From 0c306686bb33d4dd5f678b7f65e6a1798db4dd93 Mon Sep 17 00:00:00 2001
From: Daniel Liu <139250065@qq.com>
Date: Mon, 19 Jan 2026 14:43:15 +0800
Subject: [PATCH] rpc: fix limitedBuffer.Write to properly enforce size limit
 (#33545) (#1948)

Updated the `avail` calculation to correctly compute remaining capacity:
`buf.limit - len(buf.output)`, ensuring the buffer never exceeds its
configured limit regardless of how many times `Write()` is called.

Co-authored-by: Maxim Evtush <154841002+maximevtush@users.noreply.github.com>
---
 rpc/handler.go | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/rpc/handler.go b/rpc/handler.go
index e0963cf959..20dcc54713 100644
--- a/rpc/handler.go
+++ b/rpc/handler.go
@@ -612,8 +612,11 @@ type limitedBuffer struct {
 }
 
 func (buf *limitedBuffer) Write(data []byte) (int, error) {
-	avail := max(buf.limit, len(buf.output))
-	if len(data) < avail {
+	avail := buf.limit - len(buf.output)
+	if avail <= 0 {
+		return 0, errTruncatedOutput
+	}
+	if len(data) <= avail {
 		buf.output = append(buf.output, data...)
 		return len(data), nil
 	}