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CacheStore.md

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Cache Store

A Cache Store is responsible for storing and retrieving cached responses. It is also responsible for deciding which specific response to use based off of a response's Vary header (if present).

Pre-built Cache Stores

MemoryCacheStore

The MemoryCacheStore stores the responses in-memory.

Options

  • maxEntries - The maximum amount of responses to store. Default Infinity.
  • maxEntrySize - The maximum size in bytes that a response's body can be. If a response's body is greater than or equal to this, the response will not be cached.

Defining a Custom Cache Store

The store must implement the following functions:

Getter: isFull

This tells the cache interceptor if the store is full or not. If this is true, the cache interceptor will not attempt to cache the response.

Function: createReadStream

Parameters:

  • req Dispatcher.RequestOptions - Incoming request

Returns: CacheStoreReadable | Promise<CacheStoreReadable | undefined> | undefined - If the request is cached, a readable for the body is returned. Otherwise, undefined is returned.

Function: createWriteStream

Parameters:

  • req Dispatcher.RequestOptions - Incoming request
  • value CacheStoreValue - Response to store

Returns: CacheStoreWriteable | undefined - If the store is full, return undefined. Otherwise, return a writable so that the cache interceptor can stream the body and trailers to the store.

CacheStoreValue

This is an interface containing the majority of a response's data (minus the body).

Property statusCode

number - The response's HTTP status code.

Property statusMessage

string - The response's HTTP status message.

Property rawHeaders

(Buffer | Buffer[])[] - The response's headers.

Property rawTrailers

string[] | undefined - The response's trailers.

Property vary

Record<string, string> | undefined - The headers defined by the response's Vary header and their respective values for later comparison

For example, for a response like

Vary: content-encoding, accepts
content-encoding: utf8
accepts: application/json

This would be

{
  'content-encoding': 'utf8',
  accepts: 'application/json'
}

Property cachedAt

number - Time in millis that this value was cached.

Property staleAt

number - Time in millis that this value is considered stale.

Property deleteAt

number - Time in millis that this value is to be deleted from the cache. This is either the same sa staleAt or the max-stale caching directive.

The store must not return a response after the time defined in this property.

CacheStoreReadable

This extends Node's Readable and defines extra properties relevant to the cache interceptor.

Getter: value

The response's CacheStoreValue

CacheStoreWriteable

This extends Node's Writable and defines extra properties relevant to the cache interceptor.

Setter: rawTrailers

If the response has trailers, the cache interceptor will pass them to the cache interceptor through this method.