content: remove unnecessary defer in helpers

Deferring the put back of the buffer is not necessary since
it can be done immediately after use, before checking error.
This decreases the amount of the time the buffer is out
of the pool and not in use.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

content/helpers.go

@@ -136,10 +136,7 @@ func Copy(ctx context.Context, cw Writer, r io.Reader, size int64, expected dige
 		}
 	}
 
-	buf := bufPool.Get().(*[]byte)
-	defer bufPool.Put(buf)
-
-	if _, err := io.CopyBuffer(cw, r, *buf); err != nil {
+	if _, err := copyWithBuffer(cw, r); err != nil {
 		return err
 	}
 
@@ -160,11 +157,7 @@ func CopyReaderAt(cw Writer, ra ReaderAt, n int64) error {
 		return err
 	}
 
-	buf := bufPool.Get().(*[]byte)
-	defer bufPool.Put(buf)
-
-	_, err = io.CopyBuffer(cw, io.NewSectionReader(ra, ws.Offset, n), *buf)
-
+	_, err = copyWithBuffer(cw, io.NewSectionReader(ra, ws.Offset, n))
 	return err
 }
 
@@ -195,10 +188,7 @@ func seekReader(r io.Reader, offset, size int64) (io.Reader, error) {
 	}
 
 	// well then, let's just discard up to the offset
-	buf := bufPool.Get().(*[]byte)
-	defer bufPool.Put(buf)
-
-	n, err := io.CopyBuffer(ioutil.Discard, io.LimitReader(r, offset), *buf)
+	n, err := copyWithBuffer(ioutil.Discard, io.LimitReader(r, offset))
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to discard to offset")
 	}
@@ -208,3 +198,10 @@ func seekReader(r io.Reader, offset, size int64) (io.Reader, error) {
 
 	return r, nil
 }
+
+func copyWithBuffer(dst io.Writer, src io.Reader) (written int64, err error) {
+	buf := bufPool.Get().(*[]byte)
+	written, err = io.CopyBuffer(dst, src, *buf)
+	bufPool.Put(buf)
+	return
+}