Using the jupyterlab services API

This page describes how the Jupyter extension uses the [jupyterlab/services] API to connect and control Jupyter kernels.

What is it and why do we need it?

Jupyter kernels are processes that handle a set of messages called the Jupyter Messaging Protocol (or JMP for short).

[diagram of connecting to a kernel with zeromq and sending a message]

The Jupyter org has provided an npm module to help with calling into a kernel from javascript. This npm module does the following:

Opens a websocket to the Jupyter server (see raw vs jupyter for what we do when not using a Jupyter server)
Creates an IKernelConnection interface for talking to the kernel
Translates calls on the IKernelConnection to message structures
Serializes the message structures into a specific wire-protocol that all kernels must implement
Deserializes the message results from the wire-protocol back into messages, which in turn get changed into events in javascript.

The npm module essentially handles all communication to and from a kernel so that javascript can treat the kernel like a local object.