Limit Service

This module is intended to hold all of the logic for testing if site:

• would be over a given limit if they took an action (i.e. added one more thing, switched to a different limit)
• if they are over a limit already
• consistent error messages explaining why the limit has been reached

Install

npm install @simtropolis/limit-service --save

or

yarn add @simtropolis/limit-service

Usage

Below is a sample code to wire up limit service and perform few common limit checks:

const knex = require('knex');
const errors = require('@simtropolis/errors');
const LimitService = require('@simtropolis/limit-service');

// create a LimitService instance
const limitService = new LimitService();

// setup limit configuration
// currently supported limit keys are: staff, members, customThemes, customIntegrations, uploads
// all limit configs support custom "error" configuration that is a template string
const limits = {
    // staff and member are "max" type of limits accepting "max" configuration
    staff: {
        max: 1,
        error: 'Your plan supports up to {{max}} staff users. Please upgrade to add more.'
    },
    members: {
        max: 1000,
        error: 'Your plan supports up to {{max}} members. Please upgrade to reenable publishing.'
    },
    // customThemes is an allowlist type of limit accepting the "allowlist" configuration
    customThemes: {
        allowlist: ['casper', 'dawn', 'lyra'],
        error: 'All our official built-in themes are available the Starter plan, if you upgrade to one of our higher tiers you will also be able to edit and upload custom themes for your site.'
    },
    // customIntegrations is a "flag" type of limits accepting disabled boolean configuration
    customIntegrations: {
        disabled: true,
        error: 'You can use all our official, built-in integrations on the Starter plan. If you upgrade to one of our higher tiers, you’ll also be able to create and edit custom integrations and API keys for advanced workflows.'
    },
    // emails is a hybrid type of limit that can be a "flag" or a "max periodic" type
    // below is a "flag" type configuration
    emails: {
        disabled: true,
        error: 'Email sending has been temporarily disabled whilst your account is under review.'
    },
    // following is a "max periodic" type of configuration
    // note if you use this configuration, the limit service has to also get a 
    // "subscription" parameter to work as expected
    // emails: {
    //     maxPeriodic: 42,
    //     error: 'Your plan supports up to {{max}} emails. Please upgrade to reenable sending emails.'
    // }
    uploads: {
        // max key is in bytes
        max: 5000000,
        // formatting of the {{ max }} vairable is in MB, e.g: 5MB
        error: 'Your plan supports uploads of max size up to {{max}}. Please upgrade to reenable uploading.'
    }
};

// This information is needed for the limit service to work with "max periodic" limits
// The interval value has to be 'month' as thats the only interval that was needed for
// current usecase
// The startDate has to be in ISO 8601 format (https://en.wikipedia.org/wiki/ISO_8601)
const subscription = {
    interval: 'month',
    startDate: '2022-09-18T19:00:52Z'
};

// initialize the URL linking to help documentation etc.
const helpLink = 'https://simtropolis.org/help/';

// initialize knex db connection for the limit service to use when running query checks
const db = {
    knex: knex({
        client: 'mysql',
        connection: {
            user: 'root',
            password: 'toor',
            host: 'localhost',
            database: 'simtropolis',
        }
    });
};

// finish initializing the limits service
limitService.loadLimits({limits, subscription, db, helpLink, errors});

// perform limit checks

// check if there is a 'staff' limit configured
if (limitService.isLimited('staff')) {
    // throws an error if current 'staff' limit **would** go over the limit set up in configuration (max:1)
    await limitService.errorIfWouldGoOverLimit('staff');

    // same as above but overrides the default max check from max of 1 to 100
    // useful in cases you need to check if specific instance would still be over the limit if the limit changed
    await limitService.errorIfWouldGoOverLimit('staff', {max: 100});
}

// "max" types of limits have currentCountQuery method reguring a number that is currently in use for the limit
// for example it could be 1, 3, 5 or whatever amount of 'staff' is currently in the system
const staffCount = await limitService.currentCountQuery('staff');

// do something with that number
console.log(`Your current staff count is at: ${staffCount}!`);

// check if there is a 'members' limit configured
if (limitService.isLimited('members')) {
    // throws an error if current 'staff' limit **is** over the limit set up in configuration (max: 1000)
    await limitService.errorIfIsOverLimit('members');

    // same as above but overrides the default max check from max of 1000 to 10000
    // useful in cases you need to check if specific instance would still be over the limit if the limit changed
    await limitService.errorIfIsOverLimit('members', {max: 10000});
}

if (limitService.isLimited('uploads')) {
    // for the uploads limit we HAVE TO pass in the "currentCount" parameter and use bytes as a base unit
    await limitService.errorIfIsOverLimit('uploads', {currentCount: frame.file.size});
}

// check if any of the limits are acceding
if (limitService.checkIfAnyOverLimit()) {
    console.log('One of the limits has acceded!');
}

Transactions

Some limit types (max or maxPeriodic) need to fetch the current count from the database. Sometimes you need those checks to also run in a transaction. To fix that, you can pass the transacting option to all the available checks.

db.transaction((transacting) => {
    const options = {transacting};

    await limitService.errorIfWouldGoOverLimit('newsletters', options);
    await limitService.errorIfIsOverLimit('newsletters', options);
    const a = await limitService.checkIsOverLimit('newsletters', options);
    const b = await limitService.checkWouldGoOverLimit('newsletters', options);
    const c = await limitService.checkIfAnyOverLimit(options);
});

Types of limits

At the moment there are four different types of limits that limit service allows to define. These types are:

1. flag - is an "on/off" switch for certain feature. Example usecase: "disable all emails". It's identified by a disabled: true property in the "limits" configuration.
2. max - checks if the maximum amount of the resource has been used up.Example usecase: "disable creating a staff user when maximum of 5 has been reached". To configure this limit add max: NUMBER to the configuration. The limits that support max checks are: members, staff, and customIntegrations
3. maxPeriodic - it's a variation of max type with a difference that the check is done over certain period of time. Example usecase: "disable sending emails when the sent emails count has acceded a limit for last billing period". To enable this limit define maxPeriodic: NUMBER in the limit configuration and provide a subscription configuration when initializing the limit service instance. The subscription object comes as a separate parameter and has to contain two properties: startDate and interval, where startDate is a date in ISO 8601 format and period is 'month' (other values like 'year' are not supported yet)
4. allowList - checks if provided value is defined in configured "allowlist". Example usecase: "disable theme activation if it is not an official theme". To configure this limit define allowlist: ['VALUE_1', 'VALUE_2', 'VALUE_N'] property in the "limits" parameter.

Supported limits

There's a limited amount of limits that are supported by limit service. The are defined by "key" property name in the "config" module. List of currently supported limit names: members, staff, customIntegrations, emails, customThemes, uploads.

All limits can act as flag or allowList types. Only certain (members, staff, andcustomIntegrations) can have a max limit. Only emails currently supports the maxPeriodic type of limit.

Frontend usage

In case the limit check is run without direct access to the database you can override currentCountQuery functions for each "max" or "maxPeriodic" type of limit. An example usecase would be a frontend client running in a browser. A browser client can check the limit data through HTTP request and then provide that data to the limit service. Example code to do exactly that:

const limitService = new LimitService();

let limits = {
    staff: {
        max: 2,
        currentCountQuery: async () => (await fetch('/api/staff')).json().length
    }
};

limitService.loadLimits({limits, errors});

if (await limitService.checkIsOverLimit('staff')) {
    // do something as "staff" limit has been reached
};

Custom error messages

Errors returned by the limit service can be customized. When configuring the limit service through loadLimits method limits objects can specify an error property that is a template string. Additionally, "MaxLimit" limit type supports following variables- {{count}} and {{max}}.

An example configuration for "MaxLimit" limit using an error template can look like following:

"staff": {
    "max": 5,
    "error": "Your plan supports up to {{max}} staff users and you currently have {{count}}. Please upgrade to add more."
}

Develop

This is a mono repository, managed with lerna.

Follow the instructions for the top-level repo.

1. git clone this repo & cd into it as usual
2. Run yarn to install top-level dependencies.

Run

• yarn dev

Test

• yarn lint run just eslint
• yarn test run lint and tests

Copyright & License

Copyright (c) 2020-2022 Simtropolis - Released under the MIT license.