add support for suppressing ErrClosed in HandlerWithError logs

handler_with_error.go

@@ -7,11 +7,18 @@ import (
 
 // HandlerWithError implements Handler by calling the func for each
 // request and handling returned errors and results.
-type HandlerWithError func(context.Context, *Conn, *Request) (result interface{}, err error)
+func HandlerWithError(handleFunc func(context.Context, *Conn, *Request) (result interface{}, err error)) *HandlerWithErrorConfigurer {
+	return &HandlerWithErrorConfigurer{handleFunc: handleFunc}
+}
+
+type HandlerWithErrorConfigurer struct {
+	handleFunc        func(context.Context, *Conn, *Request) (result interface{}, err error)
+	suppressErrClosed bool
+}
 
 // Handle implements Handler.
-func (h HandlerWithError) Handle(ctx context.Context, conn *Conn, req *Request) {
-	result, err := h(ctx, conn, req)
+func (h *HandlerWithErrorConfigurer) Handle(ctx context.Context, conn *Conn, req *Request) {
+	result, err := h.handleFunc(ctx, conn, req)
 	if req.Notif {
 		if err != nil {
 			log.Printf("jsonrpc2 handler: notification %q handling error: %s", req.Method, err)
@@ -33,7 +40,25 @@ func (h HandlerWithError) Handle(ctx context.Context, conn *Conn, req *Request)
 
 	if !req.Notif {
 		if err := conn.SendResponse(ctx, resp); err != nil {
-			log.Printf("jsonrpc2 handler: sending response %s: %s", resp.ID, err)
+			if err != ErrClosed || !h.suppressErrClosed {
+				log.Printf("jsonrpc2 handler: sending response %s: %s", resp.ID, err)
+			}
 		}
 	}
 }
+
+// SuppressErrClosed makes the handler suppress jsonrpc2.ErrClosed errors from
+// being logged. The original handler `h` is returned.
+//
+// This is optional because only in some cases is this behavior desired. For
+// example, a handler that serves end-user connections may not want to log
+// ErrClosed because it just indicates the end-user connection has gone away
+// for any reason (they could have lost wifi connection, are no longer
+// interested in the request and closed the connection, etc) and as such it
+// would be log spam, whereas a handler that serves internal connections would
+// never expect connections to go away unexpectedly (which could indicate
+// service degradation, etc) and as such ErrClosed should always be logged.
+func (h *HandlerWithErrorConfigurer) SuppressErrClosed() Handler {
+	h.suppressErrClosed = true
+	return h
+}