使用 FormData 和 multer 上传文件

Question

我已经成功地使用 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，创建一个 FormData 对象，并使用 XMLHttpRequest 发送文件，但它不起作用，文件总是 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 已定义并且 url 是正确的，因为调用了正确的路由器方法。 fileToUpload 是一个 File 对象，通过将文件从文件系统拖放到拖放区，然后通过访问拖放事件的 dataTransfer 属性获得。

doJSONRequest 是一个创建 XMLHttpRequest 对象并发送文件等的函数（如评论中所述）。

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);
}

这里是 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]);
    }

  }
}

而我的路由器上传文件是这样的

// 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 fileToUpload 是一个名为 track 的文件（不是吗？），即中间件 upload.single("track") 是working/parsing 不正确或什么都没有，或者它可能根本不适用于 FormData，在那种情况下它会一团糟。继续使用 multer 的替代方案是什么？

如何使用 AJAX 和 multer 上传文件？

如果您需要更多详细信息，请随时询问。

Answer 1

multer 使用 multipart/form-data 内容类型请求上传文件。从你的 doRequestSetHeaders 函数中删除这个位应该可以解决你的问题：

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

您不需要指定 content-type，因为 FormData 对象已经使用了正确的编码类型。来自 docs:

The transmitted data is in the same format that the form's submit() method would use to send the data if the form's encoding type were set to multipart/form-data.

这是一个工作示例。它假定有一个 ID 为 drop-zone 的拖放区和一个 ID 为 upload-button:

的上传按钮

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。

Answer 2

到post一个被multer接受的FormData对象上传函数应该是这样的：

function uploadFile(fileToUpload, url) { 
    var formData = new FormData();
    //append file here 
    formData.append('file', fileToUpload, fileToUpload.name);
    //and append the other fields as an object here
    /* var user = {name: 'name from the form',
        email: 'email from the form' 
        etc...       
    }*/
    formData.append('user', user);

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

使用 FormData 和 multer 上传文件

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