Cchost/developer/Reverse Engineering

A ccHost Quick Reverse Engineer

by Victor

When I sat down to write the auto 'feature this playlist' feature I knew I wanted to add a menu item to the playlist's command window but I totally forgot how that menu was generated. It took less than a minute to figure it out but I thought it might be useful since I know this kind of 'view source/reverse engineer' is how most developers approach a codebase like ccHost.

Firefox has a 'Web Developer Toolbar' that I find invaluable.

• I browsed to a playlist.
• Selected 'View Style Information' from Firefox's Web Developer Toolbar which highlights the area under the cursor and gives you the CSS class selector name.
• For the menu that turned out to be 'cc_playlist_owner'
• I searched under ccskins for all occurances of that selector.
• I found the template that built the menu at ccskins/shared/playlist_2_head.tpl

   <ul class="cc_playlist_owner_menu 
                     light_bg dark_border">
   %loop(#R/menu,mi)%
       <li>
       <a target="_parent" href="%(#mi/url)%" 
              id="%(#mi/id)%" 
              class="%(#mi/class)%">%text(#mi/text)%
             </a>

   %end_loop%

• From the code in this template I could deduce the following:
  • the menu was just being displayed here. The menu was being built somewhere else.
  • the menu itself is embedded in the 'R' record
  • a few lines above is line %map(#R,records/0)% which means 'R' is result of the query ('records' is the array of a query result in a template)
  • every query must have a dataview somewhere, sure enough at the top of the template

to display this playlist, dataview = playlist_detail

• I found ccdataviews/playlist_detail.php
• Since the 'menu' is a PHP array and not a normal SQL column, I deduced there must a dataview filter that is building the menu
• Filter events are returned in an array in a dataview and there was CC_EVENT_FILTER_CART_MENU (a playlist is actually a record in the cc_tbl_carts table)
• I searched cchost_lib/* for that event and found the declaration of a handler in cchost_lib/ccextras/cc-playlist.php
• That pointed to a method in cchost_lib/ccextras/cc-playlist-browse.inc called CCPlaylistBrowse::OnFilterCartMenu

At this point I knew what event I had to handle CC_EVENT_FILTER_CART_MENU and I had an example of what the system was doing with that event in CCPlaylistBrowse::OnFilterCartMenu.