微信小程序环境下将文件上传到OSS的方法步骤

步骤 1： 配置 Bucket 跨域

客户端进行表单直传到 OSS 时，会从浏览器向 OSS 发送带有 Origin 的请求消息。OSS 对带有 Origin 头的请求消息会进行跨域规则（CORS）的验证。因此需要为 Bucket 设置跨域规则以支持 Post 方法。

步骤 2：配置外网域名到小程序的上传域名白名单中

通过 OSS 控制台查看外网域名。

登录微信小程序平台，配置小程序的上传域名白名单。

步骤 3：使用 Web 端直传实践方案 Demo 进行上传测试

下载应用服务器代码

修改 Demo 中 upload.js 的密钥和地址。

进行上传测试。

获取上传需要的签名（signature）和加密策略（policy）

使用微信小程序上传图片

使用 chooseImage API 进行图片选择，然后调用 uploadFile 进行文件上传

帮助文档

upload.js

accessid= '';accesskey= '';host = '';g_dirname = ''g_object_name = ''g_object_name_type = ''now = timestamp = Date.parse(new Date()) / 1000; var policyText = {  "expiration": "2020-01-01T12:00:00.000Z", //设置该Policy的失效时间，超过这个失效时间之后，就没有办法通过这个policy上传文件了  "conditions": [  ["content-length-range", 0, 1048576000] // 设置上传文件的大小限制  ]};var policyBase64 = Base64.encode(JSON.stringify(policyText))message = policyBase64var bytes = Crypto.HMAC(Crypto.SHA1, message, accesskey, { asBytes: true }) ;var signature = Crypto.util.bytesToBase64(bytes);function check_object_radio() {  var tt = document.getElementsByName('myradio');  for (var i = 0; i < tt.length ; i++ )  {    if(tt[i].checked)    {      g_object_name_type = tt[i].value;      break;    }  }}function get_dirname(){  dir = document.getElementById("dirname").value;  if (dir != '' && dir.indexOf('/') != dir.length - 1)  {    dir = dir + '/'  }  //alert(dir)  g_dirname = dir}function random_string(len) {　　len = len || 32;　　var chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678';  　　var maxPos = chars.length;　　var pwd = '';　　for (i = 0; i < len; i++) {  　　pwd += chars.charAt(Math.floor(Math.random() * maxPos));  }  return pwd;}function get_suffix(filename) {  pos = filename.lastIndexOf('.')  suffix = ''  if (pos != -1) {    suffix = filename.substring(pos)  }  return suffix;}function calculate_object_name(filename){  if (g_object_name_type == 'local_name')  {    g_object_name += "${filename}"  }  else if (g_object_name_type == 'random_name')  {    suffix = get_suffix(filename)    g_object_name = g_dirname + random_string(10) + suffix  }  return ''}function get_uploaded_object_name(filename){  if (g_object_name_type == 'local_name')  {    tmp_name = g_object_name    tmp_name = tmp_name.replace("${filename}", filename);    return tmp_name  }  else if(g_object_name_type == 'random_name')  {    return g_object_name  }}function set_upload_param(up, filename, ret){  g_object_name = g_dirname;  if (filename != '') {    suffix = get_suffix(filename)    calculate_object_name(filename)  }  new_multipart_params = {    'key' : g_object_name,    'policy': policyBase64,    'OSSAccessKeyId': accessid,     'success_action_status' : '200', //让服务端返回200,不然，默认会返回204    'signature': signature,  };  up.setOption({    'url': host,    'multipart_params': new_multipart_params  });  up.start();}var uploader = new plupload.Uploader({  runtimes : 'html5,flash,silverlight,html4',  browse_button : 'selectfiles',   //multi_selection: false,  container: document.getElementById('container'),  flash_swf_url : 'lib/plupload-2.1.2/js/Moxie.swf',  silverlight_xap_url : 'lib/plupload-2.1.2/js/Moxie.xap',  url : 'http://oss.aliyuncs.com',  init: {    PostInit: function() {      document.getElementById('ossfile').innerHTML = '';      document.getElementById('postfiles').onclick = function() {      set_upload_param(uploader, '', false);      return false;      };    },    FilesAdded: function(up, files) {      plupload.each(files, function(file) {        document.getElementById('ossfile').innerHTML += '<div id="' + file.id + '">' + file.name + ' (' + plupload.formatSize(file.size) + ')<b></b>'        +'<div class="progress"><div class="progress-bar" style="width: 0%"></div></div>'        +'</div>';      });    },    BeforeUpload: function(up, file) {      check_object_radio();      get_dirname();      set_upload_param(up, file.name, true);    },    UploadProgress: function(up, file) {      var d = document.getElementById(file.id);      d.getElementsByTagName('b')[0].innerHTML = '<span>' + file.percent + "%</span>";      var prog = d.getElementsByTagName('div')[0];      var progBar = prog.getElementsByTagName('div')[0]      progBar.style.width= 2*file.percent+'px';      progBar.setAttribute('aria-valuenow', file.percent);    },    FileUploaded: function(up, file, info) {      if (info.status == 200)      {        document.getElementById(file.id).getElementsByTagName('b')[0].innerHTML = 'upload to oss success, object name:' + get_uploaded_object_name(file.name);      }      else      {        document.getElementById(file.id).getElementsByTagName('b')[0].innerHTML = info.response;      }     },    Error: function(up, err) {      document.getElementById('console').appendChild(document.createTextNode("/nError xml:" + err.response));    }  }});uploader.init();