I found a piece of code and algorithm that makes it possible to collaborate online on tree structures. I have been using Logseq for the last few months and this algorithm seems to be a way to make collaboration on an outliner possible.

Evan Wallace described this algorithm. The page also includes a demo application. I have rewritten this demo application to Go and implemented a network protocol with mangos. Mangos is a nanomsg port in Go. Mangos can use websockets. This makes it possible to use a Go backend server with nanomsg protocols to send the changes from other clients back and forth between the clients. My implementation is just a prototype.

The other part I used was the tree library by David Fig. Somehow this library fits right on top of the tree structures from the Javascript version of the CRDT algorithm.

The Go implementation that I wrote is used for command-line clients that build a tree. The changes of the clients are sent to the server and the other clients. The server does not inspect the contents of the message, it just re-transmits it to the next client.

The changes in the browser are also sent back to the server, which makes this all for exciting. This is a nice first step into building an outliner with collaboration and block or line based sync, instead of full page sync.