CachedSchemaRegistryClient without Guava dependency

[thomassteger-zkb]

Hi there,
With DGS-2487: Adding missing cache to schema registry client (#2082) you introduced a runtime dependency on guava in the kafka-schema-registry-client.
Currently, the CachedSchemaRegistryClient is the only none test class of the kafka-schema-registry-client depending on guava.

This dependency has some drawbacks:

• Overall size of the client distribution: the guava dependency including transitive dependencies adds ~3 MB
• Versions conflicts: Applications which use guava and the schema registry client at the same time, will ,sooner or later, run into version conflicts with the guava library or with one of the transitive dependencies
• Added potential security risks: Each additional dependency adds potential security risks (remember log4j). These risks need to be managed by confluent and their customers

Now would be a good time to get rid of this dependency in the kafka-schema-registry-client since it has not spread very far :-)

My Ideas:

• Rewrite the missingSchemaCache and missingIdCache in the CachedSchemaRegistryClient to use java* classes.
  or
• Provide an alternative SchemaRegistryClient implementation without the missingId/SchemaCaches (the version of the class before DGS-2487: Adding missing cache to schema registry client #2082 would do)

I would be willing to contribute :-)

Thanks

[thomassteger-zkb]

I think the ship has sailed :-(
My statements above are base on version 7.0.1 but with later versions, the usage of guava has spread to more classes.