Allow Csv Reader to Treat String as Contents of File

See PHPOffice#1285, which went stale and was closed, but recently received some positive feeback. It seems easy to implement, and the only other plaintext file format, Html, allows loading from a string. Those two reasons combined suggest that we should do it.

Author: oleibman

docs/topics/reading-and-writing-to-file.md

@@ -436,7 +436,14 @@ You can read a .csv file using the following code:
 
 ```php
 $reader = new \PhpOffice\PhpSpreadsheet\Reader\Csv();
-$spreadsheet = $reader->load("sample.csv");
+$spreadsheet = $reader->load('sample.csv');
+```
+
+You can also treat a string as if it were the contents of a CSV file as follows:
+
+```php
+$reader = new \PhpOffice\PhpSpreadsheet\Reader\Csv();
+$spreadsheet = $reader->loadSpreadsheetFromString($data);
 ```
 
 #### Setting CSV options

src/PhpSpreadsheet/Reader/Csv.php

@@ -265,6 +265,18 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
         return $this->loadIntoExisting($filename, $spreadsheet);
     }
 
+    /**
+     * Loads Spreadsheet from string.
+     */
+    public function loadSpreadsheetFromString(string $contents): Spreadsheet
+    {
+        // Create new Spreadsheet
+        $spreadsheet = new Spreadsheet();
+
+        // Load into this instance
+        return $this->loadStringOrFile('data://text/plain,' . urlencode($contents), $spreadsheet, true);
+    }
+
     private function openFileOrMemory(string $filename): void
     {
         // Open file
@@ -314,16 +326,43 @@ public function castFormattedNumberToNumeric(
         $this->preserveNumericFormatting = $preserveNumericFormatting;
     }
 
+    /**
+     * Open data uri for reading.
+     */
+    private function openDataUri(string $filename): void
+    {
+        $fileHandle = fopen($filename, 'rb');
+        if ($fileHandle === false) {
+            // @codeCoverageIgnoreStart
+            throw new ReaderException('Could not open file ' . $filename . ' for reading.');
+            // @codeCoverageIgnoreEnd
+        }
+
+        $this->fileHandle = $fileHandle;
+    }
+
     /**
      * Loads PhpSpreadsheet from file into PhpSpreadsheet instance.
      */
     public function loadIntoExisting(string $filename, Spreadsheet $spreadsheet): Spreadsheet
+    {
+        return $this->loadStringOrFile($filename, $spreadsheet, false);
+    }
+
+    /**
+     * Loads PhpSpreadsheet from file into PhpSpreadsheet instance.
+     */
+    private function loadStringOrFile(string $filename, Spreadsheet $spreadsheet, bool $dataUri): Spreadsheet
     {
         // Deprecated in Php8.1
         $iniset = $this->setAutoDetect('1');
 
         // Open file
-        $this->openFileOrMemory($filename);
+        if ($dataUri) {
+            $this->openDataUri($filename);
+        } else {
+            $this->openFileOrMemory($filename);
+        }
         $fileHandle = $this->fileHandle;
 
         // Skip BOM, if any
@@ -395,8 +434,8 @@ private function convertBoolean(&$rowDatum, bool $preserveBooleanString): void
             } elseif (strcasecmp(Calculation::getFALSE(), $rowDatum) === 0 || strcasecmp('false', $rowDatum) === 0) {
                 $rowDatum = false;
             }
-        } elseif ($rowDatum === null) {
-            $rowDatum = '';
+        } else {
+            $rowDatum = $rowDatum ?? '';
         }
     }
 

tests/PhpSpreadsheetTests/Reader/Csv/CsvLoadFromStringTest.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
+
+use PhpOffice\PhpSpreadsheet\Reader\Csv;
+use PHPUnit\Framework\TestCase;
+
+class CsvLoadFromStringTest extends TestCase
+{
+    public function testLoadFromString(): void
+    {
+        $data = <<<EOF
+1,2,3
+4,2+3,6
+"7 , 8", 9, 10
+11,"12
+13",14
+EOF;
+        $reader = new Csv();
+        $spreadsheet = $reader->loadSpreadsheetFromString($data);
+        $sheet = $spreadsheet->getActiveSheet();
+        self::AssertSame('2+3', $sheet->getCell('B2')->getValue());
+        self::AssertSame('7 , 8', $sheet->getCell('A3')->getValue());
+        self::AssertSame("12\n13", $sheet->getCell('B4')->getValue());
+    }
+}