Allow passing empty post ID to media_handle_sideload()

[swissspidy]

I stumbled upon this via ​https://wordpress.stackexchange.com/questions/291344/why-does-media-handle-sideload-upload-to-last-months-folder.

Basically, the person was trying to run media_handle_sideload( $file_array, $post_id = 0 ) to upload files. This works fine in so far as it calls wp_insert_attachment() which accepts a post ID of 0 (it's the default) so the attachment won't be associated with a specific post.

However, media_handle_sideload() doesn't fully support $post_id = 0 (or $post_id = null, for that matter) because of the if ( $post = get_post( $post_id ) ) { … } condition since get_post( 0 ) fetches the global post and overrides $time.

This means you cannot upload a media file and have $time set to today.

To reproduce:

1. Create a post with the date set to last month
2. Set this post as $GLOBALS['post']
3. Run media_handle_sideload( $file_array, 0 )
4. Notice that the upload folder will be the one from last month, not this month.

Proposed fix:

Change the condition from if ( $post = get_post( $post_id ) ) { … } to if ( $post_id && $post = get_post( $post_id ) ) { … }

Consequences:

The upload folder will point to the current month, not the date from the global post if using $post_id = 0 or $post_id = null. Not a big deal IMHO.

[AugusGils]

Made a check on $post_id to make sure it's a valid one, this to make sure the correct upload folder is used.

[andizer]

Added unit tests for covering the touched lines.

[birgire]

Thanks for patch @AugusGils and the tests @andizer

In 43119.2.diff​ there are some adjustments:

• Combines patch + tests into a single patch.
• To speed things up it avoids the download_url() and uses an existing file instead.
• Changes $default = date( '/Y/m', current_time( 'timestamp' ) ); to $default = current_time( '/Y/m/' ); for simplification.
• Some changes according to the Coding Standard.
• Adds cleanups.

Hope it helps.