69 lines
1.6 KiB
JavaScript
69 lines
1.6 KiB
JavaScript
import { Transform } from 'node:stream';
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/**
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* Backpressure on readable side is limits how many batches are in flight.
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*
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* @param {number} size - maximum items per emitted batch
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* @returns {Transform}
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*/
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export const batch = (size) => {
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if (!Number.isInteger(size) || size < 1) {
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throw new TypeError('batch(size) requires a positive integer size');
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}
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let pending = [];
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return new Transform({
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objectMode: true,
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transform(item, _encoding, callback) {
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pending.push(item);
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if (pending.length < size) {
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callback();
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return;
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}
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const full = pending;
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pending = [];
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callback(null, full);
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},
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flush(callback) {
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if (pending.length === 0) {
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callback();
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return;
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}
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const remainder = pending;
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pending = [];
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callback(null, remainder);
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},
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});
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};
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/**
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* @returns {Transform}
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*/
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export const jsonArray = () => {
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let wroteFirst = false;
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return new Transform({
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writableObjectMode: true,
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transform(item, _encoding, callback) {
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let serialized;
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try {
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serialized = JSON.stringify(item);
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} catch (err) {
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callback(err);
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return;
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}
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const prefix = wroteFirst ? ',' : '[';
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wroteFirst = true;
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callback(null, prefix + serialized);
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},
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flush(callback) {
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callback(null, wroteFirst ? ']' : '[]');
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},
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});
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};
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