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Copy pathscan-iterator.ts
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198 lines (171 loc) · 4.99 KB
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import type {ScanItem} from './scan-item.js';
import type {ScanBound} from './scan-bound.js';
import type {Invoke} from './repm-invoker.js';
import type {JSONValue} from './json.js';
import {throwIfClosed} from './transactions.js';
const defaultScanSize = 500;
export let scanPageSize = defaultScanSize;
export function setScanPageSizeForTesting(n: number): void {
scanPageSize = n;
}
export function restoreScanPageSizeForTesting(): void {
scanPageSize = defaultScanSize;
}
interface IdCloser {
close(): void;
closed: boolean;
id: number;
}
type ScanIterableKind = 'key' | 'value' | 'entry';
/**
* An async iterator that is used with {@link ReadTransaction.scan}.
*/
class ScanIterator<V> implements AsyncIterableIterator<V> {
private readonly _scanItems: ScanItem[] = [];
private _current = 0;
private _moreItemsToLoad = true;
private readonly _prefix: string;
private readonly _kind: ScanIterableKind;
private readonly _start?: ScanBound;
private _loadPromise?: Promise<void> = undefined;
private readonly _getTransaction: () => Promise<IdCloser> | IdCloser;
private readonly _shouldCloseTransaction: boolean;
private _transaction?: IdCloser = undefined;
private readonly _invoke: Invoke;
constructor(
kind: ScanIterableKind,
prefix: string,
start: ScanBound | undefined,
invoke: Invoke,
getTransaction: () => Promise<IdCloser> | IdCloser,
shouldCloseTranscation: boolean,
) {
this._kind = kind;
this._prefix = prefix;
this._start = start;
this._invoke = invoke;
this._getTransaction = getTransaction;
this._shouldCloseTransaction = shouldCloseTranscation;
}
[Symbol.asyncIterator](): AsyncIterableIterator<V> {
return this;
}
private async _ensureTransaction(): Promise<IdCloser> {
if (!this._transaction) {
this._transaction = await this._getTransaction();
}
return this._transaction;
}
async next(): Promise<IteratorResult<V>> {
throwIfClosed(await this._ensureTransaction());
// Preload if we have less than half a page left.
if (this._current + scanPageSize / 2 >= this._scanItems.length) {
if (this._moreItemsToLoad) {
// no await
this._loadPromise = this._load();
}
}
if (this._current >= this._scanItems.length) {
if (!this._moreItemsToLoad) {
return this.return();
}
this._loadPromise = this._load();
await this._loadPromise;
this._loadPromise = undefined;
return this.next();
}
const value = this._scanItems[this._current++];
switch (this._kind) {
case 'value':
return {value: value.value} as IteratorResult<V>;
case 'key':
return {value: value.key} as IteratorResult<V>;
case 'entry':
return {value: [value.key, value.value]} as IteratorResult<V>;
}
}
async return(): Promise<IteratorResult<V>> {
if (this._transaction) {
throwIfClosed(this._transaction);
if (this._shouldCloseTransaction) {
this._transaction.close();
}
}
return {done: true, value: undefined};
}
private async _load(): Promise<void> {
if (this._loadPromise) {
return this._loadPromise;
}
if (!this._moreItemsToLoad) {
throw new Error('No more items to load');
}
let start = this._start;
if (this._scanItems.length > 0) {
// We loaded some items already, so continue where we left off.
start = {
id: {
value: this._scanItems[this._scanItems.length - 1].key,
exclusive: true,
},
};
}
if (!this._transaction) {
this._transaction = await this._getTransaction();
}
const opts = {
prefix: this._prefix,
start,
limit: scanPageSize,
};
const args = {
transactionId: this._transaction.id,
opts,
};
const response = await this._invoke('scan', args);
const responseItems = response.items;
if (responseItems.length !== scanPageSize) {
this._moreItemsToLoad = false;
}
const scanItems: ScanItem[] = responseItems.map(({key, value}) => ({
key,
value: JSON.parse(value),
}));
this._scanItems.push(...scanItems);
}
}
export class ScanResult implements AsyncIterable<JSONValue> {
private readonly _args: [
string,
ScanBound | undefined,
Invoke,
() => Promise<IdCloser> | IdCloser,
boolean,
];
constructor(
...args: [
string,
ScanBound | undefined,
Invoke,
() => Promise<IdCloser> | IdCloser,
boolean,
]
) {
this._args = args;
}
[Symbol.asyncIterator](): AsyncIterableIterator<JSONValue> {
return this.values();
}
values(): AsyncIterableIterator<JSONValue> {
return this._newIterator('value');
}
keys(): AsyncIterableIterator<string> {
return this._newIterator('key');
}
entries(): AsyncIterableIterator<[string, JSONValue]> {
return this._newIterator('entry');
}
private _newIterator<V>(kind: ScanIterableKind): AsyncIterableIterator<V> {
return new ScanIterator<V>(kind, ...this._args);
}
}