@naturalcycles/nodejs-lib/dist/stream/writable/writableFork.js

Standard library for Node.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.writableFork = void 0;
const stream_1 = require("stream");
const __1 = require("../..");
/**
 * Allows "forking" a stream inside pipeline into a number of pipeline chains (2 or more).
 * Currently does NOT (!) maintain backpressure.
 * Error in the forked pipeline will propagate up to the main pipeline (and log error, to be sure).
 * Will wait until all forked pipelines are completed before completing the stream.
 *
 * @experimental
 */
function writableFork(chains, opt) {
    const readables = [];
    const allChainsDone = Promise.all(chains.map(async (chain) => {
        const readable = (0, __1.readableCreate)();
        readables.push(readable);
        return await (0, __1._pipeline)([readable, ...chain]);
    })).catch(err => {
        console.error(err); // ensure the error is logged
        throw err;
    });
    return new stream_1.Writable({
        objectMode: true,
        ...opt,
        write(chunk, _, cb) {
            // Push/fork to all sub-streams
            // No backpressure is ensured here, it'll push regardless of the
            readables.forEach(readable => readable.push(chunk));
            cb();
        },
        async final(cb) {
            try {
                // Push null (complete) to all sub-streams
                readables.forEach(readable => readable.push(null));
                console.log(`writableFork.final is waiting for all chains to be done`);
                await allChainsDone;
                console.log(`writableFork.final all chains done`);
                cb();
            }
            catch (err) {
                cb(err);
            }
        },
    });
}
exports.writableFork = writableFork;