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Stream this.push and spread operator does not work #26582

Description

@akaNightmare
  • Version: v11.10.0
  • Platform: Darwin Ivans-MacBook-Pro.local 18.2.0 Darwin Kernel Version 18.2.0: Thu Dec 20 20:46:53 PST 2018; root:xnu-4903.241.1~1/RELEASE_X86_64 x86_64

Hello, I have written a simple Transform stream to getting some extended user info:

import { Transform } from 'stream';
import { getUsersPublicInfo } from '../../user/services';

const USERS_BATCH_SIZE = 100;

/**
 * Class (extended from Transform stream)
 * for getting minimum user info for diff
 * types of reports. Returns `id`, `email`
 * and `name` in a stream as an object.
 */
export class FillUserTransform extends Transform {
    constructor(options) {
        super({
            readableObjectMode: true,
            writableObjectMode: true,
            ...(options || {}),
        });
        this._userIds = [];
    }

    /**
     * @param {{user_id: string}} chunk
     * @param {string} encoding
     * @param {Function} cb
     * @return {*}
     * @private
     */
    _transform(chunk, encoding, cb) {
        this._userIds.push(chunk.user_id);
        if (this._userIds.length >= USERS_BATCH_SIZE) {
            this._writeUserInfo(cb);
        } else {
            return void cb();
        }
    }

    _flush(cb) {
        if (this._userIds.length > 0) {
            this._writeUserInfo(cb);
        } else {
            return void cb();
        }
    }

    /**
     * @param {Function} cb
     * @return {*}
     * @private
     */
    _writeUserInfo(cb) {
        this.pause();
        getUsersPublicInfo(this._userIds)
            .then(users => {
                if (users.length > 0) {
                    this.push(...users);
                }
                this._userIds.length = 0;
                this.resume();
                cb();
            })
            .catch(err => {
                this._userIds.length = 0;
                this.resume();
                cb(err);
            });
    }
}

but this.push(...users); does not work as expected, replaced spread operator with forEach - works

users.forEach(user => {
    this.push(user);
});

Activity

  1. lpinca commented on Mar 11, 2019

    @lpinca
    Member

    I think it works as expected. readable.push() takes one chunk at max.

  2. added
    streamIssues and PRs related to Node.js streams.
    on Mar 11, 2019
  3. bnoordhuis commented on Mar 12, 2019

    @bnoordhuis
    Member

    Closing as answered.

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