Add object compression support (#6292)

Add support for streaming (golang/LZ77/snappy) compression.

cmd/xl-v1-metadata.go

@@ -34,10 +34,11 @@ const erasureAlgorithmKlauspost = "klauspost/reedsolomon/vandermonde"
 // objectPartInfo Info of each part kept in the multipart metadata
 // file after CompleteMultipartUpload() is called.
 type objectPartInfo struct {
-	Number int    `json:"number"`
-	Name   string `json:"name"`
-	ETag   string `json:"etag"`
-	Size   int64  `json:"size"`
+	Number     int    `json:"number"`
+	Name       string `json:"name"`
+	ETag       string `json:"etag"`
+	Size       int64  `json:"size"`
+	ActualSize int64  `json:"actualSize"`
 }
 
 // byObjectPartNumber is a collection satisfying sort.Interface.
@@ -250,12 +251,13 @@ func objectPartIndex(parts []objectPartInfo, partNumber int) int {
 }
 
 // AddObjectPart - add a new object part in order.
-func (m *xlMetaV1) AddObjectPart(partNumber int, partName string, partETag string, partSize int64) {
+func (m *xlMetaV1) AddObjectPart(partNumber int, partName string, partETag string, partSize int64, actualSize int64) {
 	partInfo := objectPartInfo{
-		Number: partNumber,
-		Name:   partName,
-		ETag:   partETag,
-		Size:   partSize,
+		Number:     partNumber,
+		Name:       partName,
+		ETag:       partETag,
+		Size:       partSize,
+		ActualSize: actualSize,
 	}
 
 	// Update part info if it already exists.