package allregions import ( "context" "crypto/tls" "fmt" "net" "time" "github.com/pkg/errors" "github.com/rs/zerolog" ) const ( // Used to discover HA origintunneld servers srvService = "origintunneld" srvProto = "tcp" srvName = "argotunnel.com" // Used to fallback to DoT when we can't use the default resolver to // discover HA origintunneld servers (GitHub issue #75). dotServerName = "cloudflare-dns.com" dotServerAddr = "1.1.1.1:853" dotTimeout = 15 * time.Second logFieldAddress = "address" ) // Redeclare network functions so they can be overridden in tests. var ( netLookupSRV = net.LookupSRV netLookupIP = net.LookupIP ) // EdgeAddr is a representation of possible ways to refer an edge location. type EdgeAddr struct { TCP *net.TCPAddr UDP *net.UDPAddr } // If the call to net.LookupSRV fails, try to fall back to DoT from Cloudflare directly. // // Note: Instead of DoT, we could also have used DoH. Either of these: // - directly via the JSON API (https://1.1.1.1/dns-query?ct=application/dns-json&name=_origintunneld._tcp.argotunnel.com&type=srv) // - indirectly via `tunneldns.NewUpstreamHTTPS()` // But both of these cases miss out on a key feature from the stdlib: // "The returned records are sorted by priority and randomized by weight within a priority." // (https://golang.org/pkg/net/#Resolver.LookupSRV) // Does this matter? I don't know. It may someday. Let's use DoT so we don't need to worry about it. // See also: Go feature request for stdlib-supported DoH: https://github.com/golang/go/issues/27552 var fallbackLookupSRV = lookupSRVWithDOT var friendlyDNSErrorLines = []string{ `Please try the following things to diagnose this issue:`, ` 1. ensure that argotunnel.com is returning "origintunneld" service records.`, ` Run your system's equivalent of: dig srv _origintunneld._tcp.argotunnel.com`, ` 2. ensure that your DNS resolver is not returning compressed SRV records.`, ` See GitHub issue https://github.com/golang/go/issues/27546`, ` For example, you could use Cloudflare's 1.1.1.1 as your resolver:`, ` https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/`, } // EdgeDiscovery implements HA service discovery lookup. func edgeDiscovery(log *zerolog.Logger, srvService string) ([][]*EdgeAddr, error) { log.Debug().Str("domain", "_"+srvService+"._"+srvProto+"."+srvName).Msg("looking up edge SRV record") _, addrs, err := netLookupSRV(srvService, srvProto, srvName) if err != nil { _, fallbackAddrs, fallbackErr := fallbackLookupSRV(srvService, srvProto, srvName) if fallbackErr != nil || len(fallbackAddrs) == 0 { // use the original DNS error `err` in messages, not `fallbackErr` log.Err(err).Msg("Error looking up Cloudflare edge IPs: the DNS query failed") for _, s := range friendlyDNSErrorLines { log.Error().Msg(s) } return nil, errors.Wrapf(err, "Could not lookup srv records on _%v._%v.%v", srvService, srvProto, srvName) } // Accept the fallback results and keep going addrs = fallbackAddrs } var resolvedAddrPerCNAME [][]*EdgeAddr for _, addr := range addrs { edgeAddrs, err := resolveSRV(addr) if err != nil { return nil, err } resolvedAddrPerCNAME = append(resolvedAddrPerCNAME, edgeAddrs) } return resolvedAddrPerCNAME, nil } func lookupSRVWithDOT(string, string, string) (cname string, addrs []*net.SRV, err error) { // Inspiration: https://github.com/artyom/dot/blob/master/dot.go r := &net.Resolver{ PreferGo: true, Dial: func(ctx context.Context, _ string, _ string) (net.Conn, error) { var dialer net.Dialer conn, err := dialer.DialContext(ctx, "tcp", dotServerAddr) if err != nil { return nil, err } tlsConfig := &tls.Config{ServerName: dotServerName} return tls.Client(conn, tlsConfig), nil }, } ctx, cancel := context.WithTimeout(context.Background(), dotTimeout) defer cancel() return r.LookupSRV(ctx, srvService, srvProto, srvName) } func resolveSRV(srv *net.SRV) ([]*EdgeAddr, error) { ips, err := netLookupIP(srv.Target) if err != nil { return nil, errors.Wrapf(err, "Couldn't resolve SRV record %v", srv) } if len(ips) == 0 { return nil, fmt.Errorf("SRV record %v had no IPs", srv) } addrs := make([]*EdgeAddr, len(ips)) for i, ip := range ips { addrs[i] = &EdgeAddr{ TCP: &net.TCPAddr{IP: ip, Port: int(srv.Port)}, UDP: &net.UDPAddr{IP: ip, Port: int(srv.Port)}, } } return addrs, nil } // ResolveAddrs resolves TCP address given a list of addresses. Address can be a hostname, however, it will return at most one // of the hostname's IP addresses. func ResolveAddrs(addrs []string, log *zerolog.Logger) (resolved []*EdgeAddr) { for _, addr := range addrs { tcpAddr, err := net.ResolveTCPAddr("tcp", addr) if err != nil { log.Error().Str(logFieldAddress, addr).Err(err).Msg("failed to resolve to TCP address") continue } udpAddr, err := net.ResolveUDPAddr("udp", addr) if err != nil { log.Error().Str(logFieldAddress, addr).Err(err).Msg("failed to resolve to UDP address") continue } resolved = append(resolved, &EdgeAddr{ TCP: tcpAddr, UDP: udpAddr, }) } return }