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File system-based memoization
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/** | |
* @template [T=any] | |
* @property {{ (_: T): Promise<void>} & { pending?: Promise<T> }} put | |
*/ | |
class CacheIOError extends Error { | |
constructor(cause, context) { | |
Object.assign(this, context, { cause }) | |
} | |
} | |
const { access, readFile, writeFile, constants, mkdir } = require('fs') | |
const { promisify } = require('util') | |
const path = require('path') | |
/** | |
* @template V | |
* @template [K=string] | |
* @typedef {{ | |
* has(_: K) => Promise<boolean> | |
* get(_: K): Promise<V> | |
* set(..._: [K, V]): Promise<void> | |
* }} Storage | |
*/ | |
/** | |
* @template {any} T | |
* @arg {{ | |
* serialize(_: T) => string; | |
* deserialize(_: string) => T; | |
* ext?: string | |
* dir?: string | |
* }} | |
* @return {Storage<T>} | |
*/ | |
const fileStorage = ({ | |
deserialize, | |
serialize, | |
dir = '.', | |
ext | |
} = { | |
serialize: it => JSON.stringify(it, null, 2), | |
deserialize: JSON.parse, | |
ext: 'json' | |
}) => { | |
const existsFile = (path, cb) => | |
access(path, constants.R_OK, error => cb(undefined, !error)) | |
const storage = Object.fromEntries( | |
[ existsFile, readFile, writeFile ].map(func => [ | |
func.name.replace(/File$/, ''), | |
promisify((key, ...args) => { | |
if (ext) key += `.${ext}` | |
return func(path.join(dir, key), ...args) | |
}) | |
]) | |
) | |
return { | |
has: storage.exists, | |
async get (key) { | |
return deserialize(await storage.read(key)) | |
}, | |
async set (key, value) { | |
const bucket = path.dirname(key) | |
if (!await storage.exists(bucket)) await promisify(mkdir)( | |
path.join(dir, bucket), | |
{ recursive: true } | |
) | |
return storage.write(key, serialize(value)) | |
} | |
} | |
} | |
const lazy = func => { | |
const get = () => { | |
if (!('cached' in get)) get.cached = func() | |
return get.cached | |
} | |
return get | |
} | |
/** | |
* @template [T=any] | |
* @template [P=any[]] | |
* @typedef {(..._: P) => Promise<T>} Async<T, P> | |
*/ | |
/** | |
* @template {any[]} P | |
* @template T | |
* @typedef {{ | |
* invalidate?(_: P & { | |
* cached(): Promise<T> | |
* key: string | |
* }): | boolean | void | Promise<boolean> | |
* getErrorFallback?: false | { | |
* (..._: [any, { key: string }]): boolean | Promise<T> | |
* } | |
* name?: string | |
* cache?: Storage<T> | |
* cacheId?(..._: P): string | |
* }} CacheOptions<P, T> | |
*/ | |
/** | |
* @template {Async} F | |
* @arg {F | CacheOptions< | |
* Parameters<F>, | |
* F extends Async<T> ? T : never> | |
* } options | |
* @arg {F} target | |
* @return {F} | |
*/ | |
const withCache = (options, target = options) => async (...context) => { | |
const { | |
invalidate, | |
getErrorFallback, | |
name = target.name, | |
cache = fileStorage(), | |
cacheId = args => path.join(name, JSON | |
.stringify(args) | |
.replace(/"[^"]+":/g, '') // remove keys | |
.replace(/[^\w]+/g, '-') | |
.replace(/^-+|-+$/g, '') | |
.substr(0, 30) // make it long enough to be unique | |
) | |
} = options | |
const key = cacheId(context, target) | |
const put = async promise => cache.set(key, await promise) | |
Object.assign(context, { | |
put, key, cache, target, name, | |
cached: lazy(async() => { | |
try { return await cache.get(key) } | |
catch(error) { | |
let value = getErrorFallback?.(error, context) | |
if (value?.then) return value | |
if ([getErrorFallback, value].includes(false)) raise(error) | |
Promise.reject(new CacheIOError(error)) | |
// fallback to call() by default and raise UnhandledPromiseRejectionWarning | |
return context.call() | |
} | |
}), | |
call: () => target(...context) | |
}) | |
const raise = (error, pending) => { | |
if (pending?.then) Object.assign(put, { pending }) | |
throw new CacheIOError(error, context) | |
} | |
invalidate = invalidate?.(context) | |
if (invalidate?.then) invalidate = await invalidate | |
if (invalidate || !await cache.has(key)) { | |
const promise = context.call() | |
put(promise).catch(error => { | |
/** intentionally uncaught, not to fail the call just because of put.pending error | |
* @see https://nodejs.org/api/process.html#event-unhandledrejection */ | |
raise(error, promise) | |
}) | |
return promise // also NOT await for the cache set operation | |
} | |
return await context.cached() | |
} | |
module.exports = { | |
cached: withCache, | |
CacheIOError, | |
fileStorage, | |
lazy, | |
} |
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