1 files changed, 270 insertions, 0 deletions
diff --git a/components/extensions/src/DeferredSave.jsm b/components/extensions/src/DeferredSave.jsm
new file mode 100644
index 000000000..f1537fe4b
--- /dev/null
+++ b/components/extensions/src/DeferredSave.jsm
@@ -0,0 +1,270 @@
+/* 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";
+
+const Cu = Components.utils;
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+Cu.import("resource://gre/modules/osfile.jsm");
+/* globals OS*/
+Cu.import("resource://gre/modules/Promise.jsm");
+
+// Make it possible to mock out timers for testing
+var MakeTimer = () => Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
+
+this.EXPORTED_SYMBOLS = ["DeferredSave"];
+
+// If delay parameter is not provided, default is 50 milliseconds.
+const DEFAULT_SAVE_DELAY_MS = 50;
+
+Cu.import("resource://gre/modules/Log.jsm");
+// Configure a logger at the parent 'DeferredSave' level to format
+// messages for all the modules under DeferredSave.*
+const DEFERREDSAVE_PARENT_LOGGER_ID = "DeferredSave";
+var parentLogger = Log.repository.getLogger(DEFERREDSAVE_PARENT_LOGGER_ID);
+parentLogger.level = Log.Level.Warn;
+var formatter = new Log.BasicFormatter();
+// Set parent logger (and its children) to append to
+// the Javascript section of the Browser Console
+parentLogger.addAppender(new Log.ConsoleAppender(formatter));
+// Set parent logger (and its children) to
+// also append to standard out
+parentLogger.addAppender(new Log.DumpAppender(formatter));
+
+// Provide the ability to enable/disable logging
+// messages at runtime.
+// If the "extensions.logging.enabled" preference is
+// missing or 'false', messages at the WARNING and higher
+// severity should be logged to the JS console and standard error.
+// If "extensions.logging.enabled" is set to 'true', messages
+// at DEBUG and higher should go to JS console and standard error.
+Cu.import("resource://gre/modules/Services.jsm");
+
+const PREF_LOGGING_ENABLED = "extensions.logging.enabled";
+const NS_PREFBRANCH_PREFCHANGE_TOPIC_ID = "nsPref:changed";
+
+/**
+* Preference listener which listens for a change in the
+* "extensions.logging.enabled" preference and changes the logging level of the
+* parent 'addons' level logger accordingly.
+*/
+var PrefObserver = {
+ init: function() {
+   Services.prefs.addObserver(PREF_LOGGING_ENABLED, this, false);
+   Services.obs.addObserver(this, "xpcom-shutdown", false);
+   this.observe(null, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID, PREF_LOGGING_ENABLED);
+ },
+
+ observe: function(aSubject, aTopic, aData) {
+   if (aTopic == "xpcom-shutdown") {
+     Services.prefs.removeObserver(PREF_LOGGING_ENABLED, this);
+     Services.obs.removeObserver(this, "xpcom-shutdown");
+   }
+   else if (aTopic == NS_PREFBRANCH_PREFCHANGE_TOPIC_ID) {
+     let debugLogEnabled = Services.prefs.getBoolPref(PREF_LOGGING_ENABLED, false);
+     if (debugLogEnabled) {
+       parentLogger.level = Log.Level.Debug;
+     }
+     else {
+       parentLogger.level = Log.Level.Warn;
+     }
+   }
+ }
+};
+
+PrefObserver.init();
+
+/**
+ * A module to manage deferred, asynchronous writing of data files
+ * to disk. Writing is deferred by waiting for a specified delay after
+ * a request to save the data, before beginning to write. If more than
+ * one save request is received during the delay, all requests are
+ * fulfilled by a single write.
+ *
+ * @constructor
+ * @param aPath
+ *        String representing the full path of the file where the data
+ *        is to be written.
+ * @param aDataProvider
+ *        Callback function that takes no argument and returns the data to
+ *        be written. If aDataProvider returns an ArrayBufferView, the
+ *        bytes it contains are written to the file as is.
+ *        If aDataProvider returns a String the data are UTF-8 encoded
+ *        and then written to the file.
+ * @param [optional] aDelay
+ *        The delay in milliseconds between the first saveChanges() call
+ *        that marks the data as needing to be saved, and when the DeferredSave
+ *        begins writing the data to disk. Default 50 milliseconds.
+ */
+this.DeferredSave = function(aPath, aDataProvider, aDelay) {
+  // Create a new logger (child of 'DeferredSave' logger)
+  // for use by this particular instance of DeferredSave object
+  let leafName = OS.Path.basename(aPath);
+  let logger_id = DEFERREDSAVE_PARENT_LOGGER_ID + "." + leafName;
+  this.logger = Log.repository.getLogger(logger_id);
+
+  // @type {Deferred|null}, null when no data needs to be written
+  // @resolves with the result of OS.File.writeAtomic when all writes complete
+  // @rejects with the error from OS.File.writeAtomic if the write fails,
+  //          or with the error from aDataProvider() if that throws.
+  this._pending = null;
+
+  // @type {Promise}, completes when the in-progress write (if any) completes,
+  //       kept as a resolved promise at other times to simplify logic.
+  //       Because _deferredSave() always uses _writing.then() to execute
+  //       its next action, we don't need a special case for whether a write
+  //       is in progress - if the previous write is complete (and the _writing
+  //       promise is already resolved/rejected), _writing.then() starts
+  //       the next action immediately.
+  //
+  // @resolves with the result of OS.File.writeAtomic
+  // @rejects with the error from OS.File.writeAtomic
+  this._writing = Promise.resolve(0);
+
+  // Are we currently waiting for a write to complete
+  this.writeInProgress = false;
+
+  this._path = aPath;
+  this._dataProvider = aDataProvider;
+
+  this._timer = null;
+
+  // Some counters for telemetry
+  // The total number of times the file was written
+  this.totalSaves = 0;
+
+  // The number of times the data became dirty while
+  // another save was in progress
+  this.overlappedSaves = 0;
+
+  // Error returned by the most recent write (if any)
+  this._lastError = null;
+
+  if (aDelay && (aDelay > 0))
+    this._delay = aDelay;
+  else
+    this._delay = DEFAULT_SAVE_DELAY_MS;
+}
+
+this.DeferredSave.prototype = {
+  get dirty() {
+    return this._pending || this.writeInProgress;
+  },
+
+  get lastError() {
+    return this._lastError;
+  },
+
+  // Start the pending timer if data is dirty
+  _startTimer: function() {
+    if (!this._pending) {
+      return;
+    }
+
+      this.logger.debug("Starting timer");
+    if (!this._timer)
+      this._timer = MakeTimer();
+    this._timer.initWithCallback(() => this._deferredSave(),
+                                 this._delay, Ci.nsITimer.TYPE_ONE_SHOT);
+  },
+
+  /**
+   * Mark the current stored data dirty, and schedule a flush to disk
+   * @return A Promise<integer> that will be resolved after the data is written to disk;
+   *         the promise is resolved with the number of bytes written.
+   */
+  saveChanges: function() {
+      this.logger.debug("Save changes");
+    if (!this._pending) {
+      if (this.writeInProgress) {
+          this.logger.debug("Data changed while write in progress");
+        this.overlappedSaves++;
+      }
+      this._pending = Promise.defer();
+      // Wait until the most recent write completes or fails (if it hasn't already)
+      // and then restart our timer
+      this._writing.then(count => this._startTimer(), error => this._startTimer());
+    }
+    return this._pending.promise;
+  },
+
+  _deferredSave: function() {
+    let pending = this._pending;
+    this._pending = null;
+    let writing = this._writing;
+    this._writing = pending.promise;
+
+    // In either the success or the exception handling case, we don't need to handle
+    // the error from _writing here; it's already being handled in another then()
+    let toSave = null;
+    try {
+      toSave = this._dataProvider();
+    }
+    catch (e) {
+        this.logger.error("Deferred save dataProvider failed", e);
+      writing.then(null, error => {})
+        .then(count => {
+          pending.reject(e);
+        });
+      return;
+    }
+
+    writing.then(null, error => { return 0; })
+    .then(count => {
+        this.logger.debug("Starting write");
+      this.totalSaves++;
+      this.writeInProgress = true;
+
+      OS.File.writeAtomic(this._path, toSave, {tmpPath: this._path + ".tmp"})
+      .then(
+        result => {
+          this._lastError = null;
+          this.writeInProgress = false;
+              this.logger.debug("Write succeeded");
+          pending.resolve(result);
+        },
+        error => {
+          this._lastError = error;
+          this.writeInProgress = false;
+              this.logger.warn("Write failed", error);
+          pending.reject(error);
+        });
+    });
+  },
+
+  /**
+   * Immediately save the dirty data to disk, skipping
+   * the delay of normal operation. Note that the write
+   * still happens asynchronously in the worker
+   * thread from OS.File.
+   *
+   * There are four possible situations:
+   * 1) Nothing to flush
+   * 2) Data is not currently being written, in-memory copy is dirty
+   * 3) Data is currently being written, in-memory copy is clean
+   * 4) Data is being written and in-memory copy is dirty
+   *
+   * @return Promise<integer> that will resolve when all in-memory data
+   *         has finished being flushed, returning the number of bytes
+   *         written. If all in-memory data is clean, completes with the
+   *         result of the most recent write.
+   */
+  flush: function() {
+    // If we have pending changes, cancel our timer and set up the write
+    // immediately (_deferredSave queues the write for after the most
+    // recent write completes, if it hasn't already)
+    if (this._pending) {
+        this.logger.debug("Flush called while data is dirty");
+      if (this._timer) {
+        this._timer.cancel();
+        this._timer = null;
+      }
+      this._deferredSave();
+    }
+
+    return this._writing;
+  }
+};