Initial write stream implementation

lib/fs.js

@@ -375,3 +375,90 @@ exports.realpath = function(path, callback) {
       callback(null, normalize(path));
   });
 }
+
+exports.fileWriteStream = function(path, options) {
+  return new FileWriteStream(path, options);
+};
+
+var FileWriteStream = exports.FileWriteStream = function(path, options) {
+  this.path = path;
+  this.fd = null;
+  this.closed = false;
+
+  this.flags = 'w';
+  this.encoding = 'binary';
+  this.mode = 0666;
+
+  process.mixin(this, options || {});
+
+  var
+    self = this,
+    queue = [],
+    busy = false;
+
+  queue.push([fs.open, this.path, this.flags, this.mode]);
+
+  function pump() {
+    if (busy) {
+      return;
+    }
+
+    var args = queue.shift();
+    if (!args) {
+      return self.emit('drain');
+    }
+
+    busy = true;
+
+    var method = args.shift();
+
+    args.push(function(err) {
+      busy = false;
+
+      if (err) {
+        self.emit('error', err);
+        return;
+      }
+
+      // save reference for file pointer
+      if (method === fs.open) {
+        self.fd = arguments[1];
+        self.emit('open', self.fd);
+      }
+
+      // stop pumping after close
+      if (method === fs.close) {
+        self.emit('close');
+        return;
+      }
+
+      pump();
+    });
+
+    // Inject the file pointer
+    if (method !== fs.open) {
+      args.unshift(self.fd);
+    }
+
+    method.apply(null, args);
+  };
+
+  this.write = function(data) {
+    if (this.closed) {
+      throw new Error('stream already closed');
+    }
+
+    queue.push([fs.write, data, undefined, this.encoding]);
+    pump();
+    return false;
+  };
+
+  this.close = function() {
+    this.closed = true;
+    queue.push([fs.close,]);
+    pump();
+  };
+
+  pump();
+};
+FileWriteStream.prototype.__proto__ = process.EventEmitter.prototype;

test/simple/test-file-write-stream.js

@@ -0,0 +1,47 @@
+process.mixin(require('../common'));
+
+var
+  fn = path.join(fixturesDir, "write.txt"),
+  file = fs.fileWriteStream(fn),
+
+  EXPECTED = '0123456789',
+
+  callbacks = {
+    open: -1,
+    drain: -2,
+    close: -1
+  };
+
+file
+  .addListener('open', function(fd) {
+    callbacks.open++;
+    assert.equal('number', typeof fd);
+  })
+  .addListener('drain', function() {
+    callbacks.drain++;
+    if (callbacks.drain == -1) {
+      assert.equal(EXPECTED, fs.readFileSync(fn));
+      file.write(EXPECTED);
+    } else if (callbacks.drain == 0) {
+      assert.equal(EXPECTED+EXPECTED, fs.readFileSync(fn));
+      file.close();
+    }
+  })
+  .addListener('close', function() {
+    callbacks.close++;
+    assert.throws(function() {
+      file.write('should not work anymore');
+    });
+
+    fs.unlinkSync(fn);
+  });
+
+for (var i = 0; i < 10; i++) {
+  assert.strictEqual(false, file.write(i));
+}
+
+process.addListener('exit', function() {
+  for (var k in callbacks) {
+    assert.equal(0, callbacks[k], k+' count off by '+callbacks[k]);
+  }
+});