API: Extend FileIO in optional interfaces

[aokolnychyi]

This PR extends FileIO in its optional interfaces. This way, we we can access all methods available in FileIO if we have a reference to the optional interface. Otherwise, we have to cast back.

[aokolnychyi]

@danielcweeks @rdblue @flyrain @szehon-ho @stevenzwu @jackye1995, could you take a look?

[aokolnychyi]

All these interfaces assume they are mixed-in by FileIO instances (see docs).

[rdblue]

This is not quite correct. CredentialSupplier may extend other interfaces and not just FileIO.

[aokolnychyi]

You are right. I misinterpreted the doc.

[rdblue]

I don't think we should do this for CredentialSupplier, but the other two look fine.

[stevenzwu]

@aokolnychyi this doesn't seem to be a problem in current code. I assume you ran into this need of casting in some new code you are working on?

I found the interface name of SupportsPrefixOperations less intuitive for an interface extending from FileIO. Supports just meant some extra capability. can't connect Supports... as an extended interface of FileIO.

Another downside is that S3FileIO would need to implement both SupportsBulkOperations and SupportsPrefixOperations with large overlap of base FileIO interface. not a problem for compiler. just thought a little odd.

[aokolnychyi]

@stevenzwu, this becomes an issue when we need both the optional functionality as well the core FileIO methods. I don't think these SupportsXXX can be used without FileIO as they are tightly coupled with it. It's the same pattern that Spark, for example, uses in its public APIs. These SupportsXXX simply add optional functionality to FileIO.

[stevenzwu]

agree that SupportsXXX can't be used without FileIO, as SupportsXXX declares additional capability for FileIO.

public class S3FileIO
    implements FileIO, SupportsBulkOperations, SupportsPrefixOperations

I am trying to understand the concrete issue (type cast problem) that this tries to help with. Are we trying to type cast a FileIO object to SupportsXXX interface to check the capability? Can we use instanceOf to check the capability?

if we want to access FileIO methods after type cast say SupportsBulkOperations, it won't help if we also need to access the methods from SupportsPrefixOperations. We will still need to type cast to two different SupportsXXX interfaces.

[rdblue]

Thanks, @aokolnychyi!