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iterator.ts
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iterator.ts
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import {randomBytes} from 'crypto'
import {promisify} from 'util'
import {ITER_BYTE_LENGTH} from './constants'
const randomBytesPromise = promisify(randomBytes)
// Converts a 16-byte iterator handle to a string for use as a Map key
const getKey = (iter: Uint8Array): string =>
Buffer.from(iter.buffer, iter.byteOffset, iter.length).toString('hex')
export interface CollectionIterator<STATE> {
name: string
iterator: STATE
}
export class Iterators<STATE> {
// Maps iterator handles to their associated iterators
private readonly iterators = new Map<string, CollectionIterator<STATE>>()
// Maps collection names to their number of active iterators
private readonly iteratorCounts = new Map<string, number>()
private lookupIterator(key: string) {
const iterator = this.iterators.get(key)
if (!iterator) throw new Error('Unknown iterator')
return iterator
}
async registerIterator(name: string, iterator: STATE): Promise<Uint8Array> {
const iter = await randomBytesPromise(ITER_BYTE_LENGTH)
this.iterators.set(getKey(iter), {name, iterator})
this.iteratorCounts.set(name, (this.iteratorCounts.get(name) || 0) + 1)
return iter
}
getIterator(iter: Uint8Array): STATE {
return this.lookupIterator(getKey(iter)).iterator
}
closeIterator(iter: Uint8Array): void {
const key = getKey(iter)
const {name} = this.lookupIterator(key)
this.iterators.delete(key)
const oldCount = this.iteratorCounts.get(name)
// istanbul ignore if
if (!oldCount) throw new Error('Hash has no iterators?')
if (oldCount > 1) this.iteratorCounts.set(name, oldCount - 1)
else this.iteratorCounts.delete(name)
}
checkNoIterators(name: string): void {
if (this.iteratorCounts.has(name)) {
throw new Error(`Collection ${name} has active iterators`)
}
}
}