More fine-grained validation?

[Todd O'Bryan <to...@gmail.com>]

We're considering moving our current very free-form JSON objects to Avro.
However, we have validation checks for things like max and min values on
ints, pattern matching for strings, etc.

Is there a common way people handle this kind of validation? I know you can
attach extra meta-data to types when you declare them, so that seems the
obvious place for this kind of information to live, but I'm wondering how
hard it will be to use that extra meta-data to check values and whether
anyone has already done the work.

Ideally, we'd like clients to be able to validate the objects they're
building so that they can tell whether they're sending a valid value before
it gets sent and we have to clean it up.

Does that make sense?
Todd