From 39e9acf532aa9f69a431d5e5fa34c0b1605946a0 Mon Sep 17 00:00:00 2001
From: Akshay Shah <akshay@akshayshah.org>
Date: Sun, 4 Jun 2023 20:24:05 -0700
Subject: [PATCH 1/2] Restructure JSON codec tests

In preparation for changing the logic a bit, restructure the unit tests
for the JSON codec to use named subtests and exercise the happy path.
---
 codec_test.go | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/codec_test.go b/codec_test.go
index b27e2562..fcad73fe 100644
--- a/codec_test.go
+++ b/codec_test.go
@@ -100,13 +100,22 @@ func TestStableCodec(t *testing.T) {
 func TestJSONCodec(t *testing.T) {
 	t.Parallel()
 
-	var empty emptypb.Empty
 	codec := &protoJSONCodec{name: "json"}
-	err := codec.Unmarshal([]byte{}, &empty)
-	assert.NotNil(t, err)
-	assert.True(
-		t,
-		strings.Contains(err.Error(), "valid JSON"),
-		assert.Sprintf(`error message should explain that "" is not a valid JSON object`),
-	)
+
+	t.Run("success", func(t *testing.T) {
+		t.Parallel()
+		err := codec.Unmarshal([]byte("{}"), &emptypb.Empty{})
+		assert.Nil(t, err)
+	})
+
+	t.Run("empty string", func(t *testing.T) {
+		t.Parallel()
+		err := codec.Unmarshal([]byte{}, &emptypb.Empty{})
+		assert.NotNil(t, err)
+		assert.True(
+			t,
+			strings.Contains(err.Error(), "valid JSON"),
+			assert.Sprintf(`error message should explain that "" is not a valid JSON object`),
+		)
+	})
 }

From 128a8967ce645721a14f72d7f4b251901cb758e2 Mon Sep 17 00:00:00 2001
From: Akshay Shah <akshay@akshayshah.org>
Date: Sun, 4 Jun 2023 20:25:05 -0700
Subject: [PATCH 2/2] Discard unknown JSON fields by default

The current JSON unmarshaling logic tightly couples clients and servers:
clients can't unmarshal messages containing new fields, and servers
can't unmarshal messages containing ancient fields that have since been
deleted. This is counter to the typical protobuf forward- and
backward-compatibility story, and is far more restrictive than the
binary codec. This PR loosens the default behavior to discard unknown
fields.

Fixes #477.
---
 codec.go      | 4 +++-
 codec_test.go | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/codec.go b/codec.go
index bc0fe989..fab38f0c 100644
--- a/codec.go
+++ b/codec.go
@@ -144,7 +144,9 @@ func (c *protoJSONCodec) Unmarshal(binary []byte, message any) error {
 	if len(binary) == 0 {
 		return errors.New("zero-length payload is not a valid JSON object")
 	}
-	var options protojson.UnmarshalOptions
+	// Discard unknown fields so clients and servers aren't forced to always use
+	// exactly the same version of the schema.
+	options := protojson.UnmarshalOptions{DiscardUnknown: true}
 	return options.Unmarshal(binary, protoMessage)
 }
 
diff --git a/codec_test.go b/codec_test.go
index fcad73fe..56f78bf3 100644
--- a/codec_test.go
+++ b/codec_test.go
@@ -108,6 +108,12 @@ func TestJSONCodec(t *testing.T) {
 		assert.Nil(t, err)
 	})
 
+	t.Run("unknown fields", func(t *testing.T) {
+		t.Parallel()
+		err := codec.Unmarshal([]byte(`{"foo": "bar"}`), &emptypb.Empty{})
+		assert.Nil(t, err)
+	})
+
 	t.Run("empty string", func(t *testing.T) {
 		t.Parallel()
 		err := codec.Unmarshal([]byte{}, &emptypb.Empty{})