From f3d346256d4ae3158f213639d13ba7bd9df7290c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=B8=96=E7=95=8C?= <i@sekai.icu>
Date: Tue, 6 Sep 2022 00:44:41 +0800
Subject: [PATCH] Add dontfrag control

---
 common/control/frag_linux.go   | 31 +++++++++++++++++++++++
 common/control/frag_other.go   |  7 ++++++
 common/control/frag_unix.go    | 28 +++++++++++++++++++++
 common/control/frag_windows.go | 45 ++++++++++++++++++++++++++++++++++
 4 files changed, 111 insertions(+)
 create mode 100644 common/control/frag_linux.go
 create mode 100644 common/control/frag_other.go
 create mode 100644 common/control/frag_unix.go
 create mode 100644 common/control/frag_windows.go

diff --git a/common/control/frag_linux.go b/common/control/frag_linux.go
new file mode 100644
index 0000000..5cb5fca
--- /dev/null
+++ b/common/control/frag_linux.go
@@ -0,0 +1,31 @@
+package control
+
+import (
+	"os"
+	"syscall"
+
+	N "github.com/sagernet/sing/common/network"
+
+	"golang.org/x/sys/unix"
+)
+
+func DisableUDPFragment() Func {
+	return func(network, address string, conn syscall.RawConn) error {
+		switch N.NetworkName(network) {
+		case N.NetworkUDP:
+		default:
+			return nil
+		}
+		return Raw(conn, func(fd uintptr) error {
+			if err := unix.SetsockoptInt(int(fd), unix.IPPROTO_IP, unix.IP_MTU_DISCOVER, unix.IP_PMTUDISC_DO); err != nil {
+				return os.NewSyscallError("SETSOCKOPT IP_MTU_DISCOVER IP_PMTUDISC_DO", err)
+			}
+			if network == "udp6" {
+				if err := unix.SetsockoptInt(int(fd), unix.IPPROTO_IPV6, unix.IPV6_MTU_DISCOVER, unix.IP_PMTUDISC_DO); err != nil {
+					return os.NewSyscallError("SETSOCKOPT IPV6_MTU_DISCOVER IP_PMTUDISC_DO", err)
+				}
+			}
+			return nil
+		})
+	}
+}
diff --git a/common/control/frag_other.go b/common/control/frag_other.go
new file mode 100644
index 0000000..68e0be5
--- /dev/null
+++ b/common/control/frag_other.go
@@ -0,0 +1,7 @@
+//go:build !((go1.19 && unix) || (!go1.19 && (linux || darwin)) || windows)
+
+package control
+
+func DisableUDPFragment() Func {
+	return nil
+}
diff --git a/common/control/frag_unix.go b/common/control/frag_unix.go
new file mode 100644
index 0000000..3ee6130
--- /dev/null
+++ b/common/control/frag_unix.go
@@ -0,0 +1,28 @@
+//go:build (go1.19 && unix && !linux) || (!go1.19 && darwin)
+
+package control
+
+import (
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func DisableUDPFragment() Func {
+	return func(network, address string, conn syscall.RawConn) error {
+		return Raw(conn, func(fd uintptr) error {
+			switch network {
+			case "udp4":
+				if err := unix.SetsockoptInt(int(fd), unix.IPPROTO_IP, unix.IP_DONTFRAG, 1); err != nil {
+					return os.NewSyscallError("SETSOCKOPT IP_DONTFRAG", err)
+				}
+			case "udp6":
+				if err := unix.SetsockoptInt(int(fd), unix.IPPROTO_IPV6, unix.IPV6_DONTFRAG, 1); err != nil {
+					return os.NewSyscallError("SETSOCKOPT IPV6_DONTFRAG", err)
+				}
+			}
+			return nil
+		})
+	}
+}
diff --git a/common/control/frag_windows.go b/common/control/frag_windows.go
new file mode 100644
index 0000000..bf02948
--- /dev/null
+++ b/common/control/frag_windows.go
@@ -0,0 +1,45 @@
+package control
+
+import (
+	"os"
+	"syscall"
+
+	N "github.com/sagernet/sing/common/network"
+
+	"golang.org/x/sys/windows"
+)
+
+const (
+	IP_MTU_DISCOVER   = 71
+	IPV6_MTU_DISCOVER = 71
+)
+
+// enum PMTUD_STATE from ws2ipdef.h
+const (
+	IP_PMTUDISC_NOT_SET = iota
+	IP_PMTUDISC_DO
+	IP_PMTUDISC_DONT
+	IP_PMTUDISC_PROBE
+	IP_PMTUDISC_MAX
+)
+
+func DisableUDPFragment() Func {
+	return func(network, address string, conn syscall.RawConn) error {
+		switch N.NetworkName(network) {
+		case N.NetworkUDP:
+		default:
+			return nil
+		}
+		return Raw(conn, func(fd uintptr) error {
+			if err := windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DO); err != nil {
+				return os.NewSyscallError("SETSOCKOPT IP_MTU_DISCOVER IP_PMTUDISC_DO", err)
+			}
+			if network == "udp6" {
+				if err := windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IPV6, IPV6_MTU_DISCOVER, IP_PMTUDISC_DO); err != nil {
+					return os.NewSyscallError("SETSOCKOPT IPV6_MTU_DISCOVER IP_PMTUDISC_DO", err)
+				}
+			}
+			return nil
+		})
+	}
+}