Implement filtering in reference implementation about grafeas

[ant-caichu]

i think a go-restful based framework should be imported, https://github.com/hpejustin/depark this can be a good example.

[ant-caichu]

i think, we can add Label or Annotation properties to Note and Occurrence, in that case we can use filter to list them.

[R2wenD2]

The intention here is to allow filtering on fields that already exist as a part of the occurrence or note. I don't see a case for additional labels or annotations.

The implementation will to parse a query string, reading key,values where keys are the fields of our resources.

[R2wenD2]

We'll use one of the following filtering specs:

• https://github.com/google/cel-spec
• https://cloud.google.com/logging/docs/view/advanced_filters

Both of them require an accessible parser - I'm following up on that.

[furuholm]

One aspect of this could be to go for a format that can be transformed into a database query, or will that be too restrictive?

[R2wenD2]

We need a few things:

1. A parser that will parse and validate a filter expression from query string
2. A mapping of Keys to database fields (which I think is what you're referring to, @furuholm

I'm working with the cel team to create part one of this, but once we have that part 2 can follow quickly.

We also need a real database, but that's a separate issue.

[furuholm]

Added #84 to address the database

[TristonianJones]

Hey there, I've implemented the filter parsing using the syntax of advanced filters with the backing representation as cel. Any preference on which directory the parser should go into?

[R2wenD2]

@TristonianJones Awesome! Lets put it in grafeas/server-go/filtering.

[TristonianJones]

Just curious, but any thoughts on whether this is something that you'd like to continue using? If so, the github.com/google/cel-go library can be used to evaluate ASTs generated by the filtering parser.

[vtsao]

Yes we are still planning on using what you impl'd for our filtering. Also thanks for the code pointer. @aysylu FYI this might be something you will take on.