The extension that I am working on for GSoC synchronizes an Address Book in Mozilla Thunderbird with Google Contacts. This is going to be a quick overview of how it works so far. This post assumes some basic knowledge of the Hypertext Transfer Protocol (HTTP), Thunderbird, and programming.
Basically, my extension adds an overlay to the Thunderbird Address Book, so when the Address Book opens, it starts going.
When it starts, it registers a preferences observer (so it can modify behavior as preferences change) and obtains the current preferences. I will explain preferences in more detail later. It then checks to see if there is a valid authentication token in the extension directory. If not, it shows a login prompt. When OK is pressed, it attempts to authenticate the user using Google’s Client Login method of authentication. So, it sends an HTTPS POST request to Google which then returns an authentication token that can be used repeatedly and does not expire. This token (not the username and password) is stored in a textfile in the extension directory.
Once it gets or finds a valid authentication token, adds a listener (nsIAbListener) to the Address Book Manager (nsIAbManager), sets up the file that stores the date and time of the last synchronization, and begins the synchronization process.
Preparing for Synchronization
The sync process is the longest and the one that I change most often. Right now, it gets the Address Book first (does this every time in case it was deleted, changed, etc.). Then, it gets the time of the last sync (if any) to be used later and sends an HTTP GET request to Google using the authentication token to obtain all of the user’s contacts. Once it has these, it also obtains all contacts in the specified Address Book.
Right now this process is costly in terms of asymptotic analysis (or Big O notation) with a nested for loop.
The outer for loop iterates through every contact from Google while the inner for loop iterates through every unmatched card in the address book. When it finds two cards that it considers “identical,” if the current card from Google hasn’t been matched then it sets the TB card to null (so the loop knows it was ‘matched’ and calls a method that checks the cards’ last modified date to see if any of them is new since the last sync. If so, it replaces the old card with the new one.
If the card from Google was already matched, however, that means that the card from the Address Book is a duplicate and my current implementation removes the card. In the future I may add a prompt asking the user what to do about it.
Once the inner loop is finished, if the card from Google wasn’t matched it means one of two things. Either the card is new and should be added to Thunderbird (the card’s last modified date is more recent than the last sync) or it was deleted from Thunderbird and should be removed from Google.
Once that is done, it checks any unmatched cards from Thunderbird and figures out if they should be deleted from TB or added to Google, and then does that. Due to some timing issues with HTTP Requests, there are three helper methods. There are three global arrays treated as queues for cards to delete, update, and remove. The sync method adds cards to the arrays as necessary. When the sync method is done, it calls the delete method, which then calls the add method, which in turn calls the update method.
Finishing up the sync
When the hard part is over, it writes the current date/time to a file (the last sync time), schedules another sync after the preferred interval and sets a synced boolean to true (which is checked by the listener to make sure it doesn’t act during synchronization)
Address Book Listener
Since TB 3 doesn’t have the lastModifiedDate property, I made my own rough version with an Address Book Listener. The address book listener updates the card’s ‘custom2’ property whenver a contact is modified or added to the Google Contacts address book. Using this approach, my extension should work offline. I am working on adding last modified date to Thunderbird 3, so soon an address book listener and some of the booleans required by it may become unnecessary.