93 lines
1.9 KiB
Go
93 lines
1.9 KiB
Go
package multicast
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import (
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"bytes"
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"fmt"
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"log"
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"net"
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"net/netip"
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"time"
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"git.crumpington.com/lib/ratelimiter"
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)
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func Receiver(selfVPNIP netip.Addr, ch chan<- Packet) {
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for {
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if err := receiver(selfVPNIP, ch); err != nil {
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log.Printf("[MC Receiver] %v", err)
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}
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time.Sleep(errorTimeout)
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}
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}
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func receiver(selfVPNIP netip.Addr, ch chan<- Packet) error {
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limiters := map[netip.Addr]*ratelimiter.Limiter{}
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selfIP := selfVPNIP.As4()[3]
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addr := multicastAddr(selfVPNIP)
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log.Printf("[MC Receiver] Listening on %v.", addr)
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conn, err := net.ListenMulticastUDP("udp", nil, addr)
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if err != nil {
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return fmt.Errorf("bind: %w", err)
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}
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defer conn.Close()
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buf := make([]byte, SignedPacketSize+1) // +1 to detect oversized packets
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for {
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conn.SetReadDeadline(time.Now().Add(32 * time.Second))
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n, src, err := conn.ReadFromUDPAddrPort(buf)
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if err != nil {
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if ne, ok := err.(net.Error); ok && ne.Timeout() {
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continue
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}
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return fmt.Errorf("read: %w", err)
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}
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if n != SignedPacketSize {
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continue
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}
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packet := unmarshal(buf[:n])
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if packet.PeerIP == selfIP {
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continue
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}
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// Slightly cheaper than limiting.
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age := time.Since(time.Unix(packet.Timestamp, 0))
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if age > maxPacketAge || age < -maxPacketAge {
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continue
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}
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srcAddr := src.Addr().Unmap()
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lim, ok := limiters[srcAddr]
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if !ok {
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lim = ratelimiter.New(ratelimiter.Config{
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BurstLimit: 1,
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FillPeriod: broadcastInterval / 2,
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MaxWaitCount: 0,
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})
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limiters[srcAddr] = lim
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}
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if err := lim.Limit(); err != nil {
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log.Printf("[MC Receiver] Rate limited packet from peer IP %d.", packet.PeerIP)
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continue
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}
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packet.Signed = bytes.Clone(packet.Signed)
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packet.Src = src.Addr().Unmap()
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ch <- packet
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}
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}
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func multicastAddr(vpnIP netip.Addr) *net.UDPAddr {
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b := vpnIP.As4()
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return net.UDPAddrFromAddrPort(
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netip.AddrPortFrom(
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netip.AddrFrom4([4]byte{239, b[0], b[1], b[2]}), 4560))
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}
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