Add a Pub validator for READMEs that are invalid utf-8.

utils/pub/validator/utf8_readme.dart

+// Copyright (c) 2013, 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.
+
+library utf8_readme_validator;
+
+import 'dart:async';
+import 'dart:utf';
+
+import '../../../pkg/path/lib/path.dart' as path;
+
+import '../entrypoint.dart';
+import '../io.dart';
+import '../utils.dart';
+import '../validator.dart';
+
+/// Validates that a package's README is valid utf-8.
+class Utf8ReadmeValidator extends Validator {
+  Utf8ReadmeValidator(Entrypoint entrypoint)
+    : super(entrypoint);
+
+  Future validate() {
+    return entrypoint.root.readmePath.then((readme) {
+      if (readme == null) return;
+      var bytes = readBinaryFile(readme);
+      try {
+        // The second and third arguments here are the default values. The
+        // fourth tells [decodeUtf8] to throw an ArgumentError if `bytes` isn't
+        // valid utf-8.
+        decodeUtf8(bytes, 0, null, null);
+      } on ArgumentError catch (_) {
+        warnings.add("$readme contains invalid UTF-8.\n"
+            "This will cause it to be displayed incorrectly on "
+                "pub.dartlang.org.");
+      }
+    });
+  }
+}
+