Add LateApplyDialOption and global list

clientconn.go

@@ -152,6 +152,25 @@ func NewClient(target string, opts ...DialOption) (conn *ClientConn, err error)
 	for _, opt := range opts {
 		opt.apply(&cc.dopts)
 	}
+
+	// Register ClientConn with channelz.
+	cc.channelzRegistration(target)
+	// TODO: Ideally it should be impossible to error from this function after
+	// channelz registration.  This will require removing some channelz logs
+	// from the following functions that can error.  Errors can be returned to
+	// the user, and successful logs can be emitted here, after the checks have
+	// passed and channelz is subsequently registered.
+
+	// Determine the resolver to use.
+	if err := cc.parseTargetAndFindResolver(); err != nil {
+		channelz.RemoveEntry(cc.channelz.ID)
+		return nil, err
+	}
+
+	for _, lateApplyOpt := range globalLateApplyDialOptions {
+		lateApplyOpt.DialOption(cc.parsedTarget.URL).apply(&cc.dopts)
+	}
+
 	chainUnaryClientInterceptors(cc)
 	chainStreamClientInterceptors(cc)
 
@@ -168,20 +187,6 @@ func NewClient(target string, opts ...DialOption) (conn *ClientConn, err error)
 	}
 	cc.mkp = cc.dopts.copts.KeepaliveParams
 
-	// Register ClientConn with channelz.
-	cc.channelzRegistration(target)
-
-	// TODO: Ideally it should be impossible to error from this function after
-	// channelz registration.  This will require removing some channelz logs
-	// from the following functions that can error.  Errors can be returned to
-	// the user, and successful logs can be emitted here, after the checks have
-	// passed and channelz is subsequently registered.
-
-	// Determine the resolver to use.
-	if err := cc.parseTargetAndFindResolver(); err != nil {
-		channelz.RemoveEntry(cc.channelz.ID)
-		return nil, err
-	}
 	if err = cc.determineAuthority(); err != nil {
 		channelz.RemoveEntry(cc.channelz.ID)
 		return nil, err

default_dial_option_server_option_test.go

@@ -20,6 +20,7 @@ package grpc
 
 import (
 	"fmt"
+	"net/url"
 	"strings"
 	"testing"
 
@@ -74,6 +75,30 @@ func (s) TestDisableGlobalOptions(t *testing.T) {
 	internal.ClearGlobalDialOptions()
 }
 
+type testLateApplyDialOption struct{}
+
+func (do *testLateApplyDialOption) DialOption(parsedTarget url.URL) DialOption {
+	print("parsedTarget.Scheme: ", parsedTarget.Scheme)
+	if parsedTarget.Scheme == "passthrough" {
+		return WithTransportCredentials(insecure.NewCredentials()) // credentials provided, should pass NewClient.
+	}
+	return WithReadBufferSize(10) // no credentials, should fail NewClient
+}
+
+func (s) TestGlobalLateApplyDialOption(t *testing.T) {
+	internal.AddGlobalLateApplyDialOptions.(func(opt ...LateApplyDialOption))(&testLateApplyDialOption{}) // Do I need a clear?
+	noTSecStr := "no transport security set"
+	if _, err := NewClient("fake"); !strings.Contains(fmt.Sprint(err), noTSecStr) {
+		t.Fatalf("Dialing received unexpected error: %v, want error containing \"%v\"", err, noTSecStr)
+	}
+	cc, err := NewClient("passthrough:///nice")
+	if err != nil {
+		t.Fatalf("Dialing with insecure credentials failed: %v", err)
+	}
+	defer cc.Close()
+	internal.ClearGlobalLateApplyDialOptions()
+}
+
 func (s) TestAddGlobalServerOptions(t *testing.T) {
 	const maxRecvSize = 998765
 	// Set and check the ServerOptions

dialoptions.go

@@ -21,6 +21,7 @@ package grpc
 import (
 	"context"
 	"net"
+	"net/url"
 	"time"
 
 	"google.golang.org/grpc/backoff"
@@ -43,6 +44,12 @@ func init() {
 	internal.ClearGlobalDialOptions = func() {
 		globalDialOptions = nil
 	}
+	internal.AddGlobalLateApplyDialOptions = func(opt ...LateApplyDialOption) {
+		globalLateApplyDialOptions = append(globalLateApplyDialOptions, opt...)
+	}
+	internal.ClearGlobalLateApplyDialOptions = func() {
+		globalLateApplyDialOptions = nil
+	}
 	internal.WithBinaryLogger = withBinaryLogger
 	internal.JoinDialOptions = newJoinDialOption
 	internal.DisableGlobalDialOptions = newDisableGlobalDialOptions
@@ -89,6 +96,14 @@ type DialOption interface {
 
 var globalDialOptions []DialOption
 
+// LateApplyDialOption takes a parsed target and returns a dial option to apply.
+type LateApplyDialOption interface {
+	// DialOption returns a Dial Option to apply.
+	DialOption(parsedTarget url.URL) DialOption
+}
+
+var globalLateApplyDialOptions []LateApplyDialOption
+
 // EmptyDialOption does not alter the dial configuration. It can be embedded in
 // another structure to build custom dial options.
 //

internal/internal.go

@@ -106,6 +106,14 @@ var (
 	// This is used in the 1.0 release of gcp/observability, and thus must not be
 	// deleted or changed.
 	ClearGlobalDialOptions func()
+
+	// AddGlobalLateApplyDialOptions adds a slice of lateApplyDialOptions that
+	// will be configured for newly created ClientConns.
+	AddGlobalLateApplyDialOptions any // func (opt ...lateApplyDialOption)
+	// ClearGlobalLateApplyDialOptions clears the slice of global late apply
+	// dial options.
+	ClearGlobalLateApplyDialOptions func()
+
 	// JoinDialOptions combines the dial options passed as arguments into a
 	// single dial option.
 	JoinDialOptions any // func(...grpc.DialOption) grpc.DialOption