I'm in the process of writing an interactive debugger for capnp. It's easy
enough to manually provide a schema when connecting to another peer, but I
think it would be good long-term to support dynamic introspection as a
feature of the RPC system.
I'm quite new to capnp in general, but after reading over the
documentation, I think the best way to do this is for capnp to dictate a
standardized optional interface which returns the original
CodeGeneratorRequest that was used to implement the peer. Ideally, the code
generator could automatically implement this interface for every generated
interface, or perhaps the capnp library could automatically implement for
on Bootstrap and Accept capabilities. When interacting with services which
don't support introspection (possibly because of space, security, or other
concerns), the method call simply fails because it refers to an invalid
interface ID. The important thing is that such an interface has to have a
fixed ID to be useful, which is why I think it should be established as a
core part of capnp.
Here is my straw man version of this interface. I've selected AnyPointer so
that implementing this interface doesn't require pulling the entire capnp
schema into your own schema. Since the capnp schema is known to both
parties (even if it's a different version), this is fine.
interface Introspectable {
codeGeneratorRequest @0 () -> (cgr :AnyPointer);
}
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