bp_media_attach_media_to_message( $message )

function bp_media_attach_media_to_message( &$message ) {

	if ( bp_is_messages_media_support_enabled() && ! empty( $message->id ) && ! empty( $_POST['media'] ) ) {
		$media_list = $_POST['media'];
		$media_ids = array();

		foreach ( $media_list as $media_index => $media ) {
			$title         = ! empty( $media['name'] ) ? $media['name'] : ' ';
			$attachment_id = ! empty( $media['id'] ) ? $media['id'] : 0;

			$media_id = bp_media_add(
				array(
					'title'         => $title,
					'privacy'       => 'message',
					'attachment_id' => $attachment_id,
				)
			);

			if ( $media_id ) {
				$media_ids[] = $media_id;

				//save media is saved in attachment
				update_post_meta( $attachment_id, 'bp_media_saved', true );
			}
		}

		$media_ids = implode( ',', $media_ids );

		//save media meta for message
		bp_messages_update_meta( $message->id, 'bp_media_ids', $media_ids );
	}
}