map to json

[awalterschulze]

Add this function to all_test.go

func TestMapFieldJsonMarshal(t *testing.T) {
    m := &MessageWithMap{
        NameMapping: map[int32]string{
            1: "Rob",
            4: "Ian",
            8: "Dave",
        },
    }
    _, err := json.Marshal(m)
    if err != nil {
        t.Fatal(err)
    }
}

It will fail with
json: unsupported type: map[int32]string

Is this work just not done yet or am I understanding something incorrectly or is this a bug?
I thought that json is the new text standard for proto3 and also that proto3 supports maps?
I would guess that go needs to support marshaling proto3 structures to json or am I interpreting this in the wrong way?

[logrusorgru]

Because

{
        8: "some"
}

is not valid json. But

{
    "8": "some"
}

is valid. Only string can be key. Use map[string]Type or []Type.

[awalterschulze]

proto3 allows int32 keys in maps and proto3 says json is its standard text format.

[tv42]

@awalterschulze There's no such thing as JSON object with a non-string key. http://json.org/

[awalterschulze]

Yes I understand.

Let me add some context.

You can have:
"The following are the main new features in language version 3:
...
vii. A well-defined encoding in JSON as an alternative to binary proto encoding."
https://github.com/google/protobuf/releases/tag/v3.0.0-alpha-2

And allow maps with keys int32
"map<int32, string> name_mapping = 14;"
3ea3e05

When json does not support non-string keys
http://json.org/

And not have a plan.

[dsymonds]

I haven't seen a spec for how proto maps are meant to appear in JSON. That's probably something to file as an issue against google/protobuf.

FWIW, I don't think encoding/json is going to work with proto3 for matching the proto3 JSON spec. The encoding/json package has a fairly rigid idea of how things are meant to be rendered. We'll see, but I suspect an auxiliary jsonpb package (which will be able to have all the relevant tuning knobs) will end up as the best approach.

[dsymonds]

To be clear, JSON is not the new "text format" for proto3, but rather it is a new canonical interchange format.

[awalterschulze]

Ok so if I understand correctly:

• there will now be four canonical formats, json, prototext, compacttext and proto;
• golang/protobuf, but first google/protobuf will be working on a plan for map[]string to json.

[dsymonds]

If by "prototext" and "compacttext" you mean the output of proto.MarshalText and proto.CompactText, then they are the same format, just with differing whitespace (ignored by parsers) for layout. But that format is not intended as an interchange format.

So there's the binary wire format, which has been around forever, and now there will be JSON too.

Your second point is accurate enough. There will be a plan for the JSON output of map fields that will be consistent across all proto language implementations; I expect to wait until that is defined before modifying Go's protobuf package to support it.

[awalterschulze]

Excellent, that is what I want to hear :)

On 13 March 2015 at 12:23, David Symonds notifications@github.com wrote:

If by "prototext" and "compacttext" you mean the output of
proto.MarshalText and proto.CompactText, then they are the same format,
just with differing whitespace (ignored by parsers) for layout. But that
format is not intended as an interchange format.

So there's the binary wire format, which has been around forever, and now
there will be JSON too.

Your second point is accurate enough. There will be a plan for the JSON
output of map fields that will be consistent across all proto language
implementations; I expect to wait until that is defined before modifying
Go's protobuf package to support it.

—
Reply to this email directly or view it on GitHub
#18 (comment).

[dsymonds]

The newly added jsonpb package (see 67cbcad) supports the official JSON output format. It includes map output.