reflip

Redis-backed or file-backed feature flipping middleware for connect/express.js. It should be straightforward to write additional storage adapters.

Example

var Reflip = require('reflip'),
    express = require('express');

var reflip = new Reflip(
{
    storage: new Reflip.RedisAdapter(
    {
        client: redis.createClient(),
        namespace: 'myapp:',
        ttl: 60 * 1000
    }),
});

reflip.register('aardvarks', 'custom', function(request)
{
    return reflip.check('aardvark-enabled') && !!request.user;
});

var app = express();
app.use(express.session()); // etc
app.use(reflip.flip());

app.get('/aardvarks', serveArdvarks);
app.get('/anteaters', reflip.gate('anteaters'), serveAnteaters);

function serveArdvarks(request, response)
{
    // has access to the session info; can make exciting decisions
    if (!request.check('aardvarks') || request.session.alpacasPreferred)
    {
        response.redirect('/alpacas');
        return;
    }

    response.render('aardvarks');
}

function serveAnteaters(request, response)
{
    // if we reach here at all, the anteater feature is enabled
    response.render('anteaters');
}

API

new Reflip(options)

The options object may include the following fields:

• storage: a storage adapter; can be nil if you are operating from a predefined object only
• default: default response for unknown features; defaults to false
• httpcode: the status code to use when blocking requests for disabled features; defaults to 404
• features: an object pre-defining feature defaults; is overridden after ttl milliseconds by the values in remote storage if that is enabled
• exportName: the name of the function to hang onto each request object; use if check() would conflict with other Connect middleware

reflip.register('feature-name', function(request) {})

Register a custom feature name with a function that decides based on the request object if it is enabled or not. Can return a promise. (This is a lie; I need to make this work.)

reflip.register(new Reflip.Feature(opts))

Register a pre-constructed feature that makes its decisions in any manner you define.

reflip.flip()

The middleware that decorates each request object with the result of feature checks.

app.use(reflip.flip());

The middleware pre-calculates the answers for all feature checks & adds a check() function to each request object.

request.check('feature-name')

Determines if the named feature is turned on or not. Returns a falsey value if this feature is off for this request. Returns a truthy value if it should be enabled. If the feature is of type grouped, it will return a string indicating which group this request is in.

request.check()

Returns the internal cache of all feature names and their corresponding states for this request. Note that mutating the cache will affect the results returned by request.check('feature-name').

reflip.gate('feature-name', [failureHandler])

Use as middleware for specific routes; responds to the request with reflip.httpcode if the feature is not enabled for that request.

app.get('/anteaters', reflip.gate('anteaters'), serveAnteaters);

Alternatively, you can provide a failureHandler function that returns a custom response. The reflip.httpcode property will be ignored if a failure handler is specified.

app.get('/anteaters', reflip.gate('anteaters', function(request, response)
{
    response.json(403,
    {
        code: 'ForbiddenError',
        message: 'This feature is unavailable.'
    });
}), serveAnteaters);

reflip.refresh()

Forces the adapter layer to refresh; normally called by the interval timer. Returns a promise that resolves when the lookup is complete. Updates the list of features completely, adding new ones and removing older ones. Also updates the timeout.

Feature

The feature object represents a feature that can be flipped on or off.

var feature = new Reflip.Feature(
{
    name: 'anteaters',
    type: 'metered',
    chance: 50,
});

Valid types:

• boolean: on or off.
• metered: the feature has a percent chance of being turned on
• grouped: a list of possible values for the feature, each of which has an equal chance of appearing; useful for rudimentary a/b testing
• custom: you provide the function used to decide if the feature is enabled. The checker function is given the express request object to use to make its decision.

Valid feature fields:

• name: required, string name of feature
• type: required; string type of feature
• enabled: boolean, used for boolean features
• groups: array, used for grouped features
• chance: number from 0-100, used for metered features
• checker: called by check() in lieu of other decision-making; used for custom features

File adapter

Usage: storage = new Reflip.FileAdapter({ filename: './features.json'});

Example file:

{
    "features":
    [
        {
            "name": "aardvarks",
            "type": "boolean",
            "enabled": true
        },
        {
            "name": "archaeopteryx",
            "type": "boolean",
            "enabled": false
        },
        {
            "name": "anteaters",
            "type": "metered",
            "enabled": true,
            "chance": 25
        },
        {
            "name": "alpacas",
            "type": "grouped",
            "enabled": true,
            "groups": [ "a", "b", "c" ]
        }
    ]
}

The ttl field, if present in the features hash, is ignored. The file adapter uses fs.watch() to observe changes in the file. The usual fs.watch() caveats apply.

Redis adapter

var storage = new Reflip.RedisAdapter(
{
    client: redis.createClient(), // or supply `host` and `port` fields
    namespace: 'key-prefix:',     // optional
    ttl: 60000                    // optional; refresh interval in milliseconds; defaults to 5 minutes
});

The redis adapter expects to find the following keys:

• key-prefix:ttl: integer giving time until next refresh, in milliseconds
• key-prefix:features: set giving string feature names
• key-prefix:<name>: hash, one per feature. The hash is passed directly to the Feature constructor as documented above.

TODO

The module should work well as a express middleware right now. However, it would be nice to have conveniences for adding/editing/removing feature switches from redis, out of band of the Reflip instance (since it is intended to update itself periodically). Maybe a tiny web app that does nothing but update redis?

LICENSE

MIT.