Built custom favicon.ico file creator

Followed wikipedia-defined ICO file format info, and used with
Intervention's good bmp support, to create a working proof-of-concept.

app/Settings/AppSettingsStore.php

@@ -2,16 +2,16 @@
 
 namespace BookStack\Settings;
 
+use BookStack\Uploads\FaviconHandler;
 use BookStack\Uploads\ImageRepo;
 use Illuminate\Http\Request;
 
 class AppSettingsStore
 {
-    protected ImageRepo $imageRepo;
+    public function __construct(
-
+        protected ImageRepo $imageRepo,
-    public function __construct(ImageRepo $imageRepo)
+        protected FaviconHandler $faviconHandler,
-    {
+    ) {
-        $this->imageRepo = $imageRepo;
     }
 
     public function storeFromUpdateRequest(Request $request, string $category)
@@ -39,6 +39,8 @@ class AppSettingsStore
                 $icon = $this->imageRepo->saveNew($iconFile, 'system', 0, $size, $size);
                 setting()->put('app-icon-' . $size, $icon->url);
             }
+
+            $this->faviconHandler->saveForUploadedImage($iconFile);
         }
 
         // Clear icon image if requested

app/Uploads/FaviconHandler.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace BookStack\Uploads;
+
+use Illuminate\Http\UploadedFile;
+use Intervention\Image\ImageManager;
+
+class FaviconHandler
+{
+    public function __construct(
+        protected ImageManager $imageTool
+    ) {
+    }
+
+    /**
+     * Save the given UploadedFile instance as the application favicon.
+     */
+    public function saveForUploadedImage(UploadedFile $file): void
+    {
+        $imageData = file_get_contents($file->getRealPath());
+        $image = $this->imageTool->make($imageData);
+        $image->resize(32, 32);
+        $bmpData = $image->encode('bmp');
+        $icoData = $this->bmpToIco($bmpData, 32, 32);
+
+        // TODO - Below are test paths
+        file_put_contents(public_path('uploads/test.ico'), $icoData);
+        file_put_contents(public_path('uploads/test.bmp'), $bmpData);
+
+        // TODO - Permission check for icon overwrite
+        // TODO - Write to correct location
+        // TODO - Handle deletion and restore of original icon on user icon clear
+    }
+
+    /**
+     * Convert BMP image data to ICO file format.
+     * Built following the file format info from Wikipedia:
+     * https://en.wikipedia.org/wiki/ICO_(file_format)
+     */
+    protected function bmpToIco(string $bmpData, int $width, int $height): string
+    {
+        // Trim off the header of the bitmap file
+        $rawBmpData = substr($bmpData, 14);
+
+        // 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 32.
+        $entry .= pack('v', 0x20);
+        // Size of the image data in bytes
+        $entry .= pack('V', strlen($rawBmpData));
+        // 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 . $rawBmpData;
+    }
+}