xl/fs: Move few functions into common code. (#1453)

- PutObject()
- PutObjectPart()
- NewMultipartUpload()
- AbortMultipartUpload()

Implementations across both FS and XL object layer
share common implementation.

object-common.go

@@ -17,6 +17,9 @@
 package main
 
 import (
+	"crypto/md5"
+	"encoding/hex"
+	"io"
 	"path"
 	"sort"
 )
@@ -98,6 +101,76 @@ func deleteBucket(storage StorageAPI, bucket string) error {
 	return nil
 }
 
+// putObjectCommon - create an object, is a common function for both object layers.
+func putObjectCommon(storage StorageAPI, bucket string, object string, size int64, data io.Reader, metadata map[string]string) (string, error) {
+	// Verify if bucket is valid.
+	if !IsValidBucketName(bucket) {
+		return "", (BucketNameInvalid{Bucket: bucket})
+	}
+	if !IsValidObjectName(object) {
+		return "", (ObjectNameInvalid{
+			Bucket: bucket,
+			Object: object,
+		})
+	}
+	// Check whether the bucket exists.
+	if isExist, err := isBucketExist(storage, bucket); err != nil {
+		return "", err
+	} else if !isExist {
+		return "", BucketNotFound{Bucket: bucket}
+	}
+
+	fileWriter, err := storage.CreateFile(bucket, object)
+	if err != nil {
+		return "", toObjectErr(err, bucket, object)
+	}
+
+	// Initialize md5 writer.
+	md5Writer := md5.New()
+
+	// Instantiate a new multi writer.
+	multiWriter := io.MultiWriter(md5Writer, fileWriter)
+
+	// Instantiate checksum hashers and create a multiwriter.
+	if size > 0 {
+		if _, err = io.CopyN(multiWriter, data, size); err != nil {
+			if clErr := safeCloseAndRemove(fileWriter); clErr != nil {
+				return "", clErr
+			}
+			return "", toObjectErr(err)
+		}
+	} else {
+		if _, err = io.Copy(multiWriter, data); err != nil {
+			if clErr := safeCloseAndRemove(fileWriter); clErr != nil {
+				return "", clErr
+			}
+			return "", err
+		}
+	}
+
+	newMD5Hex := hex.EncodeToString(md5Writer.Sum(nil))
+	// md5Hex representation.
+	var md5Hex string
+	if len(metadata) != 0 {
+		md5Hex = metadata["md5Sum"]
+	}
+	if md5Hex != "" {
+		if newMD5Hex != md5Hex {
+			if err = safeCloseAndRemove(fileWriter); err != nil {
+				return "", err
+			}
+			return "", BadDigest{md5Hex, newMD5Hex}
+		}
+	}
+	err = fileWriter.Close()
+	if err != nil {
+		return "", err
+	}
+
+	// Return md5sum, successfully wrote object.
+	return newMD5Hex, nil
+}
+
 // isUploadIDExists - verify if a given uploadID exists and is valid.
 func isUploadIDExists(storage StorageAPI, bucket, object, uploadID string) (bool, error) {
 	uploadIDPath := path.Join(bucket, object, uploadID)