Editing of media descriptions is now possible as well

src/Factory/Api/Mastodon/Attachment.php

@@ -51,6 +51,33 @@ class Attachment extends BaseFactory
 	{
 		$attachments = [];
 		foreach (Post\Media::getByURIId($uriId, [Post\Media::AUDIO, Post\Media::VIDEO, Post\Media::IMAGE]) as $attachment) {
+			$attachments[] = $this->createFromMediaArray($attachment);
+		}
+
+		return $attachments;
+	}
+
+	/**
+	 * @param int $id id of the media
+	 * @return array
+	 * @throws HTTPException\InternalServerErrorException
+	 */
+	public function createFromId(int $id): array
+	{
+		$attachment = Post\Media::getById($id);
+		if (empty($attachment)) {
+			return [];
+		}
+		return $this->createFromMediaArray($attachment);
+	}
+
+	/**
+	 * @param array $attachment
+	 * @return array
+	 * @throws HTTPException\InternalServerErrorException
+	 */
+	private function createFromMediaArray(array $attachment): array
+	{
 		$filetype = !empty($attachment['mimetype']) ? strtolower(substr($attachment['mimetype'], 0, strpos($attachment['mimetype'], '/'))) : '';
 
 		if (($filetype == 'audio') || ($attachment['type'] == Post\Media::AUDIO)) {
@@ -80,10 +107,7 @@ class Attachment extends BaseFactory
 		}
 
 		$object        = new \Friendica\Object\Api\Mastodon\Attachment($attachment, $type, $url, $preview, $remote);
-			$attachments[] = $object->toArray();
-		}
-
-		return $attachments;
+		return $object->toArray();
 	}
 
 	/**

src/Model/Post/Media.php

@@ -697,6 +697,30 @@ class Media
 		return DBA::selectToArray('post-media', [], $condition, ['order' => ['id']]);
 	}
 
+	/**
+	 * Retrieves the media attachment with the provided media id.
+	 *
+	 * @param int $id  id
+	 * @return array|bool Array on success, false on error
+	 * @throws \Exception
+	 */
+	public static function getById(int $id)
+	{
+		return DBA::selectFirst('post-media', [], ['id' => $id]);
+	}
+
+	/**
+	 * Update post-media entries
+	 *
+	 * @param array $fields
+	 * @param int $id
+	 * @return bool
+	 */
+	public static function updateById(array $fields, int $id): bool
+	{
+		return DBA::update('post-media', $fields, ['id' => $id]);
+	}
+
 	/**
 	 * Checks if media attachments are associated with the provided item ID.
 	 *

src/Module/Api/Mastodon/Media.php

@@ -25,6 +25,7 @@ use Friendica\Core\Logger;
 use Friendica\Core\System;
 use Friendica\DI;
 use Friendica\Model\Photo;
+use Friendica\Model\Post;
 use Friendica\Module\BaseApi;
 
 /**
@@ -71,8 +72,16 @@ class Media extends BaseApi
 
 		$photo = Photo::selectFirst(['resource-id'], ['id' => $this->parameters['id'], 'uid' => $uid]);
 		if (empty($photo['resource-id'])) {
+			$media = Post\Media::getById($this->parameters['id']);
+			if (empty($media['uri-id'])) {
 				DI::mstdnError()->RecordNotFound();
 			}
+			if (!Post::exists(['uri-id' => $media['uri-id'], 'uid' => $uid, 'origin' => true])) {
+				DI::mstdnError()->RecordNotFound();
+			}
+			Post\Media::updateById(['description' => $request['description']], $this->parameters['id']);
+			System::jsonExit(DI::mstdnAttachment()->createFromId($this->parameters['id']));
+		}
 
 		Photo::update(['desc' => $request['description']], ['resource-id' => $photo['resource-id']]);