Add simple implementation (command handler) for avatar upload.

src/Core/Commands/UploadAvatarCommand.php

@@ -0,0 +1,30 @@
+<?php namespace Flarum\Core\Commands;
+
+use RuntimeException;
+
+class UploadAvatarCommand
+{
+    public $userId;
+
+    /**
+     * @var \Symfony\Component\HttpFoundation\File\UploadedFile
+     */
+    public $file;
+
+    public $actor;
+
+    public function __construct($userId, $file, $actor)
+    {
+        if (empty($userId) || !intval($userId)) {
+            throw new RuntimeException('No valid user ID specified.');
+        }
+
+        if (is_null($file)) {
+            throw new RuntimeException('No file to upload');
+        }
+
+        $this->userId = $userId;
+        $this->file = $file;
+        $this->actor = $actor;
+    }
+}

src/Core/Events/AvatarWillBeUploaded.php

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+<?php namespace Flarum\Core\Events;
+
+use Flarum\Core\Models\User;
+
+class AvatarWillBeUploaded
+{
+    public $user;
+
+    public $command;
+
+    public function __construct(User $user, $command)
+    {
+        $this->user = $user;
+        $this->command = $command;
+    }
+}

src/Core/Handlers/Commands/UploadAvatarCommandHandler.php

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+<?php namespace Flarum\Core\Handlers\Commands;
+
+use Flarum\Core\Commands\UploadAvatarCommand;
+use Flarum\Core\Events\AvatarWillBeUploaded;
+use Flarum\Core\Repositories\UserRepositoryInterface;
+use Flarum\Core\Support\DispatchesEvents;
+use Illuminate\Support\Str;
+use League\Flysystem\Adapter\Local;
+use League\Flysystem\FilesystemInterface;
+use League\Flysystem\MountManager;
+
+class UploadAvatarCommandHandler
+{
+    use DispatchesEvents;
+
+    /**
+     * @var UserRepositoryInterface
+     */
+    protected $users;
+
+    /**
+     * @var FilesystemInterface
+     */
+    protected $uploadDir;
+
+    public function __construct(UserRepositoryInterface $users, FilesystemInterface $uploadDir)
+    {
+        $this->users = $users;
+        $this->uploadDir = $uploadDir;
+    }
+
+    public function handle(UploadAvatarCommand $command)
+    {
+        $user = $this->users->findOrFail($command->userId);
+
+        // Make sure the current user is allowed to edit the user profile.
+        // This will let admins and the user themselves pass through, and
+        // throw an exception otherwise.
+        $user->assertCan($command->actor, 'edit');
+
+        $filename = $command->file->getFilename();
+        $uploadName = Str::lower(Str::quickRandom()) . '.jpg';
+
+        $mount = new MountManager([
+            'source' => new Local($command->file->getPath()),
+            'target' => $this->uploadDir,
+        ]);
+
+        $user->changeAvatarUrl($uploadName);
+
+        event(new AvatarWillBeUploaded($user, $command));
+
+        $mount->move("source://$filename", "target://$uploadName");
+        $user->save();
+        $this->dispatchEventsFor($user);
+
+        return $user;
+    }
+}