简单的接收文件上传下载（Express+Multer）

注意：Multer只能处理表单形式的文件上传

var express = require('express');
var app = express();
const fs = require('fs');
var multer  = require('multer');

//只能以Form形式上传name为mFile的文件
//var upload = multer({ dest: 'upload/'}).single('mFile');
var upload = multer({dest:'upload/'}).any();
app.get('/', function(req, res) {
    console.log("--------访问根目录--------");
  res.send('hello, express');
  res.end();
});

app.get('/download',function(req,res){
    console.log("---------访问下载路径-------------"); 
    var pathname = "/small.docx";
    var realPath = "assets" + pathname;
    fs.exists(realPath, function (exists) {
        if (!exists) {
            console.log("文件不存在");
            res.writeHead(404, {
                'Content-Type': 'text/plain'
            });

            res.write("This request URL " + pathname + " was not found on this server.");
            res.end();
        } else {
            console.log("文件存在");
            fs.readFile(realPath, "binary", function (err, file) {
                if (err) {
                    res.writeHead(500, {
                        'Content-Type': 'text/plain'
                    });
                    console.log("读取文件错误");
                    res.end(err);
                } else {
                    res.writeHead(200, {
                        'Content-Type': 'text/html'
                    });
                    console.log("读取文件完毕，正在发送......");

                    res.write(file, "binary");

                    res.end();
                    console.log("文件发送完毕");
                }
            });
        }
    });
});

app.post('/upload',function(req,res){
    console.log("---------访问上传路径-------------"); 

/** When using the "single"
      data come in "req.file" regardless of the attribute "name". **/
    upload(req, res, function (err) {
    //添加错误处理
     if (err) {
          console.log(err);
          return;
      } 
      req.file = req.files[0];
      var tmp_path = req.file.path;
      console.log(tmp_path);

      /** The original name of the uploaded file
          stored in the variable "originalname". **/
      var target_path = 'uploads/' + req.file.originalname;

      /** A better way to copy the uploaded file. **/
      console.log(target_path);


      if (!fs.existsSync('uploads/')) {
            fs.mkdirSync('uploads/');
      }

      var src = fs.createReadStream(tmp_path);
      var dest = fs.createWriteStream(target_path);
      src.pipe(dest);
      src.on('end', function() { 
        res.end(); 
      });
      src.on('error', function(err) { 
        
        res.end(); 
        console.log(err);
      });
        
    });


   
});

var port = 20001;
var hostname = '127.0.0.1';
app.listen(port,hostname,() => {
  console.log(`Server running at http://${hostname}:${port}/`);
});