From 62f707c2bb4ed2920a0c8d82aa0965b1853a047e Mon Sep 17 00:00:00 2001
From: realyxl <realyuxuanli@gmail.com>
Date: Sat, 1 Aug 2026 13:35:42 +0800
Subject: [PATCH] hysteria2: Fix obfs silently disabling socket buffer sizing

SalamanderPacketConn and GeckoPacketConn embed the net.PacketConn
interface, which hides SetReadBuffer/SetWriteBuffer. quic-go's type
assertion in setReceiveBuffer/setSendBuffer then fails and the socket
keeps net.core.rmem_default instead of the 8 MB it asks for.

Re-expose both methods, resolving the underlying conn with common.Cast
as hysteria/hop.go does.
---
 hysteria2/gecko.go      |  8 ++++++++
 hysteria2/salamander.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/hysteria2/gecko.go b/hysteria2/gecko.go
index 7578b39..5b5552f 100644
--- a/hysteria2/gecko.go
+++ b/hysteria2/gecko.go
@@ -68,6 +68,14 @@ func (g *GeckoPacketConn) Upstream() any {
 	return g.PacketConn
 }
 
+func (g *GeckoPacketConn) SetReadBuffer(bytes int) error {
+	return trySetReadBuffer(g.PacketConn, bytes)
+}
+
+func (g *GeckoPacketConn) SetWriteBuffer(bytes int) error {
+	return trySetWriteBuffer(g.PacketConn, bytes)
+}
+
 func (g *GeckoPacketConn) WriteTo(p []byte, addr net.Addr) (int, error) {
 	if len(p) == 0 {
 		return 0, nil
diff --git a/hysteria2/salamander.go b/hysteria2/salamander.go
index a18ea5f..e0bd028 100644
--- a/hysteria2/salamander.go
+++ b/hysteria2/salamander.go
@@ -2,6 +2,7 @@ package hysteria2
 
 import (
 	"net"
+	"os"
 
 	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/buf"
@@ -73,6 +74,34 @@ func (s *SalamanderPacketConn) Upstream() any {
 	return s.PacketConn
 }
 
+func (s *SalamanderPacketConn) SetReadBuffer(bytes int) error {
+	return trySetReadBuffer(s.PacketConn, bytes)
+}
+
+func (s *SalamanderPacketConn) SetWriteBuffer(bytes int) error {
+	return trySetWriteBuffer(s.PacketConn, bytes)
+}
+
+func trySetReadBuffer(conn net.PacketConn, bytes int) error {
+	udpConn, isUDPConn := common.Cast[interface {
+		SetReadBuffer(bytes int) error
+	}](conn)
+	if !isUDPConn {
+		return os.ErrInvalid
+	}
+	return udpConn.SetReadBuffer(bytes)
+}
+
+func trySetWriteBuffer(conn net.PacketConn, bytes int) error {
+	udpConn, isUDPConn := common.Cast[interface {
+		SetWriteBuffer(bytes int) error
+	}](conn)
+	if !isUDPConn {
+		return os.ErrInvalid
+	}
+	return udpConn.SetWriteBuffer(bytes)
+}
+
 type VectorisedSalamanderPacketConn struct {
 	SalamanderPacketConn
 	writer N.VectorisedPacketWriter