//go:build !windows package aghnet import ( "context" "fmt" "net" "strings" "sync" "time" "github.com/AdguardTeam/golibs/errors" "github.com/AdguardTeam/golibs/netutil" "github.com/AdguardTeam/golibs/stringutil" ) // defaultHostGen is the default method of generating host for Refresh. func defaultHostGen() (host string) { // TODO(e.burkov): Use strings.Builder. return fmt.Sprintf("test%d.org", time.Now().UnixNano()) } // systemResolvers is a default implementation of SystemResolvers interface. type systemResolvers struct { // addrsLock protects addrs. addrsLock sync.RWMutex // addrs is the set that contains cached local resolvers' addresses. addrs *stringutil.Set // resolver is used to fetch the resolvers' addresses. resolver *net.Resolver // hostGenFunc generates hosts to resolve. hostGenFunc HostGenFunc } const ( // errBadAddrPassed is returned when dialFunc can't parse an IP address. errBadAddrPassed errors.Error = "the passed string is not a valid IP address" // errFakeDial is an error which dialFunc is expected to return. errFakeDial errors.Error = "this error signals the successful dialFunc work" // errUnexpectedHostFormat is returned by validateDialedHost when the host has // more than one percent sign. errUnexpectedHostFormat errors.Error = "unexpected host format" ) // refresh implements the SystemResolvers interface for *systemResolvers. func (sr *systemResolvers) refresh() (err error) { defer func() { err = errors.Annotate(err, "systemResolvers: %w") }() _, err = sr.resolver.LookupHost(context.Background(), sr.hostGenFunc()) dnserr := &net.DNSError{} if errors.As(err, &dnserr) && dnserr.Err == errFakeDial.Error() { return nil } return err } func newSystemResolvers(hostGenFunc HostGenFunc) (sr SystemResolvers) { if hostGenFunc == nil { hostGenFunc = defaultHostGen } s := &systemResolvers{ resolver: &net.Resolver{ PreferGo: true, }, hostGenFunc: hostGenFunc, addrs: stringutil.NewSet(), } s.resolver.Dial = s.dialFunc return s } // validateDialedHost validated the host used by resolvers in dialFunc. func validateDialedHost(host string) (err error) { defer func() { err = errors.Annotate(err, "parsing %q: %w", host) }() parts := strings.Split(host, "%") switch len(parts) { case 1: // host case 2: // Remove the zone and check the IP address part. host = parts[0] default: return errUnexpectedHostFormat } if _, err = netutil.ParseIP(host); err != nil { return errBadAddrPassed } return nil } // dockerEmbeddedDNS is the address of Docker's embedded DNS server. // // See // https://github.com/moby/moby/blob/v1.12.0/docs/userguide/networking/dockernetworks.md. const dockerEmbeddedDNS = "127.0.0.11" // dialFunc gets the resolver's address and puts it into internal cache. func (sr *systemResolvers) dialFunc(_ context.Context, _, address string) (_ net.Conn, err error) { // Just validate the passed address is a valid IP. var host string host, err = netutil.SplitHost(address) if err != nil { // TODO(e.burkov): Maybe use a structured errBadAddrPassed to // allow unwrapping of the real error. return nil, fmt.Errorf("%s: %w", err, errBadAddrPassed) } // Exclude Docker's embedded DNS server, as it may cause recursion if // the container is set as the host system's default DNS server. // // See https://github.com/AdguardTeam/AdGuardHome/issues/3064. // // TODO(a.garipov): Perhaps only do this when we are in the container? // Maybe use an environment variable? if host == dockerEmbeddedDNS { return nil, errFakeDial } err = validateDialedHost(host) if err != nil { return nil, fmt.Errorf("validating dialed host: %w", err) } sr.addrsLock.Lock() defer sr.addrsLock.Unlock() sr.addrs.Add(host) return nil, errFakeDial } func (sr *systemResolvers) Get() (rs []string) { sr.addrsLock.RLock() defer sr.addrsLock.RUnlock() return sr.addrs.Values() }