| /* |
| * |
| * Copyright 2018 gRPC authors. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| * |
| */ |
| |
| // Package dns implements a dns resolver to be installed as the default resolver |
| // in grpc. |
| package dns |
| |
| import ( |
| "context" |
| "encoding/json" |
| "errors" |
| "fmt" |
| "net" |
| "os" |
| "strconv" |
| "strings" |
| "sync" |
| "time" |
| |
| grpclbstate "google.golang.org/grpc/balancer/grpclb/state" |
| "google.golang.org/grpc/grpclog" |
| "google.golang.org/grpc/internal/envconfig" |
| "google.golang.org/grpc/internal/grpcrand" |
| "google.golang.org/grpc/resolver" |
| "google.golang.org/grpc/serviceconfig" |
| ) |
| |
| // EnableSRVLookups controls whether the DNS resolver attempts to fetch gRPCLB |
| // addresses from SRV records. Must not be changed after init time. |
| var EnableSRVLookups = false |
| |
| var logger = grpclog.Component("dns") |
| |
| func init() { |
| resolver.Register(NewBuilder()) |
| } |
| |
| const ( |
| defaultPort = "443" |
| defaultDNSSvrPort = "53" |
| golang = "GO" |
| // txtPrefix is the prefix string to be prepended to the host name for txt record lookup. |
| txtPrefix = "_grpc_config." |
| // In DNS, service config is encoded in a TXT record via the mechanism |
| // described in RFC-1464 using the attribute name grpc_config. |
| txtAttribute = "grpc_config=" |
| ) |
| |
| var ( |
| errMissingAddr = errors.New("dns resolver: missing address") |
| |
| // Addresses ending with a colon that is supposed to be the separator |
| // between host and port is not allowed. E.g. "::" is a valid address as |
| // it is an IPv6 address (host only) and "[::]:" is invalid as it ends with |
| // a colon as the host and port separator |
| errEndsWithColon = errors.New("dns resolver: missing port after port-separator colon") |
| ) |
| |
| var ( |
| defaultResolver netResolver = net.DefaultResolver |
| // To prevent excessive re-resolution, we enforce a rate limit on DNS |
| // resolution requests. |
| minDNSResRate = 30 * time.Second |
| ) |
| |
| var customAuthorityDialler = func(authority string) func(ctx context.Context, network, address string) (net.Conn, error) { |
| return func(ctx context.Context, network, address string) (net.Conn, error) { |
| var dialer net.Dialer |
| return dialer.DialContext(ctx, network, authority) |
| } |
| } |
| |
| var customAuthorityResolver = func(authority string) (netResolver, error) { |
| host, port, err := parseTarget(authority, defaultDNSSvrPort) |
| if err != nil { |
| return nil, err |
| } |
| |
| authorityWithPort := net.JoinHostPort(host, port) |
| |
| return &net.Resolver{ |
| PreferGo: true, |
| Dial: customAuthorityDialler(authorityWithPort), |
| }, nil |
| } |
| |
| // NewBuilder creates a dnsBuilder which is used to factory DNS resolvers. |
| func NewBuilder() resolver.Builder { |
| return &dnsBuilder{} |
| } |
| |
| type dnsBuilder struct{} |
| |
| // Build creates and starts a DNS resolver that watches the name resolution of the target. |
| func (b *dnsBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) { |
| host, port, err := parseTarget(target.Endpoint, defaultPort) |
| if err != nil { |
| return nil, err |
| } |
| |
| // IP address. |
| if ipAddr, ok := formatIP(host); ok { |
| addr := []resolver.Address{{Addr: ipAddr + ":" + port}} |
| cc.UpdateState(resolver.State{Addresses: addr}) |
| return deadResolver{}, nil |
| } |
| |
| // DNS address (non-IP). |
| ctx, cancel := context.WithCancel(context.Background()) |
| d := &dnsResolver{ |
| host: host, |
| port: port, |
| ctx: ctx, |
| cancel: cancel, |
| cc: cc, |
| rn: make(chan struct{}, 1), |
| disableServiceConfig: opts.DisableServiceConfig, |
| } |
| |
| if target.Authority == "" { |
| d.resolver = defaultResolver |
| } else { |
| d.resolver, err = customAuthorityResolver(target.Authority) |
| if err != nil { |
| return nil, err |
| } |
| } |
| |
| d.wg.Add(1) |
| go d.watcher() |
| d.ResolveNow(resolver.ResolveNowOptions{}) |
| return d, nil |
| } |
| |
| // Scheme returns the naming scheme of this resolver builder, which is "dns". |
| func (b *dnsBuilder) Scheme() string { |
| return "dns" |
| } |
| |
| type netResolver interface { |
| LookupHost(ctx context.Context, host string) (addrs []string, err error) |
| LookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*net.SRV, err error) |
| LookupTXT(ctx context.Context, name string) (txts []string, err error) |
| } |
| |
| // deadResolver is a resolver that does nothing. |
| type deadResolver struct{} |
| |
| func (deadResolver) ResolveNow(resolver.ResolveNowOptions) {} |
| |
| func (deadResolver) Close() {} |
| |
| // dnsResolver watches for the name resolution update for a non-IP target. |
| type dnsResolver struct { |
| host string |
| port string |
| resolver netResolver |
| ctx context.Context |
| cancel context.CancelFunc |
| cc resolver.ClientConn |
| // rn channel is used by ResolveNow() to force an immediate resolution of the target. |
| rn chan struct{} |
| // wg is used to enforce Close() to return after the watcher() goroutine has finished. |
| // Otherwise, data race will be possible. [Race Example] in dns_resolver_test we |
| // replace the real lookup functions with mocked ones to facilitate testing. |
| // If Close() doesn't wait for watcher() goroutine finishes, race detector sometimes |
| // will warns lookup (READ the lookup function pointers) inside watcher() goroutine |
| // has data race with replaceNetFunc (WRITE the lookup function pointers). |
| wg sync.WaitGroup |
| disableServiceConfig bool |
| } |
| |
| // ResolveNow invoke an immediate resolution of the target that this dnsResolver watches. |
| func (d *dnsResolver) ResolveNow(resolver.ResolveNowOptions) { |
| select { |
| case d.rn <- struct{}{}: |
| default: |
| } |
| } |
| |
| // Close closes the dnsResolver. |
| func (d *dnsResolver) Close() { |
| d.cancel() |
| d.wg.Wait() |
| } |
| |
| func (d *dnsResolver) watcher() { |
| defer d.wg.Done() |
| for { |
| select { |
| case <-d.ctx.Done(): |
| return |
| case <-d.rn: |
| } |
| |
| state, err := d.lookup() |
| if err != nil { |
| d.cc.ReportError(err) |
| } else { |
| d.cc.UpdateState(*state) |
| } |
| |
| // Sleep to prevent excessive re-resolutions. Incoming resolution requests |
| // will be queued in d.rn. |
| t := time.NewTimer(minDNSResRate) |
| select { |
| case <-t.C: |
| case <-d.ctx.Done(): |
| t.Stop() |
| return |
| } |
| } |
| } |
| |
| func (d *dnsResolver) lookupSRV() ([]resolver.Address, error) { |
| if !EnableSRVLookups { |
| return nil, nil |
| } |
| var newAddrs []resolver.Address |
| _, srvs, err := d.resolver.LookupSRV(d.ctx, "grpclb", "tcp", d.host) |
| if err != nil { |
| err = handleDNSError(err, "SRV") // may become nil |
| return nil, err |
| } |
| for _, s := range srvs { |
| lbAddrs, err := d.resolver.LookupHost(d.ctx, s.Target) |
| if err != nil { |
| err = handleDNSError(err, "A") // may become nil |
| if err == nil { |
| // If there are other SRV records, look them up and ignore this |
| // one that does not exist. |
| continue |
| } |
| return nil, err |
| } |
| for _, a := range lbAddrs { |
| ip, ok := formatIP(a) |
| if !ok { |
| return nil, fmt.Errorf("dns: error parsing A record IP address %v", a) |
| } |
| addr := ip + ":" + strconv.Itoa(int(s.Port)) |
| newAddrs = append(newAddrs, resolver.Address{Addr: addr, ServerName: s.Target}) |
| } |
| } |
| return newAddrs, nil |
| } |
| |
| var filterError = func(err error) error { |
| if dnsErr, ok := err.(*net.DNSError); ok && !dnsErr.IsTimeout && !dnsErr.IsTemporary { |
| // Timeouts and temporary errors should be communicated to gRPC to |
| // attempt another DNS query (with backoff). Other errors should be |
| // suppressed (they may represent the absence of a TXT record). |
| return nil |
| } |
| return err |
| } |
| |
| func handleDNSError(err error, lookupType string) error { |
| err = filterError(err) |
| if err != nil { |
| err = fmt.Errorf("dns: %v record lookup error: %v", lookupType, err) |
| logger.Info(err) |
| } |
| return err |
| } |
| |
| func (d *dnsResolver) lookupTXT() *serviceconfig.ParseResult { |
| ss, err := d.resolver.LookupTXT(d.ctx, txtPrefix+d.host) |
| if err != nil { |
| if envconfig.TXTErrIgnore { |
| return nil |
| } |
| if err = handleDNSError(err, "TXT"); err != nil { |
| return &serviceconfig.ParseResult{Err: err} |
| } |
| return nil |
| } |
| var res string |
| for _, s := range ss { |
| res += s |
| } |
| |
| // TXT record must have "grpc_config=" attribute in order to be used as service config. |
| if !strings.HasPrefix(res, txtAttribute) { |
| logger.Warningf("dns: TXT record %v missing %v attribute", res, txtAttribute) |
| // This is not an error; it is the equivalent of not having a service config. |
| return nil |
| } |
| sc := canaryingSC(strings.TrimPrefix(res, txtAttribute)) |
| return d.cc.ParseServiceConfig(sc) |
| } |
| |
| func (d *dnsResolver) lookupHost() ([]resolver.Address, error) { |
| var newAddrs []resolver.Address |
| addrs, err := d.resolver.LookupHost(d.ctx, d.host) |
| if err != nil { |
| err = handleDNSError(err, "A") |
| return nil, err |
| } |
| for _, a := range addrs { |
| ip, ok := formatIP(a) |
| if !ok { |
| return nil, fmt.Errorf("dns: error parsing A record IP address %v", a) |
| } |
| addr := ip + ":" + d.port |
| newAddrs = append(newAddrs, resolver.Address{Addr: addr}) |
| } |
| return newAddrs, nil |
| } |
| |
| func (d *dnsResolver) lookup() (*resolver.State, error) { |
| srv, srvErr := d.lookupSRV() |
| addrs, hostErr := d.lookupHost() |
| if hostErr != nil && (srvErr != nil || len(srv) == 0) { |
| return nil, hostErr |
| } |
| |
| state := resolver.State{Addresses: addrs} |
| if len(srv) > 0 { |
| state = grpclbstate.Set(state, &grpclbstate.State{BalancerAddresses: srv}) |
| } |
| if !d.disableServiceConfig { |
| state.ServiceConfig = d.lookupTXT() |
| } |
| return &state, nil |
| } |
| |
| // formatIP returns ok = false if addr is not a valid textual representation of an IP address. |
| // If addr is an IPv4 address, return the addr and ok = true. |
| // If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true. |
| func formatIP(addr string) (addrIP string, ok bool) { |
| ip := net.ParseIP(addr) |
| if ip == nil { |
| return "", false |
| } |
| if ip.To4() != nil { |
| return addr, true |
| } |
| return "[" + addr + "]", true |
| } |
| |
| // parseTarget takes the user input target string and default port, returns formatted host and port info. |
| // If target doesn't specify a port, set the port to be the defaultPort. |
| // If target is in IPv6 format and host-name is enclosed in square brackets, brackets |
| // are stripped when setting the host. |
| // examples: |
| // target: "www.google.com" defaultPort: "443" returns host: "www.google.com", port: "443" |
| // target: "ipv4-host:80" defaultPort: "443" returns host: "ipv4-host", port: "80" |
| // target: "[ipv6-host]" defaultPort: "443" returns host: "ipv6-host", port: "443" |
| // target: ":80" defaultPort: "443" returns host: "localhost", port: "80" |
| func parseTarget(target, defaultPort string) (host, port string, err error) { |
| if target == "" { |
| return "", "", errMissingAddr |
| } |
| if ip := net.ParseIP(target); ip != nil { |
| // target is an IPv4 or IPv6(without brackets) address |
| return target, defaultPort, nil |
| } |
| if host, port, err = net.SplitHostPort(target); err == nil { |
| if port == "" { |
| // If the port field is empty (target ends with colon), e.g. "[::1]:", this is an error. |
| return "", "", errEndsWithColon |
| } |
| // target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port |
| if host == "" { |
| // Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed. |
| host = "localhost" |
| } |
| return host, port, nil |
| } |
| if host, port, err = net.SplitHostPort(target + ":" + defaultPort); err == nil { |
| // target doesn't have port |
| return host, port, nil |
| } |
| return "", "", fmt.Errorf("invalid target address %v, error info: %v", target, err) |
| } |
| |
| type rawChoice struct { |
| ClientLanguage *[]string `json:"clientLanguage,omitempty"` |
| Percentage *int `json:"percentage,omitempty"` |
| ClientHostName *[]string `json:"clientHostName,omitempty"` |
| ServiceConfig *json.RawMessage `json:"serviceConfig,omitempty"` |
| } |
| |
| func containsString(a *[]string, b string) bool { |
| if a == nil { |
| return true |
| } |
| for _, c := range *a { |
| if c == b { |
| return true |
| } |
| } |
| return false |
| } |
| |
| func chosenByPercentage(a *int) bool { |
| if a == nil { |
| return true |
| } |
| return grpcrand.Intn(100)+1 <= *a |
| } |
| |
| func canaryingSC(js string) string { |
| if js == "" { |
| return "" |
| } |
| var rcs []rawChoice |
| err := json.Unmarshal([]byte(js), &rcs) |
| if err != nil { |
| logger.Warningf("dns: error parsing service config json: %v", err) |
| return "" |
| } |
| cliHostname, err := os.Hostname() |
| if err != nil { |
| logger.Warningf("dns: error getting client hostname: %v", err) |
| return "" |
| } |
| var sc string |
| for _, c := range rcs { |
| if !containsString(c.ClientLanguage, golang) || |
| !chosenByPercentage(c.Percentage) || |
| !containsString(c.ClientHostName, cliHostname) || |
| c.ServiceConfig == nil { |
| continue |
| } |
| sc = string(*c.ServiceConfig) |
| break |
| } |
| return sc |
| } |