Additional argument validation for LEFT(), MID() and RIGHT() text functions (#1909)

* Additional argument validation for LEFT(), MID() and RIGHT() text functions

Author: Mark Baker

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 ### Fixed
 
 - Fixed issue with Xlsx@listWorksheetInfo not returning any data
+- Fixed invalid arguments triggering mb_substr() error in LEFT(), MID() and RIGHT() text functions. [Issue #640](https://github.com/PHPOffice/PhpSpreadsheet/issues/640)
 
 ## 1.17.1 - 2021-03-01
 

src/PhpSpreadsheet/Calculation/TextData.php

@@ -299,7 +299,7 @@ public static function LEFT($value = '', $chars = 1)
         $value = Functions::flattenSingleValue($value);
         $chars = Functions::flattenSingleValue($chars);
 
-        if ($chars < 0) {
+        if (!is_numeric($chars) || $chars < 0) {
             return Functions::VALUE();
         }
 
@@ -325,18 +325,14 @@ public static function MID($value = '', $start = 1, $chars = null)
         $start = Functions::flattenSingleValue($start);
         $chars = Functions::flattenSingleValue($chars);
 
-        if (($start < 1) || ($chars < 0)) {
+        if (!is_numeric($start) || $start < 1 || !is_numeric($chars) || $chars < 0) {
             return Functions::VALUE();
         }
 
         if (is_bool($value)) {
             $value = ($value) ? Calculation::getTRUE() : Calculation::getFALSE();
         }
 
-        if (empty($chars)) {
-            return '';
-        }
-
         return mb_substr($value, --$start, $chars, 'UTF-8');
     }
 
@@ -353,7 +349,7 @@ public static function RIGHT($value = '', $chars = 1)
         $value = Functions::flattenSingleValue($value);
         $chars = Functions::flattenSingleValue($chars);
 
-        if ($chars < 0) {
+        if (!is_numeric($chars) || $chars < 0) {
             return Functions::VALUE();
         }
 

tests/data/Calculation/TextData/LEFT.php

@@ -16,6 +16,16 @@
         'QWERTYUIOP',
         -1,
     ],
+    [
+        '#VALUE!',
+        'QWERTYUIOP',
+        'NaN',
+    ],
+    [
+        '#VALUE!',
+        'QWERTYUIOP',
+        null,
+    ],
     [
         'ABC',
         'ABCDEFGHI',

tests/data/Calculation/TextData/MID.php

@@ -26,7 +26,19 @@
         -1,
     ],
     [
-        '',
+        '#VALUE!',
+        'QWERTYUIOP',
+        'NaN',
+        1,
+    ],
+    [
+        '#VALUE!',
+        'QWERTYUIOP',
+        2,
+        'NaN',
+    ],
+    [
+        '#VALUE!',
         'QWERTYUIOP',
         5,
     ],

tests/data/Calculation/TextData/RIGHT.php

@@ -16,6 +16,16 @@
         'QWERTYUIOP',
         -1,
     ],
+    [
+        '#VALUE!',
+        'QWERTYUIOP',
+        'NaN',
+    ],
+    [
+        '#VALUE!',
+        'QWERTYUIOP',
+        null,
+    ],
     [
         'GHI',
         'ABCDEFGHI',