jsonpb: does not support FieldMask

[nodirt]

Go implementation of JSONPB does not support well-known proto type FieldMask, which has special JSON encoding.

What version of protobuf and what language are you using?
Version: ddf2292

What did you do?

package main

import (
	"fmt"

	"google.golang.org/genproto/protobuf/field_mask"

	"github.com/golang/protobuf/jsonpb"
)

func main() {
	fm := &field_mask.FieldMask{Paths: []string{"a", "b"}}
	m := &jsonpb.Marshaler{}
	marshaled, _ := m.MarshalToString(fm)
	fmt.Println(marshaled)
	// expected: "a,b"
	// actual: {paths: ["a", "b"]}

	fm = &field_mask.FieldMask{}
	marshaled = "a,b"
	err := jsonpb.UnmarshalString(marshaled, fm)
	fmt.Println("error:", err)
}

What did you expect to see?

"a,b"
nil

What did you see instead?

{"paths":["a","b"]}
error: invalid character 'a' looking for beginning of value

[dsnet]

Thanks for filing. I marked with with "api-v2" since I rewrote the jsonpb package and the new implementation handles this.

See https://go-review.googlesource.com/c/protobuf/+/134495/1/encoding/jsonpb/known.go#94

[peats-bond]

Can we get a status update on this? I think this may be better suited under a bug rather than an enhancement request.

[cybrcodr]

This is implemented in v2, which we're not quite ready for a release yet. v1 will get the change when we update it to use v2 underneath. The release may take a while though.

[peats-bond]

Do you have any public documents discussing v2 timelines/details?

[cybrcodr]

#364 (comment) provides links to v2 design details. We don't have published timelines. You can follow updates on our repo at https://go.googlesource.com/protobuf.

[dsnet]

The new protojson package addresses this issue and has been released as part of google.golang.org/protobuf@v1.20.0. There are no plans to backport support of FieldMask to the older jsonpb implementation. Fixing it sadly breaks too many users who assume the incorrect behavior for FieldMask.