fix: remove disabling of multipart combine small parts

This reverts https://github.com/distribution/distribution/pull/3556

This feature is currently broken and requires more fundamental changes
in the S3 driver. Until then it's better to remove it.

Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>

docs/content/storage-drivers/s3.md

@@ -59,6 +59,10 @@ Amazon S3 or S3 compatible services for object storage.
 
 `loglevel`: (optional) Valid values are: `off` (default), `debug`, `debugwithsigning`, `debugwithhttpbody`, `debugwithrequestretries`, `debugwithrequesterrors` and `debugwitheventstreambody`. See the [AWS SDK for Go API reference](https://docs.aws.amazon.com/sdk-for-go/api/aws/#LogLevelType) for details.
 
+**NOTE:** Currently the S3 storage driver does not support S3 API compatible storage that
+does not allow combining the last part in the multipart upload into a part that is bigger
+than the preconfigured `chunkSize`.
+
 ## S3 permission scopes
 
 The following AWS policy is required by the registry for push and pull. Make sure to replace `S3_BUCKET_NAME` with the name of your bucket.

registry/storage/driver/s3-aws/s3.go

@@ -111,7 +111,6 @@ type DriverParameters struct {
 	MultipartCopyChunkSize      int64
 	MultipartCopyMaxConcurrency int64
 	MultipartCopyThresholdSize  int64
-	MultipartCombineSmallPart   bool
 	RootDirectory               string
 	StorageClass                string
 	UserAgent                   string
@@ -165,7 +164,6 @@ type driver struct {
 	MultipartCopyChunkSize      int64
 	MultipartCopyMaxConcurrency int64
 	MultipartCopyThresholdSize  int64
-	MultipartCombineSmallPart   bool
 	RootDirectory               string
 	StorageClass                string
 	ObjectACL                   string
@@ -405,23 +403,6 @@ func FromParameters(ctx context.Context, parameters map[string]interface{}) (*Dr
 		return nil, fmt.Errorf("the useDualStack parameter should be a boolean")
 	}
 
-	mutlipartCombineSmallPart := true
-	combine := parameters["multipartcombinesmallpart"]
-	switch combine := combine.(type) {
-	case string:
-		b, err := strconv.ParseBool(combine)
-		if err != nil {
-			return nil, fmt.Errorf("the multipartcombinesmallpart parameter should be a boolean")
-		}
-		mutlipartCombineSmallPart = b
-	case bool:
-		mutlipartCombineSmallPart = combine
-	case nil:
-		// do nothing
-	default:
-		return nil, fmt.Errorf("the multipartcombinesmallpart parameter should be a boolean")
-	}
-
 	sessionToken := ""
 
 	accelerateBool := false
@@ -457,7 +438,6 @@ func FromParameters(ctx context.Context, parameters map[string]interface{}) (*Dr
 		multipartCopyChunkSize,
 		multipartCopyMaxConcurrency,
 		multipartCopyThresholdSize,
-		mutlipartCombineSmallPart,
 		fmt.Sprint(rootDirectory),
 		storageClass,
 		fmt.Sprint(userAgent),
@@ -608,7 +588,6 @@ func New(ctx context.Context, params DriverParameters) (*Driver, error) {
 		MultipartCopyChunkSize:      params.MultipartCopyChunkSize,
 		MultipartCopyMaxConcurrency: params.MultipartCopyMaxConcurrency,
 		MultipartCopyThresholdSize:  params.MultipartCopyThresholdSize,
-		MultipartCombineSmallPart:   params.MultipartCombineSmallPart,
 		RootDirectory:               params.RootDirectory,
 		StorageClass:                params.StorageClass,
 		ObjectACL:                   params.ObjectACL,
@@ -1636,7 +1615,7 @@ func (w *writer) flush() error {
 	}
 
 	buf := bytes.NewBuffer(w.ready.data)
-	if w.driver.MultipartCombineSmallPart && (w.pending.Len() > 0 && w.pending.Len() < int(w.driver.ChunkSize)) {
+	if w.pending.Len() > 0 && w.pending.Len() < int(w.driver.ChunkSize) {
 		if _, err := buf.Write(w.pending.data); err != nil {
 			return err
 		}

registry/storage/driver/s3-aws/s3_test.go

@@ -42,7 +42,6 @@ func init() {
 		forcePathStyle = os.Getenv("AWS_S3_FORCE_PATH_STYLE")
 		sessionToken   = os.Getenv("AWS_SESSION_TOKEN")
 		useDualStack   = os.Getenv("S3_USE_DUALSTACK")
-		combineSmallPart = os.Getenv("MULTIPART_COMBINE_SMALL_PART")
 		accelerate     = os.Getenv("S3_ACCELERATE")
 		logLevel       = os.Getenv("S3_LOGLEVEL")
 	)
@@ -93,14 +92,6 @@ func init() {
 			useDualStackBool, err = strconv.ParseBool(useDualStack)
 		}
 
-		multipartCombineSmallPart := true
-		if combineSmallPart != "" {
-			multipartCombineSmallPart, err = strconv.ParseBool(combineSmallPart)
-			if err != nil {
-				return nil, err
-			}
-		}
-
 		accelerateBool := true
 		if accelerate != "" {
 			accelerateBool, err = strconv.ParseBool(accelerate)
@@ -125,7 +116,6 @@ func init() {
 			defaultMultipartCopyChunkSize,
 			defaultMultipartCopyMaxConcurrency,
 			defaultMultipartCopyThresholdSize,
-			multipartCombineSmallPart,
 			rootDirectory,
 			storageClass,
 			driverName + "-test",