httpuv-style file uploading

Use HTTP POST to upload files rather than sending 4K chunks
one at a time over the websocket. This is massively faster and
also means no binary websocket support is needed. In theory
this approach should be compatible with Shiny Server.

Currently the client side code still uses File API which means
IE8 and 9 users are out of luck.

inst/www/shared/shiny.js

@@ -678,19 +678,12 @@
   // make it do something useful.
   var FileProcessor = function(files) {
     this.files = files;
-    this.fileReader = new FileReader();
     this.fileIndex = -1;
-    this.pos = 0;
     // Currently need to use small chunk size because R-Websockets can't
     // handle continuation frames
-    this.chunkSize = 4096;
     this.aborted = false;
     this.completed = false;
     
-    var self = this;
-    $(this.fileReader).on('load', function(evt) {
-      self.$endReadChunk();
-    });
     // TODO: Register error/abort callbacks
     
     this.$run();
@@ -700,13 +693,7 @@
     this.onBegin = function(files, cont) {
       setTimeout(cont, 0);
     };
-    this.onFileBegin = function(file, cont) {
-      setTimeout(cont, 0);
-    };
-    this.onFileChunk = function(file, offset, blob, cont) {
-      setTimeout(cont, 0);
-    };
-    this.onFileEnd = function(file, cont) {
+    this.onFile = function(file, cont) {
       setTimeout(cont, 0);
     };
     this.onComplete = function() {
@@ -763,45 +750,8 @@
       // in the middle of processing a file, or have just finished
       // processing a file.
       
-      var file = this.files[this.fileIndex];
-      if (this.pos >= file.size) {
-        // We've read past the end of this file--it's done
-        this.fileIndex++;
-        this.pos = 0;
-        this.onFileEnd(file, this.$getRun());
-      }
-      else if (this.pos == 0) {
-        // We're just starting with this file, need to call onFileBegin
-        // before we actually start reading
-        var called = false;
-        this.onFileBegin(file, function() {
-          if (called)
-            return;
-          called = true;
-          self.$beginReadChunk();
-        });
-      }
-      else {
-        // We're neither starting nor ending--just start the next chunk
-        this.$beginReadChunk();
-      }
-    };
-    
-    // Starts asynchronous read of the current chunk of the current file
-    this.$beginReadChunk = function() {
-      var file = this.files[this.fileIndex];
-      var blob = slice(file, this.pos, this.pos + this.chunkSize);
-      this.fileReader.readAsArrayBuffer(blob);
-    };
-    
-    // Called when a chunk has been successfully read
-    this.$endReadChunk = function() {
-      var file = this.files[this.fileIndex];
-      var offset = this.pos;
-      var data = this.fileReader.result;
-      this.pos = this.pos + this.chunkSize;
-      this.onFileChunk(file, offset, makeBlob([data]),
-                       this.$getRun());
+      var file = this.files[this.fileIndex++];
+      this.onFile(file, this.$getRun());
     };
   }).call(FileProcessor.prototype);
 
@@ -1147,42 +1097,43 @@
         'uploadInit', [],
         function(response) {
           self.jobId = response.jobId;
+          self.uploadUrl = response.uploadUrl;
           cont();
         },
         function(error) {
         });
     };
-    this.onFileBegin = function(file, cont) {
+    this.onFile = function(file, cont) {
+      var self = this;
       this.onProgress(file, 0);
-      
-      this.makeRequest(
-        'uploadFileBegin', [this.jobId, file.name, file.type, file.size],
-        function(response) {
-          cont();
-        },
-        function(error) {
-        });
-    };
-    this.onFileChunk = function(file, offset, blob, cont) {
-      this.onProgress(file, (offset + blob.size) / file.size);
 
-      this.makeRequest(
-        'uploadFileChunk', [this.jobId],
-        function(response) {
-          cont();
+      $.ajax(this.uploadUrl, {
+        type: 'POST',
+        cache: false,
+        headers: {
+          'Shiny-File-Name': file.name,
+          'Shiny-File-Type': file.type
         },
-        function(error) {
+        xhr: function() {
+          var xhrVal = $.ajaxSettings.xhr();
+          if (xhrVal.upload) {
+            xhrVal.upload.onprogress = function(e) {
+              if (e.lengthComputable) {
+                self.onProgress(file, (e.loaded / e.total));
+              }
+            }
+          }
+          return xhrVal;
         },
-        [blob]);
-    };
-    this.onFileEnd = function(file, cont) {
-      this.makeRequest(
-        'uploadFileEnd', [this.jobId],
-        function(response) {
-          cont();
-        },
-        function(error) {
-        });
+        data: file,
+        processData: false,
+        complete: function(jqXHR, textStatus) {
+          if (textStatus == 'success') {
+            cont();
+          }
+          // TODO: Message and reset state on error?
+        }
+      });
     };
     this.onComplete = function() {
       this.makeRequest(