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diff --git a/browser/components/translation/GoogleTranslator.jsm b/browser/components/translation/GoogleTranslator.jsm
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+++ b/browser/components/translation/GoogleTranslator.jsm
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["GoogleTranslator"];
+
+const { PromiseUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/PromiseUtils.sys.mjs"
+);
+const { httpRequest } = ChromeUtils.importESModule(
+  "resource://gre/modules/Http.sys.mjs"
+);
+
+// The maximum amount of net data allowed per request on Google's API.
+const MAX_REQUEST_DATA = 5000; // XXX This is the Bing value
+
+// The maximum number of chunks allowed to be translated in a single
+// request.
+const MAX_REQUEST_CHUNKS = 128; // Undocumented, but the de facto upper limit.
+
+// Self-imposed limit of 15 requests. This means that a page that would need
+// to be broken in more than 15 requests won't be fully translated.
+// The maximum amount of data that we will translate for a single page
+// is MAX_REQUESTS * MAX_REQUEST_DATA.
+const MAX_REQUESTS = 15;
+
+const URL = "https://translation.googleapis.com/language/translate/v2";
+
+/**
+ * Translates a webpage using Google's Translation API.
+ *
+ * @param translationDocument  The TranslationDocument object that represents
+ *                             the webpage to be translated
+ * @param sourceLanguage       The source language of the document
+ * @param targetLanguage       The target language for the translation
+ *
+ * @returns {Promise}          A promise that will resolve when the translation
+ *                             task is finished.
+ */
+var GoogleTranslator = function(
+  translationDocument,
+  sourceLanguage,
+  targetLanguage
+) {
+  this.translationDocument = translationDocument;
+  this.sourceLanguage = sourceLanguage;
+  this.targetLanguage = targetLanguage;
+  this._pendingRequests = 0;
+  this._partialSuccess = false;
+  this._translatedCharacterCount = 0;
+};
+
+GoogleTranslator.prototype = {
+  /**
+   * Performs the translation, splitting the document into several chunks
+   * respecting the data limits of the API.
+   *
+   * @returns {Promise}          A promise that will resolve when the translation
+   *                             task is finished.
+   */
+  async translate() {
+    let currentIndex = 0;
+    this._onFinishedDeferred = PromiseUtils.defer();
+
+    // Let's split the document into various requests to be sent to
+    // Google's Translation API.
+    for (let requestCount = 0; requestCount < MAX_REQUESTS; requestCount++) {
+      // Generating the text for each request can be expensive, so
+      // let's take the opportunity of the chunkification process to
+      // allow for the event loop to attend other pending events
+      // before we continue.
+      await new Promise(resolve => Services.tm.dispatchToMainThread(resolve));
+
+      // Determine the data for the next request.
+      let request = this._generateNextTranslationRequest(currentIndex);
+
+      // Create a real request to the server, and put it on the
+      // pending requests list.
+      let googleRequest = new GoogleRequest(
+        request.data,
+        this.sourceLanguage,
+        this.targetLanguage
+      );
+      this._pendingRequests++;
+      googleRequest
+        .fireRequest()
+        .then(this._chunkCompleted.bind(this), this._chunkFailed.bind(this));
+
+      currentIndex = request.lastIndex;
+      if (request.finished) {
+        break;
+      }
+    }
+
+    return this._onFinishedDeferred.promise;
+  },
+
+  /**
+   * Function called when a request sent to the server completed successfully.
+   * This function handles calling the function to parse the result and the
+   * function to resolve the promise returned by the public `translate()`
+   * method when there's no pending request left.
+   *
+   * @param   request   The GoogleRequest sent to the server.
+   */
+  _chunkCompleted(googleRequest) {
+    if (this._parseChunkResult(googleRequest)) {
+      this._partialSuccess = true;
+      // Count the number of characters successfully translated.
+      this._translatedCharacterCount += googleRequest.characterCount;
+    }
+
+    this._checkIfFinished();
+  },
+
+  /**
+   * Function called when a request sent to the server has failed.
+   * This function handles deciding if the error is transient or means the
+   * service is unavailable (zero balance on the key or request credentials are
+   * not in an active state) and calling the function to resolve the promise
+   * returned by the public `translate()` method when there's no pending.
+   * request left.
+   *
+   * @param   aError   [optional] The XHR object of the request that failed.
+   */
+  _chunkFailed(aError) {
+    this._checkIfFinished();
+  },
+
+  /**
+   * Function called when a request sent to the server has completed.
+   * This function handles resolving the promise
+   * returned by the public `translate()` method when all chunks are completed.
+   */
+  _checkIfFinished() {
+    // Check if all pending requests have been
+    // completed and then resolves the promise.
+    // If at least one chunk was successful, the
+    // promise will be resolved positively which will
+    // display the "Success" state for the infobar. Otherwise,
+    // the "Error" state will appear.
+    if (--this._pendingRequests == 0) {
+      if (this._partialSuccess) {
+        this._onFinishedDeferred.resolve({
+          characterCount: this._translatedCharacterCount,
+        });
+      } else {
+        this._onFinishedDeferred.reject("failure");
+      }
+    }
+  },
+
+  /**
+   * This function parses the result returned by Bing's Http.svc API,
+   * which is a XML file that contains a number of elements. To our
+   * particular interest, the only part of the response that matters
+   * are the <TranslatedText> nodes, which contains the resulting
+   * items that were sent to be translated.
+   *
+   * @param   request      The request sent to the server.
+   * @returns boolean      True if parsing of this chunk was successful.
+   */
+  _parseChunkResult(googleRequest) {
+    let results;
+    try {
+      let response = googleRequest.networkRequest.response;
+      results = JSON.parse(response).data.translations;
+    } catch (e) {
+      return false;
+    }
+    let len = results.length;
+    if (len != googleRequest.translationData.length) {
+      // This should never happen, but if the service returns a different number
+      // of items (from the number of items submitted), we can't use this chunk
+      // because all items would be paired incorrectly.
+      return false;
+    }
+
+    let error = false;
+    for (let i = 0; i < len; i++) {
+      try {
+        let result = results[i].translatedText;
+        let root = googleRequest.translationData[i][0];
+        if (root.isSimpleRoot && result.includes("&")) {
+          // If the result contains HTML entities, we need to convert them as
+          // simple roots expect a plain text result.
+          let doc = new DOMParser().parseFromString(result, "text/html");
+          result = doc.body.firstChild.nodeValue;
+        }
+        root.parseResult(result);
+      } catch (e) {
+        error = true;
+      }
+    }
+
+    return !error;
+  },
+
+  /**
+   * This function will determine what is the data to be used for
+   * the Nth request we are generating, based on the input params.
+   *
+   * @param startIndex What is the index, in the roots list, that the
+   *                   chunk should start.
+   */
+  _generateNextTranslationRequest(startIndex) {
+    let currentDataSize = 0;
+    let currentChunks = 0;
+    let output = [];
+    let rootsList = this.translationDocument.roots;
+
+    for (let i = startIndex; i < rootsList.length; i++) {
+      let root = rootsList[i];
+      let text = this.translationDocument.generateTextForItem(root);
+      if (!text) {
+        continue;
+      }
+
+      let newCurSize = currentDataSize + text.length;
+      let newChunks = currentChunks + 1;
+
+      if (newCurSize > MAX_REQUEST_DATA || newChunks > MAX_REQUEST_CHUNKS) {
+        // If we've reached the API limits, let's stop accumulating data
+        // for this request and return. We return information useful for
+        // the caller to pass back on the next call, so that the function
+        // can keep working from where it stopped.
+        return {
+          data: output,
+          finished: false,
+          lastIndex: i,
+        };
+      }
+
+      currentDataSize = newCurSize;
+      currentChunks = newChunks;
+      output.push([root, text]);
+    }
+
+    return {
+      data: output,
+      finished: true,
+      lastIndex: 0,
+    };
+  },
+};
+
+/**
+ * Represents a request (for 1 chunk) sent off to Google's service.
+ *
+ * @params translationData  The data to be used for this translation,
+ *                          generated by the generateNextTranslationRequest...
+ *                          function.
+ * @param sourceLanguage    The source language of the document.
+ * @param targetLanguage    The target language for the translation.
+ *
+ */
+function GoogleRequest(translationData, sourceLanguage, targetLanguage) {
+  this.translationData = translationData;
+  this.sourceLanguage = sourceLanguage;
+  this.targetLanguage = targetLanguage;
+  this.characterCount = 0;
+}
+
+GoogleRequest.prototype = {
+  /**
+   * Initiates the request
+   */
+  fireRequest() {
+    let key =
+      Services.cpmm.sharedData.get("translationKey") ||
+      Services.prefs.getStringPref("browser.translation.google.apiKey", "");
+    if (!key) {
+      return Promise.reject("no API key");
+    }
+
+    // Prepare the request body.
+    let postData = [
+      ["key", key],
+      ["source", this.sourceLanguage],
+      ["target", this.targetLanguage],
+    ];
+
+    for (let [, text] of this.translationData) {
+      postData.push(["q", text]);
+      this.characterCount += text.length;
+    }
+
+    // Set up request options.
+    return new Promise((resolve, reject) => {
+      let options = {
+        onLoad: (responseText, xhr) => {
+          resolve(this);
+        },
+        onError(e, responseText, xhr) {
+          reject(xhr);
+        },
+        postData,
+      };
+
+      // Fire the request.
+      this.networkRequest = httpRequest(URL, options);
+    });
+  },
+};