servant-0.14: A family of combinators for defining webservices APIs

Safe HaskellNone
LanguageHaskell2010

Servant.Utils.Links

Contents

Description

Type safe generation of internal links.

Given an API with a few endpoints:

>>> :set -XDataKinds -XTypeFamilies -XTypeOperators
>>> import Servant.API
>>> import Servant.Utils.Links
>>> import Data.Proxy
>>> 
>>> type Hello = "hello" :> Get '[JSON] Int
>>> type Bye   = "bye"   :> QueryParam "name" String :> Delete '[JSON] NoContent
>>> type API   = Hello :<|> Bye
>>> let api = Proxy :: Proxy API

It is possible to generate links that are guaranteed to be within API with safeLink. The first argument to safeLink is a type representing the API you would like to restrict links to. The second argument is the destination endpoint you would like the link to point to, this will need to end with a verb like GET or POST. Further arguments may be required depending on the type of the endpoint. If everything lines up you will get a Link out the other end.

You may omit QueryParams and the like should you not want to provide them, but types which form part of the URL path like Capture must be included. The reason you may want to omit QueryParams is that safeLink is a bit magical: if parameters are included that could take input it will return a function that accepts that input and generates a link. This is best shown with an example. Here, a link is generated with no parameters:

>>> let hello = Proxy :: Proxy ("hello" :> Get '[JSON] Int)
>>> toUrlPiece (safeLink api hello :: Link)
"hello"

If the API has an endpoint with parameters then we can generate links with or without those:

>>> let with = Proxy :: Proxy ("bye" :> QueryParam "name" String :> Delete '[JSON] NoContent)
>>> toUrlPiece $ safeLink api with (Just "Hubert")
"bye?name=Hubert"

>>> let without = Proxy :: Proxy ("bye" :> Delete '[JSON] NoContent)
>>> toUrlPiece $ safeLink api without
"bye"

If you would like create a helper for generating links only within that API, you can partially apply safeLink if you specify a correct type signature like so:

>>> :set -XConstraintKinds
>>> :{
>>> let apiLink :: (IsElem endpoint API, HasLink endpoint)
>>> => Proxy endpoint -> MkLink endpoint Link
>>> apiLink = safeLink api
>>> :}

safeLink' allows to make specialise the output:

>>> safeLink' toUrlPiece api without
"bye"

>>> :{
>>> let apiTextLink :: (IsElem endpoint API, HasLink endpoint)
>>> => Proxy endpoint -> MkLink endpoint Text
>>> apiTextLink = safeLink' toUrlPiece api
>>> :}

>>> apiTextLink without
"bye"

Attempting to construct a link to an endpoint that does not exist in api will result in a type error like this:

>>> let bad_link = Proxy :: Proxy ("hello" :> Delete '[JSON] NoContent)
>>> safeLink api bad_link
...
...Could not deduce...
...

This error is essentially saying that the type family couldn't find bad_link under api after trying the open (but empty) type family IsElem' as a last resort.

Synopsis

Documentation

module Servant.API.TypeLevel

Building and using safe links

Note that URI is from the Network.URI module in the network-uri package.

safeLink Source #

Arguments

:: (IsElem endpoint api, HasLink endpoint) 
=> Proxy api

The whole API that this endpoint is a part of

-> Proxy endpoint

The API endpoint you would like to point to

-> MkLink endpoint Link 

Create a valid (by construction) relative URI with query params.

This function will only typecheck if endpoint is part of the API api

safeLink' Source #

Arguments

:: (IsElem endpoint api, HasLink endpoint) 
=> (Link -> a) 
-> Proxy api

The whole API that this endpoint is a part of

-> Proxy endpoint

The API endpoint you would like to point to

-> MkLink endpoint a 

More general safeLink.

allLinks :: forall api. HasLink api => Proxy api -> MkLink api Link Source #

Create all links in an API.

Note that the api type must be restricted to the endpoints that have valid links to them.

>>> type API = "foo" :> Capture "name" Text :> Get '[JSON] Text :<|> "bar" :> Capture "name" Int :> Get '[JSON] Double
>>> let fooLink :<|> barLink = allLinks (Proxy :: Proxy API)
>>> :t fooLink
fooLink :: Text -> Link
>>> :t barLink
barLink :: Int -> Link

Note: nested APIs don't work well with this approach

>>> :kind! MkLink (Capture "nest" Char :> (Capture "x" Int :> Get '[JSON] Int :<|> Capture "y" Double :> Get '[JSON] Double)) Link
MkLink (Capture "nest" Char :> (Capture "x" Int :> Get '[JSON] Int :<|> Capture "y" Double :> Get '[JSON] Double)) Link :: *
= Char -> (Int -> Link) :<|> (Double -> Link)

allLinks' :: forall api a. HasLink api => (Link -> a) -> Proxy api -> MkLink api a Source #

More general allLinks. See safeLink'.

data URI :: * #

Represents a general universal resource identifier using its component parts.

For example, for the URI

  foo://anonymous@www.haskell.org:42/ghc?query#frag

the components are:

Constructors

URI 

Fields

Instances

Eq URI 

Methods

(==) :: URI -> URI -> Bool #

(/=) :: URI -> URI -> Bool #

Data URI 

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> URI -> c URI #

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c URI #

toConstr :: URI -> Constr #

dataTypeOf :: URI -> DataType #

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c URI) #

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c URI) #

gmapT :: (forall b. Data b => b -> b) -> URI -> URI #

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> URI -> r #

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> URI -> r #

gmapQ :: (forall d. Data d => d -> u) -> URI -> [u] #

gmapQi :: Int -> (forall d. Data d => d -> u) -> URI -> u #

gmapM :: Monad m => (forall d. Data d => d -> m d) -> URI -> m URI #

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> URI -> m URI #

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> URI -> m URI #

Ord URI 

Methods

compare :: URI -> URI -> Ordering #

(<) :: URI -> URI -> Bool #

(<=) :: URI -> URI -> Bool #

(>) :: URI -> URI -> Bool #

(>=) :: URI -> URI -> Bool #

max :: URI -> URI -> URI #

min :: URI -> URI -> URI #

Show URI 

Methods

showsPrec :: Int -> URI -> ShowS #

show :: URI -> String #

showList :: [URI] -> ShowS #

Generic URI 

Associated Types

type Rep URI :: * -> * #

Methods

from :: URI -> Rep URI x #

to :: Rep URI x -> URI #

NFData URI 

Methods

rnf :: URI -> () #

type Rep URI 

Adding custom types

class HasLink endpoint where Source #

Construct a toLink for an endpoint.

Minimal complete definition

toLink

Associated Types

type MkLink endpoint (a :: *) Source #

Methods

toLink Source #

Arguments

:: (Link -> a) 
-> Proxy endpoint

The API endpoint you would like to point to

-> Link 
-> MkLink endpoint a 

data Link Source #

A safe link datatype. The only way of constructing a Link is using safeLink, which means any Link is guaranteed to be part of the mentioned API.

linkURI :: Link -> URI Source #

Transform Link into URI.

>>> type API = "something" :> Get '[JSON] Int
>>> linkURI $ safeLink (Proxy :: Proxy API) (Proxy :: Proxy API)
something

>>> type API = "sum" :> QueryParams "x" Int :> Get '[JSON] Int
>>> linkURI $ safeLink (Proxy :: Proxy API) (Proxy :: Proxy API) [1, 2, 3]
sum?x[]=1&x[]=2&x[]=3

>>> type API = "foo/bar" :> Get '[JSON] Int
>>> linkURI $ safeLink (Proxy :: Proxy API) (Proxy :: Proxy API)
foo%2Fbar

>>> type SomeRoute = "abc" :> Capture "email" String :> Put '[JSON] ()
>>> let someRoute = Proxy :: Proxy SomeRoute
>>> safeLink someRoute someRoute "test@example.com"
Link {_segments = ["abc","test%40example.com"], _queryParams = []}

>>> linkURI $ safeLink someRoute someRoute "test@example.com"
abc/test%40example.com

linkURI' :: LinkArrayElementStyle -> Link -> URI Source #

Configurable linkURI.

>>> type API = "sum" :> QueryParams "x" Int :> Get '[JSON] Int
>>> linkURI' LinkArrayElementBracket $ safeLink (Proxy :: Proxy API) (Proxy :: Proxy API) [1, 2, 3]
sum?x[]=1&x[]=2&x[]=3

>>> linkURI' LinkArrayElementPlain $ safeLink (Proxy :: Proxy API) (Proxy :: Proxy API) [1, 2, 3]
sum?x=1&x=2&x=3

data LinkArrayElementStyle Source #

How to encode array query elements.

Constructors

LinkArrayElementBracket
foo[]=1&foo[]=2
LinkArrayElementPlain
foo=1&foo=2

Instances

Bounded LinkArrayElementStyle Source # 
Enum LinkArrayElementStyle Source # 
Eq LinkArrayElementStyle Source # 
Ord LinkArrayElementStyle Source # 
Show LinkArrayElementStyle Source # 

Link accessors

data Param Source #

Query parameter.

Constructors

SingleParam String Text 
ArrayElemParam String Text 
FlagParam String 

Instances

linkSegments :: Link -> [String] Source #

linkQueryParams :: Link -> [Param] Source #