Correctly handle optional length in HTTP output stream writeFrom

tests/standalone/io/regress_7097_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+import 'dart:uri';
+
+void main() {
+  var client = new HttpClient();
+  var server = new HttpServer();
+
+  var count = 0;
+  server.defaultRequestHandler = (HttpRequest request, HttpResponse response) {
+    List<int> data = [];
+    request.inputStream.onData = () {
+      data.addAll(request.inputStream.read());
+    };
+    request.inputStream.onClosed = () {
+      count++;
+      Expect.equals(count, data.length);
+      switch (count - 1) {
+        case 0:
+          response.outputStream.writeFrom([65, 66, 67], 1, 1);
+          break;
+        case 1:
+          response.outputStream.writeFrom([65, 66, 67], 1);
+          break;
+        case 2:
+          response.outputStream.writeFrom([65, 66, 67]);
+          break;
+        default:
+          Expect.fail("Unexpected state");
+      }
+      response.outputStream.close();
+    };
+  };
+  server.listen('127.0.0.1', 0);
+
+  Future makeRequest(int n) {
+    var completer = new Completer();
+    var url = new Uri.fromString("http://localhost:${server.port}");
+    var connection = client.openUrl("POST", url);
+    connection.onRequest = (HttpClientRequest request) {
+      request.contentLength = n + 1;
+      switch (n) {
+        case 0:
+          request.outputStream.writeFrom([65, 66, 67], 1, 1);
+          break;
+        case 1:
+          request.outputStream.writeFrom([65, 66, 67], 1);
+          break;
+        case 2:
+          request.outputStream.writeFrom([65, 66, 67]);
+          break;
+        default:
+          Expect.fail("Unexpected state");
+      }
+      request.outputStream.close();
+    };
+    connection.onResponse = (HttpClientResponse response) {
+      List<int> data = [];
+      response.inputStream.onData = () {
+        data.addAll(response.inputStream.read());
+      };
+      response.inputStream.onClosed = () {
+        Expect.equals(count, data.length);
+        completer.complete(null);
+      };
+    };
+    return completer.future;
+  }
+
+  makeRequest(0).then((_) {
+    makeRequest(1).then((_) {
+      makeRequest(2).then((_) {
+        client.shutdown();
+        server.close();
+      });
+    });
+  });
+}