tcp基本框架

tcpip/header/tcp.go

@@ -1,6 +1,9 @@
 package header
 
-import "netstack/tcpip"
+import (
+	"encoding/binary"
+	"netstack/tcpip"
+)
 
 /*
  0                   1                   2                   3
@@ -24,6 +27,50 @@ import "netstack/tcpip"
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
 
+// TCPFields contains the fields of a TCP packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+// tcp首部字段
+type TCPFields struct {
+	// SrcPort is the "source port" field of a TCP packet.
+	SrcPort uint16
+
+	// DstPort is the "destination port" field of a TCP packet.
+	DstPort uint16
+
+	// SeqNum is the "sequence number" field of a TCP packet.
+	SeqNum uint32
+
+	// AckNum is the "acknowledgement number" field of a TCP packet.
+	AckNum uint32
+
+	// DataOffset is the "data offset" field of a TCP packet.
+	DataOffset uint8
+
+	// Flags is the "flags" field of a TCP packet.
+	Flags uint8
+
+	// WindowSize is the "window size" field of a TCP packet.
+	WindowSize uint16
+
+	// Checksum is the "checksum" field of a TCP packet.
+	Checksum uint16
+
+	// UrgentPointer is the "urgent pointer" field of a TCP packet.
+	UrgentPointer uint16
+}
+
+const (
+	srcPort     = 0
+	dstPort     = 2
+	seqNum      = 4
+	ackNum      = 8
+	dataOffset  = 12
+	tcpFlags    = 13
+	winSize     = 14
+	tcpChecksum = 16
+	urgentPtr   = 18
+)
+
 // TCP represents a TCP header stored in a byte array.
 type TCP []byte
 
@@ -34,3 +81,13 @@ const (
 	// TCPProtocolNumber is TCP's transport protocol number.
 	TCPProtocolNumber tcpip.TransportProtocolNumber = 6
 )
+
+// SourcePort returns the "source port" field of the tcp header.
+func (b TCP) SourcePort() uint16 {
+	return binary.BigEndian.Uint16(b[srcPort:])
+}
+
+// DestinationPort returns the "destination port" field of the tcp header.
+func (b TCP) DestinationPort() uint16 {
+	return binary.BigEndian.Uint16(b[dstPort:])
+}