Check for MIME type to know if CSV reader can read a file

CSV reader used to accept any file without any kind of check. That made
users incorrectly believe that things were ok, even though there is no
way for CSV reader to read anything else that plain text files.

Fixes #167

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Avoid potentially unsupported PSR-16 cache keys - [#354](https://github.com/PHPOffice/PhpSpreadsheet/issues/354) 
+- Check for MIME type to know if CSV reader can read a file - [#167](https://github.com/PHPOffice/PhpSpreadsheet/issues/167) 
 
 ## [1.1.0] - 2018-01-28
 

src/PhpSpreadsheet/Reader/Csv.php

@@ -195,11 +195,11 @@ protected function inferSeparator()
             }
 
             $meanSquareDeviations[$delimiter] = array_reduce(
-                $series,
-                function ($sum, $value) use ($median) {
-                    return $sum + pow($value - $median, 2);
-                }
-            ) / count($series);
+                    $series,
+                    function ($sum, $value) use ($median) {
+                        return $sum + pow($value - $median, 2);
+                    }
+                ) / count($series);
         }
 
         // ... and pick the delimiter with the smallest mean square deviation (in case of ties, the order in potentialDelimiters is respected)
@@ -476,6 +476,13 @@ public function canRead($pFilename)
 
         fclose($this->fileHandle);
 
-        return true;
+        $type = mime_content_type($pFilename);
+        $supportedTypes = [
+            'text/csv',
+            'text/plain',
+            'inode/x-empty',
+        ];
+
+        return in_array($type, $supportedTypes, true);
     }
 }

tests/PhpSpreadsheetTests/Reader/CsvTest.php

@@ -63,4 +63,30 @@ public function providerDelimiterDetection()
             ],
         ];
     }
+
+    /**
+     * @dataProvider providerCanLoad
+     *
+     * @param bool $expected
+     * @param string $filename
+     */
+    public function testCanLoad($expected, $filename)
+    {
+        $reader = new Csv();
+        self::assertSame($expected, $reader->canRead($filename));
+    }
+
+    public function providerCanLoad()
+    {
+        return [
+            [false, 'data/Reader/Ods/data.ods'],
+            [false, 'data/Reader/Xml/WithoutStyle.xml'],
+            [true, 'data/Reader/CSV/enclosure.csv'],
+            [true, 'data/Reader/CSV/semicolon_separated.csv'],
+            [true, 'data/Reader/HTML/csv_with_angle_bracket.csv'],
+            [true, 'data/Reader/CSV/empty.csv'],
+            [true, '../samples/Reader/sampleData/example1.csv'],
+            [true, '../samples/Reader/sampleData/example2.csv'],
+        ];
+    }
 }