From 64d0b93a7a1e85d58d11ac38c9404af80018f239 Mon Sep 17 00:00:00 2001
From: Quinn Slack <qslack@qslack.com>
Date: Sun, 22 Jan 2017 16:05:00 -0800
Subject: [PATCH] propagate JSON "null" result instead of treating it as Go nil
 (and field-not-present in JSON)

---
 jsonrpc2.go    | 15 +++++++++++++--
 object_test.go |  5 +++--
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/jsonrpc2.go b/jsonrpc2.go
index c7724ac..7b921f3 100644
--- a/jsonrpc2.go
+++ b/jsonrpc2.go
@@ -377,7 +377,10 @@ func (c *Conn) Call(ctx context.Context, method string, params, result interface
 		if err != nil {
 			return err
 		}
-		if result != nil && call.response.Result != nil {
+		if result != nil {
+			if call.response.Result == nil {
+				call.response.Result = &jsonNull
+			}
 			// TODO(sqs): error handling
 			if err := json.Unmarshal(*call.response.Result, result); err != nil {
 				return err
@@ -390,6 +393,8 @@ func (c *Conn) Call(ctx context.Context, method string, params, result interface
 	}
 }
 
+var jsonNull = json.RawMessage("null")
+
 // Notify is like Call, but it returns when the notification request
 // is sent (without waiting for a response, because JSON-RPC
 // notifications do not have responses).
@@ -595,7 +600,13 @@ func (m *anyMessage) UnmarshalJSON(data []byte) error {
 	case !isRequest && isResponse:
 		v = &m.response
 	}
-	return json.Unmarshal(data, v)
+	if err := json.Unmarshal(data, v); err != nil {
+		return err
+	}
+	if !isRequest && isResponse && m.response.Error == nil && m.response.Result == nil {
+		m.response.Result = &jsonNull
+	}
+	return nil
 }
 
 // anyValueWithExplicitNull is used to distinguish {} from
diff --git a/object_test.go b/object_test.go
index c614712..906d99b 100644
--- a/object_test.go
+++ b/object_test.go
@@ -36,6 +36,7 @@ func TestAnyMessage(t *testing.T) {
 }
 
 func TestMessageCodec(t *testing.T) {
+	obj := json.RawMessage(`{"foo":"bar"}`)
 	tests := []struct {
 		v, vempty interface{}
 	}{
@@ -44,8 +45,8 @@ func TestMessageCodec(t *testing.T) {
 			vempty: &Request{ID: ID{Num: 123}},
 		},
 		{
-			v:      &Response{ID: ID{Num: 123}},
-			vempty: &Response{ID: ID{Num: 123}},
+			v:      &Response{ID: ID{Num: 123}, Result: &obj},
+			vempty: &Response{ID: ID{Num: 123}, Result: &obj},
 		},
 	}
 	for _, test := range tests {