diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..cd46ca6
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module github.com/sourcegraph/jsonrpc2
+
+go 1.13
+
+require github.com/gorilla/websocket v1.4.1
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..1f9b923
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/gorilla/websocket v1.4.1 h1:q7AeDBpnBk8AogcD4DSag/Ukw/KV+YhzLj2bP5HvKCM=
+github.com/gorilla/websocket v1.4.1/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
diff --git a/handler_with_error.go b/handler_with_error.go
index 13ac1c0..51d087b 100644
--- a/handler_with_error.go
+++ b/handler_with_error.go
@@ -11,7 +11,8 @@ func HandlerWithError(handleFunc func(context.Context, *Conn, *Request) (result
 	return &HandlerWithErrorConfigurer{handleFunc: handleFunc}
 }
 
-// HandlerWithErrorConfigurer is a handler configuration struct
+
+// HandlerWithErrorConfigurer is a handler created by HandlerWithError.
 type HandlerWithErrorConfigurer struct {
 	handleFunc        func(context.Context, *Conn, *Request) (result interface{}, err error)
 	suppressErrClosed bool
diff --git a/jsonrpc2.go b/jsonrpc2.go
index 00f4acf..594f754 100644
--- a/jsonrpc2.go
+++ b/jsonrpc2.go
@@ -221,8 +221,6 @@ const (
 	CodeMethodNotFound = -32601
 	CodeInvalidParams  = -32602
 	CodeInternalError  = -32603
-	// codeServerErrorStart = -32099
-	// codeServerErrorEnd   = -32000
 )
 
 // Handler handles JSON-RPC requests and notifications.
@@ -642,9 +640,8 @@ func (m *anyMessage) UnmarshalJSON(data []byte) error {
 		if len(msgs) == 0 {
 			return errors.New("jsonrpc2: invalid empty batch")
 		}
-		for i := range msgs {
-			var m = msgs[i]
-			if err := checkType(&m); err != nil {
+		for _, msg := range msgs {
+			if err := checkType(&msg); err != nil {
 				return err
 			}
 		}
@@ -695,10 +692,3 @@ func (v *anyValueWithExplicitNull) UnmarshalJSON(data []byte) error {
 	return json.Unmarshal(data, &v.value)
 }
 
-/*
-var (
-	errInvalidRequestJSON  = errors.New("jsonrpc2: request must be either a JSON object or JSON array")
-	errInvalidResponseJSON = errors.New("jsonrpc2: response must be either a JSON object or JSON array")
-)
-*/
-