I'm trying to write a simple node.js program to sync a few address books from a CardDAV server to a local MySQL database. I'm using the node dav client.
I know CardDAV supports only syncing changes since the last sync via sync-token and I see some references to sync tokens when I browse through the source and readme of the dav client. But, I'm very new to DAV, so I'm not 100% sure how to put it all together.
I'm guessing I need to store the sync token (and level?) the server sends back after I run a sync and then include that in my next sync request. Am I on the right track?
Building a CardDAV client is a great resource which describes how all that works, including WebDAV Sync, which is what you are looking for.
Note that a server is not required to provided WebDAV sync (and quite a few don't). Also note that even if they support WebDAV sync, they can expire the tokens however/whenever they want (e.g. some only store a single token, or only for a limited time).
In short: do not rely on WebDAV-sync. If it is not available, or the token is expired, you need to fallback to a full, regular sync (comparing href's and etag's).
I'm guessing I need to store the sync token (and level?) the server sends back after I run a sync and then include that in my next sync request. Am I on the right track?
Yes you are on the right track. Sync-tokens are usually per collection (Depth:1, I think they can be Depth:infinity, but I'm not sure). So you need to store it alongside the URL of the collection you are syncing. Then in the next sync-request, you embed it into the sync-report. If the token is still valid, you get back the new/deleted/changed records. If the token was invalidated, you need to perform a full sync.
Hope that helps :-)