Use If-Modified-Since when fetching appcast

[kornelski]

No description provided.

[zorgiepoo]

This could be useful. Tricky part may be caching based on the updater bundle + old bundle to update.

[lostminds]

I'm not sure what this exactly refers to, but if it refers to checking the appcast modified date on the server this could be misleading if the appcast is not a static file. In my setup the appcast is for example dynamically generated by a version management backend on the server that handles versions across the website, downloads, appcast and other external updates.

[kornelski]

If the server doesn't generate Last-Modified or doesn't actively parse If-Modified-Since and respond with 304, then it won't have any effect and will behave just like a regular file download.

The only situation where it could cause problems would be if you intentionally implemented support for request validation and did it incorrectly. But that's not really different from incorrectly implementing any other aspect of feed serving.