Scott Carey wrote:
There has been talk that AvroGen would handle features like this (as well as
many others) in time. However this is one that should probably be addressed at
the JSON level regardless of the future direction of AvroGen.
Note that JSON schemas and protocols need to be standalone, containing
the full lexical closure of schemas referenced, when they are included
in data files and exchanged in RPC handshakes without reference to
external data. Thus I am reluctant to add a JSON syntax for file
inclusion. Rather, I think a pre-processor is appropriate. The
pre-processor would not be run on schemas included in files or exchanged
in RPC handshakes, but would be run for schemas read from files.
I have experimented with using the m4 pre-processor for this purpose,
and found it a bit awkward. Perhaps someone can develop macros for m4
that make it palatable, or perhaps we can develop a custom pre-processor
for JSON.
We might exploit otherwise-illegal JSON syntax, like backquotes, for
pre-processor directives. An include might look something like:
{"protocol": "org.foo.BarProtocol",
"types": [
`include org.foo.Bar`,
...
]
}
Also note that a protocol file (.avpr) need not actually define any
messages but can be used to define a set of types that reference one
another. This is a stopgap, but a useful one.
Doug
