Make the oauth2 lib handle OAuth2 401 errors.

pkg/oauth2/lib/src/utils.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.
 
 library utils;
 
 import 'dart:uri';
 import 'dart:isolate';
 import 'dart:crypto';
 
@@ skipping 47 matching lines @@
 /// This will always return a list of two elements or fewer.
 List<String> split1(String toSplit, String pattern) {
   if (toSplit.isEmpty) return <String>[];
 
   var index = toSplit.indexOf(pattern);
   if (index == -1) return [toSplit];
   return [toSplit.substring(0, index),
       toSplit.substring(index + pattern.length)];
 }
 
+/// A WWW-Authenticate header value, parsed as per [RFC 2617][].
+///
+/// [RFC 2617]: http://tools.ietf.org/html/rfc2617
+class AuthenticateHeader {
+  final String scheme;
+  final Map<String, String> parameters;
+
+  AuthenticateHeader(this.scheme, this.parameters);
+
+  /// Parses a header string. Throws a [FormatException] if the header is
+  /// invalid.
+  factory AuthenticateHeader.parse(String header) {
+    var split = split1(header, ' ');
+    if (split.length == 0) {
+      throw new FormatException('Invalid WWW-Authenticate header: "$header"');
+    } else if (split.length == 1 || split[1].trim().isEmpty) {
+      return new AuthenticateHeader(split[0].toLowerCase(), {});
+    }
+    var scheme = split[0].toLowerCase();
+    var paramString = split[1];
+
+    // From http://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html.
+    var tokenChar = r'[^\0-\x1F()<>@,;:\\"/\[\]?={} \t\x7F]';
+    var quotedStringChar = r'(?:[^\0-\x1F\x7F"]|\\.)';
+    var regexp = new RegExp('^ *($tokenChar+)="($quotedStringChar*)" *(, *)?');
+
+    var parameters = {};
+    var match;
+    do {
+      match = regexp.firstMatch(paramString);
+      if (match == null) {
+        throw new FormatException('Invalid WWW-Authenticate header: "$header"');
+      }
+
+      paramString = paramString.substring(match.end);
+      parameters[match.group(1).toLowerCase()] = match.group(2);
+    } while (match.group(3) != null);
+
+    if (!paramString.trim().isEmpty) {
+      throw new FormatException('Invalid WWW-Authenticate header: "$header"');
+    }
+
+    return new AuthenticateHeader(scheme, parameters);
+  }
+}
+
 /// Returns a [Future] that asynchronously completes to `null`.
 Future get async {
   var completer = new Completer();
   new Timer(0, (_) => completer.complete(null));
   return completer.future;
 }