用Node.js中的fs.createReadStream替换fs.readFile [英] Replacing fs.readFile with fs.createReadStream in Node.js
问题描述
我有从目录中读取图像并将其发送到index.html的代码。
I have code for reading an image from directory and sending it to index.html.
我试图用fs.createReadStream替换fs.readFile但我有不知道如何实现这个，因为我找不到一个好的例子。
I am trying to replace fs.readFile with fs.createReadStream but i have no idea how to implement this as i can not find a good example.
这是我得到的（index.js）
Here is what i got (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') });
});
});
index.html
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 >
推荐答案
以下方法仅使用核心模块并读取块从 stream.Readable 实例返回 fs.createReadStream（）并将这些块返回为缓冲。如果你不打算回流块，这不是一个很好的方法。您将把文件保存在内存中的 Buffer 中，因此它只适用于合理大小的文件。
The below approach only uses core modules and reads the chunks from the stream.Readable instance returned from fs.createReadStream() and returns those chunks back as a Buffer. This isn't that great of an approach if you're not going to stream the chunks back. You're going to hold the file within a Buffer which resides in memory, so its only a good solution for reasonably sized files.
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
对于流数据使用 HTTP 几乎总是更好的想法，因为它内置到协议中，你永远不需要一次性将数据加载到内存中你可以 pipe（）将文件流直接发送到响应。
HTTP Response Stream Example
Its almost always a better idea to use HTTP for streaming data since its built into the protocol and you'd never need to load the data into memory all at once since you can pipe() the file stream directly to the response.
这是一个非常基本的例子，没有响铃和口哨，只是为了演示如何 pipe（） a 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。
This is a very basic example without the bells and whistles and just is to demonstrate how to pipe() a stream.Readable to a http.ServerResponse. the example uses Express but it works the exact same way using http or https from the Node.js Core API.
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}`);
});
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