package packet import ( "context" "net/netip" "github.com/rs/zerolog" ) // ICMPRouter sends ICMP messages and listens for their responses type ICMPRouter interface { // Serve starts listening for responses to the requests until context is done Serve(ctx context.Context) error // Request sends an ICMP message. Implementations should not modify pk after the function returns. Request(pk *ICMP, responder FunnelUniPipe) error } // Upstream of raw packets type Upstream interface { // ReceivePacket waits for the next raw packet from upstream ReceivePacket(ctx context.Context) (RawPacket, error) } // Router routes packets between Upstream and ICMPRouter. Currently it rejects all other type of ICMP packets type Router struct { upstream Upstream returnPipe FunnelUniPipe globalConfig *GlobalRouterConfig logger *zerolog.Logger } // GlobalRouterConfig is the configuration shared by all instance of Router. type GlobalRouterConfig struct { ICMPRouter ICMPRouter IPv4Src netip.Addr IPv6Src netip.Addr Zone string } func NewRouter(globalConfig *GlobalRouterConfig, upstream Upstream, returnPipe FunnelUniPipe, logger *zerolog.Logger) *Router { return &Router{ upstream: upstream, returnPipe: returnPipe, globalConfig: globalConfig, logger: logger, } } func (r *Router) Serve(ctx context.Context) error { icmpDecoder := NewICMPDecoder() encoder := NewEncoder() for { rawPacket, err := r.upstream.ReceivePacket(ctx) if err != nil { return err } // Drop packets if ICMPRouter wasn't created if r.globalConfig == nil { continue } icmpPacket, err := icmpDecoder.Decode(rawPacket) if err != nil { r.logger.Err(err).Msg("Failed to decode ICMP packet from quic datagram") continue } if icmpPacket.TTL <= 1 { if err := r.sendTTLExceedMsg(icmpPacket, rawPacket, encoder); err != nil { r.logger.Err(err).Msg("Failed to return ICMP TTL exceed error") } continue } icmpPacket.TTL-- if err := r.globalConfig.ICMPRouter.Request(icmpPacket, r.returnPipe); err != nil { r.logger.Err(err). Str("src", icmpPacket.Src.String()). Str("dst", icmpPacket.Dst.String()). Interface("type", icmpPacket.Type). Msg("Failed to send ICMP packet") continue } } } func (r *Router) sendTTLExceedMsg(pk *ICMP, rawPacket RawPacket, encoder *Encoder) error { var srcIP netip.Addr if pk.Dst.Is4() { srcIP = r.globalConfig.IPv4Src } else { srcIP = r.globalConfig.IPv6Src } ttlExceedPacket := NewICMPTTLExceedPacket(pk.IP, rawPacket, srcIP) encodedTTLExceed, err := encoder.Encode(ttlExceedPacket) if err != nil { return err } return r.returnPipe.SendPacket(pk.Src, encodedTTLExceed) }