# nodejs读写大文件 - fengmk2

# nodejs读写大文件

## 限制

大文件读写操作，由于内存限制问题，不要直接使用[fs.readFile](http://nodejs.org/docs/v0.5.4/api/fs.html#fs.readFile) 和 [fs.writeFile](http://nodejs.org/docs/v0.5.4/api/fs.html#fs.writeFile)。
必须使用[fs.ReadStream](http://nodejs.org/docs/v0.5.4/api/fs.html#fs.ReadStream) 和 [fs.WriteStream](http://nodejs.org/docs/v0.5.4/api/fs.html#fs.WriteStream) 来对文件进行读写操作。

## [fs.ReadStream](http://nodejs.org/docs/v0.5.4/api/fs.html#fs.ReadStream)：上传大文件

```js
var urlparse = require("url").parse,
  http = require("http"),
  fs = require("fs");

function upload(url, uploadfile, callback) {
  var urlinfo = urlparse(url);
  var options = {
    method: "POST",
    host: urlinfo.host,
    path: urlinfo.pathname,
  };
  if (urlinfo.port) {
    options.port = urlinfo.port;
  }
  if (urlinfo.search) {
    options.path += urlinfo.search;
  }
  var req = http.request(options, function (res) {
    var chunks = [],
      length = 0;
    res.on("data", function (chunk) {
      length += chunk.length;
      chunks.push(chunk);
    });
    res.on("end", function () {
      var buffer = new Buffer(length);
      // delay copy
      for (var i = 0, pos = 0, size = chunks.length; i < size; i++) {
        chunks[i].copy(buffer, pos);
        pos += chunks[i].length;
      }
      res.body = buffer;
      callback(null, res);
    });
  });
  var readstream = fs.createReadStream(uploadfile);
  readstream.on("data", function (chunk) {
    console.log("write", chunk.length);
    req.write(chunk);
  });
  readstream.on("end", function () {
    req.end();
  });
}

upload("http://weibo.com/", "/tmp/bigfile.pdf", function (err, res) {
  console.log(res.statusCode, res.headers);
});
```

## [fs.WriteStream](http://nodejs.org/docs/v0.5.4/api/fs.html#fs.WriteStream)：下载大文件

```js
var urlparse = require("url").parse,
  http = require("http"),
  fs = require("fs");

function download(url, savefile, callback) {
  console.log("download", url, "to", savefile);
  var urlinfo = urlparse(url);
  var options = {
    method: "GET",
    host: urlinfo.host,
    path: urlinfo.pathname,
  };
  if (urlinfo.port) {
    options.port = urlinfo.port;
  }
  if (urlinfo.search) {
    options.path += urlinfo.search;
  }
  var req = http.request(options, function (res) {
    var writestream = fs.createWriteStream(savefile);
    writestream.on("close", function () {
      callback(null, res);
    });
    res.pipe(writestream);
  });
  req.end();
}

download("http://weibo.com/", "/tmp/downfile.html", function (err, res) {
  console.log(res.statusCode, res.headers);
});
```

## 有爱

本文示例中为了凸显文件操作部分，异常处理部分代码已去除，请读者自行补全。
^\_^ 希望本文对你有用