Add resource parameter handling to html, csv and xls writers

src/PhpSpreadsheet/Writer/Csv.php

@@ -4,6 +4,7 @@ namespace PhpOffice\PhpSpreadsheet\Writer;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Exception as WriterException;
 
 class Csv extends BaseWriter
 {
@@ -77,7 +78,7 @@ class Csv extends BaseWriter
     /**
      * Save PhpSpreadsheet to file.
      *
-     * @param string $pFilename
+     * @param resource|string $pFilename
      *
      * @throws Exception
      */
@@ -92,9 +93,14 @@ class Csv extends BaseWriter
         Calculation::setArrayReturnType(Calculation::RETURN_ARRAY_AS_VALUE);
 
         // Open file
+        if (is_resource($pFilename)) {
+            $fileHandle = $pFilename;
+        } else {
             $fileHandle = fopen($pFilename, 'wb+');
+        }
+
         if ($fileHandle === false) {
-            throw new Exception("Could not open file $pFilename for writing.");
+            throw new WriterException("Could not open file $pFilename for writing.");
         }
 
         if ($this->excelCompatibility) {
@@ -126,6 +132,8 @@ class Csv extends BaseWriter
         }
 
         // Close file
+        rewind($fileHandle);
+
         fclose($fileHandle);
 
         Calculation::setArrayReturnType($saveArrayReturnType);

src/PhpSpreadsheet/Writer/Html.php

@@ -146,7 +146,7 @@ class Html extends BaseWriter
     /**
      * Save Spreadsheet to file.
      *
-     * @param string $pFilename
+     * @param resource|string $pFilename
      *
      * @throws WriterException
      */
@@ -164,7 +164,12 @@ class Html extends BaseWriter
         $this->buildCSS(!$this->useInlineCss);
 
         // Open file
+        if (is_resource($pFilename)) {
+            $fileHandle = $pFilename;
+        } else {
             $fileHandle = fopen($pFilename, 'wb+');
+        }
+
         if ($fileHandle === false) {
             throw new WriterException("Could not open file $pFilename for writing.");
         }

src/PhpSpreadsheet/Writer/Xls.php

@@ -115,7 +115,7 @@ class Xls extends BaseWriter
     /**
      * Save Spreadsheet to file.
      *
-     * @param string $pFilename
+     * @param resource|string $pFilename
      *
      * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
      */