From 183c492b81034f0a2ec3746f6ca3df69c80c1dd7 Mon Sep 17 00:00:00 2001
From: Shane Jonas <jonas.shane@gmail.com>
Date: Tue, 23 Sep 2025 10:29:46 -0400
Subject: [PATCH] fix: allow JSON-RPC error data in responses

---
 rpcserver/jsonrpc_server.go      | 12 ++++++++++--
 rpcserver/jsonrpc_server_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/rpcserver/jsonrpc_server.go b/rpcserver/jsonrpc_server.go
index 21d597a..472bfa7 100644
--- a/rpcserver/jsonrpc_server.go
+++ b/rpcserver/jsonrpc_server.go
@@ -146,6 +146,14 @@ func (h *JSONRPCHandler) writeJSONRPCResponse(w http.ResponseWriter, response JS
 }
 
 func (h *JSONRPCHandler) writeJSONRPCError(w http.ResponseWriter, id any, code int, msg string) {
+	h.writeJSONRPCErrorWithData(w, id, code, msg, nil)
+}
+
+func (h *JSONRPCHandler) writeJSONRPCErrorWithData(w http.ResponseWriter, id any, code int, msg string, data any) {
+	var dataPtr *any
+	if data != nil {
+		dataPtr = &data
+	}
 	res := JSONRPCResponse{
 		JSONRPC: "2.0",
 		ID:      id,
@@ -153,7 +161,7 @@ func (h *JSONRPCHandler) writeJSONRPCError(w http.ResponseWriter, id any, code i
 		Error: &JSONRPCError{
 			Code:    code,
 			Message: msg,
-			Data:    nil,
+			Data:    dataPtr,
 		},
 	}
 	h.writeJSONRPCResponse(w, res)
@@ -324,7 +332,7 @@ func (h *JSONRPCHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	result, err := method.call(ctx, req.Params)
 	if err != nil {
 		if jsonRPCErr, ok := err.(*JSONRPCError); ok {
-			h.writeJSONRPCError(w, req.ID, jsonRPCErr.Code, jsonRPCErr.Message)
+			h.writeJSONRPCErrorWithData(w, req.ID, jsonRPCErr.Code, jsonRPCErr.Message, jsonRPCErr.Data)
 		} else {
 			h.writeJSONRPCError(w, req.ID, CodeCustomError, err.Error())
 		}
diff --git a/rpcserver/jsonrpc_server_test.go b/rpcserver/jsonrpc_server_test.go
index ac9b5e7..e6bed00 100644
--- a/rpcserver/jsonrpc_server_test.go
+++ b/rpcserver/jsonrpc_server_test.go
@@ -143,6 +143,33 @@ func TestJSONRPCServerDefaultLiveAndReady(t *testing.T) {
 	require.Equal(t, http.StatusNotFound, rr.Code)
 }
 
+func TestJSONRPCErrorDataIsPreserved(t *testing.T) {
+	handlerMethod := func(ctx context.Context, arg int) (int, error) {
+		errorData := any("some error data")
+		return 0, &JSONRPCError{
+			Code:    1234,
+			Message: "test error",
+			Data:    &errorData,
+		}
+	}
+
+	handler, err := NewJSONRPCHandler(map[string]interface{}{
+		"testError": handlerMethod,
+	}, JSONRPCHandlerOpts{})
+	require.NoError(t, err)
+
+	httpServer := httptest.NewServer(handler)
+	defer httpServer.Close()
+
+	client := rpcclient.NewClient(httpServer.URL)
+	resp, err := client.Call(context.Background(), "testError", 1)
+	require.NoError(t, err)
+	require.NotNil(t, resp.Error)
+	require.Equal(t, 1234, resp.Error.Code)
+	require.Equal(t, "test error", resp.Error.Message)
+	require.Equal(t, "some error data", resp.Error.Data)
+}
+
 func TestJSONRPCServerReadyzOK(t *testing.T) {
 	handler := testHandler(JSONRPCHandlerOpts{
 		ReadyHandler: func(w http.ResponseWriter, r *http.Request) error {