better null handling in (Request).params and (Response).result (#7)

This makes the MarshalJSON/UnmarshalJSON methods centralize the logic, instead of requiring callers to occasionally munge responses to make them valid to later JSON-marshal.

object_test.go

@@ -1,6 +1,7 @@
 package jsonrpc2
 
 import (
+	"bytes"
 	"encoding/json"
 	"reflect"
 	"testing"
@@ -35,32 +36,93 @@ func TestAnyMessage(t *testing.T) {
 	}
 }
 
-func TestMessageCodec(t *testing.T) {
+func TestRequest_MarshalUnmarshalJSON(t *testing.T) {
+	null := json.RawMessage("null")
 	obj := json.RawMessage(`{"foo":"bar"}`)
 	tests := []struct {
-		v, vempty interface{}
+		data []byte
+		want Request
 	}{
 		{
-			v:      &Request{ID: ID{Num: 123}},
-			vempty: &Request{ID: ID{Num: 123}},
+			data: []byte(`{"method":"m","params":{"foo":"bar"},"id":123,"jsonrpc":"2.0"}`),
+			want: Request{ID: ID{Num: 123}, Method: "m", Params: &obj},
 		},
 		{
-			v:      &Response{ID: ID{Num: 123}, Result: &obj},
-			vempty: &Response{ID: ID{Num: 123}, Result: &obj},
+			data: []byte(`{"method":"m","params":null,"id":123,"jsonrpc":"2.0"}`),
+			want: Request{ID: ID{Num: 123}, Method: "m", Params: &null},
+		},
+		{
+			data: []byte(`{"method":"m","id":123,"jsonrpc":"2.0"}`),
+			want: Request{ID: ID{Num: 123}, Method: "m", Params: nil},
 		},
 	}
 	for _, test := range tests {
-		b, err := json.Marshal(test.v)
+		var got Request
+		if err := json.Unmarshal(test.data, &got); err != nil {
+			t.Error(err)
+			continue
+		}
+		if !reflect.DeepEqual(got, test.want) {
+			t.Errorf("%q: got %+v, want %+v", test.data, got, test.want)
+			continue
+		}
+		data, err := json.Marshal(got)
 		if err != nil {
-			t.Fatal(err)
+			t.Error(err)
+			continue
 		}
-
-		if err := json.Unmarshal(b, test.vempty); err != nil {
-			t.Fatal(err)
-		}
-
-		if !reflect.DeepEqual(test.vempty, test.v) {
-			t.Errorf("got %+v, want %+v", test.vempty, test.v)
+		if !bytes.Equal(data, test.data) {
+			t.Errorf("got JSON %q, want %q", data, test.data)
+		}
+	}
+}
+
+func TestResponse_MarshalUnmarshalJSON(t *testing.T) {
+	null := json.RawMessage("null")
+	obj := json.RawMessage(`{"foo":"bar"}`)
+	tests := []struct {
+		data  []byte
+		want  Response
+		error bool
+	}{
+		{
+			data: []byte(`{"id":123,"result":{"foo":"bar"},"jsonrpc":"2.0"}`),
+			want: Response{ID: ID{Num: 123}, Result: &obj},
+		},
+		{
+			data: []byte(`{"id":123,"result":null,"jsonrpc":"2.0"}`),
+			want: Response{ID: ID{Num: 123}, Result: &null},
+		},
+		{
+			data:  []byte(`{"id":123,"jsonrpc":"2.0"}`),
+			want:  Response{ID: ID{Num: 123}, Result: nil},
+			error: true, // either result or error field must be set
+		},
+	}
+	for _, test := range tests {
+		var got Response
+		if err := json.Unmarshal(test.data, &got); err != nil {
+			t.Error(err)
+			continue
+		}
+		if !reflect.DeepEqual(got, test.want) {
+			t.Errorf("%q: got %+v, want %+v", test.data, got, test.want)
+			continue
+		}
+		data, err := json.Marshal(got)
+		if err != nil {
+			if test.error {
+				continue
+			}
+			t.Error(err)
+			continue
+		}
+		if test.error {
+			t.Errorf("%q: expected error", test.data)
+			continue
+		}
+		if !bytes.Equal(data, test.data) {
+			t.Errorf("got JSON %q, want %q", data, test.data)
 		}
 	}
 }