BookStack/app/Uploads/FaviconHandler.php

<?php

namespace BookStack\Uploads;

use Illuminate\Http\UploadedFile;

class FaviconHandler
{
    protected string $path;

    public function __construct(
        protected ImageResizer $imageResizer,
    ) {
        $this->path = public_path('favicon.ico');
    }

    /**
     * Save the given UploadedFile instance as the application favicon.
     */
    public function saveForUploadedImage(UploadedFile $file): void
    {
        if (!is_writeable($this->path)) {
            return;
        }

        $imageData = file_get_contents($file->getRealPath());
        $pngData = $this->imageResizer->resizeImageData($imageData, 32, 32, false, 'png');
        $icoData = $this->pngToIco($pngData, 32, 32);

        file_put_contents($this->path, $icoData);
    }

    /**
     * Restore the original favicon image.
     * Returned boolean indicates if the copy occurred.
     */
    public function restoreOriginal(): bool
    {
        $permissionItem = file_exists($this->path) ? $this->path : dirname($this->path);
        if (!is_writeable($permissionItem)) {
            return false;
        }

        return copy($this->getOriginalPath(), $this->path);
    }

    /**
     * Restore the original favicon image if no favicon image is already in use.
     * Returns a boolean to indicate if the file exists.
     */
    public function restoreOriginalIfNotExists(): bool
    {
        if (file_exists($this->path)) {
            return true;
        }

        return $this->restoreOriginal();
    }

    /**
     * Get the path to the favicon file.
     */
    public function getPath(): string
    {
        return $this->path;
    }

    /**
     * Get the path of the original favicon copy.
     */
    public function getOriginalPath(): string
    {
        return public_path('icon.ico');
    }

    /**
     * Convert PNG image data to ICO file format.
     * Built following the file format info from Wikipedia:
     * https://en.wikipedia.org/wiki/ICO_(file_format)
     */
    protected function pngToIco(string $pngData, int $width, int $height): string
    {
        // ICO header
        $header = pack('v', 0x00); // Reserved. Must always be 0
        $header .= pack('v', 0x01); // Specifies ico image
        $header .= pack('v', 0x01); // Specifies number of images

        // ICO Image Directory
        $entry = hex2bin(dechex($width)); // Image width
        $entry .= hex2bin(dechex($height)); // Image height
        $entry .= "\0"; // Color palette, typically 0
        $entry .= "\0"; // Reserved

        // Color planes, Appears to remain 1 for bmp image data
        $entry .= pack('v', 0x01);
        // Bits per pixel, can range from 1 to 32. From testing conversion
        // via intervention from png typically provides this as 24.
        $entry .= pack('v', 0x00);
        // Size of the image data in bytes
        $entry .= pack('V', strlen($pngData));
        // Offset of the bmp data from file start
        $entry .= pack('V', strlen($header) + strlen($entry) + 4);

        // Join & return the combined parts of the ICO image data
        return $header . $entry . $pngData;
    }
}