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54 lines
1.2 KiB
Go
54 lines
1.2 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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// UDPHeader represents an UDP packet header.
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type UDPHeader struct {
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IPHeader
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SrcPort uint16
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DstPort uint16
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}
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const (
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udpHeaderLength = 8
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// udpTotalHeaderLength is the length of all headers in a UDP packet.
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udpTotalHeaderLength = ipHeaderLength + udpHeaderLength
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)
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func (UDPHeader) Len() int {
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return udpTotalHeaderLength
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}
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func (h UDPHeader) Marshal(buf []byte) error {
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if len(buf) < udpTotalHeaderLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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// The caller does not need to set this.
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h.IPProto = UDP
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length := len(buf) - h.IPHeader.Len()
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put16(buf[20:22], h.SrcPort)
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put16(buf[22:24], h.DstPort)
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put16(buf[24:26], uint16(length))
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put16(buf[26:28], 0) // blank checksum
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h.IPHeader.MarshalPseudo(buf)
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// UDP checksum with IP pseudo header.
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put16(buf[26:28], ipChecksum(buf[8:]))
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h.IPHeader.Marshal(buf)
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return nil
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}
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func (h *UDPHeader) ToResponse() {
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h.SrcPort, h.DstPort = h.DstPort, h.SrcPort
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h.IPHeader.ToResponse()
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}
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