Implementing the xBrowserSync API

For about a year, I’ve used the Brave browser, mostly due to its built-in ad blocking and its bookmark sync feature. I have been using Brave on four different devices (three Linux laptops and one Android phone running GrapheneOS), so the bookmark sync feature is very useful.

But this article on the privacy features of numerous browsers is rather scathing about Brave. So I decided to try Ungoogled-Chromium, along with the uBlock Origin and uMatrix extensions.

Then the problem was to find a replacement for bookmark syncing. Fortunately there is a project called xBrowserSync that solves this problem. It provides extensions for browsers, as well as an Android app that works surprisingly well.

xBrowserSync works by storing encrypted bookmark data on a server, and the project offers their own free server for this purpose. Being that I’m on a mission to reduce my dependency on third party servers, I looked into seeing if I could host my own xBrowserSync server. xBrowserSync provides the source code for their server, but I found its huge pile of Node.js code and dependencies rather intimidating. I also found a couple of reimplementations of the server written in Go (xSyn and xbsapi), but building these projects also seemed intimidating.

In short, I’m a bit lazy and would rather not have to learn a new programming language system (Go or Node.js) that I’m already predisposed to dislike. My impression of Node.js in particular is one of horror at the sheer number of packages that have to loaded in order to do build the most basic of projects.

So I decided to write my own implementation of the xBrowserSync API in Crystal, a compiled Ruby-like language that is perfectly suited for implementing small API servers. I used Crystal a few years ago to build a book cover URL server for Koha, and was very pleased with how much faster it ran than the Node.js server it replaced. It also had the added advantage of being written in a much more pleasing programming language.

It took me about a day to write the xBrowserSync API server in Crystal; you can find the result here. I call it by the very imaginative name of “xbs”. It turns out that the API is very simple; you can find the complete specification here. The number of paths it requires is very small, and you don’t need a fancy web framework to do the routing and serving. Instead, you can easily use regular expressions to parse the request paths, and the Crystal HTTP class provides everything you need to implement a fast, efficient server.

Another advantage of using Crystal to build an API server is that deployment is very simple: you have a single binary executable file that can be invoked from systemd, and which can be placed behind a reverse proxy in Apache. The README for the project has details about this.

One thing to note about the xBrowserSync API is that it can store very large amounts of data. It doesn’t use incremental diffs. Instead, whenever you change your bookmarks in a browser, xBrowserSync copies the entire bookmark tree (in encrypted form) to your API server. So for example, the resulting bookmark data for my browser came to about 300K bytes (I have accumulated a lot of bookmarks over the years). The default free xBrowserSync service has a limit on the size of the data it can store. You have to upgrade to a paid plan to get more storage. This was another reason why I decided to self-host my own server: I could implement any size limit I chose.