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gaia/apps/keyboard/js/settings/layout_dictionary_downloader.js

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+'use strict';
+
+(function(exports) {
+
+var LayoutDictionaryDownloader = function(imEngineId, dictFilename) {
+  this.imEngineId = imEngineId;
+  this.dictFilename = dictFilename;
+
+  this._xhr = null;
+};
+
+// Remote URLs to download the data. We require the remote server to have
+// CORS turned on since we are not asking for SystemXHR permission.
+LayoutDictionaryDownloader.prototype.REMOTE_URL =
+  'https://fxos.cdn.mozilla.net/dictionaries/%imEngineId/%ver/%dictFilename';
+
+// If the data schema changes in an incompatible way, we must bump the
+// version-to-download here.
+LayoutDictionaryDownloader.prototype.ENGINE_DATA_VERSIONS = Object.freeze({
+  'latin': 1
+});
+
+LayoutDictionaryDownloader.prototype.onprogress = null;
+
+LayoutDictionaryDownloader.prototype.load = function() {
+  if (this._xhr) {
+    throw new Error('LayoutDictionaryDownloader: Already downloading...');
+  }
+
+  var p = new Promise(function(resolve, reject) {
+    var url = this.REMOTE_URL
+      .replace('%imEngineId', this.imEngineId)
+      .replace('%ver', this.ENGINE_DATA_VERSIONS[this.imEngineId])
+      .replace('%dictFilename', this.dictFilename);
+
+    var xhr = this._xhr = new XMLHttpRequest();
+    xhr.open('GET', url, true);
+    xhr.responseType = 'arraybuffer';
+
+    xhr.onprogress = function(evt) {
+      if (typeof this.onprogress === 'function') {
+        this.onprogress(evt.loaded, evt.total);
+      }
+    }.bind(this);
+
+    xhr.onloadend = function() {
+      this._xhr = null;
+
+      var data = xhr.response;
+      // We will only resolve the promise when the data is verified.
+      // For any other situration, we simply return the HTTP status code as
+      // a rejected placeholder value.
+      // (it doesn't really matter if you got 200/404/500
+      // or anything if it's not what you are looking for right :-/?)
+      if (data && this._verifyData(data)) {
+        if (typeof this.onprogress === 'function') {
+          this.onprogress(data.byteLength, data.byteLength);
+        }
+
+        resolve(data);
+      } else {
+        reject(xhr.statusText);
+      }
+    }.bind(this);
+
+    xhr.send();
+  }.bind(this));
+
+  return p;
+};
+
+LayoutDictionaryDownloader.prototype.abort = function() {
+  if (!this._xhr) {
+    throw new Error('LayoutDictionaryDownloader: ' +
+      'Not downloading but abort is called.');
+  }
+
+  this._xhr.abort();
+
+  this._xhr = null;
+};
+
+LayoutDictionaryDownloader.prototype._verifyData = function(buffer) {
+  switch (this.imEngineId) {
+    case 'latin':
+      // There is only first 8 bytes to check -- we can't be sure if the data
+      // is truncated. However that shouldn't happen since our CDN sends out
+      // Content-Length header.
+      //
+      // TODO: Harden the verification here in some way.
+      //
+      if (!(buffer instanceof ArrayBuffer) || buffer.byteLength < 8) {
+        return false;
+      }
+      var view = new Uint8Array(buffer, 0, 8);
+      return (String.fromCharCode.apply(String, view) === 'FxOSDICT');
+
+    default:
+      throw new Error('LayoutDictionaryDownloader: ' +
+        'No verify method available for this imEngine.');
+  }
+};
+
+exports.LayoutDictionaryDownloader = LayoutDictionaryDownloader;
+
+}(window));