Return custom HTTP status codes

[rb090]

Hi 👋,

I start using your library to provide a GraphQL API endpoint. I am working on the error handling right now. I read your documentation Exceptions and Partial Data regarding this. Returning errors like described there works very well.

I am coming from the REST world and there I am used to return corresponding HTTP Status codes in case that sth went wrong. So fe. when my code throws an IllegalArgumentException somewhere, I like to return fe. HTTP status code 400 (bad request) and an error json:

{
  "title": "Sth went wrong",
  "message": "Some message here explaining more"
}

Can you please tell me whether sth similar is possible in graphql and with your library?

Probably not with DataFetcherResult because there, HTTP status code is always 200.

Can I throw somehow a custom graphql exception which produces a similar result like I would like it to have?

Thanks in regards for any suggestion on this. Please be patient with me, it is my 1st GQL server project 🙈

[rb090]

So to maybe wireframe my question a bit in code, if I have a mutation like this:

class MyMutation : Mutation {

    fun sampleMutationDoingSth(user: User): ReturnObject? {

        val result = methodCallWhichCanThrow(user: user)

        return ReturnObject(userName=result.name)
    }
}

It would be nice if in case that methodCallWhichCanThrow throws an exception like fe. an IllegalStateException the server responds with an HTTP Status code different than 200. Fe. HTTP Status code 500.

ATM in case of an exception the server returns this and HTTP status code 200:

{
    "data": {
        "sampleMutationDoingSth": null
    },
    "errors": [
        {
            "message": "Exception while fetching data (/sampleMutationDoingSth) : <EXCEPTION message here>",
            "locations": [
                {
                    "line": 2,
                    "column": 5
                }
            ],
            "path": [
                "sampleMutationDoingSth"
            ]
        }
    ]
}

I am really thankful for any hint on this. I already read that it is not usual that graphql server return "error http status codes" in case of errors like fe. REST APIs would do. But I also saw Rust GQL server doing this fe.

And you also do this in case that I try to read out headers within my mutation by using DataFetchingEnvironment. And the header I expect is not there. Then GQL server answers me with HTTP Status 400 which is exactly the right thing.

And also what I would like the server to do in case an exception is thrown within my code.

[dariuszkuc]

Hello 👋
In general, as long as GraphQL server can resolve your request and respond with well formed response then the return status should be 200. There are number of great talks/blog posts that cover this topic - I highly recommend to check out Guide to GraphQL Errors by Marc-Andre and 200 OK! talk from Sasha.

As an FYI, there is a draft spec for implementing GraphQL over HTTP that attempts to add back some of the status codes back to the responses -> https://graphql.github.io/graphql-over-http/draft. It introduces new application/graphql-response+json media type that allows you to specify custom status code and "should" become the "standard" starting Jan 1st 2025. Until then the standard is to use application/json.

While we don't cover some of the optional behavior (related to new application/graphql-response+json media type), GraphQL Kotlin servers are http spec compliant.

[rb090]

Hi @dariuszkuc,

thanks a lot for your answer and the explanations. That helped a lot. I reviewed them and make some thoughts about it. I understood the points and how to realize the error handling within a GraphQL library 🙂. So thanks a lot for this.

My favorite solution from Guide to GraphQL Errors is the "Stage 6a: Error Union List + Interface" 🙂. I hope that this can be build with the graphql-kotlin. And I will also check in detail how it fits in our environment with an error list and stuff.