Update go dependencies (#4524)

vendor/google.golang.org/grpc/resolver/dns/dns_resolver.go

@@ -47,6 +47,8 @@ const (
 	defaultFreq       = time.Minute * 30
 	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="
@@ -64,6 +66,9 @@ var (
 
 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) {
@@ -239,7 +244,13 @@ func (d *dnsResolver) watcher() {
 			return
 		case <-d.t.C:
 		case <-d.rn:
+			if !d.t.Stop() {
+				// Before resetting a timer, it should be stopped to prevent racing with
+				// reads on it's channel.
+				<-d.t.C
+			}
 		}
+
 		result, sc := d.lookup()
 		// Next lookup should happen within an interval defined by d.freq. It may be
 		// more often due to exponential retry on empty address list.
@@ -252,6 +263,16 @@ func (d *dnsResolver) watcher() {
 		}
 		d.cc.NewServiceConfig(sc)
 		d.cc.NewAddress(result)
+
+		// 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
+		}
 	}
 }
 
@@ -282,7 +303,7 @@ func (d *dnsResolver) lookupSRV() []resolver.Address {
 }
 
 func (d *dnsResolver) lookupTXT() string {
-	ss, err := d.resolver.LookupTXT(d.ctx, d.host)
+	ss, err := d.resolver.LookupTXT(d.ctx, txtPrefix+d.host)
 	if err != nil {
 		grpclog.Infof("grpc: failed dns TXT record lookup due to %v.\n", err)
 		return ""

vendor/google.golang.org/grpc/resolver/passthrough/passthrough.go

@@ -45,7 +45,7 @@ type passthroughResolver struct {
 }
 
 func (r *passthroughResolver) start() {
-	r.cc.NewAddress([]resolver.Address{{Addr: r.target.Endpoint}})
+	r.cc.UpdateState(resolver.State{Addresses: []resolver.Address{{Addr: r.target.Endpoint}}})
 }
 
 func (*passthroughResolver) ResolveNow(o resolver.ResolveNowOption) {}

vendor/google.golang.org/grpc/resolver/resolver.go

@@ -20,6 +20,10 @@
 // All APIs in this package are experimental.
 package resolver
 
+import (
+	"google.golang.org/grpc/serviceconfig"
+)
+
 var (
 	// m is a map from scheme to resolver builder.
 	m = make(map[string]Builder)
@@ -98,6 +102,16 @@ type BuildOption struct {
 	DisableServiceConfig bool
 }
 
+// State contains the current Resolver state relevant to the ClientConn.
+type State struct {
+	Addresses []Address // Resolved addresses for the target
+	// ServiceConfig is the parsed service config; obtained from
+	// serviceconfig.Parse.
+	ServiceConfig serviceconfig.Config
+
+	// TODO: add Err error
+}
+
 // ClientConn contains the callbacks for resolver to notify any updates
 // to the gRPC ClientConn.
 //
@@ -106,17 +120,38 @@ type BuildOption struct {
 // testing, the new implementation should embed this interface. This allows
 // gRPC to add new methods to this interface.
 type ClientConn interface {
+	// UpdateState updates the state of the ClientConn appropriately.
+	UpdateState(State)
 	// NewAddress is called by resolver to notify ClientConn a new list
 	// of resolved addresses.
 	// The address list should be the complete list of resolved addresses.
+	//
+	// Deprecated: Use UpdateState instead.
 	NewAddress(addresses []Address)
 	// NewServiceConfig is called by resolver to notify ClientConn a new
 	// service config. The service config should be provided as a json string.
+	//
+	// Deprecated: Use UpdateState instead.
 	NewServiceConfig(serviceConfig string)
 }
 
 // Target represents a target for gRPC, as specified in:
 // https://github.com/grpc/grpc/blob/master/doc/naming.md.
+// It is parsed from the target string that gets passed into Dial or DialContext by the user. And
+// grpc passes it to the resolver and the balancer.
+//
+// If the target follows the naming spec, and the parsed scheme is registered with grpc, we will
+// parse the target string according to the spec. e.g. "dns://some_authority/foo.bar" will be parsed
+// into &Target{Scheme: "dns", Authority: "some_authority", Endpoint: "foo.bar"}
+//
+// If the target does not contain a scheme, we will apply the default scheme, and set the Target to
+// be the full target string. e.g. "foo.bar" will be parsed into
+// &Target{Scheme: resolver.GetDefaultScheme(), Endpoint: "foo.bar"}.
+//
+// If the parsed scheme is not registered (i.e. no corresponding resolver available to resolve the
+// endpoint), we set the Scheme to be the default scheme, and set the Endpoint to be the full target
+// string. e.g. target string "unknown_scheme://authority/endpoint" will be parsed into
+// &Target{Scheme: resolver.GetDefaultScheme(), Endpoint: "unknown_scheme://authority/endpoint"}.
 type Target struct {
 	Scheme    string
 	Authority string