node-tailor/lib/streams/async-stream.js

Tailor assembles a web page from multiple fragments

'use strict';

const stream = require('stream');
const BufferConcatStream = require('./buffer-concat-stream');

module.exports = class AsyncStream extends stream.Transform {
    constructor() {
        super({ objectMode: true });
        this.streams = 0;
    }

    _transform(st, encoding, done) {
        this.streams += 1;
        st.pipe(
            new BufferConcatStream(data => {
                this.streams -= 1;
                this.push(data);
                if (this.streams === 0) {
                    this.emit('alldone');
                }
            })
        );
        st.on('error', err => {
            this.streams -= 1;
            this.emit('error', err);
        });
        done();
    }

    _flush(done) {
        if (this.streams === 0) {
            done();
        } else {
            this.on('alldone', done);
        }
    }
};