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Inter Process Communication#

A Lens Extension can utilize IPC to send information between the renderer and main processes. This is useful when wanting to communicate directly within your extension.

For example, if a user logs into a service that your extension is a facade for and main needs to know some information so that you can start syncing items to the Catalog, this would be a good way to send that information along.

IPC channels are sectioned off per extension. Meaning that each extension can only communicate with itself.

Types of Communication#

There are two flavours of communication that are provided:

  • Event based (IPC)
  • Request based (RPC)

Event Based or IPC#

This is the same as an Event Emitter but is not limited to just one Javascript process. This is a good option when you need to report that something has happened but you don't need a response.

This is a fully two-way form of communication. Both main and renderer can do this sort of IPC.

Request Based or RPC#

This is more like a Remote Procedure Call (RPC) or Send-Receive-Reply (SRR). With this sort of communication the caller needs to wait for the result from the other side. This is accomplished by await-ing the returned Promise<any>.

This is a unidirectional form of communication. Only renderer can initiate this kind of request, and only main can receive and respond to this kind of request.

Registering IPC Handlers and Listeners#

The general terminology is as follows:

  • A "handler" is the function that responds to a "Request Based IPC" event.
  • A "listener" is the function that is called when a "Event Based IPC" event is emitted.

To register either a handler or a listener, you should do something like the following:

main.ts: 

import { Main } from "@k8slens/extensions";
import { IpcMain } from "./helpers/main";

export class ExampleExtensionMain extends Main.LensExtension {
  onActivate() {
    IpcMain.createInstance(this);
  }
}

This file shows that you need to create an instance of the store to be able to use IPC. Lens will automatically clean up that store and all the handlers on deactivation and uninstall.

helpers/main.ts: 

import { Main } from "@k8slens/extensions";

export class IpcMain extends Main.Ipc {
  constructor(extension: Main.LensExtension) {
    super(extension);

    this.listen("initialize", onInitialize);
  }
}

function onInitialize(event: Types.IpcMainEvent, id: string) {
  console.log(`starting to initialize: ${id}`);
}

In other files, it is not necessary to pass around any instances. You should be able to just call IpcMain.getInstance() anywhere it is needed in your extension.

renderer.ts: 

import { Renderer } from "@k8slens/extensions";
import { IpcRenderer } from "./helpers/renderer";

export class ExampleExtensionRenderer extends Renderer.LensExtension {
  onActivate() {
    const ipc = IpcRenderer.createInstance(this);

    setTimeout(() => ipc.broadcast("initialize", "an-id"), 5000);
  }
}

It is also needed to create an instance to broadcast messages too.

helpers/renderer.ts: 

import { Renderer } from "@k8slens/extensions";

export class IpcRenderer extends Renderer.Ipc {}

It is necessary to create child classes of these abstract class's in your extension before you can use them.

As this example shows: the channel names must be the same. It should also be noted that "listeners" and "handlers" are specific to either renderer or main. There is no behind the scenes transfer of these functions.

To register a "handler" call IpcMain.getInstance().handle(...). The cleanup of these handlers is handled by Lens itself.

The listen() methods on Main.Ipc and Renderer.Ipc return a Disposer, or more specifically, a () => void. This can be optionally called to remove the listener early.

Calling either IpcRenderer.getInstance().broadcast(...) or IpcMain.getInstance().broadcast(...) sends an event to all renderer frames and to main. Because of this, no matter where you broadcast from, all listeners in main and renderer will be notified.

Allowed Values#

This IPC mechanism utilizes the Structured Clone Algorithm for serialization. This means that more types than what are JSON serializable can be used, but not all the information will be passed through.

Using Request Based Communication#

If you are meaning to do a request based call from renderer, you should do const res = await IpcRenderer.getInstance().invoke(<channel>, ...<args>)); instead.