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