buffer: combine checking range of sourceStart in `buf.copy`

Merging 2 checking range of sourceStart into 1. Plus,
add test case to increase coverage if sourceStart is greater
than length of source.

PR-URL: https://github.com/nodejs/node/pull/47758
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

1 files changed, 2 insertions, 8 deletions

diff --git a/lib/buffer.js b/lib/buffer.js
index ec20e3432f..0ff7c1920a 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -222,8 +222,8 @@ function _copy(source, target, targetStart, sourceStart, sourceEnd) {
     sourceStart = 0;
   } else {
     sourceStart = toInteger(sourceStart, 0);
-    if (sourceStart < 0)
-      throw new ERR_OUT_OF_RANGE('sourceStart', '>= 0', sourceStart);
+    if (sourceStart < 0 || sourceStart > source.length)
+      throw new ERR_OUT_OF_RANGE('sourceStart', `>= 0 && <= ${source.length}`, sourceStart);
   }
 
   if (sourceEnd === undefined) {
@@ -237,12 +237,6 @@ function _copy(source, target, targetStart, sourceStart, sourceEnd) {
   if (targetStart >= target.length || sourceStart >= sourceEnd)
     return 0;
 
-  if (sourceStart > source.length) {
-    throw new ERR_OUT_OF_RANGE('sourceStart',
-                               `<= ${source.length}`,
-                               sourceStart);
-  }
-
   return _copyActual(source, target, targetStart, sourceStart, sourceEnd);
 }