CODEWITHSUNDEEP
jsonvalidationhaskell
TomTom
TomTom

Reputation: 2940

How to validate JSON with schema in Haskell?

I want to validate JSON with a schema. hjsonschema seemed like a good choice as it is fairly new and supports the latest draft. But the plotly json schema always gives me valid responses.

I may be misunderstanding something here but this should not be valid JSON

bad.json

{
    "fjsdklj" : 5
}

even though it is considered valid by the following code

module Main where

import           Control.Applicative
import           Data.Aeson
import           Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as H
import           Data.Monoid
import qualified Data.ByteString.Lazy as B
import qualified Data.JsonSchema as JS
import Data.Maybe

main :: IO ()
main = do
    schemaJSON <- (fromJust . decode) <$> B.readFile "simple-schema.json"
    bad <- (fromJust . decode) <$> B.readFile "bad.json"
    let schemaData = JS.RawSchema {
                        JS._rsURI = Nothing,
                        JS._rsData = schemaJSON
                        }
    schema <- compileSchema (JS.SchemaGraph schemaData H.empty) schemaData
    checkResults (JS.validate schema bad)

compileSchema :: JS.SchemaGraph -> JS.RawSchema -> IO (JS.Schema JS.Draft4Failure)
compileSchema graph rs =
  case JS.compileDraft4 graph rs of
    Left failure -> error $ "Not a valid schema: " <> show failure
    Right schema -> return schema

checkResults :: [JS.ValidationFailure JS.Draft4Failure] -> IO ()
checkResults [] = putStrLn "Just fine"
checkResults x = putStrLn $ "ERROR: " ++ show x

simple-schema.json is the plotly schema and bad.json the snippet I posted above.

Upvotes: 2

Views: 776

Answers (1)

zakyggaps
zakyggaps

Reputation: 3080

It's nothing about Haskell.

Your schema doesn't have a required property at top level so an empty json object is acceptable.

Also it contains no "additionalProperties": false property so anything that does not fit into one of the defined patterns are ignored.

BTW I doubt whether it's a valid Draft4 json schema. It passed the validation of the Draft4 meta-schema but the syntax is a little bit different, maybe something Python-specific. You'd better run the test suites which came along with the hjsonscheme package to see if everything works fine.

Upvotes: 5

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