1 files changed, 143 insertions, 0 deletions
diff --git a/browser/components/translation/LanguageDetector.jsm b/browser/components/translation/LanguageDetector.jsm
new file mode 100644
index 000000000..a65d6eda1
--- /dev/null
+++ b/browser/components/translation/LanguageDetector.jsm
@@ -0,0 +1,143 @@
+/* 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";
+
+this.EXPORTED_SYMBOLS = ["LanguageDetector"];
+
+Components.utils.import("resource://gre/modules/Timer.jsm");
+Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
+
+// Since Emscripten can handle heap growth, but not heap shrinkage, we
+// need to refresh the worker after we've processed a particularly large
+// string in order to prevent unnecessary resident memory growth.
+//
+// These values define the cut-off string length and the idle timeout
+// (in milliseconds) before destroying a worker. Once a string of the
+// maximum size has been processed, the worker is marked for
+// destruction, and is terminated as soon as it has been idle for the
+// given timeout.
+//
+// 1.5MB. This is the approximate string length that forces heap growth
+// for a 2MB heap.
+var LARGE_STRING = 1.5 * 1024 * 1024;
+var IDLE_TIMEOUT = 10 * 1000;
+
+const WORKER_URL = "resource:///modules/translation/cld-worker.js";
+
+var workerManager = {
+  detectionQueue: [],
+
+  detectLanguage(aParams) {
+    return this.workerReady.then(worker => {
+      return new Promise(resolve => {
+        this.detectionQueue.push({resolve});
+        worker.postMessage(aParams);
+      });
+    }).then(result => {
+      // We have our asynchronous result from the worker.
+      //
+      // Determine if our input was large enough to trigger heap growth,
+      // or if we're already waiting to destroy the worker when it's
+      // idle. If so, schedule termination after the idle timeout.
+      if (aParams.text.length >= LARGE_STRING || this._idleTimeout != null)
+        this.flushWorker();
+
+      return result;
+    })
+  },
+
+  _worker: null,
+  _workerReadyPromise: null,
+
+  get workerReady() {
+    if (!this._workerReadyPromise)
+      this._workerReadyPromise = new Promise(resolve => {
+        let worker = new Worker(WORKER_URL);
+        worker.onmessage = (aMsg) => {
+          if (aMsg.data == "ready")
+            resolve(worker);
+          else
+            this.detectionQueue.shift().resolve(aMsg.data);
+        };
+        this._worker = worker;
+      });
+
+    return this._workerReadyPromise;
+  },
+
+  // Holds the ID of the current pending idle cleanup setTimeout.
+  _idleTimeout: null,
+
+  // Schedule the current worker to be terminated after the idle timeout.
+  flushWorker() {
+    if (this._idleTimeout != null)
+      clearTimeout(this._idleTimeout);
+
+    this._idleTimeout = setTimeout(this._flushWorker.bind(this), IDLE_TIMEOUT);
+  },
+
+  // Immediately terminate the worker, as long as there no pending
+  // results. Otherwise, reschedule termination until after the next
+  // idle timeout.
+  _flushWorker() {
+    if (this.detectionQueue.length)
+      this.flushWorker();
+    else {
+      if (this._worker)
+        this._worker.terminate();
+
+      this._worker = null;
+      this._workerReadyPromise = null;
+      this._idleTimeout = null;
+    }
+  },
+};
+
+this.LanguageDetector = {
+  /**
+   * Detect the language of a given string.
+   *
+   * The argument may be either a string containing the text to analyze,
+   * or an object with the following properties:
+   *
+   *  - 'text' The text to analyze.
+   *
+   *  - 'isHTML' (optional) A boolean, indicating whether the text
+   *      should be analyzed as HTML rather than plain text.
+   *
+   *  - 'language' (optional) A string indicating the expected language.
+   *      For text extracted from HTTP documents, this is expected to
+   *      come from the Content-Language header.
+   *
+   *  - 'tld' (optional) A string indicating the top-level domain of the
+   *      document the text was extracted from.
+   *
+   *  - 'encoding' (optional) A string describing the encoding of the
+   *      document the string was extracted from. Note that, regardless
+   *      of the value of this property, the 'text' property must be a
+   *      UTF-16 JavaScript string.
+   *
+   * @returns {Promise<Object>}
+   * @resolves When detection is finished, with a object containing
+   * these fields:
+   *  - 'language' (string with a language code)
+   *  - 'confident' (boolean) Whether the detector is confident of the
+   *      result.
+   *  - 'languages' (array) An array of up to three elements, containing
+   *      the most prevalent languages detected. It contains a
+   *      'languageCode' property, containing the ISO language code of
+   *      the language, and a 'percent' property, describing the
+   *      approximate percentage of the input which is in that language.
+   *      For text of an unknown language, the result may contain an
+   *      entry with the languge code 'un', indicating the percent of
+   *      the text which is unknown.
+   */
+  detectLanguage: function(aParams) {
+    if (typeof aParams == "string")
+      aParams = { text: aParams };
+
+    return workerManager.detectLanguage(aParams);
+  },
+};