exceljs/lib/utils/stuttered-pipe.js

Excel Workbook Manager - Read and Write xlsx and csv Files.

/**
 * Copyright (c) 2015 Guyon Roche
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * 
 */
"use strict";

var events = require("events");

var utils = require("./utils");

// =============================================================================
// StutteredPipe - Used to slow down streaming so GC can get a look in
var StutteredPipe = module.exports = function(readable, writable, options) {
    var self = this;
    options = options || {};
    
    this.readable = readable;
    this.writable = writable;
    this.bufSize = options.bufSize || 16384;
    this.autoPause = options.autoPause || false;
    
    this.paused = false;
    this.eod = false;
    this.scheduled = null;
    
    readable.on('end', function() {
        //console.log("Input Stream ended")
        self.eod = true;
        writable.end();
    });
    
    // need to have some way to communicate speed of stream
    // back from the consumer
    readable.on('readable', function() {
        if (!self.paused) {
            self.resume();
        }
    });
    this._schedule();
}

utils.inherits(StutteredPipe, events.EventEmitter, {
    pause: function() {
        this.paused = true;
    },
    resume: function() {
        if (!this.eod) {
            if (this.scheduled !== null) {
                clearImmediate(this.scheduled);
            }
            this._schedule();
        }
    },
    _schedule: function() {
        var self = this;
        this.scheduled = setImmediate(function() {
            self.scheduled = null;
            if (!self.eod && !self.paused) {
                var data = self.readable.read(self.bufSize);
                if (data && data.length) {
                    self.writable.write(data);
                    
                    if (!self.paused && !self.autoPause) {
                        self._schedule();
                    }
                } else {
                    if (!self.paused) {
                        self._schedule();
                    }
                }
            }
        });
    }
});