package origin import ( "context" "crypto/tls" "fmt" "net" "time" "github.com/pkg/errors" log "github.com/sirupsen/logrus" ) const ( // Used to discover HA Warp servers srvService = "warp" srvProto = "tcp" srvName = "cloudflarewarp.com" // Used to fallback to DoT when we can't use the default resolver to // discover HA Warp servers (GitHub issue #75). dotServerName = "cloudflare-dns.com" dotServerAddr = "1.1.1.1:853" dotTimeout = time.Duration(15 * time.Second) ) var friendlyDNSErrorLines = []string{ `Please try the following things to diagnose this issue:`, ` 1. ensure that cloudflarewarp.com is returning "warp" service records.`, ` Run your system's equivalent of: dig srv _warp._tcp.cloudflarewarp.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/`, } func ResolveEdgeIPs(logger *log.Logger, addresses []string) ([]*net.TCPAddr, error) { if len(addresses) > 0 { var tcpAddrs []*net.TCPAddr for _, address := range addresses { // Addresses specified (for testing, usually) tcpAddr, err := net.ResolveTCPAddr("tcp", address) if err != nil { return nil, err } tcpAddrs = append(tcpAddrs, tcpAddr) } return tcpAddrs, nil } // HA service discovery lookup _, addrs, err := net.LookupSRV(srvService, srvProto, srvName) if err != nil { // 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=_warp._tcp.cloudflarewarp.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 r := fallbackResolver(dotServerName, dotServerAddr) ctx, cancel := context.WithTimeout(context.Background(), dotTimeout) defer cancel() _, fallbackAddrs, fallbackErr := r.LookupSRV(ctx, srvService, srvProto, srvName) if fallbackErr != nil || len(fallbackAddrs) == 0 { // use the original DNS error `err` in messages, not `fallbackErr` logger.Errorln("Error looking up Cloudflare edge IPs: the DNS query failed:", err) for _, s := range friendlyDNSErrorLines { logger.Errorln(s) } return nil, errors.Wrap(err, "Could not lookup srv records on _warp._tcp.cloudflarewarp.com") } // Accept the fallback results and keep going addrs = fallbackAddrs } var resolvedIPsPerCNAME [][]*net.TCPAddr var lookupErr error for _, addr := range addrs { ips, err := ResolveSRVToTCP(addr) if err != nil || len(ips) == 0 { // don't return early, we might be able to resolve other addresses lookupErr = err continue } resolvedIPsPerCNAME = append(resolvedIPsPerCNAME, ips) } ips := FlattenServiceIPs(resolvedIPsPerCNAME) if lookupErr == nil && len(ips) == 0 { return nil, fmt.Errorf("Unknown service discovery error") } return ips, lookupErr } func ResolveSRVToTCP(srv *net.SRV) ([]*net.TCPAddr, error) { ips, err := net.LookupIP(srv.Target) if err != nil { return nil, err } addrs := make([]*net.TCPAddr, len(ips)) for i, ip := range ips { addrs[i] = &net.TCPAddr{IP: ip, Port: int(srv.Port)} } return addrs, nil } // FlattenServiceIPs transposes and flattens the input slices such that the // first element of the n inner slices are the first n elements of the result. func FlattenServiceIPs(ipsByService [][]*net.TCPAddr) []*net.TCPAddr { var result []*net.TCPAddr for len(ipsByService) > 0 { filtered := ipsByService[:0] for _, ips := range ipsByService { if len(ips) == 0 { // sanity check continue } result = append(result, ips[0]) if len(ips) > 1 { filtered = append(filtered, ips[1:]) } } ipsByService = filtered } return result } // Inspiration: https://github.com/artyom/dot/blob/master/dot.go func fallbackResolver(serverName, serverAddress string) *net.Resolver { return &net.Resolver{ PreferGo: true, Dial: func(ctx context.Context, _ string, _ string) (net.Conn, error) { var dialer net.Dialer conn, err := dialer.DialContext(ctx, "tcp", serverAddress) if err != nil { return nil, err } tlsConfig := &tls.Config{ServerName: serverName} return tls.Client(conn, tlsConfig), nil }, } }