41 lines
1.2 KiB
Go
41 lines
1.2 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package disco
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import (
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"bytes"
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"encoding/binary"
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"net/netip"
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"tailscale.com/tailcfg"
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"tailscale.com/types/key"
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)
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// ToPCAPFrame marshals the bytes for a pcap record that describe a disco frame.
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//
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// Warning: Alloc garbage. Acceptable while capturing.
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func ToPCAPFrame(src netip.AddrPort, derpNodeSrc key.NodePublic, payload []byte) []byte {
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var (
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b bytes.Buffer
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flag uint8
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)
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b.Grow(128) // Most disco frames will probably be smaller than this.
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if src.Addr() == tailcfg.DerpMagicIPAddr {
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flag |= 0x01
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}
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b.WriteByte(flag) // 1b: flag
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derpSrc := derpNodeSrc.Raw32()
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b.Write(derpSrc[:]) // 32b: derp public key
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binary.Write(&b, binary.LittleEndian, uint16(src.Port())) // 2b: port
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addr, _ := src.Addr().MarshalBinary()
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binary.Write(&b, binary.LittleEndian, uint16(len(addr))) // 2b: len(addr)
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b.Write(addr) // Xb: addr
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binary.Write(&b, binary.LittleEndian, uint16(len(payload))) // 2b: len(payload)
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b.Write(payload) // Xb: payload
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return b.Bytes()
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}
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