使用node.js下载大文件,避免高内存消耗

Question

我正在尝试创建一个文件下载器作为后台服务,但是当一个大文件被调度时,它首先被放入内存中,然后在下载结束时将文件写入磁盘.

考虑到我可能同时下载了大量文件,如何将文件逐渐写入磁盘保存内存？

这是我正在使用的代码:

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");
    });

});

Answer 1

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);
        });

    });

这非常有效.

Answer 2

请求包是否适合您的使用？

它可以让你做这样的事情：

request(downloadurl).pipe(fs.createWriteStream(downloadtohere))

Answer 3

看看http-request：

// shorthand syntax, buffered response
http.get('http://localhost/get', function (err, res) {
    if (err) throw err;
    console.log(res.code, res.headers, res.buffer.toString());
});

// save the response to 'myfile.bin' with a progress callback
http.get({
    url: 'http://localhost/get',
    progress: function (current, total) {
        console.log('downloaded %d bytes from %d', current, total);
    }
}, 'myfile.bin', function (err, res) {
    if (err) throw err;
    console.log(res.code, res.headers, res.file);
});