From 4f62d14421d1574a97d3ef08104ab855e49c2ad5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotr=20Miko=C5=82ajczyk?= <piomiko41@gmail.com>
Date: Fri, 10 Apr 2026 14:02:59 +0200
Subject: [PATCH] Use errors.As instead of direct cast in geth errorMessage

---
 rpc/json.go | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/rpc/json.go b/rpc/json.go
index b0e6092169..52a7f04d80 100644
--- a/rpc/json.go
+++ b/rpc/json.go
@@ -126,12 +126,12 @@ func errorMessage(err error) *jsonrpcMessage {
 		Code:    ErrcodeDefault,
 		Message: err.Error(),
 	}}
-	ec, ok := err.(Error)
-	if ok {
+	var ec Error
+	if errors.As(err, &ec) {
 		msg.Error.Code = ec.ErrorCode()
 	}
-	de, ok := err.(DataError)
-	if ok {
+	var de DataError
+	if errors.As(err, &de) {
 		msg.Error.Data = de.ErrorData()
 	}
 	return msg
@@ -158,6 +158,19 @@ func (err *jsonError) ErrorData() interface{} {
 	return err.Data
 }
 
+// Is reports whether target carries the same JSON-RPC error code as err.
+// This allows errors.Is(receivedErr, sentinel) to work on the client side
+// when receivedErr is a jsonError reconstructed from the wire and sentinel
+// is any error that exposes an ErrorCode() int method.
+func (err *jsonError) Is(target error) bool {
+	type errorCoder interface{ ErrorCode() int }
+	t, ok := target.(errorCoder)
+	if !ok {
+		return false
+	}
+	return err.Code == t.ErrorCode()
+}
+
 // Conn is a subset of the methods of net.Conn which are sufficient for ServerCodec.
 type Conn interface {
 	io.ReadWriteCloser