From 3ac3b24635fae8a8a71c3bbaf2f64d1f07a0000f Mon Sep 17 00:00:00 2001
From: Erik Dubbelboer <erik@dubbelboer.com>
Date: Mon, 27 Apr 2026 12:28:40 +0900
Subject: [PATCH] server: keep hijacked reader out of pool (#2184)

When KeepHijackedConns is enabled, the hijacked connection may outlive the
HijackHandler. The wrapper continues reading through the buffered reader
after the handler returns, so returning that reader to the pool can let
another connection reset it while the hijacked connection is still in use.

Keep the buffered reader owned by the escaped hijacked connection in
keep-open mode. Add a regression test that forces reader-pool reuse
and verifies buffered data remains available after the handler returns.
---
 server.go      |  4 +++-
 server_test.go | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/server.go b/server.go
index b3c24d7..9e93e3f 100644
--- a/server.go
+++ b/server.go
@@ -2667,7 +2667,9 @@ func hijackConnHandler(ctx *RequestCtx, r io.Reader, c net.Conn, s *Server, h Hi
 	hjc := s.acquireHijackConn(r, c)
 	h(hjc)
 
-	if br, ok := r.(*bufio.Reader); ok {
+	// When the caller keeps using the hijacked connection after return,
+	// the buffered reader must remain owned by that escaped connection.
+	if br, ok := r.(*bufio.Reader); ok && !s.KeepHijackedConns {
 		releaseReader(s, br)
 	}
 	if !s.KeepHijackedConns {
diff --git a/server_test.go b/server_test.go
index 094e557..d643ec0 100644
--- a/server_test.go
+++ b/server_test.go
@@ -2933,6 +2933,51 @@ func TestRequestCtxHijackReduceMemoryUsage(t *testing.T) {
 	})
 }
 
+func TestRequestCtxHijackKeepHijackedConnsKeepsReaderOutOfPool(t *testing.T) {
+	t.Parallel()
+
+	s := &Server{
+		KeepHijackedConns: true,
+	}
+	ctx := &RequestCtx{s: s}
+
+	firstConn := &readWriter{}
+	firstConn.r.WriteString("first")
+	secondConn := &readWriter{}
+	secondConn.r.WriteString("second")
+
+	br := bufio.NewReaderSize(firstConn, 1)
+
+	var hijacked net.Conn
+	hijackConnHandler(ctx, br, firstConn, s, func(c net.Conn) {
+		hijacked = c
+	})
+
+	if hijacked == nil {
+		t.Fatal("expected hijacked connection")
+	}
+
+	if v := s.readerPool.Get(); v != nil {
+		v.(*bufio.Reader).Reset(secondConn)
+	}
+
+	buf := make([]byte, len("first"))
+	if _, err := io.ReadFull(hijacked, buf); err != nil {
+		t.Fatalf("unexpected read error from hijacked connection: %v", err)
+	}
+	if string(buf) != "first" {
+		t.Fatalf("unexpected hijacked data %q. Expecting %q", buf, "first")
+	}
+
+	if err := hijacked.Close(); err != nil {
+		t.Fatalf("unexpected close error from hijacked connection: %v", err)
+	}
+
+	if v := s.readerPool.Get(); v != nil {
+		t.Fatal("did not expect hijacked reader to be released after close")
+	}
+}
+
 func TestRequestCtxHijackNoResponse(t *testing.T) {
 	t.Parallel()