servant

问题 What's the appropriate way to make a Servant handler respond with a redirection? I am working in a navigation REST app and I would like to respond to POST requests that create resources with a redirection to the corresponding GET resource list paths. So for instance POST /foos should redirect to GET /foos after creating a foo. I could not find a clear way to do that in the documentation. 回答1: There is one simple (but slightly hacky) answer, and a lead for making the first option obsolete

问题 My site is built in Haskell/Servant and Wai/Warp. I need to redirect all requests from my domain.com to www.domain.com with the the 301 or 302 status. I know I can do that with the help of Wai/Warp somehow. How exactly? startApp :: IO () startApp = run 1234 app 回答1: The package wai-util has a convenience function redirect' to create such a Response , so you should be able to do something like app :: Application app req respond = respond =<< redirect' status302 [] uri where Just uri = parseURI

问题 I'd like to use Servant's ClientM monad with finally :: MonadBaseControl IO m => m a -> m b -> m a , but am faced with error No instance for (MonadBaseControl IO ClientM) . Oddly, this exact instance appears to be defined already, be it from an internal module. Do I need to explicitly import such instances somehow? 回答1: It works fine if, as Daniel said, you import the module that defines the desired instance: Prelude> import Control.Exception.Lifted Prelude Control.Exception.Lifted> import

问题 I'm working on an API integration that ignores the existence of XML or JSON in favor of just appending character data. (The Metro2 format, if interested) I'm simplifying, but imagine that a person needs to be serialized like this: At pos 0, 4 chars: Number of bytes in the message At pos 5: 6 chars: "PERSON" hard coded At pos 11: 20 chars: Name, left-aligned and space-padded At pos 21: 8 chars: Birthday, YYYYMMDD At pos 29: 3 chars: Age, right-aligned and zero-padded Numeric fields are always

问题 I would like to use Shakespearean Templates (Licius + Hamlet + Julius) from the Yesod.But I have some difficulty with this. The following code from enter link description here works: type TestAPI = "tests" :> Get '[JSON] [Test] :<|> "test" :> Get '[JSON] Test :<|> "TestHTML.html" :> Get '[HTML] Page_TestHTML serverTestAPI :: ServerT TestAPI AppM serverTestAPI = tests :<|> test :<|> testHtml data Page_TestHTML = Page_TestHTML instance ToMarkup Page_TestHTML where toMarkup Page_TestHTML =

问题 How i can use shakespeare (from yesod) for servant webservices APIs? I try: type TestAPI = "tests" :> Get '[JSON] [Test] :<|> "Test.html" :> Get '[HTML] Html serverTestAPI :: ServerT TestAPI AppM serverTestAPI = tests :<|> test :<|> testHtml tests :: AppM [Test] tests = do return [ Test 1 "Test 1" , Test 2 "Test 2" ] testHtml = [hamlet| $doctype 5 ......... |] But I get error! 回答1: As @Carsten points out, in this case what you want is shamlet . The key thing is implementing proper instances

问题 I was reading the Servant documentation and came across this line: type UserAPI = "users" :> QueryParam "sortby" SortBy :> Get '[JSON] [User] What is the ' doing to that list? 回答1: This is DataKinds in action, which: lifts values at the type level, and lifts types to the kind level This however causes confusion at the type level. Now, in types, [X] might either be [X] :: * , the list-of- X type, or instead we might have [X] :: [T] due to the lifting -- that is the value [X] (list containing

问题 I am trying to add a functionality to my servant server that would get a file from Amazon S3 and stream it back to the user. Because files can be big I don't want to download them locally and then serve them to clients, I'd rather prefer to stream them directly from S3 to clients. I use Amazonka for what I do with S3 and I can get a stream for an S3 file as a Conduit sink. But now I don't know how to get from Sink to EitherT ServantErr IO a . Can anyone explain me how to do it or show me some

问题 I'm trying to use persistent-postgresql with servant. I have a User model. I want to have an endpoint that takes an id and returns the user with that id. According to other answers I can use toSqlKey to turn an Int64 into a Key to feed to get . My function looks like: oneUser :: Int64 -> App (Entity User) oneUser userId = do maybeUser <- runDb $ get $ toSqlKey userId case maybeUser of Nothing -> throwError err404 Just user -> return user When I try to compile I get the error Couldn't match

问题 In the Servant docs, we have the following api: type API = "position" :> Capture "x" Int :> Capture "y" Int :> Get '[JSON] Position :<|> "hello" :> QueryParam "name" String :> Get '[JSON] HelloMessage :<|> "marketing" :> ReqBody '[JSON] ClientInfo :> Post '[JSON] Email and we can define client functions like so: api :: Proxy API api = Proxy position :<|> hello :<|> marketing = client api If our api type instead looked like: type API = QueryParam "test" Int :> ( "position" :> Capture "x" Int :