service/s3: Add support for accelerate with dualstack (#887)

Adds support for using S3 accelerate with Dualstack IPv4 with IPv6. To
enable Dualstack with accelerate set the `Config.UseDualstack` and
`Config.S3UseAccelerate`.

```go
sess := session.New()
svc := s3.New(sess, &aws.Config{
	S3UseAccelerate: aws.Bool(true),
	UseDualStack:    aws.Bool(true),
})

result, err := svc.GetObject(&s3.GetObjectInput{
	Bucket: aws.String("my_bucket"),
	Key:    aws.String("my_key"),
})

// Request made to:
// https://my_bucket.s3-accelerate.dualstack.amazonaws.com/my_key
```

aws/config.go

@@ -137,9 +137,6 @@ type Config struct {
 	// accelerate enabled. If the bucket is not enabled for accelerate an error
 	// will be returned. The bucket name must be DNS compatible to also work
 	// with accelerate.
-	//
-	// Not compatible with UseDualStack requests will fail if both flags are
-	// specified.
 	S3UseAccelerate *bool
 
 	// Set this to `true` to disable the EC2Metadata client from overriding the

service/s3/host_style_bucket.go

@@ -1,6 +1,7 @@
 package s3
 
 import (
+	"bytes"
 	"fmt"
 	"net/url"
 	"regexp"
@@ -37,14 +38,6 @@ var accelerateOpBlacklist = operationBlacklist{
 func updateEndpointForS3Config(r *request.Request) {
 	forceHostStyle := aws.BoolValue(r.Config.S3ForcePathStyle)
 	accelerate := aws.BoolValue(r.Config.S3UseAccelerate)
-	useDualStack := aws.BoolValue(r.Config.UseDualStack)
-
-	if useDualStack && accelerate {
-		r.Error = awserr.New("InvalidParameterException",
-			fmt.Sprintf("configuration aws.Config.UseDualStack is not compatible with aws.Config.Accelerate"),
-			nil)
-		return
-	}
 
 	if accelerate && accelerateOpBlacklist.Continue(r) {
 		if forceHostStyle {
@@ -75,6 +68,10 @@ func updateEndpointForHostStyle(r *request.Request) {
 	moveBucketToHost(r.HTTPRequest.URL, bucket)
 }
 
+var (
+	accelElem = []byte("s3-accelerate.dualstack.")
+)
+
 func updateEndpointForAccelerate(r *request.Request) {
 	bucket, ok := bucketNameFromReqParams(r.Params)
 	if !ok {
@@ -93,6 +90,22 @@ func updateEndpointForAccelerate(r *request.Request) {
 
 	// Change endpoint from s3(-[a-z0-1-])?.amazonaws.com to s3-accelerate.amazonaws.com
 	r.HTTPRequest.URL.Host = replaceHostRegion(r.HTTPRequest.URL.Host, "accelerate")
+
+	if aws.BoolValue(r.Config.UseDualStack) {
+		host := []byte(r.HTTPRequest.URL.Host)
+
+		// Strip region from hostname
+		if idx := bytes.Index(host, accelElem); idx >= 0 {
+			start := idx + len(accelElem)
+			if end := bytes.IndexByte(host[start:], '.'); end >= 0 {
+				end += start + 1
+				copy(host[start:], host[end:])
+				host = host[:len(host)-(end-start)]
+				r.HTTPRequest.URL.Host = string(host)
+			}
+		}
+	}
+
 	moveBucketToHost(r.HTTPRequest.URL, bucket)
 }
 

service/s3/host_style_bucket_test.go

@@ -50,6 +50,12 @@ var (
 		{"a.b.c", "http://a.b.c.s3-accelerate.amazonaws.com/", ""},
 		{"a$b$c", "http://s3-mock-region.amazonaws.com/%7BBucket%7D", "InvalidParameterException"},
 	}
+
+	accelerateDualstack = []s3BucketTest{
+		{"abc", "https://abc.s3-accelerate.dualstack.amazonaws.com/", ""},
+		{"a.b.c", "https://s3.dualstack.mock-region.amazonaws.com/%7BBucket%7D", "InvalidParameterException"},
+		{"a$b$c", "https://s3.dualstack.mock-region.amazonaws.com/%7BBucket%7D", "InvalidParameterException"},
+	}
 )
 
 func runTests(t *testing.T, svc *s3.S3, tests []s3BucketTest) {
@@ -74,6 +80,14 @@ func TestAccelerateNoSSLBucketBuild(t *testing.T) {
 	runTests(t, s, accelerateNoSSLTests)
 }
 
+func TestAccelerateDualstackBucketBuild(t *testing.T) {
+	s := s3.New(unit.Session, &aws.Config{
+		S3UseAccelerate: aws.Bool(true),
+		UseDualStack:    aws.Bool(true),
+	})
+	runTests(t, s, accelerateDualstack)
+}
+
 func TestHostStyleBucketBuild(t *testing.T) {
 	s := s3.New(unit.Session)
 	runTests(t, s, sslTests)