// 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.

part of dart._http;

class _HttpHeaders implements HttpHeaders {
  final Map<String, List<String>> _headers;
  // The original header names keyed by the lowercase header names.
  Map<String, String>? _originalHeaderNames;
  final String protocolVersion;

  bool _mutable = true; // Are the headers currently mutable?
  List<String>? _noFoldingHeaders;

  int _contentLength = -1;
  bool _persistentConnection = true;
  bool _chunkedTransferEncoding = false;
  String? _host;
  int? _port;

  final int _defaultPortForScheme;

  _HttpHeaders(this.protocolVersion,
      {int defaultPortForScheme = HttpClient.defaultHttpPort,
      _HttpHeaders? initialHeaders})
      : _headers = new HashMap<String, List<String>>(),
        _defaultPortForScheme = defaultPortForScheme {
    if (initialHeaders != null) {
      initialHeaders._headers.forEach((name, value) => _headers[name] = value);
      _contentLength = initialHeaders._contentLength;
      _persistentConnection = initialHeaders._persistentConnection;
      _chunkedTransferEncoding = initialHeaders._chunkedTransferEncoding;
      _host = initialHeaders._host;
      _port = initialHeaders._port;
    }
    if (protocolVersion == "1.0") {
      _persistentConnection = false;
      _chunkedTransferEncoding = false;
    }
  }

  List<String>? operator [](String name) => _headers[_validateField(name)];

  String? value(String name) {
    name = _validateField(name);
    List<String>? values = _headers[name];
    if (values == null) return null;
    assert(values.isNotEmpty);
    if (values.length > 1) {
      throw new HttpException("More than one value for header $name");
    }
    return values[0];
  }

  void add(String name, value, {bool preserveHeaderCase = false}) {
    _checkMutable();
    String lowercaseName = _validateField(name);

    if (preserveHeaderCase && name != lowercaseName) {
      (_originalHeaderNames ??= {})[lowercaseName] = name;
    } else {
      _originalHeaderNames?.remove(lowercaseName);
    }
    _addAll(lowercaseName, value);
  }

  void _addAll(String name, value) {
    if (value is Iterable) {
      for (var v in value) {
        _add(name, _validateValue(v));
      }
    } else {
      _add(name, _validateValue(value));
    }
  }

  void set(String name, Object value, {bool preserveHeaderCase = false}) {
    _checkMutable();
    String lowercaseName = _validateField(name);
    _headers.remove(lowercaseName);
    _originalHeaderNames?.remove(lowercaseName);
    if (lowercaseName == HttpHeaders.transferEncodingHeader) {
      _chunkedTransferEncoding = false;
    }
    if (preserveHeaderCase && name != lowercaseName) {
      (_originalHeaderNames ??= {})[lowercaseName] = name;
    }
    _addAll(lowercaseName, value);
  }

  void remove(String name, Object value) {
    _checkMutable();
    name = _validateField(name);
    value = _validateValue(value);
    List<String>? values = _headers[name];
    if (values != null) {
      values.remove(_valueToString(value));
      if (values.length == 0) {
        _headers.remove(name);
        _originalHeaderNames?.remove(name);
      }
    }
    if (name == HttpHeaders.transferEncodingHeader && value == "chunked") {
      _chunkedTransferEncoding = false;
    }
  }

  void removeAll(String name) {
    _checkMutable();
    name = _validateField(name);
    _headers.remove(name);
    _originalHeaderNames?.remove(name);
  }

  void forEach(void action(String name, List<String> values)) {
    _headers.forEach((String name, List<String> values) {
      String originalName = _originalHeaderName(name);
      action(originalName, values);
    });
  }

  void noFolding(String name) {
    name = _validateField(name);
    (_noFoldingHeaders ??= <String>[]).add(name);
  }

  bool get persistentConnection => _persistentConnection;

  void set persistentConnection(bool persistentConnection) {
    _checkMutable();
    if (persistentConnection == _persistentConnection) return;
    if (persistentConnection) {
      if (protocolVersion == "1.1") {
        remove(HttpHeaders.connectionHeader, "close");
      } else {
        if (_contentLength < 0) {
          throw new HttpException(
              "Trying to set 'Connection: Keep-Alive' on HTTP 1.0 headers with "
              "no ContentLength");
        }
        add(HttpHeaders.connectionHeader, "keep-alive");
      }
    } else {
      if (protocolVersion == "1.1") {
        add(HttpHeaders.connectionHeader, "close");
      } else {
        remove(HttpHeaders.connectionHeader, "keep-alive");
      }
    }
    _persistentConnection = persistentConnection;
  }

  int get contentLength => _contentLength;

  void set contentLength(int contentLength) {
    _checkMutable();
    if (protocolVersion == "1.0" &&
        persistentConnection &&
        contentLength == -1) {
      throw new HttpException(
          "Trying to clear ContentLength on HTTP 1.0 headers with "
          "'Connection: Keep-Alive' set");
    }
    if (_contentLength == contentLength) return;
    _contentLength = contentLength;
    if (_contentLength >= 0) {
      if (chunkedTransferEncoding) chunkedTransferEncoding = false;
      _set(HttpHeaders.contentLengthHeader, contentLength.toString());
    } else {
      _headers.remove(HttpHeaders.contentLengthHeader);
      if (protocolVersion == "1.1") {
        chunkedTransferEncoding = true;
      }
    }
  }

  bool get chunkedTransferEncoding => _chunkedTransferEncoding;

  void set chunkedTransferEncoding(bool chunkedTransferEncoding) {
    _checkMutable();
    if (chunkedTransferEncoding && protocolVersion == "1.0") {
      throw new HttpException(
          "Trying to set 'Transfer-Encoding: Chunked' on HTTP 1.0 headers");
    }
    if (chunkedTransferEncoding == _chunkedTransferEncoding) return;
    if (chunkedTransferEncoding) {
      List<String>? values = _headers[HttpHeaders.transferEncodingHeader];
      if (values == null || !values.contains("chunked")) {
        // Headers does not specify chunked encoding - add it if set.
        _addValue(HttpHeaders.transferEncodingHeader, "chunked");
      }
      contentLength = -1;
    } else {
      // Headers does specify chunked encoding - remove it if not set.
      remove(HttpHeaders.transferEncodingHeader, "chunked");
    }
    _chunkedTransferEncoding = chunkedTransferEncoding;
  }

  String? get host => _host;

  void set host(String? host) {
    _checkMutable();
    _host = host;
    _updateHostHeader();
  }

  int? get port => _port;

  void set port(int? port) {
    _checkMutable();
    _port = port;
    _updateHostHeader();
  }

  DateTime? get ifModifiedSince {
    List<String>? values = _headers[HttpHeaders.ifModifiedSinceHeader];
    if (values != null) {
      assert(values.isNotEmpty);
      try {
        return HttpDate.parse(values[0]);
      } on Exception {
        return null;
      }
    }
    return null;
  }

  void set ifModifiedSince(DateTime? ifModifiedSince) {
    _checkMutable();
    if (ifModifiedSince == null) {
      _headers.remove(HttpHeaders.ifModifiedSinceHeader);
    } else {
      // Format "ifModifiedSince" header with date in Greenwich Mean Time (GMT).
      String formatted = HttpDate.format(ifModifiedSince.toUtc());
      _set(HttpHeaders.ifModifiedSinceHeader, formatted);
    }
  }

  DateTime? get date {
    List<String>? values = _headers[HttpHeaders.dateHeader];
    if (values != null) {
      assert(values.isNotEmpty);
      try {
        return HttpDate.parse(values[0]);
      } on Exception {
        return null;
      }
    }
    return null;
  }

  void set date(DateTime? date) {
    _checkMutable();
    if (date == null) {
      _headers.remove(HttpHeaders.dateHeader);
    } else {
      // Format "DateTime" header with date in Greenwich Mean Time (GMT).
      String formatted = HttpDate.format(date.toUtc());
      _set(HttpHeaders.dateHeader, formatted);
    }
  }

  DateTime? get expires {
    List<String>? values = _headers[HttpHeaders.expiresHeader];
    if (values != null) {
      assert(values.isNotEmpty);
      try {
        return HttpDate.parse(values[0]);
      } on Exception {
        return null;
      }
    }
    return null;
  }

  void set expires(DateTime? expires) {
    _checkMutable();
    if (expires == null) {
      _headers.remove(HttpHeaders.expiresHeader);
    } else {
      // Format "Expires" header with date in Greenwich Mean Time (GMT).
      String formatted = HttpDate.format(expires.toUtc());
      _set(HttpHeaders.expiresHeader, formatted);
    }
  }

  ContentType? get contentType {
    var values = _headers[HttpHeaders.contentTypeHeader];
    if (values != null) {
      return ContentType.parse(values[0]);
    } else {
      return null;
    }
  }

  void set contentType(ContentType? contentType) {
    _checkMutable();
    if (contentType == null) {
      _headers.remove(HttpHeaders.contentTypeHeader);
    } else {
      _set(HttpHeaders.contentTypeHeader, contentType.toString());
    }
  }

  void clear() {
    _checkMutable();
    _headers.clear();
    _contentLength = -1;
    _persistentConnection = true;
    _chunkedTransferEncoding = false;
    _host = null;
    _port = null;
  }

  // [name] must be a lower-case version of the name.
  void _add(String name, value) {
    assert(name == _validateField(name));
    // Use the length as index on what method to call. This is notable
    // faster than computing hash and looking up in a hash-map.
    switch (name.length) {
      case 4:
        if (HttpHeaders.dateHeader == name) {
          _addDate(name, value);
          return;
        }
        if (HttpHeaders.hostHeader == name) {
          _addHost(name, value);
          return;
        }
        break;
      case 7:
        if (HttpHeaders.expiresHeader == name) {
          _addExpires(name, value);
          return;
        }
        break;
      case 10:
        if (HttpHeaders.connectionHeader == name) {
          _addConnection(name, value);
          return;
        }
        break;
      case 12:
        if (HttpHeaders.contentTypeHeader == name) {
          _addContentType(name, value);
          return;
        }
        break;
      case 14:
        if (HttpHeaders.contentLengthHeader == name) {
          _addContentLength(name, value);
          return;
        }
        break;
      case 17:
        if (HttpHeaders.transferEncodingHeader == name) {
          _addTransferEncoding(name, value);
          return;
        }
        if (HttpHeaders.ifModifiedSinceHeader == name) {
          _addIfModifiedSince(name, value);
          return;
        }
    }
    _addValue(name, value);
  }

  void _addContentLength(String name, value) {
    if (value is int) {
      contentLength = value;
    } else if (value is String) {
      contentLength = int.parse(value);
    } else {
      throw new HttpException("Unexpected type for header named $name");
    }
  }

  void _addTransferEncoding(String name, value) {
    if (value == "chunked") {
      chunkedTransferEncoding = true;
    } else {
      _addValue(HttpHeaders.transferEncodingHeader, value);
    }
  }

  void _addDate(String name, value) {
    if (value is DateTime) {
      date = value;
    } else if (value is String) {
      _set(HttpHeaders.dateHeader, value);
    } else {
      throw new HttpException("Unexpected type for header named $name");
    }
  }

  void _addExpires(String name, value) {
    if (value is DateTime) {
      expires = value;
    } else if (value is String) {
      _set(HttpHeaders.expiresHeader, value);
    } else {
      throw new HttpException("Unexpected type for header named $name");
    }
  }

  void _addIfModifiedSince(String name, value) {
    if (value is DateTime) {
      ifModifiedSince = value;
    } else if (value is String) {
      _set(HttpHeaders.ifModifiedSinceHeader, value);
    } else {
      throw new HttpException("Unexpected type for header named $name");
    }
  }

  void _addHost(String name, value) {
    if (value is String) {
      int pos = value.indexOf(":");
      if (pos == -1) {
        _host = value;
        _port = HttpClient.defaultHttpPort;
      } else {
        if (pos > 0) {
          _host = value.substring(0, pos);
        } else {
          _host = null;
        }
        if (pos + 1 == value.length) {
          _port = HttpClient.defaultHttpPort;
        } else {
          try {
            _port = int.parse(value.substring(pos + 1));
          } on FormatException {
            _port = null;
          }
        }
      }
      _set(HttpHeaders.hostHeader, value);
    } else {
      throw new HttpException("Unexpected type for header named $name");
    }
  }

  void _addConnection(String name, value) {
    var lowerCaseValue = value.toLowerCase();
    if (lowerCaseValue == 'close') {
      _persistentConnection = false;
    } else if (lowerCaseValue == 'keep-alive') {
      _persistentConnection = true;
    }
    _addValue(name, value);
  }

  void _addContentType(String name, value) {
    _set(HttpHeaders.contentTypeHeader, value);
  }

  void _addValue(String name, Object value) {
    List<String> values = (_headers[name] ??= <String>[]);
    values.add(_valueToString(value));
  }

  String _valueToString(Object value) {
    if (value is DateTime) {
      return HttpDate.format(value);
    } else if (value is String) {
      return value; // TODO(39784): no _validateValue?
    } else {
      return _validateValue(value.toString()) as String;
    }
  }

  void _set(String name, String value) {
    assert(name == _validateField(name));
    _headers[name] = <String>[value];
  }

  void _checkMutable() {
    if (!_mutable) throw new HttpException("HTTP headers are not mutable");
  }

  void _updateHostHeader() {
    var host = _host;
    if (host != null) {
      bool defaultPort = _port == null || _port == _defaultPortForScheme;
      _set("host", defaultPort ? host : "$host:$_port");
    }
  }

  bool _foldHeader(String name) {
    if (name == HttpHeaders.setCookieHeader) return false;
    var noFoldingHeaders = _noFoldingHeaders;
    return noFoldingHeaders == null || !noFoldingHeaders.contains(name);
  }

  void _finalize() {
    _mutable = false;
  }

  void _build(BytesBuilder builder) {
    _headers.forEach((name, values) {
      bool fold = _foldHeader(name);
      var nameData = name.codeUnits;
      builder.add(nameData);
      builder.addByte(_CharCode.COLON);
      builder.addByte(_CharCode.SP);
      for (int i = 0; i < values.length; i++) {
        if (i > 0) {
          if (fold) {
            builder.addByte(_CharCode.COMMA);
            builder.addByte(_CharCode.SP);
          } else {
            builder.addByte(_CharCode.CR);
            builder.addByte(_CharCode.LF);
            builder.add(nameData);
            builder.addByte(_CharCode.COLON);
            builder.addByte(_CharCode.SP);
          }
        }
        builder.add(values[i].codeUnits);
      }
      builder.addByte(_CharCode.CR);
      builder.addByte(_CharCode.LF);
    });
  }

  String toString() {
    StringBuffer sb = new StringBuffer();
    _headers.forEach((String name, List<String> values) {
      String originalName = _originalHeaderName(name);
      sb..write(originalName)..write(": ");
      bool fold = _foldHeader(name);
      for (int i = 0; i < values.length; i++) {
        if (i > 0) {
          if (fold) {
            sb.write(", ");
          } else {
            sb..write("\n")..write(originalName)..write(": ");
          }
        }
        sb.write(values[i]);
      }
      sb.write("\n");
    });
    return sb.toString();
  }

  List<Cookie> _parseCookies() {
    // Parse a Cookie header value according to the rules in RFC 6265.
    var cookies = <Cookie>[];
    void parseCookieString(String s) {
      int index = 0;

      bool done() => index == -1 || index == s.length;

      void skipWS() {
        while (!done()) {
          if (s[index] != " " && s[index] != "\t") return;
          index++;
        }
      }

      String parseName() {
        int start = index;
        while (!done()) {
          if (s[index] == " " || s[index] == "\t" || s[index] == "=") break;
          index++;
        }
        return s.substring(start, index);
      }

      String parseValue() {
        int start = index;
        while (!done()) {
          if (s[index] == " " || s[index] == "\t" || s[index] == ";") break;
          index++;
        }
        return s.substring(start, index);
      }

      bool expect(String expected) {
        if (done()) return false;
        if (s[index] != expected) return false;
        index++;
        return true;
      }

      while (!done()) {
        skipWS();
        if (done()) return;
        String name = parseName();
        skipWS();
        if (!expect("=")) {
          index = s.indexOf(';', index);
          continue;
        }
        skipWS();
        String value = parseValue();
        try {
          cookies.add(new _Cookie(name, value));
        } catch (_) {
          // Skip it, invalid cookie data.
        }
        skipWS();
        if (done()) return;
        if (!expect(";")) {
          index = s.indexOf(';', index);
          continue;
        }
      }
    }

    List<String>? values = _headers[HttpHeaders.cookieHeader];
    if (values != null) {
      values.forEach((headerValue) => parseCookieString(headerValue));
    }
    return cookies;
  }

  static String _validateField(String field) {
    for (var i = 0; i < field.length; i++) {
      if (!_HttpParser._isTokenChar(field.codeUnitAt(i))) {
        throw new FormatException(
            "Invalid HTTP header field name: ${json.encode(field)}", field, i);
      }
    }
    return field.toLowerCase();
  }

  static Object _validateValue(Object value) {
    if (value is! String) return value;
    for (var i = 0; i < (value as String).length; i++) {
      if (!_HttpParser._isValueChar((value as String).codeUnitAt(i))) {
        throw new FormatException(
            "Invalid HTTP header field value: ${json.encode(value)}", value, i);
      }
    }
    return value;
  }

  String _originalHeaderName(String name) {
    // TODO: Update syntax to_originalHeaderNames?[name].
    return _originalHeaderNames?.[name] ?? name;
  }
}

class _HeaderValue implements HeaderValue {
  String _value;
  Map<String, String?>? _parameters;
  Map<String, String?>? _unmodifiableParameters;

  _HeaderValue([this._value = "", Map<String, String?> parameters = const {}]) {
    // TODO(40614): Remove once non-nullability is sound.
    Map<String, String?>? nullableParameters = parameters;
    if (nullableParameters != null && nullableParameters.isNotEmpty) {
      _parameters = new HashMap<String, String?>.from(nullableParameters);
    }
  }

  static _HeaderValue parse(String value,
      {String parameterSeparator = ";",
      String? valueSeparator,
      bool preserveBackslash = false}) {
    // Parse the string.
    var result = new _HeaderValue();
    result._parse(value, parameterSeparator, valueSeparator, preserveBackslash);
    return result;
  }

  String get value => _value;

  Map<String, String?> _ensureParameters() =>
      _parameters ??= <String, String?>{};

  Map<String, String?> get parameters =>
      _unmodifiableParameters ??= UnmodifiableMapView(_ensureParameters());

  static bool _isToken(String token) {
    if (token.isEmpty) {
      return false;
    }
    final delimiters = "\"(),/:;<=>?@[\]{}";
    for (int i = 0; i < token.length; i++) {
      int codeUnit = token.codeUnitAt(i);
      if (codeUnit <= 32 ||
          codeUnit >= 127 ||
          delimiters.indexOf(token[i]) >= 0) {
        return false;
      }
    }
    return true;
  }

  String toString() {
    StringBuffer sb = new StringBuffer();
    sb.write(_value);
    var parameters = this._parameters;
    if (parameters != null && parameters.length > 0) {
      parameters.forEach((String name, String? value) {
        sb..write("; ")..write(name);
        if (value != null) {
          sb.write("=");
          if (_isToken(value)) {
            sb.write(value);
          } else {
            sb.write('"');
            int start = 0;
            for (int i = 0; i < value.length; i++) {
              // Can use codeUnitAt here instead.
              int codeUnit = value.codeUnitAt(i);
              if (codeUnit == 92 /* backslash */ ||
                  codeUnit == 34 /* double quote */) {
                sb.write(value.substring(start, i));
                sb.write(r'\');
                start = i;
              }
            }
            sb..write(value.substring(start))..write('"');
          }
        }
      });
    }
    return sb.toString();
  }

  void _parse(String s, String parameterSeparator, String? valueSeparator,
      bool preserveBackslash) {
    int index = 0;

    bool done() => index == s.length;

    void skipWS() {
      while (!done()) {
        if (s[index] != " " && s[index] != "\t") return;
        index++;
      }
    }

    String parseValue() {
      int start = index;
      while (!done()) {
        var char = s[index];
        if (char == " " ||
            char == "\t" ||
            char == valueSeparator ||
            char == parameterSeparator) break;
        index++;
      }
      return s.substring(start, index);
    }

    void expect(String expected) {
      if (done() || s[index] != expected) {
        throw new HttpException("Failed to parse header value");
      }
      index++;
    }

    bool maybeExpect(String expected) {
      if (done() || !s.startsWith(expected, index)) {
        return false;
      }
      index++;
      return true;
    }

    void parseParameters() {
      var parameters = _ensureParameters();

      String parseParameterName() {
        int start = index;
        while (!done()) {
          var char = s[index];
          if (char == " " ||
              char == "\t" ||
              char == "=" ||
              char == parameterSeparator ||
              char == valueSeparator) break;
          index++;
        }
        return s.substring(start, index).toLowerCase();
      }

      String parseParameterValue() {
        if (!done() && s[index] == "\"") {
          // Parse quoted value.
          StringBuffer sb = new StringBuffer();
          index++;
          while (!done()) {
            var char = s[index];
            if (char == "\\") {
              if (index + 1 == s.length) {
                throw new HttpException("Failed to parse header value");
              }
              if (preserveBackslash && s[index + 1] != "\"") {
                sb.write(char);
              }
              index++;
            } else if (char == "\"") {
              index++;
              return sb.toString();
            }
            char = s[index];
            sb.write(char);
            index++;
          }
          throw new HttpException("Failed to parse header value");
        } else {
          // Parse non-quoted value.
          return parseValue();
        }
      }

      while (!done()) {
        skipWS();
        if (done()) return;
        String name = parseParameterName();
        skipWS();
        if (maybeExpect("=")) {
          skipWS();
          String value = parseParameterValue();
          if (name == 'charset' && this is _ContentType) {
            // Charset parameter of ContentTypes are always lower-case.
            value = value.toLowerCase();
          }
          parameters[name] = value;
          skipWS();
        } else if (name.isNotEmpty) {
          parameters[name] = null;
        }
        if (done()) return;
        // TODO: Implement support for multi-valued parameters.
        if (s[index] == valueSeparator) return;
        expect(parameterSeparator);
      }
    }

    skipWS();
    _value = parseValue();
    skipWS();
    if (done()) return;
    if (s[index] == valueSeparator) return;
    maybeExpect(parameterSeparator);
    parseParameters();
  }
}

class _ContentType extends _HeaderValue implements ContentType {
  String _primaryType = "";
  String _subType = "";

  _ContentType(String primaryType, String subType, String? charset,
      Map<String, String?> parameters)
      : _primaryType = primaryType,
        _subType = subType,
        super("") {
    // TODO(40614): Remove once non-nullability is sound.
    String emptyIfNull(String? string) => string ?? "";
    _primaryType = emptyIfNull(_primaryType);
    _subType = emptyIfNull(_subType);
    _value = "$_primaryType/$_subType";
    // TODO(40614): Remove once non-nullability is sound.
    Map<String, String?>? nullableParameters = parameters;
    if (nullableParameters != null) {
      var parameterMap = _ensureParameters();
      nullableParameters.forEach((String key, String? value) {
        String lowerCaseKey = key.toLowerCase();
        if (lowerCaseKey == "charset") {
          value = value?.toLowerCase();
        }
        parameterMap[lowerCaseKey] = value;
      });
    }
    if (charset != null) {
      _ensureParameters()["charset"] = charset.toLowerCase();
    }
  }

  _ContentType._();

  static _ContentType parse(String value) {
    var result = new _ContentType._();
    result._parse(value, ";", null, false);
    int index = result._value.indexOf("/");
    if (index == -1 || index == (result._value.length - 1)) {
      result._primaryType = result._value.trim().toLowerCase();
    } else {
      result._primaryType =
          result._value.substring(0, index).trim().toLowerCase();
      result._subType = result._value.substring(index + 1).trim().toLowerCase();
    }
    return result;
  }

  String get mimeType => '$primaryType/$subType';

  String get primaryType => _primaryType;

  String get subType => _subType;

  String? get charset => parameters["charset"];
}

class _Cookie implements Cookie {
  String _name;
  String _value;
  DateTime? expires;
  int? maxAge;
  String? domain;
  String? path;
  bool httpOnly = false;
  bool secure = false;

  _Cookie(String name, String value)
      : _name = _validateName(name),
        _value = _validateValue(value),
        httpOnly = true;

  String get name => _name;
  String get value => _value;

  set name(String newName) {
    _validateName(newName);
    _name = newName;
  }

  set value(String newValue) {
    _validateValue(newValue);
    _value = newValue;
  }

  _Cookie.fromSetCookieValue(String value)
      : _name = "",
        _value = "" {
    // Parse the 'set-cookie' header value.
    _parseSetCookieValue(value);
  }

  // Parse a 'set-cookie' header value according to the rules in RFC 6265.
  void _parseSetCookieValue(String s) {
    int index = 0;

    bool done() => index == s.length;

    String parseName() {
      int start = index;
      while (!done()) {
        if (s[index] == "=") break;
        index++;
      }
      return s.substring(start, index).trim();
    }

    String parseValue() {
      int start = index;
      while (!done()) {
        if (s[index] == ";") break;
        index++;
      }
      return s.substring(start, index).trim();
    }

    void parseAttributes() {
      String parseAttributeName() {
        int start = index;
        while (!done()) {
          if (s[index] == "=" || s[index] == ";") break;
          index++;
        }
        return s.substring(start, index).trim().toLowerCase();
      }

      String parseAttributeValue() {
        int start = index;
        while (!done()) {
          if (s[index] == ";") break;
          index++;
        }
        return s.substring(start, index).trim().toLowerCase();
      }

      while (!done()) {
        String name = parseAttributeName();
        String value = "";
        if (!done() && s[index] == "=") {
          index++; // Skip the = character.
          value = parseAttributeValue();
        }
        if (name == "expires") {
          expires = HttpDate._parseCookieDate(value);
        } else if (name == "max-age") {
          maxAge = int.parse(value);
        } else if (name == "domain") {
          domain = value;
        } else if (name == "path") {
          path = value;
        } else if (name == "httponly") {
          httpOnly = true;
        } else if (name == "secure") {
          secure = true;
        }
        if (!done()) index++; // Skip the ; character
      }
    }

    _name = _validateName(parseName());
    if (done() || _name.length == 0) {
      throw new HttpException("Failed to parse header value [$s]");
    }
    index++; // Skip the = character.
    _value = _validateValue(parseValue());
    if (done()) return;
    index++; // Skip the ; character.
    parseAttributes();
  }

  String toString() {
    StringBuffer sb = new StringBuffer();
    sb..write(_name)..write("=")..write(_value);
    var expires = this.expires;
    if (expires != null) {
      sb..write("; Expires=")..write(HttpDate.format(expires));
    }
    if (maxAge != null) {
      sb..write("; Max-Age=")..write(maxAge);
    }
    if (domain != null) {
      sb..write("; Domain=")..write(domain);
    }
    if (path != null) {
      sb..write("; Path=")..write(path);
    }
    if (secure) sb.write("; Secure");
    if (httpOnly) sb.write("; HttpOnly");
    return sb.toString();
  }

  static String _validateName(String newName) {
    const separators = const [
      "(",
      ")",
      "<",
      ">",
      "@",
      ",",
      ";",
      ":",
      "\\",
      '"',
      "/",
      "[",
      "]",
      "?",
      "=",
      "{",
      "}"
    ];
    if (newName == null) throw new ArgumentError.notNull("name");
    for (int i = 0; i < newName.length; i++) {
      int codeUnit = newName.codeUnitAt(i);
      if (codeUnit <= 32 ||
          codeUnit >= 127 ||
          separators.indexOf(newName[i]) >= 0) {
        throw new FormatException(
            "Invalid character in cookie name, code unit: '$codeUnit'",
            newName,
            i);
      }
    }
    return newName;
  }

  static String _validateValue(String newValue) {
    if (newValue == null) throw new ArgumentError.notNull("value");
    // Per RFC 6265, consider surrounding "" as part of the value, but otherwise
    // double quotes are not allowed.
    int start = 0;
    int end = newValue.length;
    if (2 <= newValue.length &&
        newValue.codeUnits[start] == 0x22 &&
        newValue.codeUnits[end - 1] == 0x22) {
      start++;
      end--;
    }

    for (int i = start; i < end; i++) {
      int codeUnit = newValue.codeUnits[i];
      if (!(codeUnit == 0x21 ||
          (codeUnit >= 0x23 && codeUnit <= 0x2B) ||
          (codeUnit >= 0x2D && codeUnit <= 0x3A) ||
          (codeUnit >= 0x3C && codeUnit <= 0x5B) ||
          (codeUnit >= 0x5D && codeUnit <= 0x7E))) {
        throw new FormatException(
            "Invalid character in cookie value, code unit: '$codeUnit'",
            newValue,
            i);
      }
    }
    return newValue;
  }
}