1 files changed, 314 insertions, 0 deletions
diff --git a/browser/components/sessionstore/_SessionFile.jsm b/browser/components/sessionstore/_SessionFile.jsm
new file mode 100644
index 000000000..173f6035d
--- /dev/null
+++ b/browser/components/sessionstore/_SessionFile.jsm
@@ -0,0 +1,314 @@
+/* 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 = ["_SessionFile"];
+
+/**
+ * Implementation of all the disk I/O required by the session store.
+ * This is a private API, meant to be used only by the session store.
+ * It will change. Do not use it for any other purpose.
+ *
+ * Note that this module implicitly depends on one of two things:
+ * 1. either the asynchronous file I/O system enqueues its requests
+ *   and never attempts to simultaneously execute two I/O requests on
+ *   the files used by this module from two distinct threads; or
+ * 2. the clients of this API are well-behaved and do not place
+ *   concurrent requests to the files used by this module.
+ *
+ * Otherwise, we could encounter bugs, especially under Windows,
+ *   e.g. if a request attempts to write sessionstore.js while
+ *   another attempts to copy that file.
+ *
+ * This implementation uses OS.File, which guarantees property 1.
+ */
+
+const Cu = Components.utils;
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/osfile.jsm");
+Cu.import("resource://gre/modules/Promise.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
+  "resource://gre/modules/NetUtil.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "FileUtils",
+  "resource://gre/modules/FileUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "Task",
+  "resource://gre/modules/Task.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "console",
+  "resource://gre/modules/Console.jsm");
+
+// An encoder to UTF-8.
+XPCOMUtils.defineLazyGetter(this, "gEncoder", function() {
+  return new TextEncoder();
+});
+// A decoder.
+XPCOMUtils.defineLazyGetter(this, "gDecoder", function() {
+  return new TextDecoder();
+});
+
+this._SessionFile = {
+  /**
+   * A promise fulfilled once initialization (either synchronous or
+   * asynchronous) is complete.
+   */
+  promiseInitialized: function() {
+    return SessionFileInternal.promiseInitialized;
+  },
+  /**
+   * Read the contents of the session file, asynchronously.
+   */
+  read: function() {
+    return SessionFileInternal.read();
+  },
+  /**
+   * Read the contents of the session file, synchronously.
+   */
+  syncRead: function() {
+    return SessionFileInternal.syncRead();
+  },
+  /**
+   * Write the contents of the session file, asynchronously.
+   */
+  write: function(aData) {
+    return SessionFileInternal.write(aData);
+  },
+  /**
+   * Create a backup copy, asynchronously.
+   */
+  createBackupCopy: function() {
+    return SessionFileInternal.createBackupCopy();
+  },
+  /**
+   * Wipe the contents of the session file, asynchronously.
+   */
+  wipe: function() {
+    return SessionFileInternal.wipe();
+  }
+};
+
+Object.freeze(_SessionFile);
+
+/**
+ * Utilities for dealing with promises and Task.jsm
+ */
+const TaskUtils = {
+  /**
+   * Add logging to a promise.
+   *
+   * @param {Promise} promise
+   * @return {Promise} A promise behaving as |promise|, but with additional
+   * logging in case of uncaught error.
+   */
+  captureErrors: function(promise) {
+    return promise.then(
+      null,
+      function onError(reason) {
+        console.error("Uncaught asynchronous error:", reason);
+        throw reason;
+      }
+    );
+  },
+  /**
+   * Spawn a new Task from a generator.
+   *
+   * This function behaves as |Task.spawn|, with the exception that it
+   * adds logging in case of uncaught error. For more information, see
+   * the documentation of |Task.jsm|.
+   *
+   * @param {generator} gen Some generator.
+   * @return {Promise} A promise built from |gen|, with the same semantics
+   * as |Task.spawn(gen)|.
+   */
+  spawn: function spawn(gen) {
+    return this.captureErrors(Task.spawn(gen));
+  }
+};
+
+var SessionFileInternal = {
+  /**
+   * A promise fulfilled once initialization is complete
+   */
+  promiseInitialized: Promise.defer(),
+
+  /**
+   * The path to sessionstore.js
+   */
+  path: OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.js"),
+
+  /**
+   * The path to sessionstore.bak
+   */
+  backupPath: OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.bak"),
+
+  /**
+   * Utility function to safely read a file synchronously.
+   * @param aPath
+   *        A path to read the file from.
+   * @returns string if successful, undefined otherwise.
+   */
+  readAuxSync: function(aPath) {
+    let text;
+    try {
+      let file = new FileUtils.File(aPath);
+      let chan = NetUtil.newChannel({
+        uri: NetUtil.newURI(file),
+        loadUsingSystemPrincipal: true
+      });
+      let stream = chan.open();
+      text = NetUtil.readInputStreamToString(stream, stream.available(),
+        {charset: "utf-8"});
+    } catch (e if e.result == Components.results.NS_ERROR_FILE_NOT_FOUND) {
+      // Ignore exceptions about non-existent files.
+    } catch (ex) {
+      // Any other error.
+      console.error("Uncaught error:", ex);
+    } finally {
+      return text;
+    }
+  },
+
+  /**
+   * Read the sessionstore file synchronously.
+   *
+   * This function is meant to serve as a fallback in case of race
+   * between a synchronous usage of the API and asynchronous
+   * initialization.
+   *
+   * In case if sessionstore.js file does not exist or is corrupted (something
+   * happened between backup and write), attempt to read the sessionstore.bak
+   * instead.
+   */
+  syncRead: function() {
+    // First read the sessionstore.js.
+    let text = this.readAuxSync(this.path);
+    if (typeof text === "undefined") {
+      // If sessionstore.js does not exist or is corrupted, read sessionstore.bak.
+      text = this.readAuxSync(this.backupPath);
+    }
+    return text || "";
+  },
+
+  /**
+   * Utility function to safely read a file asynchronously.
+   * @param aPath
+   *        A path to read the file from.
+   * @param aReadOptions
+   *        Read operation options.
+   *        |outExecutionDuration| option will be reused and can be
+   *        incrementally updated by the worker process.
+   * @returns string if successful, undefined otherwise.
+   */
+  readAux: function(aPath, aReadOptions) {
+    let self = this;
+    return TaskUtils.spawn(function() {
+      let text;
+      try {
+        let bytes = yield OS.File.read(aPath, undefined, aReadOptions);
+        text = gDecoder.decode(bytes);
+      } catch (ex if self._isNoSuchFile(ex)) {
+        // Ignore exceptions about non-existent files.
+      } catch (ex) {
+        // Any other error.
+        console.error("Uncaught error - with the file: " + self.path, ex);
+      }
+      throw new Task.Result(text);
+    });
+  },
+
+  /**
+   * Read the sessionstore file asynchronously.
+   *
+   * In case sessionstore.js file does not exist or is corrupted (something
+   * happened between backup and write), attempt to read the sessionstore.bak
+   * instead.
+   */
+  read: function() {
+    let self = this;
+    return TaskUtils.spawn(function task() {
+      // Specify |outExecutionDuration| option to hold the combined duration of
+      // the asynchronous reads off the main thread (of both sessionstore.js and
+      // sessionstore.bak, if necessary). If sessionstore.js does not exist or
+      // is corrupted, |outExecutionDuration| will register the time it took to
+      // attempt to read the file. It will then be subsequently incremented by
+      // the read time of sessionsore.bak.
+      let readOptions = {
+        outExecutionDuration: null
+      };
+      // First read the sessionstore.js.
+      let text = yield self.readAux(self.path, readOptions);
+      if (typeof text === "undefined") {
+        // If sessionstore.js does not exist or is corrupted, read the
+        // sessionstore.bak.
+        text = yield self.readAux(self.backupPath, readOptions);
+      }
+      // Return either the content of the sessionstore.bak if it was read
+      // successfully or an empty string otherwise.
+      throw new Task.Result(text || "");
+    });
+  },
+
+  write: function(aData) {
+    let refObj = {};
+    let self = this;
+    return TaskUtils.spawn(function task() {
+      let bytes = gEncoder.encode(aData);
+
+      try {
+        let promise = OS.File.writeAtomic(self.path, bytes, {tmpPath: self.path + ".tmp"});
+        yield promise;
+      } catch (ex) {
+        console.error("Could not write session state file: " + self.path, ex);
+      }
+    });
+  },
+
+  createBackupCopy: function() {
+    let backupCopyOptions = {
+      outExecutionDuration: null
+    };
+    let self = this;
+    return TaskUtils.spawn(function task() {
+      try {
+        yield OS.File.move(self.path, self.backupPath, backupCopyOptions);
+      } catch (ex if self._isNoSuchFile(ex)) {
+        // Ignore exceptions about non-existent files.
+      } catch (ex) {
+        console.error("Could not backup session state file: " + self.path, ex);
+        throw ex;
+      }
+    });
+  },
+
+  wipe: function() {
+    let self = this;
+    return TaskUtils.spawn(function task() {
+      try {
+        yield OS.File.remove(self.path);
+      } catch (ex if self._isNoSuchFile(ex)) {
+        // Ignore exceptions about non-existent files.
+      } catch (ex) {
+        console.error("Could not remove session state file: " + self.path, ex);
+        throw ex;
+      }
+
+      try {
+        yield OS.File.remove(self.backupPath);
+      } catch (ex if self._isNoSuchFile(ex)) {
+        // Ignore exceptions about non-existent files.
+      } catch (ex) {
+        console.error("Could not remove session state backup file: " + self.path, ex);
+        throw ex;
+      }
+    });
+  },
+
+  _isNoSuchFile: function(aReason) {
+    return aReason instanceof OS.File.Error && aReason.becauseNoSuchFile;
+  }
+};