Support S3 multipart uploads

Signed-off-by: Adrien Fillon <adrien.fillon@cdiscount.com>

pkg/objstore/s3/s3.go

@@ -233,7 +233,15 @@ func (b *Bucket) Exists(ctx context.Context, name string) (bool, error) {
 
 // Upload the contents of the reader as an object into the bucket.
 func (b *Bucket) Upload(ctx context.Context, name string, r io.Reader) error {
-	_, err := b.client.PutObjectWithContext(ctx, b.name, name, r, -1,
+	fileSize := int64(-1)
+	fileInfo, err := r.(*os.File).Stat()
+	if err != nil {
+		return errors.Errorf("Could not stat local file %s", name)
+	} else {
+		fileSize = fileInfo.Size()
+	}
+
+	_, err = b.client.PutObjectWithContext(ctx, b.name, name, r, fileSize,
 		minio.PutObjectOptions{ServerSideEncryption: b.sse},
 	)