resolver: Add new fields to resolver.BuildOption struct to support di…

…aling a remote name resolver (#3098)

These fields will be used by resolver implementations which need to talk
to a remote name resolver.

resolver/resolver.go

@@ -21,6 +21,10 @@
 package resolver
 
 import (
+	"context"
+	"net"
+
+	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/serviceconfig"
 )
 
@@ -105,8 +109,27 @@ type Address struct {
 // BuildOption includes additional information for the builder to create
 // the resolver.
 type BuildOption struct {
-	// DisableServiceConfig indicates whether resolver should fetch service config data.
+	// DisableServiceConfig indicates whether a resolver implementation should
+	// fetch service config data.
 	DisableServiceConfig bool
+	// DialCreds is the transport credentials used by the ClientConn for
+	// communicating with the target gRPC service (set via
+	// WithTransportCredentials). In cases where a name resolution service
+	// requires the same credentials, the resolver may use this field. In most
+	// cases though, it is not appropriate, and this field may be ignored.
+	DialCreds credentials.TransportCredentials
+	// CredsBundle is the credentials bundle used by the ClientConn for
+	// communicating with the target gRPC service (set via
+	// WithCredentialsBundle). In cases where a name resolution service
+	// requires the same credentials, the resolver may use this field. In most
+	// cases though, it is not appropriate, and this field may be ignored.
+	CredsBundle credentials.Bundle
+	// Dialer is the custom dialer used by the ClientConn for dialling the
+	// target gRPC service (set via WithDialer). In cases where a name
+	// resolution service requires the same dialer, the resolver may use this
+	// field. In most cases though, it is not appropriate, and this field may
+	// be ignored.
+	Dialer func(context.Context, string) (net.Conn, error)
 }
 
 // State contains the current Resolver state relevant to the ClientConn.

resolver_conn_wrapper.go

@@ -25,6 +25,7 @@ import (
 	"time"
 
 	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
@@ -87,13 +88,24 @@ func newCCResolverWrapper(cc *ClientConn) (*ccResolverWrapper, error) {
 		done: grpcsync.NewEvent(),
 	}
 
+	var credsClone credentials.TransportCredentials
+	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
+		credsClone = creds.Clone()
+	}
+	rbo := resolver.BuildOption{
+		DisableServiceConfig: cc.dopts.disableServiceConfig,
+		DialCreds:            credsClone,
+		CredsBundle:          cc.dopts.copts.CredsBundle,
+		Dialer:               cc.dopts.copts.Dialer,
+	}
+
 	var err error
 	// We need to hold the lock here while we assign to the ccr.resolver field
 	// to guard against a data race caused by the following code path,
 	// rb.Build-->ccr.ReportError-->ccr.poll-->ccr.resolveNow, would end up
 	// accessing ccr.resolver which is being assigned here.
 	ccr.resolverMu.Lock()
-	ccr.resolver, err = rb.Build(cc.parsedTarget, ccr, resolver.BuildOption{DisableServiceConfig: cc.dopts.disableServiceConfig})
+	ccr.resolver, err = rb.Build(cc.parsedTarget, ccr, rbo)
 	if err != nil {
 		return nil, err
 	}