Add websocket.UnknownMessage (#1065)

Instead of always skipping structured messages of an unknonw type with a
generic log message, the websocket client will provide them to the configured
handler in the Unknown field of the IncomingMessage type.

Existing message handlers already defensively handle unexpected message types
by explicitly checking for msg.WebhookEvent or msg.RequestLogEvent.

pkg/websocket/messages.go

@@ -2,13 +2,26 @@ package websocket
 
 import (
 	"encoding/json"
-	"fmt"
 )
 
 // IncomingMessage represents any incoming message sent by Stripe.
 type IncomingMessage struct {
 	*WebhookEvent
 	*RequestLogEvent
+
+	// Unknown will be present if the incoming message type does not match the
+	// list known to the CLI.
+	Unknown *UnknownMessage
+}
+
+// UnknownMessage represents an incoming message with a type that's unknown
+// to the CLI, and therefore cannot be deserialized into a structured type.
+type UnknownMessage struct {
+	// Type is the value of the type field in the message's data.
+	Type string
+
+	// Data contains the raw data of the message.
+	Data []byte
 }
 
 // UnmarshalJSON deserializes incoming messages sent by Stripe into the
@@ -23,21 +36,18 @@ func (m *IncomingMessage) UnmarshalJSON(data []byte) error {
 
 	switch incomingMessageTypeOnly.Type {
 	case "webhook_event":
-		var evt WebhookEvent
-		if err := json.Unmarshal(data, &evt); err != nil {
+		if err := json.Unmarshal(data, &m.WebhookEvent); err != nil {
 			return err
 		}
-
-		m.WebhookEvent = &evt
 	case "request_log_event":
-		var evt RequestLogEvent
-		if err := json.Unmarshal(data, &evt); err != nil {
+		if err := json.Unmarshal(data, &m.RequestLogEvent); err != nil {
 			return err
 		}
-
-		m.RequestLogEvent = &evt
 	default:
-		return fmt.Errorf("Unexpected message type: %s", incomingMessageTypeOnly.Type)
+		m.Unknown = &UnknownMessage{
+			Type: incomingMessageTypeOnly.Type,
+			Data: data,
+		}
 	}
 
 	return nil

pkg/websocket/messages_test.go

@@ -13,7 +13,9 @@ func TestUnmarshalUnknownIncomingMsg(t *testing.T) {
 
 	var msg IncomingMessage
 	err := json.Unmarshal([]byte(data), &msg)
-	require.EqualError(t, err, "Unexpected message type: unknown_type")
+	require.NoError(t, err)
+	require.Equal(t, "unknown_type", msg.Unknown.Type)
+	require.Equal(t, data, string(msg.Unknown.Data))
 }
 
 func TestMarshalWebhookEventAck(t *testing.T) {