I think your current Any JSON design requires that protobuf serialization be
able to fail. This is definitely a major change from proto2 and something the
conformance test does not explore.
1. Decode a valid JSON-encoded message with an Any field in an unknown schema.
2. Attempt to encode it in protobuf format.
If the descriptor cannot be fetched, then step #2 here must fail.
(The alternative would be for #1 to fail in this case, but that would imply
that JSON-to-JSON transcoding must fail in some circumstances.)
If Any had been defined slightly differently, then transcoding would be
trivial. If you are unable to change the current definition of Any, please
consider introducing an alternative:
package google.protobuf;
message Other {
string type_url = 1;
oneof encoded {
bytes protobuf = 2;
google.protobuf.Value json = 3;
}
}
This is trivial to transcode: it only requires that the final consumer be able
to decode whatever format the originator attached. Intermediate systems can
freely transcode without needing to understand the schema at all, since the
‘protobuf’ field here can be represented in JSON and the ‘json’ field can be
encoded to protobuf. The actual JSON serialization is very similar to the
current Any serialization (with the addition of the extra “json” tag).
Cheers,
Tim
> On Feb 5, 2016, at 1:53 PM, Josh Haberman <haber...@google.com> wrote:
>
> Hi Tim,
>
> I think your analysis is correct. The answer to your question is that it's
> not possible to transcode Any from JSON <-> protobuf unless you have the
> schema. That is one of the reasons why the type URL exists as a way to fetch
> schemas for types you otherwise wouldn't know about.
>
> I'm glad the conformance suite was helpful!
>
> Best,
> Josh
>
> On Wednesday, February 3, 2016 at 1:37:40 PM UTC-8, Tim Kientzle wrote:
> I’m trying to implement Any, including proper JSON and protobuf encoding, and
> the following scenario has me stumped:
>
>
>
> I’m looking at the any.proto file, which includes this example:
>
>
>
> Sample proto file:
>
> // package google.profile;
>
> // message Person {
>
> // string first_name = 1;
>
> // string last_name = 2;
>
> // }
>
>
>
> Resulting JSON encoding:
>
> // {
>
> // "@type": "type.googleapis.com/google.profile.Person",
>
> // "firstName": <string>,
>
> // "lastName": <string>
>
> // }
>
>
>
> The scenario I’m trying to understand involves three systems:
>
>
>
> Originating system:
>
> * Knows google.profile and writes out the JSON above
>
>
>
> Middle system:
>
> * Reads the JSON example above
>
> * Does *not* know google.profile (doesn’t have the descriptor and has no way
> to get it)
>
> * Writes out protobuf
>
>
>
> Receiving system:
>
> * Knows google.profile and reads the protobuf
>
>
>
> In particular: What is the protobuf serialization between the middle and
> receiving systems?
>
>
>
> Without the descriptor, the middle system cannot poduce the “real" protobuf
> binary format (the field numbers aren’t in that format), so the only option
> would seem to be to serialize the JSON data as a protobuf Struct
> representation (which in turn has interesting implications for the receiving
> system). Am I missing some other option?
>
>
>
> Tim
>
>
>
> P.S. Nice work on the conformance test suite, by the way! That clarified a
> *lot* of details about the expected handling for protobuf JSON format.
>
>
>
>
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