Exception handling in GraphQLContextFactory

[dhartung]

Inside my custom GraphQLContextFactory I parse a JWT Token and extract relevant fields into the configmap. This process might fail if the token is not valid or does not meet the specification. When throwing an exception, I would expect my DataFetcherExceptionHandler to handle this exception and return a fitting message to the client. However, the DataFetcherExceptionHandler is not called and instead a wrapped Internal server error is returned:

{
    "timestamp": "2022-06-15T07:30:45.120+00:00",
    "path": "/graphql",
    "status": 500,
    "error": "Internal Server Error",
    "requestId": "3707c8f1-18176"
}

What's best practice to catch this exception and wrap it into the default GraphQl error response?

I'm using version 5.5.0 with the following minimal example:

@Component
class ApplicationGraphQlContextFactory : SpringGraphQLContextFactory<SpringGraphQLContext>() {
    override suspend fun generateContextMap(request: ServerRequest): Map<*, Any> {
        throw IllegalArgumentException("French fries")
    }

    override suspend fun generateContext(request: ServerRequest) = SpringGraphQLContext(request)
}

@Component
class ApplicationDataFetcherExceptionHandler : DataFetcherExceptionHandler {
    class KotlinGraphQLError(
        private val code: Int,
        private val message: String?,
    ) : GraphQLError {
        override fun getErrorType(): ErrorClassification = ErrorType.DataFetchingException

        override fun getExtensions(): Map<String, Any> = mapOf("code" to code)

        override fun getMessage(): String = message ?: ""

        override fun getLocations(): List<SourceLocation>? = null
    }

    override fun onException(handlerParameters: DataFetcherExceptionHandlerParameters): DataFetcherExceptionHandlerResult {
        val exception: Throwable = handlerParameters.exception

        val error = KotlinGraphQLError(code = 1, message = exception.message)
        return DataFetcherExceptionHandlerResult.newResult(error).build()
    }
}

[dariuszkuc]

Hello 👋
Generation of context happens before the GraphQL execution (link so the handler won't run as this logic is outside of graphql-java execution engine.

Personally I would parse the JWT token in a webfilter and return appropriate HTTP status if it is not valid.