使用node.js下载大文件，避免高内存消耗 [英] Download large file with node.js avoiding high memory consumption

问题描述

我正在尝试创建一个文件下载器作为后台服务，但是当调度大文件时，它首先放入内存中，然后在下载结束时将文件写入磁盘。

I`m trying to create a file downloader as a background service but when a large file is scheduled, it's first put in memory and then, at the end of the download the file is written to disk.

考虑到我可能同时下载大量文件，如何将文件逐渐写入磁盘保存内存？

How can I make the file be wrote gradually to the disk preserving memory considering that I may have lots of files being downloaded at the same time?

以下是我正在使用的代码：

Here's the code I`m using:

var sys = require("sys"),
    http = require("http"),
    url = require("url"),
    path = require("path"),
    fs = require("fs"),
    events = require("events");

var downloadfile = "http://nodejs.org/dist/node-v0.2.6.tar.gz";

var host = url.parse(downloadfile).hostname
var filename = url.parse(downloadfile).pathname.split("/").pop()

var theurl = http.createClient(80, host);
var requestUrl = downloadfile;
sys.puts("Downloading file: " + filename);
sys.puts("Before download request");
var request = theurl.request('GET', requestUrl, {"host": host});
request.end();

var dlprogress = 0;


setInterval(function () {
   sys.puts("Download progress: " + dlprogress + " bytes");
}, 1000);


request.addListener('response', function (response) {
    response.setEncoding('binary')
    sys.puts("File size: " + response.headers['content-length'] + " bytes.")
    var body = '';
    response.addListener('data', function (chunk) {
        dlprogress += chunk.length;
        body += chunk;
    });
    response.addListener("end", function() {
        fs.writeFileSync(filename, body, 'binary');
        sys.puts("After download finished");
    });

});

推荐答案

我将回调更改为：

request.addListener('response', function (response) {
        var downloadfile = fs.createWriteStream(filename, {'flags': 'a'});
        sys.puts("File size " + filename + ": " + response.headers['content-length'] + " bytes.");
        response.addListener('data', function (chunk) {
            dlprogress += chunk.length;
            downloadfile.write(chunk, encoding='binary');
        });
        response.addListener("end", function() {
            downloadfile.end();
            sys.puts("Finished downloading " + filename);
        });

    });

这完美无缺。

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