diff options
Diffstat (limited to 'pkg/tcpip/header/tcp.go')
| -rw-r--r-- | pkg/tcpip/header/tcp.go | 68 |
1 files changed, 32 insertions, 36 deletions
diff --git a/pkg/tcpip/header/tcp.go b/pkg/tcpip/header/tcp.go index 6e3ee2e50..e656ebb15 100644 --- a/pkg/tcpip/header/tcp.go +++ b/pkg/tcpip/header/tcp.go @@ -22,16 +22,17 @@ import ( "gvisor.googlesource.com/gvisor/pkg/tcpip/seqnum" ) +// These constants are the offsets of the respective fields in the TCP header. const ( - srcPort = 0 - dstPort = 2 - seqNum = 4 - ackNum = 8 - dataOffset = 12 - tcpFlags = 13 - winSize = 14 - tcpChecksum = 16 - urgentPtr = 18 + TCPSrcPortOffset = 0 + TCPDstPortOffset = 2 + TCPSeqNumOffset = 4 + TCPAckNumOffset = 8 + TCPDataOffset = 12 + TCPFlagsOffset = 13 + TCPWinSizeOffset = 14 + TCPChecksumOffset = 16 + TCPUrgentPtrOffset = 18 ) const ( @@ -179,27 +180,27 @@ const ( // SourcePort returns the "source port" field of the tcp header. func (b TCP) SourcePort() uint16 { - return binary.BigEndian.Uint16(b[srcPort:]) + return binary.BigEndian.Uint16(b[TCPSrcPortOffset:]) } // DestinationPort returns the "destination port" field of the tcp header. func (b TCP) DestinationPort() uint16 { - return binary.BigEndian.Uint16(b[dstPort:]) + return binary.BigEndian.Uint16(b[TCPDstPortOffset:]) } // SequenceNumber returns the "sequence number" field of the tcp header. func (b TCP) SequenceNumber() uint32 { - return binary.BigEndian.Uint32(b[seqNum:]) + return binary.BigEndian.Uint32(b[TCPSeqNumOffset:]) } // AckNumber returns the "ack number" field of the tcp header. func (b TCP) AckNumber() uint32 { - return binary.BigEndian.Uint32(b[ackNum:]) + return binary.BigEndian.Uint32(b[TCPAckNumOffset:]) } // DataOffset returns the "data offset" field of the tcp header. func (b TCP) DataOffset() uint8 { - return (b[dataOffset] >> 4) * 4 + return (b[TCPDataOffset] >> 4) * 4 } // Payload returns the data in the tcp packet. @@ -209,32 +210,32 @@ func (b TCP) Payload() []byte { // Flags returns the flags field of the tcp header. func (b TCP) Flags() uint8 { - return b[tcpFlags] + return b[TCPFlagsOffset] } // WindowSize returns the "window size" field of the tcp header. func (b TCP) WindowSize() uint16 { - return binary.BigEndian.Uint16(b[winSize:]) + return binary.BigEndian.Uint16(b[TCPWinSizeOffset:]) } // Checksum returns the "checksum" field of the tcp header. func (b TCP) Checksum() uint16 { - return binary.BigEndian.Uint16(b[tcpChecksum:]) + return binary.BigEndian.Uint16(b[TCPChecksumOffset:]) } // SetSourcePort sets the "source port" field of the tcp header. func (b TCP) SetSourcePort(port uint16) { - binary.BigEndian.PutUint16(b[srcPort:], port) + binary.BigEndian.PutUint16(b[TCPSrcPortOffset:], port) } // SetDestinationPort sets the "destination port" field of the tcp header. func (b TCP) SetDestinationPort(port uint16) { - binary.BigEndian.PutUint16(b[dstPort:], port) + binary.BigEndian.PutUint16(b[TCPDstPortOffset:], port) } // SetChecksum sets the checksum field of the tcp header. func (b TCP) SetChecksum(checksum uint16) { - binary.BigEndian.PutUint16(b[tcpChecksum:], checksum) + binary.BigEndian.PutUint16(b[TCPChecksumOffset:], checksum) } // CalculateChecksum calculates the checksum of the tcp segment. @@ -258,20 +259,20 @@ func (b TCP) ParsedOptions() TCPOptions { } func (b TCP) encodeSubset(seq, ack uint32, flags uint8, rcvwnd uint16) { - binary.BigEndian.PutUint32(b[seqNum:], seq) - binary.BigEndian.PutUint32(b[ackNum:], ack) - b[tcpFlags] = flags - binary.BigEndian.PutUint16(b[winSize:], rcvwnd) + binary.BigEndian.PutUint32(b[TCPSeqNumOffset:], seq) + binary.BigEndian.PutUint32(b[TCPAckNumOffset:], ack) + b[TCPFlagsOffset] = flags + binary.BigEndian.PutUint16(b[TCPWinSizeOffset:], rcvwnd) } // Encode encodes all the fields of the tcp header. func (b TCP) Encode(t *TCPFields) { b.encodeSubset(t.SeqNum, t.AckNum, t.Flags, t.WindowSize) - binary.BigEndian.PutUint16(b[srcPort:], t.SrcPort) - binary.BigEndian.PutUint16(b[dstPort:], t.DstPort) - b[dataOffset] = (t.DataOffset / 4) << 4 - binary.BigEndian.PutUint16(b[tcpChecksum:], t.Checksum) - binary.BigEndian.PutUint16(b[urgentPtr:], t.UrgentPointer) + binary.BigEndian.PutUint16(b[TCPSrcPortOffset:], t.SrcPort) + binary.BigEndian.PutUint16(b[TCPDstPortOffset:], t.DstPort) + b[TCPDataOffset] = (t.DataOffset / 4) << 4 + binary.BigEndian.PutUint16(b[TCPChecksumOffset:], t.Checksum) + binary.BigEndian.PutUint16(b[TCPUrgentPtrOffset:], t.UrgentPointer) } // EncodePartial updates a subset of the fields of the tcp header. It is useful @@ -290,18 +291,13 @@ func (b TCP) EncodePartial(partialChecksum, length uint16, seqnum, acknum uint32 b.encodeSubset(seqnum, acknum, flags, rcvwnd) // Add the contributions of the passed-in fields to the checksum. - checksum = Checksum(b[seqNum:seqNum+8], checksum) - checksum = Checksum(b[winSize:winSize+2], checksum) + checksum = Checksum(b[TCPSeqNumOffset:TCPSeqNumOffset+8], checksum) + checksum = Checksum(b[TCPWinSizeOffset:TCPWinSizeOffset+2], checksum) // Encode the checksum. b.SetChecksum(^checksum) } -// TCPChecksumOffset returns offset of the checksum field. -func TCPChecksumOffset() uint16 { - return tcpChecksum -} - // ParseSynOptions parses the options received in a SYN segment and returns the // relevant ones. opts should point to the option part of the TCP Header. func ParseSynOptions(opts []byte, isAck bool) TCPSynOptions { |