Nodejs advanced: file upload example based on express+multer

Overview

Image uploading is a frequently used function in web development, and the node community also has relatively complete support in this regard.

Commonly used open source components include multer, formidable, etc. With the help of these two open source components, image uploading can be easily accomplished.

This article mainly explains the following content, and subsequent chapters will dig deeper into the technical implementation details.

Basic example: Use express and multer to upload single or multiple images.

Commonly used API: Get information about uploaded images.

Advanced use: Customize the saved image path and name.

Environment initialization

is very simple, just one line of command.

npm install express multer multer --save

Below each example, there are the following two files

➜ upload-custom-filename git:(master) ✗ tree -L 1
.
├── app.js # 服务端代码，用来处理文件上传请求
├── form.html # 前端页面，用来上传文件

Basic example: single image upload

app.js.

var fs = require('fs');
var express = require('express');
var multer = require('multer')
 
var app = express();
var upload = multer({ dest: 'upload/' });
 
// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
  res.send({ret_code: '0'});
});
 
app.get('/form', function(req, res, next){
  var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
  res.send(form);
});
 
app.listen(3000);

form.html.

<form action="/upload-single" method="post" enctype="multipart/form-data">
  <h2 id="单图上传">单图上传</h2>
  <input type="file" name="logo">
  <input type="submit" value="提交">
</form>

Run the service.

node app.js

Visit http://127.0.0.1:3000/form, select the image, click "Submit", done. Then, you will see an additional image in the upload directory.

Basic example: multi-image upload

The code couldn’t be simpler, just change the previous upload.single('logo') to upload.array('logo', 2). Indicates: Supports uploading 2 images at the same time, and the name attribute is logo.

app.js.

   
var fs = require('fs');
var express = require('express');
var multer = require('multer')
 
var app = express();
var upload = multer({ dest: 'upload/' });
 
// 多图上传
app.post('/upload', upload.array('logo', 2), function(req, res, next){
  res.send({ret_code: '0'});
});
 
app.get('/form', function(req, res, next){
  var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
  res.send(form);
});
 
app.listen(3000);

form.html.

<form action="/upload-multi" method="post" enctype="multipart/form-data">
  <h2 id="多图上传">多图上传</h2>
  <input type="file" name="logos">
  <input type="file" name="logos">
  <input type="submit" value="提交">
</form>

The same test steps, no need to repeat them.

Get information about uploaded pictures

Many times, in addition to saving pictures on the server, we also need to do many other things, such as saving picture information into the database.

Commonly used information such as original file name, file type, file size, local save path, etc. With the help of multer, we can easily obtain this information.

This is still an example of single file upload. At this time, multer will write the file information to req.file, as shown in the following code.

app.js.

var fs = require('fs');
var express = require('express');
var multer = require('multer')
 
var app = express();
var upload = multer({ dest: 'upload/' });
 
// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
  var file = req.file;
 
  console.log('文件类型：%s', file.mimetype);
  console.log('原始文件名：%s', file.originalname);
  console.log('文件大小：%s', file.size);
  console.log('文件保存路径：%s', file.path);
 
  res.send({ret_code: '0'});
});
 
app.get('/form', function(req, res, next){
  var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
  res.send(form);
});
 
app.listen(3000);

form.html.

<form action="/upload" method="post" enctype="multipart/form-data">
  <h2 id="单图上传">单图上传</h2>
  <input type="file" name="logo">
  <input type="submit" value="提交">
</form>

Start the service and upload the file, you will see the information printed on the console.

File type: image/png
Original file name: 1.png
File size: 18379
File saving path: upload/b7e4bb22375695d92689e45b551873d9

Customized file upload path, name

Sometimes, we want to customize the file The upload path, name, and multer can also be easily implemented.

Customizing the local saving path

is very simple. For example, if we want to upload files to the my-upload directory, just modify the dest configuration item.

var upload = multer({ dest: 'upload/' });

Under the above configuration, all resources are saved in the same directory. Sometimes we need to personalize settings for different files, then you can refer to the next section.

Customize the locally saved file name

The code is a little longer, but the same simple. multer provides the storage parameter to personalize the path and file name of resource saving.

Usage notes are as follows:

destination: Set the saving path of the resource. Note that without this configuration item, it will be saved under /tmp/uploads by default. Additionally, the path needs to be created yourself.

filename: Set the file name of the resource saved locally.

app.js.

var fs = require('fs');
var express = require('express');
var multer = require('multer')
 
var app = express();
 
var createFolder = function(folder){
  try{
    fs.accessSync(folder);
  }catch(e){
    fs.mkdirSync(folder);
  }
};
 
var uploadFolder = './upload/';
 
createFolder(uploadFolder);
 
// 通过 filename 属性定制
var storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, uploadFolder);  // 保存的路径，备注：需要自己创建
  },
  filename: function (req, file, cb) {
    // 将保存文件名设置为 字段名 + 时间戳，比如 logo-1478521468943
    cb(null, file.fieldname + '-' + Date.now());
  }
});
 
// 通过 storage 选项来对 上传行为 进行定制化
var upload = multer({ storage: storage })
 
// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
  var file = req.file;
  res.send({ret_code: '0'});
});
 
app.get('/form', function(req, res, next){
  var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
  res.send(form);
});
 
app.listen(3000);

form.html.

<form action="/upload" method="post" enctype="multipart/form-data">
  <h2 id="单图上传">单图上传</h2>
  <input type="file" name="logo">
  <input type="submit" value="提交">
</form>

I won’t go into details about the test steps, just visit it and you will know the effect.

Written at the back

This article introduces the basic usage of multer and does not cover too many principles. As the saying goes, it is better to teach a man to fish than to teach him to fish. In the following chapters, the details of file uploading will be excavated so that readers can have a deeper understanding of file uploading.