From 5a1990d1d8b30168c427fc76468dd482a90957eb Mon Sep 17 00:00:00 2001
From: Maxim Evtush <154841002+maximevtush@users.noreply.github.com>
Date: Tue, 13 Jan 2026 14:25:53 +0200
Subject: [PATCH] rpc: fix limitedBuffer.Write to properly enforce size limit
 (#33545)

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.
---
 rpc/handler.go | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/rpc/handler.go b/rpc/handler.go
index 45558d5821..462519d872 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
 	}