Add GetObjectNInfo to object layer (#6449)

The new call combines GetObjectInfo and GetObject, and returns an
object with a ReadCloser interface.

Also adds a number of end-to-end encryption tests at the handler
level.

cmd/gateway/b2/gateway-b2.go

@@ -23,6 +23,7 @@ import (
 	"hash"
 	"io"
 	"io/ioutil"
+	"net/http"
 
 	"strings"
 	"sync"
@@ -394,6 +395,28 @@ func (l *b2Objects) ListObjectsV2(ctx context.Context, bucket, prefix, continuat
 	return loi, nil
 }
 
+// GetObjectNInfo - returns object info and locked object ReadCloser
+func (l *b2Objects) GetObjectNInfo(ctx context.Context, bucket, object string, rs *minio.HTTPRangeSpec, h http.Header) (gr *minio.GetObjectReader, err error) {
+	var objInfo minio.ObjectInfo
+	objInfo, err = l.GetObjectInfo(ctx, bucket, object, minio.ObjectOptions{})
+	if err != nil {
+		return nil, err
+	}
+
+	var startOffset, length int64
+	startOffset, length, err = rs.GetOffsetLength(objInfo.Size)
+	if err != nil {
+		return nil, err
+	}
+
+	pr, pw := io.Pipe()
+	go func() {
+		err := l.GetObject(ctx, bucket, object, startOffset, length, pw, objInfo.ETag, minio.ObjectOptions{})
+		pw.CloseWithError(err)
+	}()
+	return minio.NewGetObjectReaderFromReader(pr, objInfo), nil
+}
+
 // GetObject reads an object from B2. Supports additional
 // parameters like offset and length which are synonymous with
 // HTTP Range requests.