Apollo Error Code lost when using mergeSchemas

[ksmithut]

It is expected that the error codes and other error extensions maintain themselves when returning to the client. When using mergeSchemas, when a custom error is thrown using ApolloError, the error code is lost. Although it's understandable why this might happen when merging remote schemas, this even happens with local schemas. An example server (or set of servers) and example curl requests show the difference in results:

To reproduce, run:

mkdir apollo-server-error-test && cd $_
npm i apollo-server graphql
touch index.js

Put the following into index.js:

index.js

const {
  ApolloServer,
  ApolloError,
  makeExecutableSchema,
  mergeSchemas,
  gql
} = require('apollo-server')

const schema = makeExecutableSchema({
  typeDefs: gql`
    type Query {
      available: Boolean!
    }
  `,
  resolvers: {
    Query: {
      available() {
        throw new ApolloError('some error', 'MY_CUSTOM_ERROR_CODE')
      }
    }
  }
})

const apolloServer = new ApolloServer({ schema })
apolloServer.listen(8000)

const apolloServerBadErrors = new ApolloServer({
  schema: mergeSchemas({ schemas: [schema] })
})
apolloServerBadErrors.listen(8001)

Then run NODE_ENV=production node index (production to suppress stack trace from output).

After that, run the following curl commands and you'll get the respective results:

---

# From "good" server
curl -X POST http://localhost:8000/graphql \
  -H 'Content-Type:application/json' \
  -H 'Accept:application/json' \
  -d '{"query":"query{available}"}' 

response

{
  "data": null,
  "errors": [
    {
      "message": "some error",
      "locations": [{ "line": 1, "column": 7 }],
      "path": ["available"],
      "extensions": { "code": "MY_CUSTOM_ERROR_CODE" }
    }
  ]
}

---

# From "bad" server
curl -X POST http://localhost:8001/graphql \
  -H 'Content-Type:application/json' \
  -H 'Accept:application/json' \
  -d '{"query":"query{available}"}' 

response

{
  "data": null,
  "errors": [
    {
      "message": "some error",
      "locations": [{ "line": 1, "column": 7 }],
      "path": ["available"],
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR",
        "exception": {
          "errors": [
            { "message": "some error", "locations": [], "path": ["available"] }
          ]
        }
      }
    }
  ]
}

---

Perhaps this is as designed, but it would be awesome if there was a way to propagate error codes up through the mergeSchemas "firewall".

[ph55]

I've opened bug in graphql-tools, not sure on whom side the fix.
ardatan/graphql-tools#1037

[arc-008]

Resolved for me after importing "extractExtensionDefinitions". ardatan/graphql-tools#1037 (comment)

[robertontiu]

Is there a fix for this? We are providing some more information besides code under extensions but everything seems to be lost now that we are using mergeSchemas.

[abernix]

@robertontiu I don't believe there's fix for this yet. Would it be something you'd be interested in looking into? I suspect (though I'm not certain; debugging would be required), the problem lies in the graphql-tools repository, possibly within one of the three different prongs of the conditional which starts off within the schemas.forEach loop here:

https://github.com/apollographql/graphql-tools/blob/641d7058fdf4b7af08a92a770c0b9a4f0febea29/src/stitching/mergeSchemas.ts#L100-L101

There are different forms of schemas that graphql-tools accepts, each with subtle intentional nuances. One of those might be off?

[hwillson]

Quick note - the original reproduction listed here no longer fails when using a modern day version of apollo-server (it was likely fixed by ardatan/graphql-tools#637), but this problem still persists when the error is thrown a bit differently. Here's a new reproduction that shows the problem: https://github.com/hwillson/graphql-tools-stitching-errors

I'll work on addressing this in graphql-tools, and will post back here when the fix is ready.

[jbaxleyiii]

This is fixed in newer versions

[electerious]

It still seems to be a thing #4807

[glasser]

As mentioned on #4807, mergeSchemas is part of graphql-tools; the old version "conveniently" re-exported from Apollo Server is not maintained.