How to unmarshal JSON into protobuf containing oneof definitions using jsonpb?

Question

I'm currently failing to unmarshal a JSON snippet which is generated by jsonpb. Maybe it's just some kind of misunderstanding on my side, but when looking at the tests I'd expect it to work somehow.

Here's the relevant snippet of the pb.proto:

syntax = "proto3";
package pb;

message Parameter {
    string name = 1;
    oneof value {
        string str_value = 2;
        int32 int_value = 3;
        bool bool_value = 4;
        float float_value = 5;
    }
}

message ParameterSet {
    bytes raw = 1;
    repeated Parameter parameters = 2;
}

message ParameterSets {
    map<string,ParameterSet> sets = 1;
}

Testing marshaling/unmarshaling using this simple snippet fails:

package main

import (
    "fmt"
    "github.com/gogo/protobuf/jsonpb"
    "strings"
)

func main() {
    m := jsonpb.Marshaler{}
    str, err := m.MarshalToString(&pb.ParameterSets{Sets: map[string]*pb.ParameterSet{
        "parameter": {
            Raw: []byte{0, 1, 2, 3, 4, 5, 6, 1, 2},
            Parameters: []*pb.Parameter{
                {Name: "itest", Value: &pb.Parameter_IntValue{42}},
                {Name: "stest", Value: &pb.Parameter_StrValue{"Foobar"}},
                {Name: "btest", Value: &pb.Parameter_BoolValue{true}},
                {Name: "ftest", Value: &pb.Parameter_FloatValue{41.99}},
           },
        },
    }},)
    fmt.Println(str)
    fmt.Println(err)

    sets := pb.ParameterSets{}
    err = jsonpb.Unmarshal(strings.NewReader(str), &sets)
    fmt.Println(sets)
    fmt.Println(err)
}

It results in:

{"sets":{"parameter":{"raw":"AAECAwQFBgEC","parameters":[{"name":"itest","intValue":42},{"name":"stest","strValue":"Foobar"},{"name":"btest","boolValue":true},{"name":"ftest","floatValue":41.99}]}}}
<nil>
{map[]}
unknown field "intValue" in pb.Parameter

How can I get the oneof values back in the proto object?

Answer 1

You have a Type mix up due to the two vendor folders. A type declared in two vendor folders is not the same, even if the code for them is exactly the same.

Thus for example: prototest-master/vendor/github.com/gogo/proto/messageSet (A) is not of the same type as prototest-master/proto/vendor/github.com/gogo/proto/messageSet (B) even as their imports are the same (github.com/gogo/proto)

In your project's main.go the construction of the marshaler jsonpb.Marshaler{} uses the types from (A) where the actual messages like &pb.ParameterSets{... use the types from (B) to construct itself.

Since jsonpb seems to do a lot of reflection stuff it breaks on the mixing of the two types.

A better solution is to use just one vendor folder to be clear on the types everyone uses. I would just ditch the (B) vendor folder because it adds nothing.