Issue Summary

When uploading an attachment from the 'Insert link' dialog present in the page editor, an upload error is always displayed, even when the upload is successful.

A quick code investigation shows that the backend API behaviour and response have not changed and the bug is likely present in the frontend code (confluence-frontend/plugin/src/main/resources/includes/js/attachment-uploader.js).

Steps to Reproduce

1. Edit any page
2. Open 'Insert link' dialog from editor toolbar
3. Select 'Files' tab
4. Click 'Browse' and select any file for upload

Expected Results

Uploaded file appears at top of list and highlighted.

Actual Results

The newly uploaded file does not appear in the list of available attachments and the following error is displayed:

Could not upload the file to Confluence. The server may be unavailable. 

Workaround

When the error message is shown, close the 'Insert link' dialog and reopen it. You should then observe that the file has indeed been uploaded successfully and does appear in the list of available attachments.