2021-02-14 15:47:14 +09:00
---
title: Distill Thumbnail from .afphoto and .afdesign
date: 2021-02-14T13:30:00
---
Nextcloud does not have support for generating thumbnails from Affinity Photo and Affinity Design. Fine, I'll do it myself.
# Digging Binary
Glancing at `.afphoto` and `.afdesign` in Finder, I noticed that it has a QuickLook support and an ability to show the thumbnail image. So these files should have thumbnail image somewhere inside its binary.
I wrote a simple script to seek for thumbnail image inside a binary and save it as a PNG file.
```js
const fs = require("fs");
// png spec: https://www.w3.org/TR/PNG/
const PNG_SIG = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
const IEND_SIG = Buffer.from([73, 69, 78, 68]);
function extractThumbnail(buf) {
const start = buf.indexOf(PNG_SIG);
const end = buf.indexOf(IEND_SIG, start) + IEND_SIG.length * 2; // IEND + CRC
return buf.subarray(start, end);
}
function generateThumbnail(input, output) {
const buf = fs.readFileSync(input);
const thumbBuf = extractThumbnail(buf);
fs.writeFileSync(output, thumbBuf);
}
generateThumbnail(process.argv[2], process.argv[3] || "output.png");
```
That's right. This script just scrapes a binary file and distill a portion of which starts with `PNG` signature and ends with `IEND` .
Now I can generate a thumbnail image from arbitrary `.afphoto` and `.afdesign` file. Let's move on delving into Nextcloud source code.
# Tweaking Nextcloud
2021-02-14 17:24:36 +09:00
I have a bit of experience in tweaking Nextcloud source code before, where I implemented thumbnail generator for PDFs, so it should be easier this time, hopefully.
2021-02-14 15:47:14 +09:00
Long story short, I got Nextcloud generates thumbnail images for Affinity files by implementing `ProviderV2` class.
```php lib/private/Preview/Affinity.php
< ?php
namespace OC\Preview;
use OCP\Files\File;
use OCP\IImage;
use OCP\ILogger;
class Affinity extends ProviderV2 {
public function getMimeType(): string {
return '/application\/x-affinity-(?:photo|design)/';
}
public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
$tmpPath = $this->getLocalFile($file);
$handle = fopen($tmpPath, 'rb');
$fsize = filesize($tmpPath);
$contents = fread($handle, $fsize);
$start = strrpos($contents, "\x89PNG");
$end = strrpos($contents, "IEND", $start);
$subarr = substr($contents, $start, $end - $start + 8 );
fclose($handle);
$this->cleanTmpFiles();
$image = new \OC_Image();
$image->loadFromData($subarr);
$image->scaleDownToFit($maxX, $maxY);
return $image->valid() ? $image : null;
}
}
```
```patch lib/private/PreviewManager.php
@@ -363,6 +365,8 @@
$this->registerCoreProvider(Preview\Krita::class, '/application\/x-krita/');
$this->registerCoreProvider(Preview\MP3::class, '/audio\/mpeg/');
$this->registerCoreProvider(Preview\OpenDocument::class, '/application\/vnd.oasis.opendocument.*/');
+ $this->registerCoreProvider(Preview\Affinity::class, '/application\/x-affinity-(?:photo|design)/');
// SVG, Office and Bitmap require imagick
if (extension_loaded('imagick')) {
```
```patch lib/composer/composer/autoload_static.php
@@ -1226,6 +1226,7 @@
'OC\\OCS\\Result' => __DIR__ . '/../../..' . '/lib/private/OCS/Result.php',
'OC\\PreviewManager' => __DIR__ . '/../../..' . '/lib/private/PreviewManager.php',
'OC\\PreviewNotAvailableException' => __DIR__ . '/../../..' . '/lib/private/PreviewNotAvailableException.php',
+ 'OC\\Preview\\Affinity' => __DIR__ . '/../../..' . '/lib/private/Preview/Affinity.php',
'OC\\Preview\\BMP' => __DIR__ . '/../../..' . '/lib/private/Preview/BMP.php',
'OC\\Preview\\BackgroundCleanupJob' => __DIR__ . '/../../..' . '/lib/private/Preview/BackgroundCleanupJob.php',
'OC\\Preview\\Bitmap' => __DIR__ . '/../../..' . '/lib/private/Preview/Bitmap.php',
```
```patch lib/composer/composer/autoload_classmap.php
@@ -1197,6 +1197,7 @@
'OC\\OCS\\Result' => $baseDir . '/lib/private/OCS/Result.php',
'OC\\PreviewManager' => $baseDir . '/lib/private/PreviewManager.php',
'OC\\PreviewNotAvailableException' => $baseDir . '/lib/private/PreviewNotAvailableException.php',
+ 'OC\\Preview\\Affinity' => $baseDir . '/lib/private/Preview/Affinity.php',
'OC\\Preview\\BMP' => $baseDir . '/lib/private/Preview/BMP.php',
'OC\\Preview\\BackgroundCleanupJob' => $baseDir . '/lib/private/Preview/BackgroundCleanupJob.php',
'OC\\Preview\\Bitmap' => $baseDir . '/lib/private/Preview/Bitmap.php',
```

It works!
# Bonus: PDF thumbnail generator
```php lib/private/Preview/PDF.php
< ?php
namespace OC\Preview;
use OCP\Files\File;
use OCP\IImage;
class PDF extends ProviderV2 {
public function getMimeType(): string {
return '/application\/pdf/';
}
public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
$tmpPath = $this->getLocalFile($file);
$outputPath = \OC::$server->getTempManager()->getTemporaryFile();
$gsBin = \OC_Helper::findBinaryPath('gs');
$cmd = $gsBin . " -o " . escapeshellarg($outputPath) . " -sDEVICE=jpeg -sPAPERSIZE=a4 -dLastPage=1 -dPDFFitPage -dJPEGQ=90 -r144 " . escapeshellarg($tmpPath);
shell_exec($cmd);
$this->cleanTmpFiles();
$image = new \OC_Image();
$image->loadFromFile($outputPath);
$image->scaleDownToFit($maxX, $maxY);
unlink($outputPath);
return $image->valid() ? $image : null;
}
}
```