Add "/file.js" buffered disk I/O object.

This is similar to the class node.File which was removed in
82cb1b5acb.

Needs documentation.

lib/file.js

@@ -0,0 +1,128 @@
+exports.debugLevel = 0; // Increase to get more verbose debug output
+
+function debugMessage (msg) {
+  if (exports.debugLevel > 0) {
+    node.error(__filename + ": " + msg.toString());
+  }
+}
+
+function debugObject (obj) {
+  if (exports.debugLevel > 0) {
+    node.error(__filename + ": " + JSON.stringify(obj));
+  }
+}
+
+exports.File = function (filename, mode, options) {
+  var self = this;
+
+  options = options || {};
+  self.encoding = options.encoding || "utf8";
+
+  self.filename = filename;
+
+  self.actionQueue = [];
+  self.currentAction = null;
+
+  switch (mode) {
+    case "r":
+      self.flags = node.O_RDONLY;
+      break;
+
+    case "r+":
+      self.flags = node.O_RDWR;
+      break;
+
+    case "w":
+      self.flags = node.O_CREAT | node.O_TRUNC | node.O_WRONLY;
+      break;
+
+    case "w+":
+      self.flags = node.O_CREAT | node.O_TRUNC | node.O_RDWR;
+      break;
+
+    case "a":
+      self.flags = node.O_APPEND | node.O_CREAT | node.O_WRONLY; 
+      break;
+
+    case "a+":
+      self.flags = node.O_APPEND | node.O_CREAT | node.O_RDWR; 
+      break;
+
+    default:
+      throw new Error("Unknown mode");
+  }
+
+  self.open(self.filename, self.flags, 0666).addCallback(function (fd) {
+    debugMessage(self.filename + " opened. fd = " + fd);
+    self.fd = fd;
+  }).addErrback(function () {
+    self.emit("error", ["open"]);
+  });
+};
+
+var proto = exports.File.prototype;
+
+proto._maybeDispatch = function () {
+  var self = this;
+
+  if (self.currentAction) return;
+  self.currentAction = self.actionQueue.shift();
+  if (!self.currentAction) return;
+
+  debugObject(self.currentAction);
+
+  var args = self.currentAction.args || [];
+
+  if (self.currentAction.method != "open") {
+    args.unshift(self.fd);
+  }
+
+  var method = self.currentAction.method;
+
+  if (!args[3] && (method == "read" || method == "write")) {
+    args[3] = self.encoding;
+  }
+
+  var promise = node.fs[method].apply(self, args);
+
+  var userPromise = self.currentAction.promise;
+
+  promise.addCallback(function () {
+    node.assert(self.currentAction.promise == userPromise);
+    userPromise.emitSuccess.apply(userPromise, arguments);
+    self.currentAction = null;
+    self._maybeDispatch();
+  }).addErrback(function () {
+    debugMessage("Error in method " + method);
+    node.assert(self.currentAction.promise == userPromise);
+    userPromise.emitError.apply(userPromise, arguments);
+    self.currentAction = null;
+    self._maybeDispatch();
+  });
+};
+
+proto._queueAction = function (method, args) {
+  var userPromise = new node.Promise;
+  this.actionQueue.push({ method: method, args: args, promise: userPromise });
+  this._maybeDispatch();
+  return userPromise;
+};
+
+// FIXME the following can probably be DRY'd up with some fancy getter
+// stuff.
+
+proto.open = function (filename, flags, mode) {
+  return this._queueAction("open", [filename, flags, mode]);
+};
+
+proto.write = function (data, pos, encoding) {
+  return this._queueAction("write", [data, pos, encoding]);
+};
+
+proto.read = function (length, pos, encoding) {
+  return this._queueAction("read", [length, pos, encoding]);
+};
+
+proto.close = function () {
+  return this._queueAction("close");
+};

test/mjsunit/test-buffered-file.js

@@ -0,0 +1,38 @@
+include("common.js");
+
+var testTxt = node.path.join(fixturesDir, "test.txt");
+
+var libDir = node.path.join(testDir, "../../lib");
+node.libraryPaths.unshift(libDir);
+include("/file.js");
+
+var fileUnlinked = false;
+
+var file = new File(testTxt, "w+");
+file.write("hello\n");
+file.write("world\n");
+setTimeout(function () {
+  file.write("hello\n");
+  file.write("world\n");
+  file.close().addCallback(function () {
+    node.error("file closed...");
+    var out = node.fs.cat(testTxt).wait();
+    print("the file contains: ");
+    p(out);
+    assertEquals("hello\nworld\nhello\nworld\n", out);
+    var file2 = new File(testTxt, "r");
+    file2.read(5).addCallback(function (data) {
+      puts("read(5): " + JSON.stringify(data));
+      assertEquals("hello", data);
+      node.fs.unlink(testTxt).addCallback(function () {
+        fileUnlinked = true;
+      });
+    });
+    file2.close();
+  });
+}, 10);
+
+process.addListener("exit", function () {
+  assertTrue(fileUnlinked);
+  puts("done");
+});