Update dependencies

vendor/tailscale.com/net/packet/ip4.go

@@ -0,0 +1,116 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package packet
+
+import (
+	"encoding/binary"
+	"errors"
+	"net/netip"
+
+	"tailscale.com/types/ipproto"
+)
+
+// ip4HeaderLength is the length of an IPv4 header with no IP options.
+const ip4HeaderLength = 20
+
+// IP4Header represents an IPv4 packet header.
+type IP4Header struct {
+	IPProto ipproto.Proto
+	IPID    uint16
+	Src     netip.Addr
+	Dst     netip.Addr
+}
+
+// Len implements Header.
+func (h IP4Header) Len() int {
+	return ip4HeaderLength
+}
+
+var errWrongFamily = errors.New("wrong address family for src/dst IP")
+
+// Marshal implements Header.
+func (h IP4Header) Marshal(buf []byte) error {
+	if len(buf) < h.Len() {
+		return errSmallBuffer
+	}
+	if len(buf) > maxPacketLength {
+		return errLargePacket
+	}
+	if !h.Src.Is4() || !h.Dst.Is4() {
+		return errWrongFamily
+	}
+
+	buf[0] = 0x40 | (byte(h.Len() >> 2))                   // IPv4 + IHL
+	buf[1] = 0x00                                          // DSCP + ECN
+	binary.BigEndian.PutUint16(buf[2:4], uint16(len(buf))) // Total length
+	binary.BigEndian.PutUint16(buf[4:6], h.IPID)           // ID
+	binary.BigEndian.PutUint16(buf[6:8], 0)                // Flags + fragment offset
+	buf[8] = 64                                            // TTL
+	buf[9] = uint8(h.IPProto)                              // Inner protocol
+	// Blank checksum. This is necessary even though we overwrite
+	// it later, because the checksum computation runs over these
+	// bytes and expects them to be zero.
+	binary.BigEndian.PutUint16(buf[10:12], 0)
+	src := h.Src.As4()
+	dst := h.Dst.As4()
+	copy(buf[12:16], src[:])
+	copy(buf[16:20], dst[:])
+
+	binary.BigEndian.PutUint16(buf[10:12], ip4Checksum(buf[0:20])) // Checksum
+
+	return nil
+}
+
+// ToResponse implements Header.
+func (h *IP4Header) ToResponse() {
+	h.Src, h.Dst = h.Dst, h.Src
+	// Flip the bits in the IPID. If incoming IPIDs are distinct, so are these.
+	h.IPID = ^h.IPID
+}
+
+// ip4Checksum computes an IPv4 checksum, as specified in
+// https://tools.ietf.org/html/rfc1071
+func ip4Checksum(b []byte) uint16 {
+	var ac uint32
+	i := 0
+	n := len(b)
+	for n >= 2 {
+		ac += uint32(binary.BigEndian.Uint16(b[i : i+2]))
+		n -= 2
+		i += 2
+	}
+	if n == 1 {
+		ac += uint32(b[i]) << 8
+	}
+	for (ac >> 16) > 0 {
+		ac = (ac >> 16) + (ac & 0xffff)
+	}
+	return uint16(^ac)
+}
+
+// ip4PseudoHeaderOffset is the number of bytes by which the IPv4 UDP
+// pseudo-header is smaller than the real IPv4 header.
+const ip4PseudoHeaderOffset = 8
+
+// marshalPseudo serializes h into buf in the "pseudo-header" form
+// required when calculating UDP checksums. The pseudo-header starts
+// at buf[ip4PseudoHeaderOffset] so as to abut the following UDP
+// header, while leaving enough space in buf for a full IPv4 header.
+func (h IP4Header) marshalPseudo(buf []byte) error {
+	if len(buf) < h.Len() {
+		return errSmallBuffer
+	}
+	if len(buf) > maxPacketLength {
+		return errLargePacket
+	}
+
+	length := len(buf) - h.Len()
+	src, dst := h.Src.As4(), h.Dst.As4()
+	copy(buf[8:12], src[:])
+	copy(buf[12:16], dst[:])
+	buf[16] = 0x0
+	buf[17] = uint8(h.IPProto)
+	binary.BigEndian.PutUint16(buf[18:20], uint16(length))
+	return nil
+}