Maybe I'm being a bit dim, but could you explain what "client.foo(123)" does in this client - it appears to be a resource and 'callable' - so is this doing a GET on that resource, what about other methods?
I think GET would be a reasonable default here, perhaps 123 is a query string parameter.
For update / POST, create / PUT etc. it's less clear cut in my example language of Python since all we have is a callable, we don't have constructs such as "new" to map behaviours to (repurposing "del" isn't possible).