ut-port-cache

ut-port-cache is a multi-strategy object caching port. It is a convinient wrapper for catbox and provides on top of that the standard ut mechanisms for logging, monitoring, error handling, etc. inherited from ut-port.

Usage

This port can be used the same way as any other ut compliant port. For more information about how to bootstrap a ut port click here

Configuration

Besides logLevel, concurrency, and other configuration options which are common for all ports, ut-port-cache defines 2 additional properties:

• client - This object provides a low-level cache abstraction.
  • engine - An object or a prototype function implementing the cache strategy
  • options - The strategy configuration object

More information about how to configure the client engine and options can be found here

• policy
  • options - The policy configuration object
  • segment - Used to isolate cached items within the cache partition

More information about how to configure the policy options and segment can be found here

Both client and policy are optional. If client engine is not provided then catbox-memory will be used by default. So therefore if you need to store data in memory only then omit the client.engine configuration and just pass client.options in case it is necessary to adjust maxByteSize or allowMixedContent.

Configuration example

function cache() {
    return class cache extends require('ut-port-cache')(...arguments) {
        get defaults() {
            engine: require('catbox-redis'),
            options: {} // catbox-redis options
            policy: [
                {
                    segment: 'module.foo.get',
                    options: {} // segment 'module.foo.get' options
                },
                {
                    segment: 'bar',
                    options: {} // segment 'bar' options
                }
            ]
        }
    };
}

In the example above the port is configured to use Redis as a caching layer.

A list of all ready-to-use catbox plugins can be found here.

API

By setting up the port using the example above it will expose the following set of methods available through ut-bus:

• bus.importMethod('cache/module.entity.action')(value, {cache})

  • module.entity.action is arbitrary string, usually corresponding to a namespaced method call and helps in determining the segment
  • value is the value for the cache operation
  • cache determines the cache operation and parameters and has the following structire {operation, ttl, key: {id, params, segment}}, where:
    • operation is one of 'get', 'set', 'drop' and determines what to do.
    • ttl is optional time to keep the value in the cache, when operation is 'set', with default taken from port configuration property ttl
    • key determines the cache key, as per following:
      • id - unique string value per cache segment
      • segment - if specified non falsy value, defines the cache segment
      • params - if segment is falsy, this helps for deremining cache segmet as per following rules:
        • if it is object, the cache segment is constructed by deterministically converting the object to URL parameters, for example if params={x:1, y: 2}, the segment becomes 'module.entity.action?x=1&y=2'
        • if it is truthy, it is converted to string and appended as query string, for example if params='xyz', the cache segment is 'module.entity.action?xyz'
        • otherwise, the cache segment is simply 'module.entity.action'
  • return value is determined by cache operation as follows:
    • rejected promise when error happened during any of the cache operations
    • promise resolving to null, when 'set' operation was successful
    • promise resolving to null, when 'drop' operation was successful
    • promise resolving null, when 'get' resulted in cache miss
    • promise resolving to the cached value, when 'get' operation resulted in cache hit

Example

This is a trivial example illustrating the resquest/response signatures of all different methods.

const segment = 'global';
const id = 'asd';
const valueFoo = {x: 1, y: 2};
const valueBar = [1, 2];
Promise.resolve()
    .then(result => { // step 1
        return bus.importMethod('cache/module.foo.get')(valueFoo, {
            cache:{
                operation:'set',
                ttl: 999999,
                key:{id}
            }
        });
    })
    .then(result => { // step 2, result is null
        return bus.importMethod('cache/module.bar.get')(valueBar, {
            cache:{
                operation:'set',
                ttl: 999999,
                key:{id, segment: 'bar'}
            }
        });
    })
    .then(result => { // step 3, result is null
        return bus.importMethod('cache/module.foo.get')(undefined, {
            cache:{
                operation:'get',
                key:{id}
            }
        });
    })
    .then(result => { // step 4, result is { "x": 1, "y": 2 }
        return bus.importMethod('cache/module.bar.get')(undefined, {
            cache:{
                operation:'get',
                key:{id, segment: 'bar'}
            }
        });
    })
    .then(result => { // step 5, result is [1, 2]
        return bus.importMethod('cache/module.foo.get')(undefined, {
            cache:{
                operation:'drop',
                key:{id}
            }
        });
    })
    .then(result => { // step 6 result is null
        return bus.importMethod('cache/module.bar.get')(undefined, {
            cache:{
                operation:'drop',
                key:{id, segment: 'bar'}
            }
        });
    })
    .then(result => { // step 7 result is null
        return result;
    })
    .catch(e => { // an exception in case any of the above calls fail
        throw e;
    });

Before starting to drop the records in step 5 the redis store will have the following contents:

| key | value | | ---------------------- | ----------------------------------------------------------- | | catbox:module.foo.get | {"item":{"x":1,"y":2},"stored":1530272083808,"ttl":999999} | | catbox:bar | {"item":[1,2],"stored":1530272083811,"ttl":999999} |