package upstream import ( "net" "strings" "github.com/miekg/dns" "golang.org/x/net/context" ) // Detects the upstream type from the specified url and creates a proper Upstream object func NewUpstream(url string, bootstrap string) (Upstream, error) { proto := "udp" prefix := "" switch { case strings.HasPrefix(url, "tcp://"): proto = "tcp" prefix = "tcp://" case strings.HasPrefix(url, "tls://"): proto = "tcp-tls" prefix = "tls://" case strings.HasPrefix(url, "https://"): return NewHttpsUpstream(url, bootstrap) } hostname := strings.TrimPrefix(url, prefix) host, port, err := net.SplitHostPort(hostname) if err != nil { // Set port depending on the protocol switch proto { case "udp": port = "53" case "tcp": port = "53" case "tcp-tls": port = "853" } // Set host = hostname host = hostname } // Try to resolve the host address (or check if it's an IP address) bootstrapResolver := CreateResolver(bootstrap) ips, err := bootstrapResolver.LookupIPAddr(context.Background(), host) if err != nil || len(ips) == 0 { return nil, err } addr := ips[0].String() endpoint := net.JoinHostPort(addr, port) tlsServerName := "" if proto == "tcp-tls" && host != addr { // Check if we need to specify TLS server name tlsServerName = host } return NewDnsUpstream(endpoint, proto, tlsServerName) } func CreateResolver(bootstrap string) *net.Resolver { bootstrapResolver := net.DefaultResolver if bootstrap != "" { bootstrapResolver = &net.Resolver{ PreferGo: true, Dial: func(ctx context.Context, network, address string) (net.Conn, error) { var d net.Dialer return d.DialContext(ctx, network, bootstrap) }, } } return bootstrapResolver } // Performs a simple health-check of the specified upstream func IsAlive(u Upstream) (bool, error) { // Using ipv4only.arpa. domain as it is a part of DNS64 RFC and it should exist everywhere ping := new(dns.Msg) ping.SetQuestion("ipv4only.arpa.", dns.TypeA) resp, err := u.Exchange(context.Background(), ping) // If we got a header, we're alright, basically only care about I/O errors 'n stuff. if err != nil && resp != nil { // Silly check, something sane came back. if resp.Rcode != dns.RcodeServerFailure { err = nil } } return err == nil, err }