59 lines
1.3 KiB
Go
59 lines
1.3 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package packet
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import (
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"encoding/binary"
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"tailscale.com/types/ipproto"
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)
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// udpHeaderLength is the size of the UDP packet header, not including
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// the outer IP header.
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const udpHeaderLength = 8
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// UDP4Header is an IPv4+UDP header.
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type UDP4Header struct {
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IP4Header
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SrcPort uint16
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DstPort uint16
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}
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// Len implements Header.
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func (h UDP4Header) Len() int {
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return h.IP4Header.Len() + udpHeaderLength
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}
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// Marshal implements Header.
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func (h UDP4Header) Marshal(buf []byte) error {
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if len(buf) < h.Len() {
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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 = ipproto.UDP
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length := len(buf) - h.IP4Header.Len()
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binary.BigEndian.PutUint16(buf[20:22], h.SrcPort)
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binary.BigEndian.PutUint16(buf[22:24], h.DstPort)
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binary.BigEndian.PutUint16(buf[24:26], uint16(length))
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binary.BigEndian.PutUint16(buf[26:28], 0) // blank checksum
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// UDP checksum with IP pseudo header.
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h.IP4Header.marshalPseudo(buf)
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binary.BigEndian.PutUint16(buf[26:28], ip4Checksum(buf[ip4PseudoHeaderOffset:]))
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h.IP4Header.Marshal(buf)
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return nil
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}
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// ToResponse implements Header.
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func (h *UDP4Header) ToResponse() {
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h.SrcPort, h.DstPort = h.DstPort, h.SrcPort
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h.IP4Header.ToResponse()
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}
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