snapshot: sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1

Содержимое пина, зафиксированного в go.mod sing-box-lx, одним коммитом
без истории. Полная история SagerNet/gvisor — 1.45 ГБ и клонируется в
каждой CI-джобе; наша дельта — одна вставка в одну функцию, история для
неё не нужна.

Module path github.com/sagernet/gvisor сохранён намеренно: на него
опирается replace-директива суперпроекта.

Патч поверх — отдельным коммитом, чтобы дельта читалась одним git show
и переносилась на новый пин копированием.

SPECS/TASKS/048-GVISOR_HANDSHAKE_NIL_CRASH

pkg/tcpip/header/checksum.go

@@ -0,0 +1,107 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package header provides the implementation of the encoding and decoding of
+// network protocol headers.
+package header
+
+import (
+	"encoding/binary"
+	"fmt"
+
+	"github.com/sagernet/gvisor/pkg/tcpip"
+	"github.com/sagernet/gvisor/pkg/tcpip/checksum"
+)
+
+// PseudoHeaderChecksum calculates the pseudo-header checksum for the given
+// destination protocol and network address. Pseudo-headers are needed by
+// transport layers when calculating their own checksum.
+func PseudoHeaderChecksum(protocol tcpip.TransportProtocolNumber, srcAddr tcpip.Address, dstAddr tcpip.Address, totalLen uint16) uint16 {
+	xsum := checksum.Checksum(srcAddr.AsSlice(), 0)
+	xsum = checksum.Checksum(dstAddr.AsSlice(), xsum)
+
+	// Add the length portion of the checksum to the pseudo-checksum.
+	var tmp [2]byte
+	binary.BigEndian.PutUint16(tmp[:], totalLen)
+	xsum = checksum.Checksum(tmp[:], xsum)
+
+	return checksum.Checksum([]byte{0, uint8(protocol)}, xsum)
+}
+
+// checksumUpdate2ByteAlignedUint16 updates a uint16 value in a calculated
+// checksum.
+//
+// The value MUST begin at a 2-byte boundary in the original buffer.
+func checksumUpdate2ByteAlignedUint16(xsum, old, new uint16) uint16 {
+	// As per RFC 1071 page 4,
+	//	(4)  Incremental Update
+	//
+	//        ...
+	//
+	//        To update the checksum, simply add the differences of the
+	//        sixteen bit integers that have been changed.  To see why this
+	//        works, observe that every 16-bit integer has an additive inverse
+	//        and that addition is associative.  From this it follows that
+	//        given the original value m, the new value m', and the old
+	//        checksum C, the new checksum C' is:
+	//
+	//                C' = C + (-m) + m' = C + (m' - m)
+	if old == new {
+		return xsum
+	}
+	return checksum.Combine(xsum, checksum.Combine(new, ^old))
+}
+
+// checksumUpdate2ByteAlignedAddress updates an address in a calculated
+// checksum.
+//
+// The addresses must have the same length and must contain an even number
+// of bytes. The address MUST begin at a 2-byte boundary in the original buffer.
+func checksumUpdate2ByteAlignedAddress(xsum uint16, old, new tcpip.Address) uint16 {
+	const uint16Bytes = 2
+
+	if old.BitLen() != new.BitLen() {
+		panic(fmt.Sprintf("buffer lengths are different; old = %d, new = %d", old.BitLen()/8, new.BitLen()/8))
+	}
+
+	if oldBytes := old.BitLen() % 16; oldBytes != 0 {
+		panic(fmt.Sprintf("buffer has an odd number of bytes; got = %d", oldBytes))
+	}
+
+	oldAddr := old.AsSlice()
+	newAddr := new.AsSlice()
+
+	// As per RFC 1071 page 4,
+	//	(4)  Incremental Update
+	//
+	//        ...
+	//
+	//        To update the checksum, simply add the differences of the
+	//        sixteen bit integers that have been changed.  To see why this
+	//        works, observe that every 16-bit integer has an additive inverse
+	//        and that addition is associative.  From this it follows that
+	//        given the original value m, the new value m', and the old
+	//        checksum C, the new checksum C' is:
+	//
+	//                C' = C + (-m) + m' = C + (m' - m)
+	for len(oldAddr) != 0 {
+		// Convert the 2 byte sequences to uint16 values then apply the increment
+		// update.
+		xsum = checksumUpdate2ByteAlignedUint16(xsum, (uint16(oldAddr[0])<<8)+uint16(oldAddr[1]), (uint16(newAddr[0])<<8)+uint16(newAddr[1]))
+		oldAddr = oldAddr[uint16Bytes:]
+		newAddr = newAddr[uint16Bytes:]
+	}
+
+	return xsum
+}