mirror of
https://github.com/impact-eintr/netstack.git
synced 2025-10-05 12:56:55 +08:00
293 lines
8.8 KiB
Go
293 lines
8.8 KiB
Go
package header
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import (
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"encoding/binary"
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"fmt"
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"netstack/tcpip"
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"netstack/tcpip/seqnum"
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)
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/*
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Source Port | Destination Port |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Sequence Number |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Acknowledgment Number |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Data | |U|A|P|R|S|F| |
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| Offset| Reserved |R|C|S|S|Y|I| Window |
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| | |G|K|H|T|N|N| |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Checksum | Urgent Pointer |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Options | Padding |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| data |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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// TCPFields contains the fields of a TCP packet. It is used to describe the
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// fields of a packet that needs to be encoded.
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// tcp首部字段
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type TCPFields struct {
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// SrcPort is the "source port" field of a TCP packet.
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SrcPort uint16
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// DstPort is the "destination port" field of a TCP packet.
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DstPort uint16
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// SeqNum is the "sequence number" field of a TCP packet.
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// TCP的初始序列号ISN是随机生成的
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// 如果TCP每次连接都使用固定ISN，黑客可以很方便模拟任何IP与server建立连接
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// 如果ISN是固定的，那很可能在新连接建立后，上次连接通信的报文才到达，
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// 这种情况有概率发生老报文的seq号正好是server希望收到的新连接的报文seq。这就全乱了。
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SeqNum uint32
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// AckNum is the "acknowledgement number" field of a TCP packet.
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AckNum uint32
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// DataOffset is the "data offset" field of a TCP packet.
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DataOffset uint8
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// Flags is the "flags" field of a TCP packet.
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Flags uint8
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// WindowSize is the "window size" field of a TCP packet.
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WindowSize uint16
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// Checksum is the "checksum" field of a TCP packet.
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Checksum uint16
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// UrgentPointer is the "urgent pointer" field of a TCP packet.
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UrgentPointer uint16
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}
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const (
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srcPort = 0
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dstPort = 2
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seqNum = 4
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ackNum = 8
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dataOffset = 12
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tcpFlags = 13
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winSize = 14
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tcpChecksum = 16
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urgentPtr = 18
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)
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// Options that may be present in a TCP segment.
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const (
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TCPOptionEOL = 0
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TCPOptionNOP = 1
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TCPOptionMSS = 2
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TCPOptionWS = 3
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TCPOptionTS = 8
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TCPOptionSACKPermitted = 4
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TCPOptionSACK = 5
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)
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// SACKBlock 表示 sack 块的结构体
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type SACKBlock struct {
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// Start indicates the lowest sequence number in the block.
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Start seqnum.Value
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// End indicates the sequence number immediately following the last
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// sequence number of this block.
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End seqnum.Value
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}
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// TCPOptions tcp选项结构，这个结构不表示 syn/syn-ack 报文
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type TCPOptions struct {
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// TS is true if the TimeStamp option is enabled.
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TS bool
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// TSVal is the value in the TSVal field of the segment.
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TSVal uint32
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// TSEcr is the value in the TSEcr field of the segment.
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TSEcr uint32
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// SACKBlocks are the SACK blocks specified in the segment.
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SACKBlocks []SACKBlock
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}
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// TCP represents a TCP header stored in a byte array.
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type TCP []byte
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const (
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// TCPMinimumSize is the minimum size of a valid TCP packet.
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TCPMinimumSize = 20
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// TCPProtocolNumber is TCP's transport protocol number.
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TCPProtocolNumber tcpip.TransportProtocolNumber = 6
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)
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// SourcePort returns the "source port" field of the tcp header.
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func (b TCP) SourcePort() uint16 {
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return binary.BigEndian.Uint16(b[srcPort:])
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}
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// DestinationPort returns the "destination port" field of the tcp header.
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func (b TCP) DestinationPort() uint16 {
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return binary.BigEndian.Uint16(b[dstPort:])
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}
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// SequenceNumber returns the "sequence number" field of the tcp header.
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func (b TCP) SequenceNumber() uint32 {
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return binary.BigEndian.Uint32(b[seqNum:])
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}
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// AckNumber returns the "ack number" field of the tcp header.
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func (b TCP) AckNumber() uint32 {
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return binary.BigEndian.Uint32(b[ackNum:])
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}
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// DataOffset returns the "data offset" field of the tcp header.
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func (b TCP) DataOffset() uint8 {
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return (b[dataOffset] >> 4) * 4 // 以32bits为单位 最小为5 20bytes
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}
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// Payload returns the data in the tcp packet.
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func (b TCP) Payload() []byte {
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return b[b.DataOffset():]
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}
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// TCPViewSize TCP报文概览长度
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const TCPViewSize = IPViewSize - TCPMinimumSize
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func (b TCP) viewPayload() []byte {
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if len(b.Payload())-int(b.DataOffset()) < TCPViewSize {
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return b.Payload()
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}
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return b[b.DataOffset():][:TCPViewSize]
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}
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// Flags returns the flags field of the tcp header.
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func (b TCP) Flags() uint8 {
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return b[tcpFlags]
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}
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// WindowSize returns the "window size" field of the tcp header.
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func (b TCP) WindowSize() uint16 {
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return binary.BigEndian.Uint16(b[winSize:])
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}
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// Checksum returns the "checksum" field of the tcp header.
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func (b TCP) Checksum() uint16 {
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return binary.BigEndian.Uint16(b[tcpChecksum:])
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}
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// UrgentPtr returns the "urgentptr" field of the tcp header.
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func (b TCP) UrgentPtr() uint16 {
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return binary.BigEndian.Uint16(b[urgentPtr:])
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}
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// SetSourcePort sets the "source port" field of the tcp header.
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func (b TCP) SetSourcePort(port uint16) {
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binary.BigEndian.PutUint16(b[srcPort:], port)
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}
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// SetDestinationPort sets the "destination port" field of the tcp header.
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func (b TCP) SetDestinationPort(port uint16) {
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binary.BigEndian.PutUint16(b[dstPort:], port)
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}
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// SetChecksum sets the checksum field of the tcp header.
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func (b TCP) SetChecksum(checksum uint16) {
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binary.BigEndian.PutUint16(b[tcpChecksum:], checksum)
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}
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// Options returns a slice that holds the unparsed TCP options in the segment.
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func (b TCP) Options() []byte {
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return b[TCPMinimumSize:b.DataOffset()]
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}
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// ParseTCPOptions extracts and stores all known options in the provided byte
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// slice in a TCPOptions structure.
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func ParseTCPOptions(b []byte) TCPOptions {
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opts := TCPOptions{}
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limit := len(b)
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for i := 0; i < limit; {
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switch b[i] {
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case TCPOptionEOL: // 末尾
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i = limit
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case TCPOptionNOP: // 空值
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i++
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case TCPOptionTS: // 计时
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if i+10 > limit || (b[i+1] != 10) {
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return opts
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}
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opts.TS = true
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opts.TSVal = binary.BigEndian.Uint32(b[i+2:])
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opts.TSEcr = binary.BigEndian.Uint32(b[i+6:])
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i += 10
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case TCPOptionSACK:
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if i+2 > limit {
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// Malformed SACK block, just return and stop parsing.
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return opts
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}
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sackOptionLen := int(b[i+1])
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// TODO 需要添加
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i += sackOptionLen
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default:
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// We don't recognize this option, just skip over it.
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if i+2 > limit {
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return opts
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}
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l := int(b[i+1])
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// If the length is incorrect or if l+i overflows the
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// total options length then return false.
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if l < 2 || i+l > limit {
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return opts
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}
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i++
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}
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}
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return opts
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}
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/*
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Source Port | Destination Port |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Sequence Number |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Acknowledgment Number |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Data | |U|A|P|R|S|F| |
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| Offset| Reserved |R|C|S|S|Y|I| Window |
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| | |G|K|H|T|N|N| |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Checksum | Urgent Pointer |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Options | Padding |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| data |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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var tcpFmt string = `
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|% 16s|% 16s|
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|% 32s |
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|% 32s |
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|% 4s|% 4s|%06b|% 16s|
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|% 16s|% 16s|
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|% 8v|
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| Padding |
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%v`
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func (b TCP) String() string {
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return fmt.Sprintf(tcpFmt, atoi(b.SourcePort()), atoi(b.DestinationPort()),
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atoi(b.SequenceNumber()),
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atoi(b.AckNumber()),
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atoi(b.DataOffset()), "0", b.Flags(), atoi(b.WindowSize()),
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atoi(b.Checksum()), atoi(b.UrgentPtr()),
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ParseTCPOptions(b.Options()),
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b.viewPayload())
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}
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