s3: add S3 IPv6 support with option "dualstack_endpoint" (bool)

dualstack_endpoint=true enables IPv6 DNS lookup for S3 endpoints
in s3.go, add Options.DualstackEndpoint to support IPv6 on S3

backend/s3/s3.go

@@ -2219,6 +2219,13 @@ If it is set then rclone will use v2 authentication.
 Use this only if v4 signatures don't work, e.g. pre Jewel/v10 CEPH.`,
 			Default:  false,
 			Advanced: true,
+		}, {
+			Name: "use_dual_stack",
+			Help: `If true use AWS S3 dual-stack endpoint (IPv6 support).
+
+See [AWS Docs on Dualstack Endpoints(https://docs.aws.amazon.com/AmazonS3/latest/userguide/dual-stack-endpoints.html)`,
+			Default:  false,
+			Advanced: true,
 		}, {
 			Name:     "use_accelerate_endpoint",
 			Provider: "AWS",
@@ -2628,6 +2635,7 @@ type Options struct {
 	Region                string               `config:"region"`
 	Endpoint              string               `config:"endpoint"`
 	STSEndpoint           string               `config:"sts_endpoint"`
+	UseDualStack          bool                 `config:"use_dual_stack"`
 	LocationConstraint    string               `config:"location_constraint"`
 	ACL                   string               `config:"acl"`
 	BucketACL             string               `config:"bucket_acl"`
@@ -2956,6 +2964,9 @@ func s3Connection(ctx context.Context, opt *Options, client *http.Client) (*s3.S
 		r.addService("sts", opt.STSEndpoint)
 		awsConfig.WithEndpointResolver(r)
 	}
+	if opt.UseDualStack {
+		awsConfig.UseDualStackEndpoint = endpoints.DualStackEndpointStateEnabled
+	}
 
 	// awsConfig.WithLogLevel(aws.LogDebugWithSigning)
 	awsSessionOpts := session.Options{

backend/s3/s3_test.go

@@ -2,13 +2,23 @@
 package s3
 
 import (
+	"context"
+	"net/http"
+	"strings"
 	"testing"
 
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fstest"
 	"github.com/rclone/rclone/fstest/fstests"
 )
 
+func SetupS3Test(t *testing.T) (context.Context, *Options, *http.Client) {
+	ctx, opt := context.Background(), new(Options)
+	opt.Provider = "AWS"
+	client := getClient(ctx, opt)
+	return ctx, opt, client
+}
+
 // TestIntegration runs integration tests against the remote
 func TestIntegration(t *testing.T) {
 	fstests.Run(t, &fstests.Opt{
@@ -39,6 +49,28 @@ func TestIntegration2(t *testing.T) {
 	})
 }
 
+func TestAWSDualStackOption(t *testing.T) {
+	{
+		// test enabled
+		ctx, opt, client := SetupS3Test(t)
+		opt.UseDualStack = true
+		s3Conn, _, _ := s3Connection(ctx, opt, client)
+		if !strings.Contains(s3Conn.Endpoint, "dualstack") {
+			t.Errorf("dualstack failed got: %s, wanted: dualstack", s3Conn.Endpoint)
+			t.Fail()
+		}
+	}
+	{
+		// test default case
+		ctx, opt, client := SetupS3Test(t)
+		s3Conn, _, _ := s3Connection(ctx, opt, client)
+		if strings.Contains(s3Conn.Endpoint, "dualstack") {
+			t.Errorf("dualstack failed got: %s, NOT wanted: dualstack", s3Conn.Endpoint)
+			t.Fail()
+		}
+	}
+}
+
 func (f *Fs) SetUploadChunkSize(cs fs.SizeSuffix) (fs.SizeSuffix, error) {
 	return f.setUploadChunkSize(cs)
 }