Add fallbacks for gql.errorCode and gql.errorDetail in graphql-dgs-spring-boot-micrometer

[caseygum]

Currently, the gql.errorCode and gql.errorDetail tags are extracted from error.extensions.errorType and error.extensions.errorDetail for generic GraphQLErrors in DgsGraphQLMetricsInstrumentation.

While it's not strictly part of the GraphQL spec for error formatting, the example given on the spec, and the name of the tag itself would both suggest the key to look for in the extensions map would be code. Apollo Server also uses extensions.code.

At Indeed, most of our almost 200 federated subgraphs use Netflix DGS, but have standardized on using extensions.code for error codes. Some of our devs have complained that the tag values showing up in DataDog for gql.errorCode and gql.errorDetail are always unknown and none. I would like to add a pull request to address where the DgsGraphQLMetricsInstrumentation.kt functions errorTypeExtension() and errorDetailExtension() are updated as follows:

   // look for extensions.errorType, then extensions.code, then error.errorType
    private fun <T : GraphQLError> errorTypeExtension(error: T): String {
        return extension(error, "errorType", extension(error, "code", error.errorType.toString()))
    }

    // look for extensions.errorDetail, then error.message
    private fun <T : GraphQLError> errorDetailExtension(error: T): String {
        return extension(error, "errorDetail", error.message ?: "none")
    }

Thoughts?

[srinivasankavitha]

Thanks for the detailed explanation. I think this makes sense.