Apply Tailscale TUN offload APIs
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世界
parent
414291f6d6
commit
824e7573c0
5 changed files with 277 additions and 13 deletions
200
tun/offload.go
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200
tun/offload.go
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package tun
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import (
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"encoding/binary"
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"fmt"
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)
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// GSOType represents the type of segmentation offload.
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type GSOType int
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const (
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GSONone GSOType = iota
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GSOTCPv4
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GSOTCPv6
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GSOUDPL4
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)
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func (g GSOType) String() string {
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switch g {
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case GSONone:
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return "GSONone"
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case GSOTCPv4:
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return "GSOTCPv4"
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case GSOTCPv6:
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return "GSOTCPv6"
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case GSOUDPL4:
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return "GSOUDPL4"
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default:
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return "unknown"
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}
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}
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// GSOOptions is loosely modeled after struct virtio_net_hdr from the VIRTIO
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// specification. It is a common representation of GSO metadata that can be
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// applied to support packet GSO across tun.Device implementations.
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type GSOOptions struct {
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// GSOType represents the type of segmentation offload.
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GSOType GSOType
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// HdrLen is the sum of the layer 3 and 4 header lengths. This field may be
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// zero when GSOType == GSONone.
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HdrLen uint16
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// CsumStart is the head byte index of the packet data to be checksummed,
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// i.e. the start of the TCP or UDP header.
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CsumStart uint16
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// CsumOffset is the offset from CsumStart where the 2-byte checksum value
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// should be placed.
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CsumOffset uint16
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// GSOSize is the size of each segment exclusive of HdrLen. The tail segment
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// may be smaller than this value.
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GSOSize uint16
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// NeedsCsum may be set where GSOType == GSONone. When set, the checksum
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// at CsumStart + CsumOffset must be a partial checksum, i.e. the
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// pseudo-header sum.
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NeedsCsum bool
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}
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const (
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gsoIPv4SrcAddrOffset = 12
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gsoIPv6SrcAddrOffset = 8
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gsoTCPFlagsOffset = 13
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gsoIPProtoTCP = 6
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gsoIPProtoUDP = 17
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)
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const (
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gsoTCPFlagFIN uint8 = 0x01
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gsoTCPFlagPSH uint8 = 0x08
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)
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// GSOSplit splits packets from in into outBufs[<index>][outOffset:], writing
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// the size of each element into sizes. It returns the number of buffers
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// populated, and/or an error. Callers may pass an in slice that overlaps with
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// the first element of outBufs, i.e. &in[0] may be equal to
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// &outBufs[0][outOffset]. GSONone is a valid options.GSOType regardless of the
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// value of options.NeedsCsum. Length of each outBufs element must be greater
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// than or equal to the length of in, otherwise output may be silently truncated.
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func GSOSplit(in []byte, options GSOOptions, outBufs [][]byte, sizes []int, outOffset int) (int, error) {
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cSumAt := int(options.CsumStart) + int(options.CsumOffset)
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if cSumAt+1 >= len(in) {
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return 0, fmt.Errorf("end of checksum offset (%d) exceeds packet length (%d)", cSumAt+1, len(in))
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}
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if len(in) < int(options.HdrLen) {
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return 0, fmt.Errorf("length of packet (%d) < GSO HdrLen (%d)", len(in), options.HdrLen)
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}
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payloadLen := len(in) - int(options.HdrLen)
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if options.GSOType == GSONone || payloadLen < int(options.GSOSize) {
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if len(in) > len(outBufs[0][outOffset:]) {
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return 0, fmt.Errorf("length of packet (%d) exceeds output element length (%d)", len(in), len(outBufs[0][outOffset:]))
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}
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if options.NeedsCsum {
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initial := binary.BigEndian.Uint16(in[cSumAt:])
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in[cSumAt], in[cSumAt+1] = 0, 0
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binary.BigEndian.PutUint16(in[cSumAt:], ^Checksum(in[options.CsumStart:], initial))
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}
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sizes[0] = copy(outBufs[0][outOffset:], in)
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return 1, nil
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}
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if options.HdrLen < options.CsumStart {
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return 0, fmt.Errorf("GSO HdrLen (%d) < GSO CsumStart (%d)", options.HdrLen, options.CsumStart)
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}
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ipVersion := in[0] >> 4
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switch ipVersion {
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case 4:
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if options.GSOType != GSOTCPv4 && options.GSOType != GSOUDPL4 {
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return 0, fmt.Errorf("ip header version: %d, GSO type: %s", ipVersion, options.GSOType)
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}
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if len(in) < 20 {
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return 0, fmt.Errorf("length of packet (%d) < minimum ipv4 header size (%d)", len(in), 20)
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}
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case 6:
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if options.GSOType != GSOTCPv6 && options.GSOType != GSOUDPL4 {
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return 0, fmt.Errorf("ip header version: %d, GSO type: %s", ipVersion, options.GSOType)
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}
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if len(in) < 40 {
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return 0, fmt.Errorf("length of packet (%d) < minimum ipv6 header size (%d)", len(in), 40)
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}
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default:
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return 0, fmt.Errorf("invalid ip header version: %d", ipVersion)
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}
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iphLen := int(options.CsumStart)
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srcAddrOffset := gsoIPv6SrcAddrOffset
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addrLen := 16
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if ipVersion == 4 {
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srcAddrOffset = gsoIPv4SrcAddrOffset
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addrLen = 4
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}
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transportCsumAt := int(options.CsumStart + options.CsumOffset)
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var firstTCPSeqNum uint32
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var protocol uint8
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if options.GSOType == GSOTCPv4 || options.GSOType == GSOTCPv6 {
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protocol = gsoIPProtoTCP
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if len(in) < int(options.CsumStart)+20 {
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return 0, fmt.Errorf("length of packet (%d) < GSO CsumStart (%d) + minimum TCP header size (%d)",
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len(in), options.CsumStart, 20)
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}
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firstTCPSeqNum = binary.BigEndian.Uint32(in[options.CsumStart+4:])
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} else {
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protocol = gsoIPProtoUDP
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}
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nextSegmentDataAt := int(options.HdrLen)
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i := 0
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for ; nextSegmentDataAt < len(in); i++ {
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if i == len(outBufs) {
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return i - 1, ErrTooManySegments
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}
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nextSegmentEnd := nextSegmentDataAt + int(options.GSOSize)
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if nextSegmentEnd > len(in) {
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nextSegmentEnd = len(in)
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}
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segmentDataLen := nextSegmentEnd - nextSegmentDataAt
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totalLen := int(options.HdrLen) + segmentDataLen
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sizes[i] = totalLen
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out := outBufs[i][outOffset:]
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copy(out, in[:iphLen])
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if ipVersion == 4 {
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if i > 0 {
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id := binary.BigEndian.Uint16(out[4:])
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id += uint16(i)
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binary.BigEndian.PutUint16(out[4:], id)
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}
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out[10], out[11] = 0, 0
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binary.BigEndian.PutUint16(out[2:], uint16(totalLen))
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ipv4CSum := ^Checksum(out[:iphLen], 0)
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binary.BigEndian.PutUint16(out[10:], ipv4CSum)
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} else {
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binary.BigEndian.PutUint16(out[4:], uint16(totalLen-iphLen))
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}
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copy(out[options.CsumStart:options.HdrLen], in[options.CsumStart:options.HdrLen])
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if protocol == gsoIPProtoTCP {
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tcpSeq := firstTCPSeqNum + uint32(options.GSOSize*uint16(i))
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binary.BigEndian.PutUint32(out[options.CsumStart+4:], tcpSeq)
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if nextSegmentEnd != len(in) {
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clearFlags := gsoTCPFlagFIN | gsoTCPFlagPSH
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out[options.CsumStart+gsoTCPFlagsOffset] &^= clearFlags
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}
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} else {
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binary.BigEndian.PutUint16(out[options.CsumStart+4:], uint16(segmentDataLen)+(options.HdrLen-options.CsumStart))
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}
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copy(out[options.HdrLen:], in[nextSegmentDataAt:nextSegmentEnd])
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out[transportCsumAt], out[transportCsumAt+1] = 0, 0
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transportHeaderLen := int(options.HdrLen - options.CsumStart)
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lenForPseudo := uint16(transportHeaderLen + segmentDataLen)
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transportCSum := PseudoHeaderChecksum(protocol, in[srcAddrOffset:srcAddrOffset+addrLen], in[srcAddrOffset+addrLen:srcAddrOffset+addrLen*2], lenForPseudo)
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transportCSum = ^Checksum(out[options.CsumStart:totalLen], transportCSum)
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binary.BigEndian.PutUint16(out[options.CsumStart+options.CsumOffset:], transportCSum)
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nextSegmentDataAt += int(options.GSOSize)
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}
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return i, nil
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}
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