WireGuard, MASQUE proxies: Use Xray-core's built-in lightweight TCP/IP stack instead of gVisor as well (#7156)

https://github.com/XTLS/Xray-core/pull/7130#issuecomment-6116258188 https://github.com/XTLS/Xray-core/pull/7130#issuecomment-6120742739 https://github.com/XTLS/Xray-core/pull/7130#issuecomment-6137264458 https://github.com/XTLS/Xray-core/pull/7156#issuecomment-6202933664 https://github.com/XTLS/Xray-core/pull/7156#issuecomment-6203239736
2026-10-20 08:14:26 +00:00 · 2026-10-15 23:38:14 +00:00
parent 10879a4a8b
commit 8703fdb101
24 changed files with 3053 additions and 1430 deletions
@@ -2,8 +2,14 @@ package tun

 import (
 	"encoding/binary"
+	"math"
 	"math/bits"
 	"net/netip"
+	"slices"
+	"sync"
+	"time"
+
+	"github.com/xtls/xray-core/common/errors"
 )

 const (
@@ -16,6 +22,19 @@ const (
 	protoTCP    = 6
 	protoUDP    = 17
 	protoICMPv6 = 58
+
+	// the smallest that a link is believed to take whatever is said about it: what every IPv4 host takes,
+	// and the smallest link that IPv6 runs on
+	ipv4SmallestMTU = 576
+	ipv6SmallestMTU = 1280
+
+	// the header that an IPv6 packet has in front of each of its fragments, and its number
+	fragmentHeaderSize = 8
+	protoFragment      = 44
+	// fragmentsMost is how many packets can be waiting for the rest of their fragments,
+	// fragmentsTime how long they are waited for at most
+	fragmentsMost = 64
+	fragmentsTime = 30 * time.Second
 )

 // packet is an IP packet with its header read
@@ -24,9 +43,15 @@ type packet struct {
 	src, dst netip.Addr
 	// payload is what follows the IP header
 	payload []byte
+	// fragment is set if payload is a part of what follows the IP header: the one at offset of the packet
+	// with the number id, which has more after it or not
+	fragment bool
+	more     bool
+	offset   int
+	id       uint32
 }

-// parsePacket reads the IP header of b. Fragments are not accepted: what the system sends to the tun fits its MTU
+// parsePacket reads the IP header of b
 func parsePacket(b []byte) (p packet, ok bool) {
 	if len(b) < ipv4HeaderSize {
 		return p, false
@@ -35,9 +60,12 @@ func parsePacket(b []byte) (p packet, ok bool) {
 	case 4:
 		size := int(b[0]&0xf) * 4
 		total := int(binary.BigEndian.Uint16(b[2:]))
-		if size < ipv4HeaderSize || total < size || total > len(b) || binary.BigEndian.Uint16(b[6:])&0x3fff != 0 {
+		if size < ipv4HeaderSize || total < size || total > len(b) {
 			return p, false
 		}
+		if f := binary.BigEndian.Uint16(b[6:]); f&0x3fff != 0 {
+			p.fragment, p.more, p.offset, p.id = true, f&0x2000 != 0, int(f&0x1fff)*8, uint32(binary.BigEndian.Uint16(b[4:]))
+		}
 		p.proto = b[9]
 		p.src = netip.AddrFrom4([4]byte(b[12:16]))
 		p.dst = netip.AddrFrom4([4]byte(b[16:20]))
@@ -65,12 +93,55 @@ func parsePacket(b []byte) (p packet, ok bool) {
 			}
 			p.proto, p.payload = p.payload[0], p.payload[size:]
 		}
+		if p.proto == protoFragment {
+			f := p.payload
+			if len(f) < fragmentHeaderSize {
+				return p, false
+			}
+			p.fragment, p.more, p.offset, p.id = true, f[3]&1 != 0, int(binary.BigEndian.Uint16(f[2:])&^7), binary.BigEndian.Uint32(f[4:])
+			p.proto, p.payload = f[0], f[fragmentHeaderSize:]
+		}
 	default:
 		return p, false
 	}
 	return p, true
 }

+// verified reports whether the checksum of what the packet carries is right
+func (p packet) verified() bool {
+	data := p.payload
+	switch p.proto {
+	case protoICMPv4:
+		return checksum(sum(data, 0)) == 0
+	case protoUDP:
+		if len(data) < udpHeaderSize {
+			return false
+		}
+		// the packet may be longer than what it carries
+		size := int(binary.BigEndian.Uint16(data[4:]))
+		if size < udpHeaderSize || size > len(data) {
+			return false
+		}
+		if p.src.Is4() && data[6]|data[7] == 0 {
+			// zero stands for no checksum
+			return true
+		}
+		data = data[:size]
+	case protoTCP, protoICMPv6:
+	default:
+		return true
+	}
+	pseudo := uint64(p.proto) + uint64(len(data))
+	if p.src.Is4() {
+		src, dst := p.src.As4(), p.dst.As4()
+		pseudo = sum(dst[:], sum(src[:], pseudo))
+	} else {
+		src, dst := p.src.As16(), p.dst.As16()
+		pseudo = sum(dst[:], sum(src[:], pseudo))
+	}
+	return checksum(sum(data, pseudo)) == 0
+}
+
 // putIPHeader writes the header of a packet from src to dst into b, without its length, and returns the size of the header
 func putIPHeader(b []byte, proto byte, src, dst netip.Addr) int {
 	if src.Is4() {
@@ -159,3 +230,161 @@ func checksum(s uint64) uint16 {
 	s = s>>16 + s&0xffff
 	return ^uint16(s)
 }
+
+// writeFragments writes a packet that is larger than mtu to tun in fragments that are not. header is its IP header
+// with what follows that up to payload, which is no more than the header of a UDP packet. id is the number
+// of the packet if it is an IPv6 one
+func writeFragments(tun Tun, mtu int, id uint32, header, payload []byte) error {
+	var b [ipv6HeaderSize + fragmentHeaderSize + udpHeaderSize]byte
+	size := ipv4HeaderSize
+	if header[0]>>4 == 6 {
+		size = ipv6HeaderSize
+	}
+	n := copy(b[:], header[:size])
+	if size == ipv6HeaderSize {
+		// the number goes into a header of its own, behind the IP header. That of IPv4 has it
+		b[6], b[n] = protoFragment, header[6]
+		binary.BigEndian.PutUint32(b[n+4:], id)
+		n += fragmentHeaderSize
+	}
+	// first goes in front of payload, in the first fragment
+	first := header[size:]
+	if n+len(first) > len(b) {
+		return errors.New("no room for a header of ", len(first), " bytes in a fragment")
+	}
+	// every fragment but the last is a number of 8 bytes
+	room, total := (mtu-n)&^7, len(first)+len(payload)
+	if room < 8 {
+		return errors.New("no room for a fragment in an MTU of ", mtu)
+	}
+	for offset := 0; offset < total; {
+		h, part := b[:n], min(room, total-offset)
+		last := offset+part == total
+		if size == ipv6HeaderSize {
+			f := uint16(offset)
+			if !last {
+				f |= 1
+			}
+			binary.BigEndian.PutUint16(b[size+2:], f)
+		} else {
+			f := uint16(offset / 8)
+			if !last {
+				f |= 0x2000
+			}
+			binary.BigEndian.PutUint16(b[6:], f)
+		}
+		setIPLength(b[:size], n+part)
+		data := payload[max(offset-len(first), 0):min(offset+part-len(first), len(payload))]
+		if offset == 0 {
+			h = b[:n+copy(b[n:], first)]
+		}
+		if err := tun.WritePacket(h, data); err != nil {
+			return err
+		}
+		offset += part
+	}
+	return nil
+}
+
+// fragmented is a packet of which not every fragment has come yet
+type fragmented struct {
+	// data is what follows its IP header, as far as its last fragment that has come goes
+	data []byte
+	// parts are what of data has come, in order and apart from each other
+	parts [][2]int
+	// size is that of data when all of it has come, known from the last fragment
+	size  int
+	known bool
+	since time.Time
+}
+
+// reassembly puts the packets that come in fragments together
+type reassembly struct {
+	mu      sync.Mutex
+	packets map[fragments]*fragmented
+}
+
+// fragments is what the fragments of a packet have in common
+type fragments struct {
+	src, dst netip.Addr
+	proto    byte
+	id       uint32
+}
+
+// add takes the fragment p of a packet. With the last one that was missing, it returns the packet.
+// A packet whose fragments do not fit each other is given up
+func (r *reassembly) add(p packet) (packet, bool) {
+	fragment, offset, end := p.payload, p.offset, p.offset+len(p.payload)
+	// what an IP packet can carry
+	most := math.MaxUint16
+	if p.src.Is4() {
+		most -= ipv4HeaderSize
+	}
+	if len(fragment) == 0 || end > most || p.more && len(fragment)%8 != 0 {
+		return p, false
+	}
+	key, now := fragments{p.src, p.dst, p.proto, p.id}, time.Now()
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	f := r.packets[key]
+	if f != nil && now.Sub(f.since) > fragmentsTime {
+		// what is left of a packet whose other fragments were lost: this is one of another packet with its number
+		f = nil
+	}
+	if f == nil {
+		if _, stale := r.packets[key]; !stale && len(r.packets) >= fragmentsMost {
+			// the one that is waited for the longest makes room, not the one that comes now
+			var longest fragments
+			var since time.Time
+			for other, old := range r.packets {
+				if since.IsZero() || old.since.Before(since) {
+					longest, since = other, old.since
+				}
+			}
+			delete(r.packets, longest)
+		}
+		if r.packets == nil {
+			r.packets = make(map[fragments]*fragmented)
+		}
+		f = &fragmented{since: now}
+		r.packets[key] = f
+	}
+	for _, part := range f.parts {
+		if offset >= part[0] && end <= part[1] {
+			// came already
+			return p, false
+		}
+		if offset < part[1] && part[0] < end {
+			// fragments of one packet do not overlap: these are of two, or made to be taken for something else
+			delete(r.packets, key)
+			return p, false
+		}
+	}
+	if f.known && end > f.size || !p.more && len(f.data) > end {
+		// past its end, or an end before what came
+		delete(r.packets, key)
+		return p, false
+	}
+	if !p.more {
+		f.size, f.known = end, true
+	}
+	if len(f.data) < end {
+		f.data = append(f.data, make([]byte, end-len(f.data))...)
+	}
+	copy(f.data[offset:], fragment)
+	i := 0
+	for i < len(f.parts) && f.parts[i][1] < offset {
+		i++
+	}
+	j := i
+	for ; j < len(f.parts) && f.parts[j][0] <= end; j++ {
+		offset, end = min(offset, f.parts[j][0]), max(end, f.parts[j][1])
+	}
+	f.parts = slices.Replace(f.parts, i, j, [2]int{offset, end})
+	if !f.known || f.parts[0] != [2]int{0, f.size} {
+		return p, false
+	}
+	delete(r.packets, key)
+	p.payload, p.fragment = f.data[:f.size], false
+	return p, true
+}