Haskell combinator library for defining and serving web services.
Questions tagged [servant]
197 questions
4
votes
1 answer
Haskell Servant passing custom data to auth handler
I'm using custom monad (with reader) to easily pass data like DB pool to my handlers (before using custom monad I used to pass connection as fn argument).
This is how I've defined my custom monad :
newtype Controller a = Controller
{…
Reygoch
- 1,204
- 1
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4
votes
1 answer
Database-backed REST API with servant?
I am running into a problem setting up a simple proof of concept servant API. This is my User datatype and my API type:
data User = User { id :: Int, first_name :: String, last_name :: String } deriving (Eq, Show, Generic)
instance FromRow…
asg0451
- 493
- 4
- 13
4
votes
1 answer
How can I get access to http headers in Servant?
I have a simple servant application with rest api:
type API = "items" :> Get '[JSON] [MyData]
app :: Application
app = serve api server
api :: Proxy API
api = Proxy
server :: Server API
server = getItems
getItems :: ExceptT ServantErr IO…
user266003
3
votes
1 answer
Haskell servant combined api implementation
I am going through the servant tutorial found here. There is a partial implementation that is left for the user to figure out what it should be.
type APIFor a i =
Get '[JSON] [a]
:<|> ReqBody '[JSON] a :> PostNoContent
:<|> Capture "id" i…
Sylvoo
- 265
- 2
- 17
3
votes
1 answer
How to limit file size for multipart/form-data upload to Servant server?
The documentation at hackage.haskell.org/package/servant-multipart says about the main combinator type MultipartForm tag a following:
Note that the behavior of this combinator is configurable, by using serveWith from servant-server instead of…
adius
- 13,685
- 7
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3
votes
1 answer
Haskell Servant - What is the Purpose of serveWithContext and What Does it do That a ReaderT Can't?
I'm trying to understand the purpose of Servant's serveWithContext function. The documentation states that it's not a replacement for the ReaderT Monad, but I'm uncertain as to what problem it's trying to solve that isn't already addressed by…
Joshua Billson
- 33
- 3
3
votes
1 answer
Changing the web-root (or path-prefix) at runtime via servant?
I need to give the ability to change the web-root (or path-prefix) of my API via CLI arguments.
If my server exposes the following API paths...
/enqueue
/run
/cancel
...at startup it should be possible to change them to the following by passing a…
Saurabh Nanda
- 6,373
- 5
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3
votes
2 answers
How to access raw request body in servant application
In a servant/wai application the request body can be obtained using a combinator e.g. ReqBody '[JSON] Book. In this case the body is extracted as a value of type Book. It is not clear how the raw request body can be accessed without converting it to…
7puns
- 1,505
- 1
- 9
- 9
3
votes
2 answers
How to define a simple RIO LogFunc without bracketing execution
I'm trying to set up logging in a RIO application; yet, I don't seem to understand the logging interface.
RIO documentation encourages to define a logger and run the application as follows:
withLogFunc logOptions $ \lf -> do
let env = Env --…
Ulrich Schuster
- 1,670
- 15
- 24
3
votes
1 answer
How can I inspect/debug the body of a servant-client's request?
Full minimal example project available here: https://github.com/chrissound/217
I've read through https://docs.servant.dev/en/v0.16/cookbook/using-free-client/UsingFreeClient.html
Where I end up with:
type API = "square"
:> Capture "n" Int
:>…
Chris Stryczynski
- 30,145
- 48
- 175
- 286
3
votes
1 answer
Correctly handle invalid query parameter in Servant
I'm following along with the Servant tutorial, and I've defined the following API type:
type UsersAPI = "users" :> QueryParam "sortby" SortBy :> Get '[JSON] [UserData]
data SortBy = Id | Name | Age
instance FromHttpApiData SortBy where
…
Tomas Aschan
- 58,548
- 56
- 243
- 402
3
votes
1 answer
How to force Servant return JSON errors instead of plain strings?
By default, Servant returns plain string requests even if the requested endpoint returns JSON
$ http $S/signup email=mail@domain.com
HTTP/1.1 400 Bad Request
Connection: keep-alive
Date: Tue, 14 Apr 2020 15:59:32 GMT
Server: nginx/1.17.9…
Nik
- 9,063
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3
votes
1 answer
Answer a request with 200 or 404 based on the content of `Maybe` using Servant
I'm currently trying to implement a simple web server with servant. At the moment, I have a IO (Maybe String) that I want to expose via a GET endpoint (this might be a database lookup that may or may not return a result, hence IO and Maybe). If the…
l7r7
- 1,134
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3
votes
0 answers
How to add a specific representation of the request and response of the body of an HTTP request with Haskell Middleware
How can i add a specific representation of the request and response body in a request logger? I would like to be able to have some typeclass that allows me to achieve this representation. In the Network.Wai.Middleware.RequestLogger.JSON I can see…
emg184
- 850
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3
votes
1 answer
Serverless works locally but not when deployed
I have written a simple servant server and converted it into a lambda function that queries a MySQL db in amazon RDS. I can get it to work locally with serverless offline start however when I deploy it (serverless deploy) I get the following error…
Jimbo
- 331
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- 13