使用FormData和multer上传文件

Question

我已成功设法使用该multer模块将文件上传到节点服务器,方法是使用输入文件对话框选择文件,然后提交表单,但现在我需要而不是提交表单来创建FormData对象,并发送文件使用XMLHttpRequest,但它不工作,文件始终undefined在服务器端(路由器).

执行AJAX请求的函数是:

function uploadFile(fileToUpload, url) {

  var form_data = new FormData();

  form_data.append('track', fileToUpload, fileToUpload.name);

  // This function simply creates an XMLHttpRequest object
  // Opens the connection and sends form_data
  doJSONRequest("POST", "/tracks/upload", null, form_data, function(d) {
    console.log(d);
  })

}

请注意,fileToUpload这url是正确的,因为调用了正确的路由器方法.fileToUpload是File通过将文件从文件系统删除到dropzone,然后通过访问dataTransferdrop事件的属性获得的对象.

doJSONRequest是一个创建XMLHttpRequest对象并发送文件等的函数(如注释中所述).

function doJSONRequest(method, url, headers, data, callback){

  //all the arguments are mandatory
  if(arguments.length != 5) {
    throw new Error('Illegal argument count');
  }

  doRequestChecks(method, true, data);

  //create an ajax request
  var r = new XMLHttpRequest();

  //open a connection to the server using method on the url API
  r.open(method, url, true);

  //set the headers
  doRequestSetHeaders(r, method, headers);

  //wait for the response from the server
  r.onreadystatechange = function () {
    //correctly handle the errors based on the HTTP status returned by the called API
    if (r.readyState != 4 || (r.status != 200 && r.status != 201 && r.status != 204)){
      return;
    } else {
      if(isJSON(r.responseText))
        callback(JSON.parse(r.responseText));
      else if (callback !== null)
        callback();
    }
  };

  //set the data
  var dataToSend = null;
  if (!("undefined" == typeof data) 
    && !(data === null))
    dataToSend = JSON.stringify(data);

  //console.log(dataToSend)

  //send the request to the server
  r.send(dataToSend);
}

这是doRequestSetHeaders:

function doRequestSetHeaders(r, method, headers){

  //set the default JSON header according to the method parameter
  r.setRequestHeader("Accept", "application/json");

  if(method === "POST" || method === "PUT"){
    r.setRequestHeader("Content-Type", "application/json");
  }

  //set the additional headers
  if (!("undefined" == typeof headers) 
    && !(headers === null)){

    for(header in headers){
      //console.log("Set: " + header + ': '+ headers[header]);
      r.setRequestHeader(header, headers[header]);
    }

  }
}

我的路由器上传文件如下

// Code to manage upload of tracks
var multer = require('multer');
var uploadFolder = path.resolve(__dirname, "../../public/tracks_folder");

function validTrackFormat(trackMimeType) {
  // we could possibly accept other mimetypes...
  var mimetypes = ["audio/mp3"];
  return mimetypes.indexOf(trackMimeType) > -1;
}

function trackFileFilter(req, file, cb) {
  cb(null, validTrackFormat(file.mimetype));
}

var trackStorage = multer.diskStorage({
  // used to determine within which folder the uploaded files should be stored.
  destination: function(req, file, callback) {

    callback(null, uploadFolder);
  },

  filename: function(req, file, callback) {
    // req.body.name should contain the name of track
    callback(null, file.originalname);
  }
});

var upload = multer({
  storage: trackStorage,
  fileFilter: trackFileFilter
});


router.post('/upload', upload.single("track"), function(req, res) {
  console.log("Uploaded file: ", req.file); // Now it gives me undefined using Ajax!
  res.redirect("/"); // or /#trackuploader
});

我的猜测是multer不理解那fileToUpload是一个带有名字的文件track(不是吗？),即中间件upload.single("track")无法正常工作/解析或什么都没有,或者它可能根本无法使用FormData,在这种情况下它会是一团糟.通过保持使用multer会有什么替代方案？

如何使用AJAX和multer上传文件？

不要犹豫,询问您是否需要更多细节.

Answer 1

multer使用multipart/form-data内容类型的请求来上传文件.从您的doRequestSetHeaders函数中删除此位应该可以解决您的问题:

if(method === "POST" || method === "PUT"){
   r.setRequestHeader("Content-Type", "application/json");
}

您无需指定,content-type因为FormData对象已使用正确的编码类型.来自文档:

如果表单的编码类型设置为multipart/form-data,则传输的数据格式与表单的submit()方法用于发送数据的格式相同.

这是一个有效的例子.它假定有一个带有id的dropzone drop-zone和一个id为的上传按钮upload-button:

var dropArea  = document.getElementById("drop-zone");
var uploadBtn = document.getElementById("upload-button");
var files     = [];

uploadBtn.disabled = true;
uploadBtn.addEventListener("click", onUploadClick, false);

dropArea.addEventListener("dragenter", prevent, false);
dropArea.addEventListener("dragover",  prevent, false);
dropArea.addEventListener("drop", onFilesDropped, false);   

//----------------------------------------------------
function prevent(e){

    e.stopPropagation();
    e.preventDefault();
}

//----------------------------------------------------
function onFilesDropped(e){

    prevent(e);

    files = e.dataTransfer.files;

    if (files.length){
        uploadBtn.disabled = false;
    }
}

//----------------------------------------------------
function onUploadClick(e){

    if (files.length){
        sendFile(files[0]);
    }
}

//----------------------------------------------------
function sendFile(file){

    var formData = new FormData();
    var xhr      = new XMLHttpRequest();

    formData.append("track", file, file.name);

    xhr.open("POST", "http://localhost:3000/tracks/upload", true);

    xhr.onreadystatechange = function () {  
        if (xhr.readyState === 4) {  
            if (xhr.status === 200) {  
                console.log(xhr.responseText);
            } else {  
                console.error(xhr.statusText);  
            }  
        }  
    };

    xhr.send(formData);
}

服务器端代码是一个简单的快速应用程序,具有您提供的确切路由器代码.