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lens/docs/extensions/guides/protocol-handlers.md
Sebastian Malton 1470103fd4
Add lens:// protocol handling with a routing mechanism (#1949)
- Add lens:// protocol handling with a routing mechanism

- document the methods in an extension guide

- remove handlers when an extension is deactivated or removed

- make sure that the found extension when routing a request is currently enabled (as a backup)

- added documentation about the above behaviour to the guide

- tweaked the naming convention so that it is clearer that the router uses extension names as not IDs (which currently are folder paths)

- Convert the extension API to use an array for registering handlers

- switch design to execute both main and renderer handlers simultaneously, without any overlap checking

- change open to be a dev dep

- improve docs, export types for extensions, skip integration tests

- switch to event emitting renderer being ready

- Add logging and fix renderer:loaded send to main

Signed-off-by: Sebastian Malton <sebastian@malton.name>
2021-02-25 09:32:40 -05:00

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# Lens Protocol Handlers
Lens has a file association with the `lens://` protocol.
This means that Lens can be opened by external programs by providing a link that has `lens` as its protocol.
Lens provides a routing mechanism that extensions can use to register custom handlers.
## Registering A Protocol Handler
The field `protocolHandlers` exists both on [`LensMainExtension`](extensions/api/classes/lensmainextension/#protocolhandlers) and on [`LensRendererExtension`](extensions/api/classes/lensrendererextension/#protocolhandlers).
This field will be iterated through every time a `lens://` request gets sent to the application.
The `pathSchema` argument must comply with the [path-to-regexp](https://www.npmjs.com/package/path-to-regexp) package's `compileToRegex` function.
Once you have registered a handler it will be called when a user opens a link on their computer.
Handlers will be run in both `main` and `renderer` in parallel with no synchronization between the two processes.
Furthermore, both `main` and `renderer` are routed separately.
In other words, which handler is selected in either process is independent from the list of possible handlers in the other.
Example of registering a handler:
```typescript
import { LensMainExtension, Interface } from "@k8slens/extensions";
function rootHandler(params: Iterface.ProtocolRouteParams) {
console.log("routed to ExampleExtension", params);
}
export default class ExampleExtensionMain extends LensMainExtension {
protocolHandlers = [
pathSchema: "/",
handler: rootHandler,
]
}
```
For testing the routing of URIs the `open` (on macOS) or `xdg-open` (on most linux) CLI utilities can be used.
For the above handler, the following URI would be always routed to it:
```
open lens://extension/example-extension/
```
## Deregistering A Protocol Handler
All that is needed to deregister a handler is to remove it from the array of handlers.
## Routing Algorithm
The routing mechanism for extensions is quite straight forward.
For example consider an extension `example-extension` which is published by the `@mirantis` org.
If it were to register a handler with `"/display/:type"` as its corresponding link then we would match the following URI like this:
![Lens Protocol Link Resolution](images/routing-diag.png)
Once matched, the handler would be called with the following argument (note both `"search"` and `"pathname"` will always be defined):
```json
{
"search": {
"text": "Hello"
},
"pathname": {
"type": "notification"
}
}
```
As the diagram above shows, the search (or query) params are not considered as part of the handler resolution.
If the URI had instead been `lens://extension/@mirantis/example-extension/display/notification/green` then a third (and optional) field will have the rest of the path.
The `tail` field would be filled with `"/green"`.
If multiple `pathSchema`'s match a given URI then the most specific handler will be called.
For example consider the following `pathSchema`'s:
1. `"/"`
1. `"/display"`
1. `"/display/:type"`
1. `"/show/:id"`
The URI sub-path `"/display"` would be routed to #2 since it is an exact match.
On the other hand, the subpath `"/display/notification"` would be routed to #3.
The URI is routed to the most specific matching `pathSchema`.
This way the `"/"` (root) `pathSchema` acts as a sort of catch all or default route if no other route matches.