.