javascript – 用Node.js中的fs.createReadStream替换fs.readFile

我有从目录中读取图像并将其发送到index.html的代码.

我试图用fs.createReadStream替换fs.readFile但我不知道如何实现这个,因为我找不到一个好的例子.

这是我得到的(index.js)

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

var fs = require('fs');

http.listen(3000, function () {
     console.log('listening on *:3000');
});
app.get('/', function (req, res) {
     res.sendFile(__dirname + '/public/views/index.html');
});
io.on('connection', function (socket) {
     fs.readFile(__dirname + '/public/images/image.png', function (err, buf){
        socket.emit('image', { image: true, buffer: buf.toString('base64') });
     });
});

的index.html

<!DOCTYPE html>
<html>
<body>

<canvas id="canvas" width="200" height="100">
    Your browser does not support the HTML5 canvas tag.
</canvas>

<script src="https://cdn.socket.io/socket.io-1.2.0.js"></script>

<script>
    var socket = io();
    var ctx = document.getElementById('canvas').getContext('2d');
    socket.on("image", function (info) {
        if (info.image) {
            var img = new Image();
            img.src = 'data:image/jpeg;base64,' + info.buffer;
            ctx.drawImage(img, 0, 0);
        }
    });
</script>
</body >
</html >

解决方法:

以下方法仅使用核心模块并从fs.createReadStream()返回的stream.Readable实例中读取块,并将这些块作为Buffer返回.如果你不打算回流块,这不是一个很好的方法.您将把文件保存在驻留在内存中的Buffer中,因此它对于合理大小的文件来说只是一个很好的解决方案.

io.on('connection', function (socket) {
  fileToBuffer(__dirname + '/public/images/image.png', (err, imageBuffer) => {
    if (err) { 
      socket.emit('error', err)
    } else {
      socket.emit('image', { image: true, buffer: imageBuffer.toString('base64') }); 
    }
  });
});

const fileToBuffer = (filename, cb) => {
    let readStream = fs.createReadStream(filename);
    let chunks = [];

    // Handle any errors while reading
    readStream.on('error', err => {
        // handle error

        // File could not be read
        return cb(err);
    });

    // Listen for data
    readStream.on('data', chunk => {
        chunks.push(chunk);
    });

    // File is done being read
    readStream.on('close', () => {
        // Create a buffer of the image from the stream
        return cb(null, Buffer.concat(chunks));
    });
}

HTTP响应流示例

因为它内置到协议中,所以使用HTTP来传输数据几乎总是更好的想法,因为你可以将文件流直接传递给响应,所以你永远不需要将数据一次性加载到内存中.

这是一个非常基本的例子,没有花里胡哨,只是为了演示如何管道()一个stream.Readable到http.ServerResponse.该示例使用Express,但它使用Node.js Core API中的http或https完全相同.

const express = require('express');
const fs = require('fs');
const server = express();

const port = process.env.PORT || 1337;

server.get ('/image', (req, res) => {
    let readStream = fs.createReadStream(__dirname + '/public/images/image.png')

    // When the stream is done being read, end the response
    readStream.on('close', () => {
        res.end()
    })

    // Stream chunks to response
    readStream.pipe(res)
});

server.listen(port, () => {
    console.log(`Listening on ${port}`);
});

javascript – 用Node.js中的fs.createReadStream替换fs.readFile

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