File browser plugin should allow for setting custom HTTP headers

[jswiderski]

Are you reporting a feature or a bug?

Feature

Check if the issue is already reported

• https://dev.ckeditor.com/ticket/13791
• https://github.com/cksource/ckfinder-connector-php/issues/245#issuecomment-296366359

Provide detailed reproduction steps (if any)

Uploading dropped files allows for creating cross-origin AJAX requests by adding custom HTTP requests.

Unfortunately this is not possible in the File Browser plugin.

This is caused by the File Browser plugin currently using a standard <form> element that is submitted upon clicking the "Send it to the Server" button.

Solution

We'll implement an additional upload method for the File Browser plugin that uses XMLHttpRequest through the File Tools plugin.

The new upload method could be enabled using the config.filebrowserUploadMethod property.

The old method using the plain <form> element will still be supported as it is required by old browsers.

For 4.8.x, the <form>element will still be used by default since we cannot make backward incompatible changes in a minor release. Early adopters will already be able to enable it by setting:

config.filebrowserUploadMethod = 'xhr';

The default behavior will be changed in version 4.9.0 (#1365).

Browser Compatibility

All officially supported browsers except Internet Explorer 8 and 9.

The new feature will not be compatible with IE8 and IE9 as there is no Form Data type available there. These browsers will, however, gracefully fall back to the old <form>-based solution. As a result no custom headers will be sent, but the editor will still attempt to upload the file.

Other details

As stated in ticket https://dev.ckeditor.com/ticket/13791, it will probably be easier to create a new plugin then redesign the existing one.

• Browser: Any
• OS: Any
• CKEditor version: 4.0+
• Installed CKEditor plugins: filebrowser

[mlewand]

Improved the original report description.

[mlewand]

Note that adding this feature allows us to easily add more features, like upload progress bar. But it's outside of the scope of this issue and should be reported in a separate issue.