servant-0.16: A family of combinators for defining webservices APIs

Safe HaskellNone
LanguageHaskell2010

Servant.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.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.

Since: 0.14.1

Synopsis

Documentation

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 
Instance details

Defined in Network.URI

Methods

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

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

Data URI 
Instance details

Defined in Network.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 
Instance details

Defined in Network.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 
Instance details

Defined in Network.URI

Methods

showsPrec :: Int -> URI -> ShowS #

show :: URI -> String #

showList :: [URI] -> ShowS #

Generic URI 
Instance details

Defined in Network.URI

Associated Types

type Rep URI :: Type -> Type #

Methods

from :: URI -> Rep URI x #

to :: Rep URI x -> URI #

NFData URI 
Instance details

Defined in Network.URI

Methods

rnf :: URI -> () #

type Rep URI 
Instance details

Defined in Network.URI

Generics

data AsLink (a :: *) Source #

A type that specifies that an API record contains a set of links.

Since: 0.14.1

fieldLink :: (IsElem endpoint (ToServantApi routes), HasLink endpoint, GenericServant routes AsApi) => (routes AsApi -> endpoint) -> MkLink endpoint Link Source #

Given an API record field, create a link for that route. Only the field's type is used.

data Record route = Record
    { _get :: route :- Capture "id" Int :> Get '[JSON] String
    , _put :: route :- ReqBody '[JSON] Int :> Put '[JSON] Bool
    }
  deriving (Generic)

getLink :: Int -> Link
getLink = fieldLink _get

Since: 0.14.1

fieldLink' :: forall routes endpoint a. (IsElem endpoint (ToServantApi routes), HasLink endpoint, GenericServant routes AsApi) => (Link -> a) -> (routes AsApi -> endpoint) -> MkLink endpoint a Source #

More general version of fieldLink

Since: 0.14.1

allFieldLinks :: (HasLink (ToServantApi routes), GenericServant routes (AsLink Link), ToServant routes (AsLink Link) ~ MkLink (ToServantApi routes) Link) => routes (AsLink Link) Source #

Get all links as a record.

Since: 0.14.1

allFieldLinks' :: forall routes a. (HasLink (ToServantApi routes), GenericServant routes (AsLink a), ToServant routes (AsLink a) ~ MkLink (ToServantApi routes) a) => (Link -> a) -> routes (AsLink a) Source #

More general version of allFieldLinks.

Since: 0.14.1

Adding custom types

class HasLink endpoint where Source #

Construct a toLink for an endpoint.

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 # 
Instance details

Defined in Servant.Links

Enum LinkArrayElementStyle Source # 
Instance details

Defined in Servant.Links

Eq LinkArrayElementStyle Source # 
Instance details

Defined in Servant.Links

Ord LinkArrayElementStyle Source # 
Instance details

Defined in Servant.Links

Show LinkArrayElementStyle Source # 
Instance details

Defined in Servant.Links

Link accessors

data Param Source #

Query parameter.

Instances
Show Param Source # 
Instance details

Defined in Servant.Links

Methods

showsPrec :: Int -> Param -> ShowS #

show :: Param -> String #

showList :: [Param] -> ShowS #