system/host/fidl/examples/example-9.fidl2

library example_9;

enum EchoMe {
    zero = 0;
    one = 1;
};

interface Echo {
  1: Echo32(uint32 @uint32) -> (uint32 response);
  2: Echo64(uint64 @uint64) -> (uint64 response);
  3: EchoEnum(EchoMe req) -> (EchoMe response);
  4: EchoHandle(handle req) -> (handle response);
  5: EchoChannel(handle<channel> req) -> (handle<channel> response);
};

const EchoMe favorite_echo = zero;