Added back-end attachments-in-browser support

A query string will cause attachments to be provided inline
with an appropriate mime type.
Remaining actions:
- Tests
- Front-end functionality
- Config option?

app/Http/Controllers/Controller.php

@@ -6,6 +6,7 @@ use BookStack\Facades\Activity;
 use BookStack\Interfaces\Loggable;
 use BookStack\HasCreatorAndUpdater;
 use BookStack\Model;
+use finfo;
 use Illuminate\Foundation\Bus\DispatchesJobs;
 use Illuminate\Foundation\Validation\ValidatesRequests;
 use Illuminate\Http\Exceptions\HttpResponseException;
@@ -121,6 +122,20 @@ abstract class Controller extends BaseController
         ]);
     }
 
+    /**
+     * Create a file download response that provides the file with a content-type
+     * correct for the file, in a way so the browser can show the content in browser.
+     */
+    protected function inlineDownloadResponse(string $content, string $fileName): Response
+    {
+        $finfo = new finfo(FILEINFO_MIME_TYPE);
+        $mime = $finfo->buffer($content) ?: 'application/octet-stream';
+        return response()->make($content, 200, [
+            'Content-Type'        => $mime,
+            'Content-Disposition' => 'inline; filename="' . $fileName . '"'
+        ]);
+    }
+
     /**
      * Show a positive, successful notification to the user on next view load.
      */