在使用 multer 上传图像之前检查文件大小

Question

在将图像上传到磁盘之前，如何使用与图像传递相关的提交数据到服务器。这可能吗？如果没有，请给我另一个解决方案。
我想检查文件的大小，它应该至少为 4mp 分辨率，如果它的分辨率更小，则不应上传图像并发送错误消息

exports.uploadimg=(req,res,next)=>{
  
    uploadphoto(req, res, (err) => {
        if (err) {
            res.render("upload")
        }
        else {


    
            

          


           
            res.send("photo uloaded")
        }
    })

Answer 1

我认为您有一些多部分中间件（例如 connect-multiparty）读取 multipart/form-data 请求的请求负载。

此中间件会在 request 对象 (request.files) 上为您提供 files 对象。 files 对象的属性是每个文件上传字段的键。每个此类属性的值可以是对象（单个文件上传）或数组（多个文件上传）。嵌套在 files 对象中的每个对象都具有描述实际上传文件的属性，并允许您在以下中间件中运行您认为合适的检查。

// router declarations
const {Router} = require('express');
const multipart = require('connect-multipart');

const multipartMiddleware = multipart();

const validateFileSize = (file) => {
  /*
      Each file has the following property:

        fieldName - same as name - the field name for this file
        originalFilename - the filename that the user reports for the file
        path - the absolute path of the uploaded file on disk
        headers - the HTTP headers that were sent along with this file
        size - size of the file in bytes
    */
    // check against file size
    if (file.size < 4 * 1024 * 1024) throw new Error('File is too small');
}

const validateImageMiddleware = (req, res, next) => {
  // say we expected an upload field with key "productImage"
  const { files: { productImage } } = req;
  const isMultiple = Array.isArray(productImage);
  if (isMultiple) {
    productImage.forEach(validateFileSize);
  } else {
    validateFileSize(productImage);
  }
  // if we got here, the files were valid so we go to next handler
  next();
};

const myRouter = Router();
myRouter.post('/expect-file', multipartMiddleware, validateImageMiddleware, (req, res) => {
  // do whatever you want to do
  res.send('Success');
});