diff --git a/README.md b/README.md
index 0e906634..7cfb1a6a 100644
--- a/README.md
+++ b/README.md
@@ -65,13 +65,13 @@ Most of the magic for Flow.js happens in the user's browser, but files still nee
 
 To handle the state of upload chunks, a number of extra parameters are sent along with all requests:
 
-* `flowChunkNumber`: The index of the chunk in the current upload. First chunk is `1` (no base-0 counting here).
-* `flowTotalChunks`: The total number of chunks.  
-* `flowChunkSize`: The general chunk size. Using this value and `flowTotalSize` you can calculate the total number of chunks. Please note that the size of the data received in the HTTP might be lower than `flowChunkSize` of this for the last chunk for a file.
-* `flowTotalSize`: The total file size.
-* `flowIdentifier`: A unique identifier for the file contained in the request.
-* `flowFilename`: The original file name (since a bug in Firefox results in the file name not being transmitted in chunk multipart posts).
-* `flowRelativePath`: The file's relative path when selecting a directory (defaults to file name in all browsers except Chrome).
+* `chunkNumber`: The index of the chunk in the current upload. First chunk is `1` (no base-0 counting here).
+* `totalChunks`: The total number of chunks.  
+* `chunkSize`: The general chunk size. Using this value and `totalSize` you can calculate the total number of chunks. Please note that the size of the data received in the HTTP might be lower than `chunkSize` of this for the last chunk for a file.
+* `totalSize`: The total file size.
+* `requestId`: A unique identifier for the file contained in the request.
+* `filename`: The original file name (since a bug in Firefox results in the file name not being transmitted in chunk multipart posts).
+* `relativePath`: The file's relative path when selecting a directory (defaults to file name in all browsers except Chrome).
 
 You should allow for the same chunk to be uploaded more than once; this isn't standard behaviour, but on an unstable network environment it could happen, and this case is exactly what Flow.js is designed for.
 
@@ -195,6 +195,7 @@ added.
 * `.fileRetry(file, chunk)` Something went wrong during upload of a specific file, uploading is being 
 retried.
 * `.fileError(file, message, chunk)` An error occurred during upload of a specific file.
+* `.readErrors(files, folders, event)` This event fires before fileAdded or filesAdded events only if errors occur while reading files or folders. First argument `files` is collection of files read errors, second argument `folders` is collection of folder read errors.
 * `.uploadStart()` Upload has been started on the Flow object.
 * `.complete()` Uploading completed.
 * `.progress()` Uploading progress.
diff --git a/dist/flow.js b/dist/flow.js
index e61f0a75..b4ace2aa 100644
--- a/dist/flow.js
+++ b/dist/flow.js
@@ -230,55 +230,109 @@
      */
     webkitReadDataTransfer: function (event) {
       var $ = this;
-      var queue = event.dataTransfer.items.length;
-      var files = [];
-      each(event.dataTransfer.items, function (item) {
-        var entry = item.webkitGetAsEntry();
-        if (!entry) {
-          decrement();
-          return ;
+      getEntries(event.dataTransfer.items).then(function (result) {
+        getFiles(result.files).then(function (entries) {
+          var files = [];
+          var errors = [];
+          each(entries, function (entry) {
+            if (entry.error) {
+              errors.push(entry);
+            } else {
+              files.push(entry);
+            }
+          });
+          if (result.errors.length || errors.length) {
+            $.fire('readErrors', errors, result.errors, event);
+          }
+          if (files.length) {
+            $.addFiles(files, event);
+          }
+        });
+      });
+      function getEntries(items) {
+        var files = [];
+        var errors = [];
+        var promises = [];
+
+        function readEntry(entry, promises) {
+          if (entry.isFile) {
+            files.push(entry);
+          } else if (entry.isDirectory) {
+            promises.push(readDirectory(entry));
+          }
         }
-        if (entry.isFile) {
-          // due to a bug in Chrome's File System API impl - #149735
-          fileReadSuccess(item.getAsFile(), entry.fullPath);
-        } else {
-          readDirectory(entry.createReader());
+
+        function readDirectory(entry) {
+          var reader = entry.createReader();
+          return new Promise(function (resolve, reject) {
+            var promises = [];
+            readEntries(entry, reader, promises, resolve);
+          });
         }
-      });
-      function readDirectory(reader) {
-        reader.readEntries(function (entries) {
-          if (entries.length) {
-            queue += entries.length;
-            each(entries, function(entry) {
-              if (entry.isFile) {
-                var fullPath = entry.fullPath;
-                entry.file(function (file) {
-                  fileReadSuccess(file, fullPath);
-                }, readError);
-              } else if (entry.isDirectory) {
-                readDirectory(entry.createReader());
-              }
+
+        function readEntries(entry, reader, promises, resolve) {
+          reader.readEntries(function (entries) {
+            if (entries.length) {
+              var promises2 = [];
+              each(entries, function (entry2) {
+                readEntry(entry2, promises2);
+              });
+              promises.push(Promise.all(promises2));
+              readEntries(entry, reader, promises, resolve);
+              return;
+            }
+            resolve(Promise.all(promises));
+          }, function (error) {
+            errors.push({
+              path: entry.fullPath,
+              error: error
             });
-            readDirectory(reader);
-          } else {
-            decrement();
+            resolve(promises);
+          });
+        }
+
+        each(items, function (item) {
+          var entry = item.webkitGetAsEntry();
+          if (!entry) {
+            return;
           }
-        }, readError);
+          if (entry.isFile) {
+            // due to a bug in Chrome's File System API impl - #149735
+            files.push(getFile(item.getAsFile(), entry.fullPath));
+            return;
+          }
+          readEntry(entry, promises);
+        });
+
+        return new Promise(function (resolve, reject) {
+          return Promise.all(promises).then(function () {
+            resolve({ files: files, errors: errors });
+          });
+        });
       }
-      function fileReadSuccess(file, fullPath) {
+      function getFiles(entries) {
+        return Promise.all(entries.map(function (entry) {
+          return new Promise(function (resolve, reject) {
+            if (entry.file) {
+              var fullPath = entry.fullPath;
+              entry.file(function (file) {
+                resolve(getFile(file, fullPath));
+              }, function (file) {
+                resolve({
+                  path: entry.fullPath,
+                  error: file
+                });
+              });
+            } else {
+              resolve(entry);
+            }
+          });
+        }));
+      }
+      function getFile(file, fullPath) {
         // relative path should not start with "/"
         file.relativePath = fullPath.substring(1);
-        files.push(file);
-        decrement();
-      }
-      function readError(fileError) {
-        decrement();
-        throw fileError;
-      }
-      function decrement() {
-        if (--queue == 0) {
-          $.addFiles(files, event);
-        }
+        return file;
       }
     },
 
@@ -588,8 +642,12 @@
      * @param {Event} [event] event is optional
      */
     addFiles: function (fileList, event) {
+      var $ = this;
       var files = [];
-      each(fileList, function (file) {
+      var errors = [];
+      var promises = [];
+
+      function addFile(file) {        
         // https://github.com/flowjs/flow.js/issues/55
         if ((!ie10plus || ie10plus && file.size > 0) && !(file.size % 4096 === 0 && (file.name === '.' || file.fileName === '.'))) {
           var uniqueIdentifier = this.generateUniqueIdentifier(file);
@@ -600,16 +658,54 @@
             }
           }
         }
-      }, this);
-      if (this.fire('filesAdded', files, event)) {
-        each(files, function (file) {
-          if (this.opts.singleFile && this.files.length > 0) {
-            this.removeFile(this.files[0]);
-          }
-          this.files.push(file);
-        }, this);
-        this.fire('filesSubmitted', files, event);
       }
+      
+      /** 
+       * Chrome's FileSystem API has a bug that files from dropped folders or files from input dialog's selected folder,
+       * with read errors (has absolute paths which exceed 260 chars) will have zero file size.
+       */
+      function validateFile(file) {
+        // files with size greater than zero can upload
+        if (file.size > 0) {
+          addFile.bind($)(file);
+          return;
+        }
+        
+        // try to read from from zero size file,
+        // if error occurs than file cannot be uploaded
+        promises.push(new Promise(function (resolve, reject) {
+          var reader = new FileReader();
+          reader.onloadend = function () {
+            if (reader.error) {
+              errors.push({
+                path: file.webkitRelativePath || file.name,
+                error: reader.error
+              });
+            } else {
+              addFile.bind($)(file);
+            }
+            resolve();
+          }.bind($);
+          reader.readAsArrayBuffer(file);
+        }));
+      }
+
+      each(fileList, validateFile);
+
+      Promise.all(promises).then(function () {
+        if (errors.length) {
+          this.fire('readErrors', errors, [], event);
+        }
+        if (this.fire('filesAdded', files, event)) {
+          each(files, function (file) {
+            if (this.opts.singleFile && this.files.length > 0) {
+              this.removeFile(this.files[0]);
+            }
+            this.files.push(file);
+          }, this);
+          this.fire('filesSubmitted', files, event);
+        }
+      }.bind(this));
     },
 
 
@@ -716,12 +812,6 @@
      */
     this.flowObj = flowObj;
 
-    /**
-     * Used to store the bytes read
-     * @type {Blob|string}
-     */
-    this.bytes = null;
-
     /**
      * Reference to file
      * @type {File}
@@ -937,9 +1027,16 @@
      */
     bootstrap: function () {
       if (typeof this.flowObj.opts.initFileFn === "function") {
-        this.flowObj.opts.initFileFn(this);
+        var ret = this.flowObj.opts.initFileFn(this);
+        if (ret && 'then' in ret) {
+          ret.then(this._bootstrap.bind(this));
+          return;
+        }
       }
+      this._bootstrap();
+    },
 
+    _bootstrap: function () {
       this.abort(true);
       this.error = false;
       // Rebuild stack of chunks from file
@@ -1144,6 +1241,11 @@
      */
     this.readState = 0;
 
+    /**
+     * Used to store the bytes read
+     * @type {Blob|string}
+     */
+    this.bytes = undefined;
 
     /**
      * Bytes transferred from total request size
@@ -1280,14 +1382,14 @@
      */
     getParams: function () {
       return {
-        flowChunkNumber: this.offset + 1,
-        flowChunkSize: this.chunkSize,
-        flowCurrentChunkSize: this.endByte - this.startByte,
-        flowTotalSize: this.fileObj.size,
-        flowIdentifier: this.fileObj.uniqueIdentifier,
-        flowFilename: this.fileObj.name,
-        flowRelativePath: this.fileObj.relativePath,
-        flowTotalChunks: this.fileObj.chunks.length
+        chunkNumber: this.offset + 1,
+        chunkSize: this.chunkSize,
+        currentChunkSize: this.endByte - this.startByte,
+        totalSize: this.fileObj.size,
+        requestId: this.fileObj.uniqueIdentifier,
+        filename: this.fileObj.name,
+        relativePath: this.fileObj.relativePath,
+        totalChunks: this.fileObj.chunks.length
       };
     },
 
diff --git a/dist/flow.min.js b/dist/flow.min.js
index ef301778..1db27a62 100644
--- a/dist/flow.min.js
+++ b/dist/flow.min.js
@@ -1,2 +1,2 @@
 /*! @flowjs/flow.js 2.14.1 */
-!function(a,b,c){"use strict";function d(b){if(this.support=!("undefined"==typeof File||"undefined"==typeof Blob||"undefined"==typeof FileList||!Blob.prototype.slice&&!Blob.prototype.webkitSlice&&!Blob.prototype.mozSlice),this.support){this.supportDirectory=/Chrome/.test(a.navigator.userAgent)||/Firefox/.test(a.navigator.userAgent)||/Edge/.test(a.navigator.userAgent),this.files=[],this.defaults={chunkSize:1048576,forceChunkSize:!1,simultaneousUploads:3,singleFile:!1,fileParameterName:"file",progressCallbacksInterval:500,speedSmoothingFactor:.1,query:{},headers:{},withCredentials:!1,preprocess:null,changeRawDataBeforeSend:null,method:"multipart",testMethod:"GET",uploadMethod:"POST",prioritizeFirstAndLastChunk:!1,allowDuplicateUploads:!1,target:"/",testChunks:!0,generateUniqueIdentifier:null,maxChunkRetries:0,chunkRetryInterval:null,permanentErrors:[404,413,415,500,501],successStatuses:[200,201,202],onDropStopPropagation:!1,initFileFn:null,readFileFn:f},this.opts={},this.events={};var c=this;this.onDrop=function(a){c.opts.onDropStopPropagation&&a.stopPropagation(),a.preventDefault();var b=a.dataTransfer;b.items&&b.items[0]&&b.items[0].webkitGetAsEntry?c.webkitReadDataTransfer(a):c.addFiles(b.files,a)},this.preventEvent=function(a){a.preventDefault()},this.opts=d.extend({},this.defaults,b||{})}}function e(a,b,d){this.flowObj=a,this.bytes=null,this.file=b,this.name=b.fileName||b.name,this.size=b.size,this.relativePath=b.relativePath||b.webkitRelativePath||this.name,this.uniqueIdentifier=d===c?a.generateUniqueIdentifier(b):d,this.chunkSize=0,this.chunks=[],this.paused=!1,this.error=!1,this.averageSpeed=0,this.currentSpeed=0,this._lastProgressCallback=Date.now(),this._prevUploadedSize=0,this._prevProgress=0,this.bootstrap()}function f(a,b,c,d,e){var f="slice";a.file.slice?f="slice":a.file.mozSlice?f="mozSlice":a.file.webkitSlice&&(f="webkitSlice"),e.readFinished(a.file[f](b,c,d))}function g(a,b,c){this.flowObj=a,this.fileObj=b,this.offset=c,this.tested=!1,this.retries=0,this.pendingRetry=!1,this.preprocessState=0,this.readState=0,this.loaded=0,this.total=0,this.chunkSize=this.fileObj.chunkSize,this.startByte=this.offset*this.chunkSize,this.filename=null,this.computeEndByte=function(){var a=Math.min(this.fileObj.size,(this.offset+1)*this.chunkSize);return this.fileObj.size-a<this.chunkSize&&!this.flowObj.opts.forceChunkSize&&(a=this.fileObj.size),a},this.endByte=this.computeEndByte(),this.xhr=null;var d=this;this.event=function(a,b){b=Array.prototype.slice.call(arguments),b.unshift(d),d.fileObj.chunkEvent.apply(d.fileObj,b)},this.progressHandler=function(a){a.lengthComputable&&(d.loaded=a.loaded,d.total=a.total),d.event("progress",a)},this.testHandler=function(a){var b=d.status(!0);"error"===b?(d.event(b,d.message()),d.flowObj.uploadNextChunk()):"success"===b?(d.tested=!0,d.event(b,d.message()),d.flowObj.uploadNextChunk()):d.fileObj.paused||(d.tested=!0,d.send())},this.doneHandler=function(a){var b=d.status();if("success"===b||"error"===b)delete this.data,d.event(b,d.message()),d.flowObj.uploadNextChunk();else if(!d.fileObj.paused){d.event("retry",d.message()),d.pendingRetry=!0,d.abort(),d.retries++;var c=d.flowObj.opts.chunkRetryInterval;null!==c?setTimeout(function(){d.send()},c):d.send()}}}function h(a,b){var c=a.indexOf(b);c>-1&&a.splice(c,1)}function i(a,b){return"function"==typeof a&&(b=Array.prototype.slice.call(arguments),a=a.apply(null,b.slice(1))),a}function j(a,b){setTimeout(a.bind(b),0)}function k(a,b){return l(arguments,function(b){b!==a&&l(b,function(b,c){a[c]=b})}),a}function l(a,b,c){if(a){var d;if("undefined"!=typeof a.length){for(d=0;d<a.length;d++)if(b.call(c,a[d],d)===!1)return}else for(d in a)if(a.hasOwnProperty(d)&&b.call(c,a[d],d)===!1)return}}if(!a||!b)return void console.warn("Flowjs needs window and document objects to work");var m=a.navigator.msPointerEnabled;d.prototype={on:function(a,b){a=a.toLowerCase(),this.events.hasOwnProperty(a)||(this.events[a]=[]),this.events[a].push(b)},off:function(a,b){a!==c?(a=a.toLowerCase(),b!==c?this.events.hasOwnProperty(a)&&h(this.events[a],b):delete this.events[a]):this.events={}},fire:function(a,b){b=Array.prototype.slice.call(arguments),a=a.toLowerCase();var c=!1;return this.events.hasOwnProperty(a)&&l(this.events[a],function(a){c=a.apply(this,b.slice(1))===!1||c},this),"catchall"!=a&&(b.unshift("catchAll"),c=this.fire.apply(this,b)===!1||c),!c},webkitReadDataTransfer:function(a){function b(a){a.readEntries(function(f){f.length?(g+=f.length,l(f,function(a){if(a.isFile){var e=a.fullPath;a.file(function(a){c(a,e)},d)}else a.isDirectory&&b(a.createReader())}),b(a)):e()},d)}function c(a,b){a.relativePath=b.substring(1),h.push(a),e()}function d(a){throw e(),a}function e(){0==--g&&f.addFiles(h,a)}var f=this,g=a.dataTransfer.items.length,h=[];l(a.dataTransfer.items,function(a){var d=a.webkitGetAsEntry();return d?void(d.isFile?c(a.getAsFile(),d.fullPath):b(d.createReader())):void e()})},generateUniqueIdentifier:function(a){var b=this.opts.generateUniqueIdentifier;if("function"==typeof b)return b(a);var c=a.relativePath||a.webkitRelativePath||a.fileName||a.name;return a.size+"-"+c.replace(/[^0-9a-zA-Z_-]/gim,"")},uploadNextChunk:function(a){var b=!1;if(this.opts.prioritizeFirstAndLastChunk&&(l(this.files,function(a){return!a.paused&&a.chunks.length&&"pending"===a.chunks[0].status()?(a.chunks[0].send(),b=!0,!1):!a.paused&&a.chunks.length>1&&"pending"===a.chunks[a.chunks.length-1].status()?(a.chunks[a.chunks.length-1].send(),b=!0,!1):void 0}),b))return b;if(l(this.files,function(a){if(a.paused||l(a.chunks,function(a){if("pending"===a.status())return a.send(),b=!0,!1}),b)return!1}),b)return!0;var c=!1;return l(this.files,function(a){if(!a.isComplete())return c=!0,!1}),c||a||j(function(){this.fire("complete")},this),!1},assignBrowse:function(a,c,d,e){a instanceof Element&&(a=[a]),l(a,function(a){var f;"INPUT"===a.tagName&&"file"===a.type?f=a:(f=b.createElement("input"),f.setAttribute("type","file"),k(f.style,{visibility:"hidden",position:"absolute",width:"1px",height:"1px"}),a.appendChild(f),a.addEventListener("click",function(){f.click()},!1)),this.opts.singleFile||d||f.setAttribute("multiple","multiple"),c&&f.setAttribute("webkitdirectory","webkitdirectory"),l(e,function(a,b){f.setAttribute(b,a)});var g=this;f.addEventListener("change",function(a){a.target.value&&(g.addFiles(a.target.files,a),a.target.value="")},!1)},this)},assignDrop:function(a){"undefined"==typeof a.length&&(a=[a]),l(a,function(a){a.addEventListener("dragover",this.preventEvent,!1),a.addEventListener("dragenter",this.preventEvent,!1),a.addEventListener("drop",this.onDrop,!1)},this)},unAssignDrop:function(a){"undefined"==typeof a.length&&(a=[a]),l(a,function(a){a.removeEventListener("dragover",this.preventEvent),a.removeEventListener("dragenter",this.preventEvent),a.removeEventListener("drop",this.onDrop)},this)},isUploading:function(){var a=!1;return l(this.files,function(b){if(b.isUploading())return a=!0,!1}),a},_shouldUploadNext:function(){var a=0,b=!0,c=this.opts.simultaneousUploads;return l(this.files,function(d){l(d.chunks,function(d){if("uploading"===d.status()&&(a++,a>=c))return b=!1,!1})}),b&&a},upload:function(){var a=this._shouldUploadNext();if(a!==!1){this.fire("uploadStart");for(var b=!1,c=1;c<=this.opts.simultaneousUploads-a;c++)b=this.uploadNextChunk(!0)||b;b||j(function(){this.fire("complete")},this)}},resume:function(){l(this.files,function(a){a.isComplete()||a.resume()})},pause:function(){l(this.files,function(a){a.pause()})},cancel:function(){for(var a=this.files.length-1;a>=0;a--)this.files[a].cancel()},progress:function(){var a=0,b=0;return l(this.files,function(c){a+=c.progress()*c.size,b+=c.size}),b>0?a/b:0},addFile:function(a,b){this.addFiles([a],b)},addFiles:function(a,b){var c=[];l(a,function(a){if((!m||m&&a.size>0)&&(a.size%4096!==0||"."!==a.name&&"."!==a.fileName)){var d=this.generateUniqueIdentifier(a);if(this.opts.allowDuplicateUploads||!this.getFromUniqueIdentifier(d)){var f=new e(this,a,d);this.fire("fileAdded",f,b)&&c.push(f)}}},this),this.fire("filesAdded",c,b)&&(l(c,function(a){this.opts.singleFile&&this.files.length>0&&this.removeFile(this.files[0]),this.files.push(a)},this),this.fire("filesSubmitted",c,b))},removeFile:function(a){for(var b=this.files.length-1;b>=0;b--)this.files[b]===a&&(this.files.splice(b,1),a.abort(),this.fire("fileRemoved",a))},getFromUniqueIdentifier:function(a){var b=!1;return l(this.files,function(c){c.uniqueIdentifier===a&&(b=c)}),b},getSize:function(){var a=0;return l(this.files,function(b){a+=b.size}),a},sizeUploaded:function(){var a=0;return l(this.files,function(b){a+=b.sizeUploaded()}),a},timeRemaining:function(){var a=0,b=0;return l(this.files,function(c){c.paused||c.error||(a+=c.size-c.sizeUploaded(),b+=c.averageSpeed)}),a&&!b?Number.POSITIVE_INFINITY:a||b?Math.floor(a/b):0}},e.prototype={measureSpeed:function(){var a=Date.now()-this._lastProgressCallback;if(a){var b=this.flowObj.opts.speedSmoothingFactor,c=this.sizeUploaded();this.currentSpeed=Math.max((c-this._prevUploadedSize)/a*1e3,0),this.averageSpeed=b*this.currentSpeed+(1-b)*this.averageSpeed,this._prevUploadedSize=c}},chunkEvent:function(a,b,c){switch(b){case"progress":if(Date.now()-this._lastProgressCallback<this.flowObj.opts.progressCallbacksInterval)break;this.measureSpeed(),this.flowObj.fire("fileProgress",this,a),this.flowObj.fire("progress"),this._lastProgressCallback=Date.now();break;case"error":this.error=!0,this.abort(!0),this.flowObj.fire("fileError",this,c,a),this.flowObj.fire("error",c,this,a);break;case"success":if(this.error)return;this.measureSpeed(),this.flowObj.fire("fileProgress",this,a),this.flowObj.fire("progress"),this._lastProgressCallback=Date.now(),this.isComplete()&&(this.currentSpeed=0,this.averageSpeed=0,this.flowObj.fire("fileSuccess",this,c,a));break;case"retry":this.flowObj.fire("fileRetry",this,a)}},pause:function(){this.paused=!0,this.abort()},resume:function(){this.paused=!1,this.flowObj.upload()},abort:function(a){this.currentSpeed=0,this.averageSpeed=0;var b=this.chunks;a&&(this.chunks=[]),l(b,function(a){"uploading"===a.status()&&(a.abort(),this.flowObj.uploadNextChunk())},this)},cancel:function(){this.flowObj.removeFile(this)},retry:function(){this.bootstrap(),this.flowObj.upload()},bootstrap:function(){"function"==typeof this.flowObj.opts.initFileFn&&this.flowObj.opts.initFileFn(this),this.abort(!0),this.error=!1,this._prevProgress=0;var a=this.flowObj.opts.forceChunkSize?Math.ceil:Math.floor;this.chunkSize=i(this.flowObj.opts.chunkSize,this);for(var b=Math.max(a(this.size/this.chunkSize),1),c=0;c<b;c++)this.chunks.push(new g(this.flowObj,this,c))},progress:function(){if(this.error)return 1;if(1===this.chunks.length)return this._prevProgress=Math.max(this._prevProgress,this.chunks[0].progress()),this._prevProgress;var a=0;l(this.chunks,function(b){a+=b.progress()*(b.endByte-b.startByte)});var b=a/this.size;return this._prevProgress=Math.max(this._prevProgress,b>.9999?1:b),this._prevProgress},isUploading:function(){var a=!1;return l(this.chunks,function(b){if("uploading"===b.status())return a=!0,!1}),a},isComplete:function(){var a=!1;return l(this.chunks,function(b){var c=b.status();if("pending"===c||"uploading"===c||"reading"===c||1===b.preprocessState||1===b.readState)return a=!0,!1}),!a},sizeUploaded:function(){var a=0;return l(this.chunks,function(b){a+=b.sizeUploaded()}),a},timeRemaining:function(){if(this.paused||this.error)return 0;var a=this.size-this.sizeUploaded();return a&&!this.averageSpeed?Number.POSITIVE_INFINITY:a||this.averageSpeed?Math.floor(a/this.averageSpeed):0},getType:function(){return this.file.type&&this.file.type.split("/")[1]},getExtension:function(){return this.name.substr((~-this.name.lastIndexOf(".")>>>0)+2).toLowerCase()}},g.prototype={getParams:function(){return{flowChunkNumber:this.offset+1,flowChunkSize:this.chunkSize,flowCurrentChunkSize:this.endByte-this.startByte,flowTotalSize:this.fileObj.size,flowIdentifier:this.fileObj.uniqueIdentifier,flowFilename:this.fileObj.name,flowRelativePath:this.fileObj.relativePath,flowTotalChunks:this.fileObj.chunks.length}},getTarget:function(a,b){return 0==b.length?a:(a+=a.indexOf("?")<0?"?":"&",a+b.join("&"))},test:function(){this.xhr=new XMLHttpRequest,this.xhr.addEventListener("load",this.testHandler,!1),this.xhr.addEventListener("error",this.testHandler,!1);var a=i(this.flowObj.opts.testMethod,this.fileObj,this),b=this.prepareXhrRequest(a,!0);this.xhr.send(b)},preprocessFinished:function(){this.endByte=this.computeEndByte(),this.preprocessState=2,this.send()},readFinished:function(a){this.readState=2,this.bytes=a,this.send()},send:function(){var a=this.flowObj.opts.preprocess,b=this.flowObj.opts.readFileFn;if("function"==typeof a)switch(this.preprocessState){case 0:return this.preprocessState=1,void a(this);case 1:return}switch(this.readState){case 0:return this.readState=1,void b(this.fileObj,this.startByte,this.endByte,this.fileObj.file.type,this);case 1:return}if(this.flowObj.opts.testChunks&&!this.tested)return void this.test();this.loaded=0,this.total=0,this.pendingRetry=!1,this.xhr=new XMLHttpRequest,this.xhr.upload.addEventListener("progress",this.progressHandler,!1),this.xhr.addEventListener("load",this.doneHandler,!1),this.xhr.addEventListener("error",this.doneHandler,!1);var c=i(this.flowObj.opts.uploadMethod,this.fileObj,this),d=this.prepareXhrRequest(c,!1,this.flowObj.opts.method,this.bytes),e=this.flowObj.opts.changeRawDataBeforeSend;"function"==typeof e&&(d=e(this,d)),this.xhr.send(d)},abort:function(){var a=this.xhr;this.xhr=null,a&&a.abort()},status:function(a){return 1===this.readState?"reading":this.pendingRetry||1===this.preprocessState?"uploading":this.xhr?this.xhr.readyState<4?"uploading":this.flowObj.opts.successStatuses.indexOf(this.xhr.status)>-1?"success":this.flowObj.opts.permanentErrors.indexOf(this.xhr.status)>-1||!a&&this.retries>=this.flowObj.opts.maxChunkRetries?"error":(this.abort(),"pending"):"pending"},message:function(){return this.xhr?this.xhr.responseText:""},progress:function(){if(this.pendingRetry)return 0;var a=this.status();return"success"===a||"error"===a?1:"pending"===a?0:this.total>0?this.loaded/this.total:0},sizeUploaded:function(){var a=this.endByte-this.startByte;return"success"!==this.status()&&(a=this.progress()*a),a},prepareXhrRequest:function(a,b,c,d){var e=i(this.flowObj.opts.query,this.fileObj,this,b);e=k(e||{},this.getParams());var f=i(this.flowObj.opts.target,this.fileObj,this,b),g=null;if("GET"===a||"octet"===c){var h=[];l(e,function(a,b){h.push([encodeURIComponent(b),encodeURIComponent(a)].join("="))}),f=this.getTarget(f,h),g=d||null}else g=new FormData,l(e,function(a,b){g.append(b,a)}),"undefined"!=typeof d&&g.append(this.flowObj.opts.fileParameterName,d,this.filename||this.fileObj.file.name);return this.xhr.open(a,f,!0),this.xhr.withCredentials=this.flowObj.opts.withCredentials,l(i(this.flowObj.opts.headers,this.fileObj,this,b),function(a,b){this.xhr.setRequestHeader(b,a)},this),g}},d.evalOpts=i,d.extend=k,d.each=l,d.FlowFile=e,d.FlowChunk=g,d.version="2.14.1","object"==typeof module&&module&&"object"==typeof module.exports?module.exports=d:(a.Flow=d,"function"==typeof define&&define.amd&&define("flow",[],function(){return d}))}("undefined"!=typeof window&&window,"undefined"!=typeof document&&document);
\ No newline at end of file
+!function(a,b,c){"use strict";function d(b){if(this.support=!("undefined"==typeof File||"undefined"==typeof Blob||"undefined"==typeof FileList||!Blob.prototype.slice&&!Blob.prototype.webkitSlice&&!Blob.prototype.mozSlice),this.support){this.supportDirectory=/Chrome/.test(a.navigator.userAgent)||/Firefox/.test(a.navigator.userAgent)||/Edge/.test(a.navigator.userAgent),this.files=[],this.defaults={chunkSize:1048576,forceChunkSize:!1,simultaneousUploads:3,singleFile:!1,fileParameterName:"file",progressCallbacksInterval:500,speedSmoothingFactor:.1,query:{},headers:{},withCredentials:!1,preprocess:null,changeRawDataBeforeSend:null,method:"multipart",testMethod:"GET",uploadMethod:"POST",prioritizeFirstAndLastChunk:!1,allowDuplicateUploads:!1,target:"/",testChunks:!0,generateUniqueIdentifier:null,maxChunkRetries:0,chunkRetryInterval:null,permanentErrors:[404,413,415,500,501],successStatuses:[200,201,202],onDropStopPropagation:!1,initFileFn:null,readFileFn:f},this.opts={},this.events={};var c=this;this.onDrop=function(a){c.opts.onDropStopPropagation&&a.stopPropagation(),a.preventDefault();var b=a.dataTransfer;b.items&&b.items[0]&&b.items[0].webkitGetAsEntry?c.webkitReadDataTransfer(a):c.addFiles(b.files,a)},this.preventEvent=function(a){a.preventDefault()},this.opts=d.extend({},this.defaults,b||{})}}function e(a,b,d){this.flowObj=a,this.file=b,this.name=b.fileName||b.name,this.size=b.size,this.relativePath=b.relativePath||b.webkitRelativePath||this.name,this.uniqueIdentifier=d===c?a.generateUniqueIdentifier(b):d,this.chunkSize=0,this.chunks=[],this.paused=!1,this.error=!1,this.averageSpeed=0,this.currentSpeed=0,this._lastProgressCallback=Date.now(),this._prevUploadedSize=0,this._prevProgress=0,this.bootstrap()}function f(a,b,c,d,e){var f="slice";a.file.slice?f="slice":a.file.mozSlice?f="mozSlice":a.file.webkitSlice&&(f="webkitSlice"),e.readFinished(a.file[f](b,c,d))}function g(a,b,d){this.flowObj=a,this.fileObj=b,this.offset=d,this.tested=!1,this.retries=0,this.pendingRetry=!1,this.preprocessState=0,this.readState=0,this.bytes=c,this.loaded=0,this.total=0,this.chunkSize=this.fileObj.chunkSize,this.startByte=this.offset*this.chunkSize,this.filename=null,this.computeEndByte=function(){var a=Math.min(this.fileObj.size,(this.offset+1)*this.chunkSize);return this.fileObj.size-a<this.chunkSize&&!this.flowObj.opts.forceChunkSize&&(a=this.fileObj.size),a},this.endByte=this.computeEndByte(),this.xhr=null;var e=this;this.event=function(a,b){b=Array.prototype.slice.call(arguments),b.unshift(e),e.fileObj.chunkEvent.apply(e.fileObj,b)},this.progressHandler=function(a){a.lengthComputable&&(e.loaded=a.loaded,e.total=a.total),e.event("progress",a)},this.testHandler=function(a){var b=e.status(!0);"error"===b?(e.event(b,e.message()),e.flowObj.uploadNextChunk()):"success"===b?(e.tested=!0,e.event(b,e.message()),e.flowObj.uploadNextChunk()):e.fileObj.paused||(e.tested=!0,e.send())},this.doneHandler=function(a){var b=e.status();if("success"===b||"error"===b)delete this.data,e.event(b,e.message()),e.flowObj.uploadNextChunk();else if(!e.fileObj.paused){e.event("retry",e.message()),e.pendingRetry=!0,e.abort(),e.retries++;var c=e.flowObj.opts.chunkRetryInterval;null!==c?setTimeout(function(){e.send()},c):e.send()}}}function h(a,b){var c=a.indexOf(b);c>-1&&a.splice(c,1)}function i(a,b){return"function"==typeof a&&(b=Array.prototype.slice.call(arguments),a=a.apply(null,b.slice(1))),a}function j(a,b){setTimeout(a.bind(b),0)}function k(a,b){return l(arguments,function(b){b!==a&&l(b,function(b,c){a[c]=b})}),a}function l(a,b,c){if(a){var d;if("undefined"!=typeof a.length){for(d=0;d<a.length;d++)if(b.call(c,a[d],d)===!1)return}else for(d in a)if(a.hasOwnProperty(d)&&b.call(c,a[d],d)===!1)return}}if(!a||!b)return void console.warn("Flowjs needs window and document objects to work");var m=a.navigator.msPointerEnabled;d.prototype={on:function(a,b){a=a.toLowerCase(),this.events.hasOwnProperty(a)||(this.events[a]=[]),this.events[a].push(b)},off:function(a,b){a!==c?(a=a.toLowerCase(),b!==c?this.events.hasOwnProperty(a)&&h(this.events[a],b):delete this.events[a]):this.events={}},fire:function(a,b){b=Array.prototype.slice.call(arguments),a=a.toLowerCase();var c=!1;return this.events.hasOwnProperty(a)&&l(this.events[a],function(a){c=a.apply(this,b.slice(1))===!1||c},this),"catchall"!=a&&(b.unshift("catchAll"),c=this.fire.apply(this,b)===!1||c),!c},webkitReadDataTransfer:function(a){function b(a){function b(a,b){a.isFile?f.push(a):a.isDirectory&&b.push(c(a))}function c(a){var b=a.createReader();return new Promise(function(c,d){var f=[];e(a,b,f,c)})}function e(a,c,d,f){c.readEntries(function(g){if(g.length){var h=[];return l(g,function(a){b(a,h)}),d.push(Promise.all(h)),void e(a,c,d,f)}f(Promise.all(d))},function(b){g.push({path:a.fullPath,error:b}),f(d)})}var f=[],g=[],h=[];return l(a,function(a){var c=a.webkitGetAsEntry();if(c)return c.isFile?void f.push(d(a.getAsFile(),c.fullPath)):void b(c,h)}),new Promise(function(a,b){return Promise.all(h).then(function(){a({files:f,errors:g})})})}function c(a){return Promise.all(a.map(function(a){return new Promise(function(b,c){if(a.file){var e=a.fullPath;a.file(function(a){b(d(a,e))},function(c){b({path:a.fullPath,error:c})})}else b(a)})}))}function d(a,b){return a.relativePath=b.substring(1),a}var e=this;b(a.dataTransfer.items).then(function(b){c(b.files).then(function(c){var d=[],f=[];l(c,function(a){a.error?f.push(a):d.push(a)}),(b.errors.length||f.length)&&e.fire("readErrors",f,b.errors,a),d.length&&e.addFiles(d,a)})})},generateUniqueIdentifier:function(a){var b=this.opts.generateUniqueIdentifier;if("function"==typeof b)return b(a);var c=a.relativePath||a.webkitRelativePath||a.fileName||a.name;return a.size+"-"+c.replace(/[^0-9a-zA-Z_-]/gim,"")},uploadNextChunk:function(a){var b=!1;if(this.opts.prioritizeFirstAndLastChunk&&(l(this.files,function(a){return!a.paused&&a.chunks.length&&"pending"===a.chunks[0].status()?(a.chunks[0].send(),b=!0,!1):!a.paused&&a.chunks.length>1&&"pending"===a.chunks[a.chunks.length-1].status()?(a.chunks[a.chunks.length-1].send(),b=!0,!1):void 0}),b))return b;if(l(this.files,function(a){if(a.paused||l(a.chunks,function(a){if("pending"===a.status())return a.send(),b=!0,!1}),b)return!1}),b)return!0;var c=!1;return l(this.files,function(a){if(!a.isComplete())return c=!0,!1}),c||a||j(function(){this.fire("complete")},this),!1},assignBrowse:function(a,c,d,e){a instanceof Element&&(a=[a]),l(a,function(a){var f;"INPUT"===a.tagName&&"file"===a.type?f=a:(f=b.createElement("input"),f.setAttribute("type","file"),k(f.style,{visibility:"hidden",position:"absolute",width:"1px",height:"1px"}),a.appendChild(f),a.addEventListener("click",function(){f.click()},!1)),this.opts.singleFile||d||f.setAttribute("multiple","multiple"),c&&f.setAttribute("webkitdirectory","webkitdirectory"),l(e,function(a,b){f.setAttribute(b,a)});var g=this;f.addEventListener("change",function(a){a.target.value&&(g.addFiles(a.target.files,a),a.target.value="")},!1)},this)},assignDrop:function(a){"undefined"==typeof a.length&&(a=[a]),l(a,function(a){a.addEventListener("dragover",this.preventEvent,!1),a.addEventListener("dragenter",this.preventEvent,!1),a.addEventListener("drop",this.onDrop,!1)},this)},unAssignDrop:function(a){"undefined"==typeof a.length&&(a=[a]),l(a,function(a){a.removeEventListener("dragover",this.preventEvent),a.removeEventListener("dragenter",this.preventEvent),a.removeEventListener("drop",this.onDrop)},this)},isUploading:function(){var a=!1;return l(this.files,function(b){if(b.isUploading())return a=!0,!1}),a},_shouldUploadNext:function(){var a=0,b=!0,c=this.opts.simultaneousUploads;return l(this.files,function(d){l(d.chunks,function(d){if("uploading"===d.status()&&(a++,a>=c))return b=!1,!1})}),b&&a},upload:function(){var a=this._shouldUploadNext();if(a!==!1){this.fire("uploadStart");for(var b=!1,c=1;c<=this.opts.simultaneousUploads-a;c++)b=this.uploadNextChunk(!0)||b;b||j(function(){this.fire("complete")},this)}},resume:function(){l(this.files,function(a){a.isComplete()||a.resume()})},pause:function(){l(this.files,function(a){a.pause()})},cancel:function(){for(var a=this.files.length-1;a>=0;a--)this.files[a].cancel()},progress:function(){var a=0,b=0;return l(this.files,function(c){a+=c.progress()*c.size,b+=c.size}),b>0?a/b:0},addFile:function(a,b){this.addFiles([a],b)},addFiles:function(a,b){function c(a){if((!m||m&&a.size>0)&&(a.size%4096!==0||"."!==a.name&&"."!==a.fileName)){var c=this.generateUniqueIdentifier(a);if(this.opts.allowDuplicateUploads||!this.getFromUniqueIdentifier(c)){var d=new e(this,a,c);this.fire("fileAdded",d,b)&&g.push(d)}}}function d(a){return a.size>0?void c.bind(f)(a):void i.push(new Promise(function(b,d){var e=new FileReader;e.onloadend=function(){e.error?h.push({path:a.webkitRelativePath||a.name,error:e.error}):c.bind(f)(a),b()}.bind(f),e.readAsArrayBuffer(a)}))}var f=this,g=[],h=[],i=[];l(a,d),Promise.all(i).then(function(){h.length&&this.fire("readErrors",h,[],b),this.fire("filesAdded",g,b)&&(l(g,function(a){this.opts.singleFile&&this.files.length>0&&this.removeFile(this.files[0]),this.files.push(a)},this),this.fire("filesSubmitted",g,b))}.bind(this))},removeFile:function(a){for(var b=this.files.length-1;b>=0;b--)this.files[b]===a&&(this.files.splice(b,1),a.abort(),this.fire("fileRemoved",a))},getFromUniqueIdentifier:function(a){var b=!1;return l(this.files,function(c){c.uniqueIdentifier===a&&(b=c)}),b},getSize:function(){var a=0;return l(this.files,function(b){a+=b.size}),a},sizeUploaded:function(){var a=0;return l(this.files,function(b){a+=b.sizeUploaded()}),a},timeRemaining:function(){var a=0,b=0;return l(this.files,function(c){c.paused||c.error||(a+=c.size-c.sizeUploaded(),b+=c.averageSpeed)}),a&&!b?Number.POSITIVE_INFINITY:a||b?Math.floor(a/b):0}},e.prototype={measureSpeed:function(){var a=Date.now()-this._lastProgressCallback;if(a){var b=this.flowObj.opts.speedSmoothingFactor,c=this.sizeUploaded();this.currentSpeed=Math.max((c-this._prevUploadedSize)/a*1e3,0),this.averageSpeed=b*this.currentSpeed+(1-b)*this.averageSpeed,this._prevUploadedSize=c}},chunkEvent:function(a,b,c){switch(b){case"progress":if(Date.now()-this._lastProgressCallback<this.flowObj.opts.progressCallbacksInterval)break;this.measureSpeed(),this.flowObj.fire("fileProgress",this,a),this.flowObj.fire("progress"),this._lastProgressCallback=Date.now();break;case"error":this.error=!0,this.abort(!0),this.flowObj.fire("fileError",this,c,a),this.flowObj.fire("error",c,this,a);break;case"success":if(this.error)return;this.measureSpeed(),this.flowObj.fire("fileProgress",this,a),this.flowObj.fire("progress"),this._lastProgressCallback=Date.now(),this.isComplete()&&(this.currentSpeed=0,this.averageSpeed=0,this.flowObj.fire("fileSuccess",this,c,a));break;case"retry":this.flowObj.fire("fileRetry",this,a)}},pause:function(){this.paused=!0,this.abort()},resume:function(){this.paused=!1,this.flowObj.upload()},abort:function(a){this.currentSpeed=0,this.averageSpeed=0;var b=this.chunks;a&&(this.chunks=[]),l(b,function(a){"uploading"===a.status()&&(a.abort(),this.flowObj.uploadNextChunk())},this)},cancel:function(){this.flowObj.removeFile(this)},retry:function(){this.bootstrap(),this.flowObj.upload()},bootstrap:function(){if("function"==typeof this.flowObj.opts.initFileFn){var a=this.flowObj.opts.initFileFn(this);if(a&&"then"in a)return void a.then(this._bootstrap.bind(this))}this._bootstrap()},_bootstrap:function(){this.abort(!0),this.error=!1,this._prevProgress=0;var a=this.flowObj.opts.forceChunkSize?Math.ceil:Math.floor;this.chunkSize=i(this.flowObj.opts.chunkSize,this);for(var b=Math.max(a(this.size/this.chunkSize),1),c=0;c<b;c++)this.chunks.push(new g(this.flowObj,this,c))},progress:function(){if(this.error)return 1;if(1===this.chunks.length)return this._prevProgress=Math.max(this._prevProgress,this.chunks[0].progress()),this._prevProgress;var a=0;l(this.chunks,function(b){a+=b.progress()*(b.endByte-b.startByte)});var b=a/this.size;return this._prevProgress=Math.max(this._prevProgress,b>.9999?1:b),this._prevProgress},isUploading:function(){var a=!1;return l(this.chunks,function(b){if("uploading"===b.status())return a=!0,!1}),a},isComplete:function(){var a=!1;return l(this.chunks,function(b){var c=b.status();if("pending"===c||"uploading"===c||"reading"===c||1===b.preprocessState||1===b.readState)return a=!0,!1}),!a},sizeUploaded:function(){var a=0;return l(this.chunks,function(b){a+=b.sizeUploaded()}),a},timeRemaining:function(){if(this.paused||this.error)return 0;var a=this.size-this.sizeUploaded();return a&&!this.averageSpeed?Number.POSITIVE_INFINITY:a||this.averageSpeed?Math.floor(a/this.averageSpeed):0},getType:function(){return this.file.type&&this.file.type.split("/")[1]},getExtension:function(){return this.name.substr((~-this.name.lastIndexOf(".")>>>0)+2).toLowerCase()}},g.prototype={getParams:function(){return{chunkNumber:this.offset+1,chunkSize:this.chunkSize,currentChunkSize:this.endByte-this.startByte,totalSize:this.fileObj.size,requestId:this.fileObj.uniqueIdentifier,filename:this.fileObj.name,relativePath:this.fileObj.relativePath,totalChunks:this.fileObj.chunks.length}},getTarget:function(a,b){return 0==b.length?a:(a+=a.indexOf("?")<0?"?":"&",a+b.join("&"))},test:function(){this.xhr=new XMLHttpRequest,this.xhr.addEventListener("load",this.testHandler,!1),this.xhr.addEventListener("error",this.testHandler,!1);var a=i(this.flowObj.opts.testMethod,this.fileObj,this),b=this.prepareXhrRequest(a,!0);this.xhr.send(b)},preprocessFinished:function(){this.endByte=this.computeEndByte(),this.preprocessState=2,this.send()},readFinished:function(a){this.readState=2,this.bytes=a,this.send()},send:function(){var a=this.flowObj.opts.preprocess,b=this.flowObj.opts.readFileFn;if("function"==typeof a)switch(this.preprocessState){case 0:return this.preprocessState=1,void a(this);case 1:return}switch(this.readState){case 0:return this.readState=1,void b(this.fileObj,this.startByte,this.endByte,this.fileObj.file.type,this);case 1:return}if(this.flowObj.opts.testChunks&&!this.tested)return void this.test();this.loaded=0,this.total=0,this.pendingRetry=!1,this.xhr=new XMLHttpRequest,this.xhr.upload.addEventListener("progress",this.progressHandler,!1),this.xhr.addEventListener("load",this.doneHandler,!1),this.xhr.addEventListener("error",this.doneHandler,!1);var c=i(this.flowObj.opts.uploadMethod,this.fileObj,this),d=this.prepareXhrRequest(c,!1,this.flowObj.opts.method,this.bytes),e=this.flowObj.opts.changeRawDataBeforeSend;"function"==typeof e&&(d=e(this,d)),this.xhr.send(d)},abort:function(){var a=this.xhr;this.xhr=null,a&&a.abort()},status:function(a){return 1===this.readState?"reading":this.pendingRetry||1===this.preprocessState?"uploading":this.xhr?this.xhr.readyState<4?"uploading":this.flowObj.opts.successStatuses.indexOf(this.xhr.status)>-1?"success":this.flowObj.opts.permanentErrors.indexOf(this.xhr.status)>-1||!a&&this.retries>=this.flowObj.opts.maxChunkRetries?"error":(this.abort(),"pending"):"pending"},message:function(){return this.xhr?this.xhr.responseText:""},progress:function(){if(this.pendingRetry)return 0;var a=this.status();return"success"===a||"error"===a?1:"pending"===a?0:this.total>0?this.loaded/this.total:0},sizeUploaded:function(){var a=this.endByte-this.startByte;return"success"!==this.status()&&(a=this.progress()*a),a},prepareXhrRequest:function(a,b,c,d){var e=i(this.flowObj.opts.query,this.fileObj,this,b);e=k(e||{},this.getParams());var f=i(this.flowObj.opts.target,this.fileObj,this,b),g=null;if("GET"===a||"octet"===c){var h=[];l(e,function(a,b){h.push([encodeURIComponent(b),encodeURIComponent(a)].join("="))}),f=this.getTarget(f,h),g=d||null}else g=new FormData,l(e,function(a,b){g.append(b,a)}),"undefined"!=typeof d&&g.append(this.flowObj.opts.fileParameterName,d,this.filename||this.fileObj.file.name);return this.xhr.open(a,f,!0),this.xhr.withCredentials=this.flowObj.opts.withCredentials,l(i(this.flowObj.opts.headers,this.fileObj,this,b),function(a,b){this.xhr.setRequestHeader(b,a)},this),g}},d.evalOpts=i,d.extend=k,d.each=l,d.FlowFile=e,d.FlowChunk=g,d.version="2.14.1","object"==typeof module&&module&&"object"==typeof module.exports?module.exports=d:(a.Flow=d,"function"==typeof define&&define.amd&&define("flow",[],function(){return d}))}("undefined"!=typeof window&&window,"undefined"!=typeof document&&document);
\ No newline at end of file
diff --git a/samples/Backend on Go.md b/samples/Backend on Go.md
index 2e135286..9dc6e0ad 100644
--- a/samples/Backend on Go.md	
+++ b/samples/Backend on Go.md	
@@ -74,7 +74,7 @@ func (fn streamHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func continueUpload(w http.ResponseWriter, r *http.Request) {
-	chunkDirPath := "./incomplete/" + r.FormValue("flowFilename") + "/" + r.FormValue("flowChunkNumber")
+	chunkDirPath := "./incomplete/" + r.FormValue("filename") + "/" + r.FormValue("chunkNumber")
 	if _, err := os.Stat(chunkDirPath); err != nil {
 		w.WriteHeader(204)
 		return
@@ -84,7 +84,7 @@ func continueUpload(w http.ResponseWriter, r *http.Request) {
 func chunkedReader(w http.ResponseWriter, r *http.Request) error {
 	r.ParseMultipartForm(25)
 
-	chunkDirPath := "./incomplete/" + r.FormValue("flowFilename")
+	chunkDirPath := "./incomplete/" + r.FormValue("filename")
 	err := os.MkdirAll(chunkDirPath, 02750)
 	if err != nil {
 		return err
@@ -97,7 +97,7 @@ func chunkedReader(w http.ResponseWriter, r *http.Request) error {
 		}
 		defer src.Close()
 
-		dst, err := os.Create(chunkDirPath + "/" + r.FormValue("flowChunkNumber"))
+		dst, err := os.Create(chunkDirPath + "/" + r.FormValue("chunkNumber"))
 		if err != nil {
 			return err
 		}
diff --git a/samples/Backend on Haskell.md b/samples/Backend on Haskell.md
index 062cf132..4fdd035e 100644
--- a/samples/Backend on Haskell.md	
+++ b/samples/Backend on Haskell.md	
@@ -76,15 +76,15 @@ uploadStart = action POST (pathJSON >/> pathId </< "upload") $ \vi -> withAuth $
 chunkForm :: DeformActionM f (Upload, Int64, Word64)
 chunkForm = do
   csrfForm
-  up <- "flowIdentifier" .:> (lift . (maybeAction <=< lookupUpload) =<< deform)
+  up <- "requestId" .:> (lift . (maybeAction <=< lookupUpload) =<< deform)
   let z = uploadSize up
-  "flowFilename" .:> (deformGuard "Filename mismatch." . (uploadFilename up ==) =<< deform)
-  "flowTotalSize" .:> (deformGuard "File size mismatch." . (z ==) =<< fileSizeForm)
-  c <- "flowChunkSize" .:> (deformCheck "Chunk size too small." (256 <=) =<< deform)
-  n <- "flowTotalChunks" .:> (deformCheck "Chunk count mismatch." ((1 >=) . abs . (pred z `div` c -)) =<< deform)
-  i <- "flowChunkNumber" .:> (deformCheck "Chunk number out of range." (\i -> 0 <= i && i < n) =<< pred <$> deform)
+  "filename" .:> (deformGuard "Filename mismatch." . (uploadFilename up ==) =<< deform)
+  "totalSize" .:> (deformGuard "File size mismatch." . (z ==) =<< fileSizeForm)
+  c <- "chunkSize" .:> (deformCheck "Chunk size too small." (256 <=) =<< deform)
+  n <- "totalChunks" .:> (deformCheck "Chunk count mismatch." ((1 >=) . abs . (pred z `div` c -)) =<< deform)
+  i <- "chunkNumber" .:> (deformCheck "Chunk number out of range." (\i -> 0 <= i && i < n) =<< pred <$> deform)
   let o = c * i
-  l <- "flowCurrentChunkSize" .:> (deformCheck "Current chunk size out of range." (\l -> (c == l || i == pred n) && o + l <= z) =<< deform)
+  l <- "currentChunkSize" .:> (deformCheck "Current chunk size out of range." (\l -> (c == l || i == pred n) && o + l <= z) =<< deform)
   return (up, o, fromIntegral l)
 
 uploadChunk :: ActionRoute ()
diff --git a/samples/Node.js/flow-node.js b/samples/Node.js/flow-node.js
index 883397dd..ad49ac26 100644
--- a/samples/Node.js/flow-node.js
+++ b/samples/Node.js/flow-node.js
@@ -64,11 +64,11 @@ module.exports = flow = function(temporaryFolder) {
     //'found', filename, original_filename, identifier
     //'not_found', null, null, null
     $.get = function(req, callback) {
-        var chunkNumber = req.param('flowChunkNumber', 0);
-        var chunkSize = req.param('flowChunkSize', 0);
-        var totalSize = req.param('flowTotalSize', 0);
-        var identifier = req.param('flowIdentifier', "");
-        var filename = req.param('flowFilename', "");
+        var chunkNumber = req.param('chunkNumber', 0);
+        var chunkSize = req.param('chunkSize', 0);
+        var totalSize = req.param('totalSize', 0);
+        var identifier = req.param('requestId', "");
+        var filename = req.param('filename', "");
 
         if (validateRequest(chunkNumber, chunkSize, totalSize, identifier, filename) == 'valid') {
             var chunkFilename = getChunkFilename(chunkNumber, identifier);
@@ -93,11 +93,11 @@ module.exports = flow = function(temporaryFolder) {
         var fields = req.body;
         var files = req.files;
 
-        var chunkNumber = fields['flowChunkNumber'];
-        var chunkSize = fields['flowChunkSize'];
-        var totalSize = fields['flowTotalSize'];
-        var identifier = cleanIdentifier(fields['flowIdentifier']);
-        var filename = fields['flowFilename'];
+        var chunkNumber = fields['chunkNumber'];
+        var chunkSize = fields['chunkSize'];
+        var totalSize = fields['totalSize'];
+        var identifier = cleanIdentifier(fields['requestId']);
+        var filename = fields['filename'];
 
         if (!files[$.fileParameterName] || !files[$.fileParameterName].size) {
             callback('invalid_flow_request', null, null, null);
diff --git a/samples/Ruby backend in Sinatra.md b/samples/Ruby backend in Sinatra.md
index 9b102a5a..be033344 100644
--- a/samples/Ruby backend in Sinatra.md	
+++ b/samples/Ruby backend in Sinatra.md	
@@ -89,19 +89,19 @@ private
   ##
   # Determine if this is the last chunk based on the chunk number.
   def last_chunk?
-    params[:flowChunkNumber].to_i == params[:flowTotalChunks].to_i
+    params[:chunkNumber].to_i == params[:totalChunks].to_i
   end
 
   ##
   # ./tmp/flow/abc-123/upload.txt.part1
   def chunk_file_path
-    File.join(chunk_file_directory, "#{params[:flowFilename]}.part#{params[:flowChunkNumber]}")
+    File.join(chunk_file_directory, "#{params[:filename]}.part#{params[:chunkNumber]}")
   end
 
   ##
   # ./tmp/flow/abc-123
   def chunk_file_directory
-    File.join "tmp", "flow", params[:flowIdentifier]
+    File.join "tmp", "flow", params[:requestId]
   end
 
   ##
@@ -123,7 +123,7 @@ private
   ##
   # /final/resting/place/upload.txt
   def final_file_path
-    File.join final_file_directory, params[:flowFilename]
+    File.join final_file_directory, params[:filename]
   end
 
   ##
diff --git a/src/flow.js b/src/flow.js
index 1b016c0e..2d533cd5 100644
--- a/src/flow.js
+++ b/src/flow.js
@@ -230,55 +230,109 @@
      */
     webkitReadDataTransfer: function (event) {
       var $ = this;
-      var queue = event.dataTransfer.items.length;
-      var files = [];
-      each(event.dataTransfer.items, function (item) {
-        var entry = item.webkitGetAsEntry();
-        if (!entry) {
-          decrement();
-          return ;
+      getEntries(event.dataTransfer.items).then(function (result) {
+        getFiles(result.files).then(function (entries) {
+          var files = [];
+          var errors = [];
+          each(entries, function (entry) {
+            if (entry.error) {
+              errors.push(entry);
+            } else {
+              files.push(entry);
+            }
+          });
+          if (result.errors.length || errors.length) {
+            $.fire('readErrors', errors, result.errors, event);
+          }
+          if (files.length) {
+            $.addFiles(files, event);
+          }
+        });
+      });
+      function getEntries(items) {
+        var files = [];
+        var errors = [];
+        var promises = [];
+
+        function readEntry(entry, promises) {
+          if (entry.isFile) {
+            files.push(entry);
+          } else if (entry.isDirectory) {
+            promises.push(readDirectory(entry));
+          }
         }
-        if (entry.isFile) {
-          // due to a bug in Chrome's File System API impl - #149735
-          fileReadSuccess(item.getAsFile(), entry.fullPath);
-        } else {
-          readDirectory(entry.createReader());
+
+        function readDirectory(entry) {
+          var reader = entry.createReader();
+          return new Promise(function (resolve, reject) {
+            var promises = [];
+            readEntries(entry, reader, promises, resolve);
+          });
         }
-      });
-      function readDirectory(reader) {
-        reader.readEntries(function (entries) {
-          if (entries.length) {
-            queue += entries.length;
-            each(entries, function(entry) {
-              if (entry.isFile) {
-                var fullPath = entry.fullPath;
-                entry.file(function (file) {
-                  fileReadSuccess(file, fullPath);
-                }, readError);
-              } else if (entry.isDirectory) {
-                readDirectory(entry.createReader());
-              }
+
+        function readEntries(entry, reader, promises, resolve) {
+          reader.readEntries(function (entries) {
+            if (entries.length) {
+              var promises2 = [];
+              each(entries, function (entry2) {
+                readEntry(entry2, promises2);
+              });
+              promises.push(Promise.all(promises2));
+              readEntries(entry, reader, promises, resolve);
+              return;
+            }
+            resolve(Promise.all(promises));
+          }, function (error) {
+            errors.push({
+              path: entry.fullPath,
+              error: error
             });
-            readDirectory(reader);
-          } else {
-            decrement();
+            resolve(promises);
+          });
+        }
+
+        each(items, function (item) {
+          var entry = item.webkitGetAsEntry();
+          if (!entry) {
+            return;
+          }
+          if (entry.isFile) {
+            // due to a bug in Chrome's File System API impl - #149735
+            files.push(getFile(item.getAsFile(), entry.fullPath));
+            return;
           }
-        }, readError);
+          readEntry(entry, promises);
+        });
+
+        return new Promise(function (resolve, reject) {
+          return Promise.all(promises).then(function () {
+            resolve({ files: files, errors: errors });
+          });
+        });
+      }
+      function getFiles(entries) {
+        return Promise.all(entries.map(function (entry) {
+          return new Promise(function (resolve, reject) {
+            if (entry.file) {
+              var fullPath = entry.fullPath;
+              entry.file(function (file) {
+                resolve(getFile(file, fullPath));
+              }, function (file) {
+                resolve({
+                  path: entry.fullPath,
+                  error: file
+                });
+              });
+            } else {
+              resolve(entry);
+            }
+          });
+        }));
       }
-      function fileReadSuccess(file, fullPath) {
+      function getFile(file, fullPath) {
         // relative path should not start with "/"
         file.relativePath = fullPath.substring(1);
-        files.push(file);
-        decrement();
-      }
-      function readError(fileError) {
-        decrement();
-        throw fileError;
-      }
-      function decrement() {
-        if (--queue == 0) {
-          $.addFiles(files, event);
-        }
+        return file;
       }
     },
 
@@ -588,8 +642,12 @@
      * @param {Event} [event] event is optional
      */
     addFiles: function (fileList, event) {
+      var $ = this;
       var files = [];
-      each(fileList, function (file) {
+      var errors = [];
+      var promises = [];
+
+      function addFile(file) {        
         // https://github.com/flowjs/flow.js/issues/55
         if ((!ie10plus || ie10plus && file.size > 0) && !(file.size % 4096 === 0 && (file.name === '.' || file.fileName === '.'))) {
           var uniqueIdentifier = this.generateUniqueIdentifier(file);
@@ -600,16 +658,54 @@
             }
           }
         }
-      }, this);
-      if (this.fire('filesAdded', files, event)) {
-        each(files, function (file) {
-          if (this.opts.singleFile && this.files.length > 0) {
-            this.removeFile(this.files[0]);
-          }
-          this.files.push(file);
-        }, this);
-        this.fire('filesSubmitted', files, event);
       }
+      
+      /** 
+       * Chrome's FileSystem API has a bug that files from dropped folders or files from input dialog's selected folder,
+       * with read errors (has absolute paths which exceed 260 chars) will have zero file size.
+       */
+      function validateFile(file) {
+        // files with size greater than zero can upload
+        if (file.size > 0) {
+          addFile.bind($)(file);
+          return;
+        }
+        
+        // try to read from from zero size file,
+        // if error occurs than file cannot be uploaded
+        promises.push(new Promise(function (resolve, reject) {
+          var reader = new FileReader();
+          reader.onloadend = function () {
+            if (reader.error) {
+              errors.push({
+                path: file.webkitRelativePath || file.name,
+                error: reader.error
+              });
+            } else {
+              addFile.bind($)(file);
+            }
+            resolve();
+          }.bind($);
+          reader.readAsArrayBuffer(file);
+        }));
+      }
+
+      each(fileList, validateFile);
+
+      Promise.all(promises).then(function () {
+        if (errors.length) {
+          this.fire('readErrors', errors, [], event);
+        }
+        if (this.fire('filesAdded', files, event)) {
+          each(files, function (file) {
+            if (this.opts.singleFile && this.files.length > 0) {
+              this.removeFile(this.files[0]);
+            }
+            this.files.push(file);
+          }, this);
+          this.fire('filesSubmitted', files, event);
+        }
+      }.bind(this));
     },
 
 
@@ -1286,14 +1382,14 @@
      */
     getParams: function () {
       return {
-        flowChunkNumber: this.offset + 1,
-        flowChunkSize: this.chunkSize,
-        flowCurrentChunkSize: this.endByte - this.startByte,
-        flowTotalSize: this.fileObj.size,
-        flowIdentifier: this.fileObj.uniqueIdentifier,
-        flowFilename: this.fileObj.name,
-        flowRelativePath: this.fileObj.relativePath,
-        flowTotalChunks: this.fileObj.chunks.length
+        chunkNumber: this.offset + 1,
+        chunkSize: this.chunkSize,
+        currentChunkSize: this.endByte - this.startByte,
+        totalSize: this.fileObj.size,
+        requestId: this.fileObj.uniqueIdentifier,
+        filename: this.fileObj.name,
+        relativePath: this.fileObj.relativePath,
+        totalChunks: this.fileObj.chunks.length
       };
     },