From 670362422360022a8f87d9348d04572a412458c4 Mon Sep 17 00:00:00 2001
From: Danielle McLean <dani@00dani.me>
Date: Mon, 8 Oct 2018 09:21:53 +1100
Subject: [PATCH] Write generated HTML into Mpdf in chunks, rather than as one
 gigantic string

Due to a limitation in Mpdf, the HTML string passed to its WriteHTML method
must not exceed a particular length. PhpSpreadsheet produces one HTML string
containing all spreadsheet data when writing to HTML, which can easily exceed
Mpdf's size limit. Thus, it was impossible to write large spreadsheets to PDF
using the Mpdf writer - this change fixes that issue.

Fixes #637
Fixes #706
---
 CHANGELOG.md                           |  1 +
 src/PhpSpreadsheet/Writer/Pdf/Mpdf.php | 11 ++++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6aee7723..41489efe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 - Csv reader avoid notice when the file is empty - [#743](https://github.com/PHPOffice/PhpSpreadsheet/pull/743)
 - Fix print area parser for XLSX reader - [#734](https://github.com/PHPOffice/PhpSpreadsheet/pull/734)
 - Support overriding `DefaultValueBinder::dataTypeForValue()` without overriding `DefaultValueBinder::bindValue()` - [#735](https://github.com/PHPOffice/PhpSpreadsheet/pull/735)
+- Mpdf export can exceed pcre.backtrack_limit - [#637](https://github.com/PHPOffice/PhpSpreadsheet/issues/637)
 
 ## [1.5.0] - 2018-10-21
 
diff --git a/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php b/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php
index ad0964db..08aa6273 100644
--- a/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php
+++ b/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php
@@ -79,11 +79,12 @@ class Mpdf extends Pdf
         $pdf->SetKeywords($this->spreadsheet->getProperties()->getKeywords());
         $pdf->SetCreator($this->spreadsheet->getProperties()->getCreator());
 
-        $pdf->WriteHTML(
-            $this->generateHTMLHeader(false) .
-            $this->generateSheetData() .
-            $this->generateHTMLFooter()
-        );
+        $pdf->WriteHTML($this->generateHTMLHeader(false));
+        $html = $this->generateSheetData();
+        foreach (\array_chunk(\explode(PHP_EOL, $html), 1000) as $lines) {
+            $pdf->WriteHTML(\implode(PHP_EOL, $lines));
+        }
+        $pdf->WriteHTML($this->generateHTMLFooter());
 
         //  Write to file
         fwrite($fileHandle, $pdf->Output('', 'S'));