JS实现可恢复的文件上传示例详解

let fileId = file.name + '-' + file.size + '-' + file.lastModified;

let response = await fetch('status', {
  headers: {
    'X-File-Id': fileId
  }
});
// 服务器已有的字节数
let startByte = +await response.text();

xhr.open("POST", "upload", true);
// 文件 id，以便服务器知道我们要恢复的是哪个文件
xhr.setRequestHeader('X-File-Id', fileId);
// 发送我们要从哪个字节开始恢复，因此服务器知道我们正在恢复
xhr.setRequestHeader('X-Start-Byte', startByte);
xhr.upload.onprogress = (e) => {
  console.log(`Uploaded ${startByte + e.loaded} of ${startByte + e.total}`);
};
// 文件可以是来自 input.files[0]，或者另一个源
xhr.send(file.slice(startByte));

let http = require('http');
let static = require('node-static');
let fileServer = new static.Server('.');
let path = require('path');
let fs = require('fs');
let debug = require('debug')('example:resume-upload');
let uploads = Object.create(null);
function onUpload(req, res) {
  let fileId = req.headers['x-file-id'];
  let startByte = +req.headers['x-start-byte'];
  if (!fileId) {
    res.writeHead(400, "No file id");
    res.end();
  }
  // 我们将“无处”保存文件
  let filePath = '/dev/null';
  // 可以改用真实路径，例如
  // let filePath = path.join('/tmp', fileId);
  debug("onUpload fileId: ", fileId);
  // 初始化一个新上传
  if (!uploads[fileId]) uploads[fileId] = {};
  let upload = uploads[fileId];
  debug("bytesReceived:" + upload.bytesReceived + " startByte:" + startByte)
  let fileStream;
  // 如果 startByte 为 0 或者没设置，创建一个新文件，否则检查大小并附加到现有的大小
  if (!startByte) {
    upload.bytesReceived = 0;
    fileStream = fs.createWriteStream(filePath, {
      flags: 'w'
    });
    debug("New file created: " + filePath);
  } else {
    // 我们也可以检查磁盘上的文件大小以确保
    if (upload.bytesReceived != startByte) {
      res.writeHead(400, "Wrong start byte");
      res.end(upload.bytesReceived);
      return;
    }
    // 附加到现有文件
    fileStream = fs.createWriteStream(filePath, {
      flags: 'a'
    });
    debug("File reopened: " + filePath);
  }
  req.on('data', function(data) {
    debug("bytes received", upload.bytesReceived);
    upload.bytesReceived += data.length;
  });
  // 将 request body 发送到文件
  req.pipe(fileStream);
  // 当请求完成，并且其所有数据都以写入完成
  fileStream.on('close', function() {
    if (upload.bytesReceived == req.headers['x-file-size']) {
      debug("Upload finished");
      delete uploads[fileId];
      // 可以在这里对上传的文件进行其他操作
      res.end("Success " + upload.bytesReceived);
    } else {
      // 连接断开，我们将未完成的文件保留在周围
      debug("File unfinished, stopped at " + upload.bytesReceived);
      res.end();
    }
  });
  // 如果发生 I/O error —— 完成请求
  fileStream.on('error', function(err) {
    debug("fileStream error");
    res.writeHead(500, "File error");
    res.end();
  });
}
function onStatus(req, res) {
  let fileId = req.headers['x-file-id'];
  let upload = uploads[fileId];
  debug("onStatus fileId:", fileId, " upload:", upload);
  if (!upload) {
    res.end("0")
  } else {
    res.end(String(upload.bytesReceived));
  }
}
function accept(req, res) {
  if (req.url == '/status') {
    onStatus(req, res);
  } else if (req.url == '/upload' && req.method == 'POST') {
    onUpload(req, res);
  } else {
    fileServer.serve(req, res);
  }
}
// -----------------------------------
if (!module.parent) {
  http.createServer(accept).listen(8080);
  console.log('Server listening at port 8080');
} else {
  exports.accept = accept;
}

class Uploader {
  constructor({file, onProgress}) {
    this.file = file;
    this.onProgress = onProgress;
    // 创建唯一标识文件的 fileId
    // 我们还可以添加用户会话标识符（如果有的话），以使其更具唯一性
    this.fileId = file.name + '-' + file.size + '-' + file.lastModified;
  }
  async getUploadedBytes() {
    let response = await fetch('status', {
      headers: {
        'X-File-Id': this.fileId
      }
    });
    if (response.status != 200) {
      throw new Error("Can't get uploaded bytes: " + response.statusText);
    }
    let text = await response.text();
    return +text;
  }
  async upload() {
    this.startByte = await this.getUploadedBytes();
    let xhr = this.xhr = new XMLHttpRequest();
    xhr.open("POST", "upload", true);
    // 发送文件 id，以便服务器知道要恢复哪个文件
    xhr.setRequestHeader('X-File-Id', this.fileId);
    // 发送我们要从哪个字节开始恢复，因此服务器知道我们正在恢复
    xhr.setRequestHeader('X-Start-Byte', this.startByte);
    xhr.upload.onprogress = (e) => {
      this.onProgress(this.startByte + e.loaded, this.startByte + e.total);
    };
    console.log("send the file, starting from", this.startByte);
    xhr.send(this.file.slice(this.startByte));
    // return
    //   true —— 如果上传成功，
    //   false —— 如果被中止
    // 出现 error 时将其抛出
    return await new Promise((resolve, reject) => {
      xhr.onload = xhr.onerror = () => {
        console.log("upload end status:" + xhr.status + " text:" + xhr.statusText);
        if (xhr.status == 200) {
          resolve(true);
        } else {
          reject(new Error("Upload failed: " + xhr.statusText));
        }
      };
      // onabort 仅在 xhr.abort() 被调用时触发
      xhr.onabort = () => resolve(false);
    });
  }
  stop() {
    if (this.xhr) {
      this.xhr.abort();
    }
  }
}

<!DOCTYPE HTML>
<script src="uploader.js"></script>
<form name="upload" method="POST" enctype="multipart/form-data" action="/upload">
  <input type="file" name="myfile">
  <input type="submit" name="submit" value="Upload (Resumes automatically)">
</form>
<button onclick="uploader.stop()">Stop upload</button>
<div id="log">Progress indication</div>
<script>
  function log(html) {
    document.getElementById('log').innerHTML = html;
    console.log(html);
  }
  function onProgress(loaded, total) {
    log("progress " + loaded + ' / ' + total);
  }
  let uploader;
  document.forms.upload.onsubmit = async function(e) {
    e.preventDefault();
    let file = this.elements.myfile.files[0];
    if (!file) return;
    uploader = new Uploader({file, onProgress});
    try {
      let uploaded = await uploader.upload();
      if (uploaded) {
        log('success');
      } else {
        log('stopped');
      }
    } catch(err) {
      console.error(err);
      log('error');
    }
  };
</script>