"Duplicate type name" error when fetching similar schemas

There is a bug (at least, I think it’s unexpected behaviour) in the avsc library where it mutates the passed forSchemaOptions to add a registry to it, which then means subsequent calls using the same forSchemaOptions then crash with a “Duplicate type name” error. See https://github.com/mtth/avsc/issues/312.

This caused a crash for us because the schema registry reuses the options object between calls. So for example, given schemas 1 and 2 which both contain a record with the same name, the following code will crash:

const reg = new SchemaRegistry(
    { host: 'http://localhost:3322' },
    { forSchemaOptions: {} },
);
await reg.getSchema(1);
await reg.getSchema(2); // Error: duplicate type name

Which is obviously quite a big problem because as soon as we try and parse an old and newer version of a subject, our app crashes with this error.

It’s worth noting that the crash only happens if we specify forSchemaOptions, as otherwise forSchema gets called with undefined and there’s nothing for avsc to mutate.

So primarily I think this is a bug in avsc and I wanted you to be aware – in my opinion it should be perfectly valid for the schema registry to pass the same options into it every time. However it might be worth putting a work around in. For our use case we’re patching this line to always pass an empty registry object in:

this.schemasByRegistryId[registryId] = avro.Type.forSchema(schema, {...this.forSchemaOptions, registry: {}})

so that might be a change worth including for the time being? I’m not sure why avsc even exposes the registry as an option as it feels like an implementation detail to me, so perhaps there’s some use case I’m not aware of.

Thanks very much!

[henrymunro]

I’ve also hit this when attempting to pass logicalTypes to the avro options.

Had a go at pushing a PR, making this change locally fixed the issue: https://github.com/kafkajs/confluent-schema-registry/pull/209

[jcjp]

We are actually experiencing this issue but we don’t use forSchemaOptions property. We are setting up our schemaRegistry:

public registry = new SchemaRegistry({
    auth: { ... },
    host: { ... }
  }, {
    [SchemaType.AVRO]: {registry: typeMap}
  })

We populate the typeMap variable using this:

import avro from 'avsc'

...

for (let subj of refs) {
      if (!typeMap[subject]) {
        ...
        typeMap[subject] = avro.Type.forSchema(schema)
      }
}