mirror of
https://github.com/impact-eintr/netstack.git
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139 lines
4.4 KiB
Go
139 lines
4.4 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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)
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const (
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udpSrcPort = 0
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udpDstPort = 2
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udpLength = 4
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udpChecksum = 6
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)
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// UDPFields contains the fields of a UDP packet. It is used to describe the
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// fields of a packet that needs to be encoded.
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// udp 首部字段
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type UDPFields struct {
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// SrcPort is the "source port" field of a UDP packet.
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SrcPort uint16
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// DstPort is the "destination port" field of a UDP packet.
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DstPort uint16
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// Length is the "length" field of a UDP packet.
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Length uint16
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// Checksum is the "checksum" field of a UDP packet.
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Checksum uint16
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}
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// UDP represents a UDP header stored in a byte array.
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type UDP []byte
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const (
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// UDPMinimumSize is the minimum size of a valid UDP packet.
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UDPMinimumSize = 8
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// UDPProtocolNumber is UDP's transport protocol number.
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UDPProtocolNumber tcpip.TransportProtocolNumber = 17
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)
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/*
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UDP 是 User Datagram Protocol 的简称，中文名是用户数据报协议。UDP 只在 IP 数据报服务上增加了一点功能，就是复用和分用的功能以及差错检测，UDP 主要的特点是：
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1. UDP 是无连接的，即发送数据之前不需要建立连接，发送结束也不需要连接释放，因此减少了开销和发送数据之间的延时。
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2. UDP 是不可靠传输，尽最大努力交付，因此不需要维护复杂的连接状态。
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3. UDP 的数据报是有消息边界的，发送方发送一个报文，接收方就会完整的收到一个报文。
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4. UDP 没有拥塞控制，网络出现阻塞，UDP 是无感知的，也就不会降低发送速度。
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5. UDP 支持一对一，一对多，多对一，多对多的通信。
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*/
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/*
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|source Port|destination Port|
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| Length | UDP Checksum |
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| Data |
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*/
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// SourcePort returns the "source port" field of the udp header.
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func (b UDP) SourcePort() uint16 {
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return binary.BigEndian.Uint16(b[udpSrcPort:])
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}
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// DestinationPort returns the "destination port" field of the udp header.
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func (b UDP) DestinationPort() uint16 {
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return binary.BigEndian.Uint16(b[udpDstPort:])
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}
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// Length returns the "length" field of the udp header.
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func (b UDP) Length() uint16 {
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return binary.BigEndian.Uint16(b[udpLength:])
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}
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// Payload returns the data contained in the UDP datagram.
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func (b UDP) Payload() []byte {
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return b[UDPMinimumSize:]
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}
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// Checksum returns the "checksum" field of the udp header.
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func (b UDP) Checksum() uint16 {
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return binary.BigEndian.Uint16(b[udpChecksum:])
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}
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// SetSourcePort sets the "source port" field of the udp header.
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func (b UDP) SetSourcePort(port uint16) {
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binary.BigEndian.PutUint16(b[udpSrcPort:], port)
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}
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// SetDestinationPort sets the "destination port" field of the udp header.
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func (b UDP) SetDestinationPort(port uint16) {
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binary.BigEndian.PutUint16(b[udpDstPort:], port)
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}
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// SetChecksum sets the "checksum" field of the udp header.
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func (b UDP) SetChecksum(checksum uint16) {
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binary.BigEndian.PutUint16(b[udpChecksum:], checksum)
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}
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// CalculateChecksum calculates the checksum of the udp packet, given the total
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// length of the packet and the checksum of the network-layer pseudo-header
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// (excluding the total length) and the checksum of the payload.
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func (b UDP) CalculateChecksum(partialChecksum uint16, totalLen uint16) uint16 {
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// Add the length portion of the checksum to the pseudo-checksum.
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tmp := make([]byte, 2)
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binary.BigEndian.PutUint16(tmp, totalLen)
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checksum := Checksum(tmp, partialChecksum)
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// Calculate the rest of the checksum.
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return Checksum(b[:UDPMinimumSize], checksum)
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}
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// Encode encodes all the fields of the udp header.
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func (b UDP) Encode(u *UDPFields) {
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binary.BigEndian.PutUint16(b[udpSrcPort:], u.SrcPort)
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binary.BigEndian.PutUint16(b[udpDstPort:], u.DstPort)
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binary.BigEndian.PutUint16(b[udpLength:], u.Length)
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binary.BigEndian.PutUint16(b[udpChecksum:], u.Checksum)
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}
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var udpFmt string = `
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|% 16s|% 16s|
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|% 16s|% 16s|
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%v
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`
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func (b UDP) String() string {
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for i := range b.Payload() {
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if i != int(b.Length()-8-1) && b.Payload()[i]^b.Payload()[i+1] != 0 {
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return fmt.Sprintf(udpFmt, atoi(b.SourcePort()), atoi(b.DestinationPort()),
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atoi(b.Length()), atoi(b.Checksum()),
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b.Payload())
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}
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}
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return fmt.Sprintf(udpFmt, atoi(b.SourcePort()), atoi(b.DestinationPort()),
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atoi(b.Length()), atoi(b.Checksum()),
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fmt.Sprintf("%v x %d", b.Payload()[0], b.Length()-8))
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}
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