@alt-javascript/scanner-darkly/README.md

A Pluggable Scanner For Launch Darkly Feature Flag Variations

A Pluggable Scanner For Launch Darkly Feature Flag Variations
=============================================================

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[release notes](https://github.com/alt-javascript/scanner-darkly/blob/main/History.md)

<a name="intro">Introduction</a>
--------------------------------
A pluggable scanner for listening and acting on Launch Darkly feature flag variations in
server-side node.js.

<a name="usage">Usage</a>
-------------------------

To use the module, follow the example in the included `scan.js` file, which plays nicely with all the other
@alt-javascript modules.

The Scanner, takes an `Arctor` (or array of `Arctors`) that will act on flagged LaunchDarkly variations with
the implemented `see(clearly)` function, in this case the provided `LogArctor` outputs the changed flag value.

`scan.js`
```javascript
const LaunchDarkly = require('launchdarkly-node-server-sdk');
const ScannerDarkly = require('@alt-javascript/scanner-darkly');
const {config} = require ("@alt-javascript/config");
const {boot} = require ("@alt-javascript/boot");
const {LoggerFactory} = require ('@alt-javascript/logger');
boot({ config });


const LogArctor = require('@alt-javascript/scanner-darkly'); // this  uses booted logging config, so is required after boot().

const logger = LoggerFactory.getLogger('@alt-javascript/scanner-darkly/scan');
const ldlogger = LoggerFactory.getLogger('LaunchDarkly');
const SDK_KEY = config.get('scanner.darkly.sdk-key');
const scannerDarkly = new ScannerDarkly(
    new LogArctor('logging-levels', {"key": "user@test.com"},null),
    SDK_KEY,
    {logger : ldlogger});

scannerDarkly.init();
// ... later, on process exit.
scannerDarkly.destroy();
```

When your LaunchDarkly product, environment, sdk-key and feature flag are configured, you should see output like:

```shell
Wed Jul 28 2021 10:57:03 GMT+1000 (GMT+10:00):LaunchDarkly:info:Initializing stream processor to receive feature flag updates
Wed Jul 28 2021 10:57:04 GMT+1000 (GMT+10:00):LaunchDarkly:info:Opened LaunchDarkly stream connection
Wed Jul 28 2021 10:57:04 GMT+1000 (GMT+10:00):LaunchDarkly:debug:Received put event
Wed Jul 28 2021 10:57:15 GMT+1000 (GMT+10:00):LaunchDarkly:debug:Received patch event
Wed Jul 28 2021 10:57:15 GMT+1000 (GMT+10:00):LaunchDarkly:debug:Updating logging-levels in features
Wed Jul 28 2021 10:57:15 GMT+1000 (GMT+10:00):@alt-javascript/scanner-darkly/LogArctor:info:Variation seen clearly as {"crew_prestart/src/services":"debug"}
Wed Jul 28 2021 10:57:18 GMT+1000 (GMT+10:00):LaunchDarkly:debug:Flushing %d events2

```

<a name="arctor">Yes, its Arctor, not Actor</a>
----------------------------------------

Yes, the class is called `Arctor` _by design_, and in homage to one of my very favourite novels, 


> What does a scanner see? he asked himself. I mean, really see? Into the head? 
> Down into the heart? Does a passive infrared scanner like they used to use or a cube-type holo-scanner 
> like they use these days, the latest thing, see into me - into us - clearly or darkly? 
> I hope it does, he thought, see clearly, because I can't any longer these days see into myself. 
> I see only murk. Murk outside; murk inside. I hope, for everyone's sake, the scanners do better. 
> Because, he thought, if the scanner sees only darkly, the way I myself do, then we are cursed, 
> cursed again and like we have been continually, and we'll wind up dead this way,
> knowing very little and getting that little fragment wrong too.
> 
>― [A Scanner Darkly - Philip. K. Dick, 1977](https://en.wikipedia.org/wiki/A_Scanner_Darkly)


The movie is pretty good too, _weird good_.