Set etag properly to calculated value if available (#5106)

Fixes #5100

cmd/fs-v1-multipart.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"encoding/hex"
 	"fmt"
 	"io"
 	"os"
@@ -571,7 +572,7 @@ func (fs fsObjects) PutObjectPart(bucket, object, uploadID string, partID int, d
 		return pi, toObjectErr(err, minioMetaMultipartBucket, partPath)
 	}
 
-	md5hex := data.MD5HexString()
+	md5hex := hex.EncodeToString(data.MD5Current())
 
 	// Save the object part info in `fs.json`.
 	fsMeta.AddObjectPart(partID, partSuffix, md5hex, data.Size())

cmd/fs-v1.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"encoding/hex"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -593,8 +594,6 @@ func (fs fsObjects) PutObject(bucket string, object string, data *hash.Reader, m
 		return ObjectInfo{}, traceError(errInvalidArgument)
 	}
 
-	metadata["etag"] = data.MD5HexString()
-
 	var wlk *lock.LockedFile
 	if bucket != minioMetaBucket {
 		bucketMetaDir := pathJoin(fs.fsPath, minioMetaBucket, bucketMetaPrefix)
@@ -634,6 +633,8 @@ func (fs fsObjects) PutObject(bucket string, object string, data *hash.Reader, m
 		return ObjectInfo{}, toObjectErr(err, bucket, object)
 	}
 
+	metadata["etag"] = hex.EncodeToString(data.MD5Current())
+
 	// Should return IncompleteBody{} error when reader has fewer
 	// bytes than specified in request header.
 	if bytesWritten < data.Size() {

cmd/xl-v1-multipart.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"encoding/hex"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -694,7 +695,7 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, d
 	// Once part is successfully committed, proceed with updating XL metadata.
 	xlMeta.Stat.ModTime = UTCNow()
 
-	md5hex := data.MD5HexString()
+	md5hex := hex.EncodeToString(data.MD5Current())
 
 	// Add the current part.
 	xlMeta.AddObjectPart(partID, partSuffix, md5hex, file.Size)

cmd/xl-v1-object.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"encoding/hex"
 	"io"
 	"path"
 	"strconv"
@@ -579,7 +580,7 @@ func (xl xlObjects) PutObject(bucket string, object string, data *hash.Reader, m
 
 	// Save additional erasureMetadata.
 	modTime := UTCNow()
-	metadata["etag"] = data.MD5HexString()
+	metadata["etag"] = hex.EncodeToString(data.MD5Current())
 
 	// Guess content-type from the extension if possible.
 	if metadata["content-type"] == "" {