// 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.io;

// Global constants.
class _Const {
  // Bytes for "HTTP".
  static const HTTP = const [72, 84, 84, 80];
  // Bytes for "HTTP/1.".
  static const HTTP1DOT = const [72, 84, 84, 80, 47, 49, 46];
  // Bytes for "HTTP/1.0".
  static const HTTP10 = const [72, 84, 84, 80, 47, 49, 46, 48];
  // Bytes for "HTTP/1.1".
  static const HTTP11 = const [72, 84, 84, 80, 47, 49, 46, 49];

  static const END_CHUNKED = const [0x30, 13, 10, 13, 10];

  // Bytes for '()<>@,;:\\"/[]?={} \t'.
  static const SEPARATORS = const [40, 41, 60, 62, 64, 44, 59, 58, 92, 34, 47,
                                   91, 93, 63, 61, 123, 125, 32, 9];

  // Bytes for '()<>@,;:\\"/[]?={} \t\r\n'.
  static const SEPARATORS_AND_CR_LF = const [40, 41, 60, 62, 64, 44, 59, 58, 92,
                                             34, 47, 91, 93, 63, 61, 123, 125,
                                             32, 9, 13, 10];
}


// Frequently used character codes.
class _CharCode {
  static const int HT = 9;
  static const int LF = 10;
  static const int CR = 13;
  static const int SP = 32;
  static const int COMMA = 44;
  static const int DASH = 45;
  static const int SLASH = 47;
  static const int ZERO = 48;
  static const int ONE = 49;
  static const int COLON = 58;
  static const int SEMI_COLON = 59;
}


// States of the HTTP parser state machine.
class _State {
  static const int START = 0;
  static const int METHOD_OR_RESPONSE_HTTP_VERSION = 1;
  static const int RESPONSE_HTTP_VERSION = 2;
  static const int REQUEST_LINE_METHOD = 3;
  static const int REQUEST_LINE_URI = 4;
  static const int REQUEST_LINE_HTTP_VERSION = 5;
  static const int REQUEST_LINE_ENDING = 6;
  static const int RESPONSE_LINE_STATUS_CODE = 7;
  static const int RESPONSE_LINE_REASON_PHRASE = 8;
  static const int RESPONSE_LINE_ENDING = 9;
  static const int HEADER_START = 10;
  static const int HEADER_FIELD = 11;
  static const int HEADER_VALUE_START = 12;
  static const int HEADER_VALUE = 13;
  static const int HEADER_VALUE_FOLDING_OR_ENDING = 14;
  static const int HEADER_VALUE_FOLD_OR_END = 15;
  static const int HEADER_ENDING = 16;

  static const int CHUNK_SIZE_STARTING_CR = 17;
  static const int CHUNK_SIZE_STARTING_LF = 18;
  static const int CHUNK_SIZE = 19;
  static const int CHUNK_SIZE_EXTENSION = 20;
  static const int CHUNK_SIZE_ENDING = 21;
  static const int CHUNKED_BODY_DONE_CR = 22;
  static const int CHUNKED_BODY_DONE_LF = 23;
  static const int BODY = 24;
  static const int CLOSED = 25;
  static const int UPGRADED = 26;
  static const int FAILURE = 27;

  static const int FIRST_BODY_STATE = CHUNK_SIZE_STARTING_CR;
}

// HTTP version of the request or response being parsed.
class _HttpVersion {
  static const int UNDETERMINED = 0;
  static const int HTTP10 = 1;
  static const int HTTP11 = 2;
}

// States of the HTTP parser state machine.
class _MessageType {
  static const int UNDETERMINED = 0;
  static const int REQUEST = 1;
  static const int RESPONSE = 0;
}

class _HttpDetachedIncoming extends Stream<List<int>> {
  StreamController<List<int>> controller;
  final StreamSubscription subscription;

  List<int> carryOverData;
  bool paused;

  Completer resumeCompleter;

  _HttpDetachedIncoming(StreamSubscription this.subscription,
                        List<int> this.carryOverData,
                        Completer oldResumeCompleter) {
    controller = new StreamController<List<int>>(
        onSubscriptionStateChange: onSubscriptionStateChange,
        onPauseStateChange: onPauseStateChange);
    if (subscription == null) {
      // Socket was already closed.
      if (carryOverData != null) controller.add(carryOverData);
      controller.close();
    } else {
      pause();
      if (oldResumeCompleter != null) oldResumeCompleter.complete();
      subscription.resume();
      subscription.onData(controller.add);
      subscription.onDone(controller.close);
      subscription.onError(controller.signalError);
    }
  }

  StreamSubscription<List<int>> listen(void onData(List<int> event),
                                       {void onError(AsyncError error),
                                        void onDone(),
                                        bool unsubscribeOnError}) {
    return controller.stream.listen(
        onData,
        onError: onError,
        onDone: onDone,
        unsubscribeOnError: unsubscribeOnError);
  }

  void resume() {
    paused = false;
    if (carryOverData != null) {
      var data = carryOverData;
      carryOverData = null;
      controller.add(data);
      // If the consumer pauses again after the carry-over data, we'll not
      // continue our subscriber until the next resume.
      if (paused) return;
    }
    if (resumeCompleter != null) {
      resumeCompleter.complete();
      resumeCompleter = null;
    }
  }

  void pause() {
    paused = true;
    if (resumeCompleter == null) {
      resumeCompleter = new Completer();
      subscription.pause(resumeCompleter.future);
    }
  }

  void onPauseStateChange() {
    if (controller.isPaused) {
      pause();
    } else {
      resume();
    }
  }

  void onSubscriptionStateChange() {
    if (controller.hasSubscribers) {
      resume();
    } else {
      subscription.cancel();
    }
  }
}


/**
 * HTTP parser which parses the data stream given to [consume].
 *
 * If an HTTP parser error occours, the parser will signal an error to either
 * the current _HttpIncoming or the _parser itself.
 *
 * The connection upgrades (e.g. switching from HTTP/1.1 to the
 * WebSocket protocol) is handled in a special way. If connection
 * upgrade is specified in the headers, then on the callback to
 * [:responseStart:] the [:upgrade:] property on the [:HttpParser:]
 * object will be [:true:] indicating that from now on the protocol is
 * not HTTP anymore and no more callbacks will happen, that is
 * [:dataReceived:] and [:dataEnd:] are not called in this case as
 * there is no more HTTP data. After the upgrade the method
 * [:readUnparsedData:] can be used to read any remaining bytes in the
 * HTTP parser which are part of the protocol the connection is
 * upgrading to. These bytes cannot be processed by the HTTP parser
 * and should be handled according to whatever protocol is being
 * upgraded to.
 */
class _HttpParser
    extends Stream<_HttpIncoming>
    implements StreamConsumer<List<int>, _HttpParser> {

  factory _HttpParser.requestParser() {
    return new _HttpParser._(true);
  }

  factory _HttpParser.responseParser() {
    return new _HttpParser._(false);
  }

  _HttpParser._(this._requestParser) {
    _controller = new StreamController<_HttpIncoming>(
          onSubscriptionStateChange: _updateParsePauseState,
          onPauseStateChange: _updateParsePauseState);
    _reset();
  }


  StreamSubscription<_HttpIncoming> listen(void onData(_HttpIncoming event),
                                           {void onError(AsyncError error),
                                            void onDone(),
                                            bool unsubscribeOnError}) {
    return _controller.stream.listen(onData,
                                     onError: onError,
                                     onDone: onDone,
                                     unsubscribeOnError: unsubscribeOnError);
  }

  Future<_HttpParser> consume(Stream<List<int>> stream) {
    // Listen to the stream and handle data accordingly. When a
    // _HttpIncoming is created, _dataPause, _dataResume, _dataDone is
    // given to provide a way of controlling the parser.
    // TODO(ajohnsen): Remove _dataPause, _dataResume and _dataDone and clean up
    // how the _HttpIncoming signals the parser.
    var completer = new Completer();
    _socketSubscription = stream.listen(
        _onData,
        onError: _onError,
        onDone: () {
          _onDone();
          completer.complete(this);
        });
    return completer.future;
  }

  // From RFC 2616.
  // generic-message = start-line
  //                   *(message-header CRLF)
  //                   CRLF
  //                   [ message-body ]
  // start-line      = Request-Line | Status-Line
  // Request-Line    = Method SP Request-URI SP HTTP-Version CRLF
  // Status-Line     = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
  // message-header  = field-name ":" [ field-value ]
  void _parse() {
    assert(!_parserCalled);
    _parserCalled = true;
    try {
      if (_state == _State.CLOSED) {
        throw new HttpParserException("Data on closed connection");
      }
      if (_state == _State.FAILURE) {
        throw new HttpParserException("Data on failed connection");
      }
      while (_buffer != null &&
             _index < _buffer.length &&
             _state != _State.FAILURE &&
             _state != _State.UPGRADED) {
        if (_paused) {
          _parserCalled = false;
          return;
        }
        int byte = _buffer[_index++];
        switch (_state) {
          case _State.START:
            if (byte == _Const.HTTP[0]) {
              // Start parsing method or HTTP version.
              _httpVersionIndex = 1;
              _state = _State.METHOD_OR_RESPONSE_HTTP_VERSION;
            } else {
              // Start parsing method.
              if (!_isTokenChar(byte)) {
                throw new HttpParserException("Invalid request method");
              }
              _method_or_status_code.add(byte);
              if (!_requestParser) {
                throw new HttpParserException("Invalid response line");
              }
              _state = _State.REQUEST_LINE_METHOD;
            }
            break;

          case _State.METHOD_OR_RESPONSE_HTTP_VERSION:
            if (_httpVersionIndex < _Const.HTTP.length &&
                byte == _Const.HTTP[_httpVersionIndex]) {
              // Continue parsing HTTP version.
              _httpVersionIndex++;
            } else if (_httpVersionIndex == _Const.HTTP.length &&
                       byte == _CharCode.SLASH) {
              // HTTP/ parsed. As method is a token this cannot be a
              // method anymore.
              _httpVersionIndex++;
              if (_requestParser) {
                throw new HttpParserException("Invalid request line");
              }
              _state = _State.RESPONSE_HTTP_VERSION;
            } else {
              // Did not parse HTTP version. Expect method instead.
              for (int i = 0; i < _httpVersionIndex; i++) {
                _method_or_status_code.add(_Const.HTTP[i]);
              }
              if (byte == _CharCode.SP) {
                _state = _State.REQUEST_LINE_URI;
              } else {
                _method_or_status_code.add(byte);
                _httpVersion = _HttpVersion.UNDETERMINED;
                if (!_requestParser) {
                  throw new HttpParserException("Invalid response line");
                }
                _state = _State.REQUEST_LINE_METHOD;
              }
            }
            break;

          case _State.RESPONSE_HTTP_VERSION:
            if (_httpVersionIndex < _Const.HTTP1DOT.length) {
              // Continue parsing HTTP version.
              _expect(byte, _Const.HTTP1DOT[_httpVersionIndex]);
              _httpVersionIndex++;
            } else if (_httpVersionIndex == _Const.HTTP1DOT.length &&
                       byte == _CharCode.ONE) {
              // HTTP/1.1 parsed.
              _httpVersion = _HttpVersion.HTTP11;
              _persistentConnection = true;
              _httpVersionIndex++;
            } else if (_httpVersionIndex == _Const.HTTP1DOT.length &&
                       byte == _CharCode.ZERO) {
              // HTTP/1.0 parsed.
              _httpVersion = _HttpVersion.HTTP10;
              _persistentConnection = false;
              _httpVersionIndex++;
            } else if (_httpVersionIndex == _Const.HTTP1DOT.length + 1) {
              _expect(byte, _CharCode.SP);
              // HTTP version parsed.
              _state = _State.RESPONSE_LINE_STATUS_CODE;
            } else {
              throw new HttpParserException("Invalid response line");
            }
            break;

          case _State.REQUEST_LINE_METHOD:
            if (byte == _CharCode.SP) {
              _state = _State.REQUEST_LINE_URI;
            } else {
              if (_Const.SEPARATORS_AND_CR_LF.indexOf(byte) != -1) {
                throw new HttpParserException("Invalid request method");
              }
              _method_or_status_code.add(byte);
            }
            break;

          case _State.REQUEST_LINE_URI:
            if (byte == _CharCode.SP) {
              if (_uri_or_reason_phrase.length == 0) {
                throw new HttpParserException("Invalid request URI");
              }
              _state = _State.REQUEST_LINE_HTTP_VERSION;
              _httpVersionIndex = 0;
            } else {
              if (byte == _CharCode.CR || byte == _CharCode.LF) {
                throw new HttpParserException("Invalid request URI");
              }
              _uri_or_reason_phrase.add(byte);
            }
            break;

          case _State.REQUEST_LINE_HTTP_VERSION:
            if (_httpVersionIndex < _Const.HTTP1DOT.length) {
              _expect(byte, _Const.HTTP11[_httpVersionIndex]);
              _httpVersionIndex++;
            } else if (_httpVersionIndex == _Const.HTTP1DOT.length) {
              if (byte == _CharCode.ONE) {
                // HTTP/1.1 parsed.
                _httpVersion = _HttpVersion.HTTP11;
                _persistentConnection = true;
                _httpVersionIndex++;
              } else if (byte == _CharCode.ZERO) {
                // HTTP/1.0 parsed.
                _httpVersion = _HttpVersion.HTTP10;
                _persistentConnection = false;
                _httpVersionIndex++;
              } else {
                throw new HttpParserException("Invalid response line");
              }
            } else {
              _expect(byte, _CharCode.CR);
              _state = _State.REQUEST_LINE_ENDING;
            }
            break;

          case _State.REQUEST_LINE_ENDING:
            _expect(byte, _CharCode.LF);
            _messageType = _MessageType.REQUEST;
            _state = _State.HEADER_START;
            break;

          case _State.RESPONSE_LINE_STATUS_CODE:
            if (byte == _CharCode.SP) {
              if (_method_or_status_code.length != 3) {
                throw new HttpParserException("Invalid response status code");
              }
              _state = _State.RESPONSE_LINE_REASON_PHRASE;
            } else {
              if (byte < 0x30 && 0x39 < byte) {
                throw new HttpParserException("Invalid response status code");
              } else {
                _method_or_status_code.add(byte);
              }
            }
            break;

          case _State.RESPONSE_LINE_REASON_PHRASE:
            if (byte == _CharCode.CR) {
              if (_uri_or_reason_phrase.length == 0) {
                throw new HttpParserException("Invalid response reason phrase");
              }
              _state = _State.RESPONSE_LINE_ENDING;
            } else {
              if (byte == _CharCode.CR || byte == _CharCode.LF) {
                throw new HttpParserException("Invalid response reason phrase");
              }
              _uri_or_reason_phrase.add(byte);
            }
            break;

          case _State.RESPONSE_LINE_ENDING:
            _expect(byte, _CharCode.LF);
            _messageType == _MessageType.RESPONSE;
            _statusCode = int.parse(
                new String.fromCharCodes(_method_or_status_code));
            if (_statusCode < 100 || _statusCode > 599) {
              throw new HttpParserException("Invalid response status code");
            } else {
              // Check whether this response will never have a body.
              _noMessageBody = _statusCode <= 199 || _statusCode == 204 ||
                  _statusCode == 304;
            }
            _state = _State.HEADER_START;
            break;

          case _State.HEADER_START:
            _headers = new _HttpHeaders(version);
            if (byte == _CharCode.CR) {
              _state = _State.HEADER_ENDING;
            } else {
              // Start of new header field.
              _headerField.add(_toLowerCase(byte));
              _state = _State.HEADER_FIELD;
            }
            break;

          case _State.HEADER_FIELD:
            if (byte == _CharCode.COLON) {
              _state = _State.HEADER_VALUE_START;
            } else {
              if (!_isTokenChar(byte)) {
                throw new HttpParserException("Invalid header field name");
              }
              _headerField.add(_toLowerCase(byte));
            }
            break;

          case _State.HEADER_VALUE_START:
            if (byte == _CharCode.CR) {
              _state = _State.HEADER_VALUE_FOLDING_OR_ENDING;
            } else if (byte != _CharCode.SP && byte != _CharCode.HT) {
              // Start of new header value.
              _headerValue.add(byte);
              _state = _State.HEADER_VALUE;
            }
            break;

          case _State.HEADER_VALUE:
            if (byte == _CharCode.CR) {
              _state = _State.HEADER_VALUE_FOLDING_OR_ENDING;
            } else {
              _headerValue.add(byte);
            }
            break;

          case _State.HEADER_VALUE_FOLDING_OR_ENDING:
            _expect(byte, _CharCode.LF);
            _state = _State.HEADER_VALUE_FOLD_OR_END;
            break;

          case _State.HEADER_VALUE_FOLD_OR_END:
            if (byte == _CharCode.SP || byte == _CharCode.HT) {
              _state = _State.HEADER_VALUE_START;
            } else {
              String headerField = new String.fromCharCodes(_headerField);
              String headerValue = new String.fromCharCodes(_headerValue);
              if (headerField == "transfer-encoding" &&
                         headerValue.toLowerCase() == "chunked") {
                _chunked = true;
              }
              if (headerField == "connection") {
                List<String> tokens = _tokenizeFieldValue(headerValue);
                for (int i = 0; i < tokens.length; i++) {
                  if (tokens[i].toLowerCase() == "upgrade") {
                    _connectionUpgrade = true;
                  }
                  _headers.add(headerField, tokens[i]);
                }
              } else {
                _headers.add(headerField, headerValue);
              }
              _headerField.clear();
              _headerValue.clear();

              if (byte == _CharCode.CR) {
                _state = _State.HEADER_ENDING;
              } else {
                // Start of new header field.
                _headerField.add(_toLowerCase(byte));
                _state = _State.HEADER_FIELD;
              }
            }
            break;

          case _State.HEADER_ENDING:
            _expect(byte, _CharCode.LF);
            _headers._mutable = false;

            _transferLength = _headers.contentLength;
            // Ignore the Content-Length header if Transfer-Encoding
            // is chunked (RFC 2616 section 4.4)
            if (_chunked) _transferLength = -1;

            // If a request message has neither Content-Length nor
            // Transfer-Encoding the message must not have a body (RFC
            // 2616 section 4.3).
            if (_messageType == _MessageType.REQUEST &&
                _transferLength < 0 &&
                _chunked == false) {
              _transferLength = 0;
            }
            if (_connectionUpgrade) {
              _state = _State.UPGRADED;
              _transferLength = 0;
            }
            _createIncoming(_transferLength);
            if (_requestParser) {
              _incoming.method =
                  new String.fromCharCodes(_method_or_status_code);
              _incoming.uri =
                  Uri.parse(
                      new String.fromCharCodes(_uri_or_reason_phrase));
            } else {
              _incoming.statusCode = _statusCode;
              _incoming.reasonPhrase =
                  new String.fromCharCodes(_uri_or_reason_phrase);
            }
            _method_or_status_code.clear();
            _uri_or_reason_phrase.clear();
            if (_connectionUpgrade) {
              _incoming.upgraded = true;
              _controller.add(_incoming);
              break;
            }
            if (_chunked) {
              _state = _State.CHUNK_SIZE;
              _remainingContent = 0;
            } else if (_transferLength == 0 ||
                         (_messageType == _MessageType.RESPONSE &&
                          (_noMessageBody || _responseToMethod == "HEAD"))) {
              _reset();
              var tmp = _incoming;
              _closeIncoming();
              _controller.add(tmp);
              break;
            } else if (_transferLength > 0) {
              _remainingContent = _transferLength;
              _state = _State.BODY;
            } else {
              // Neither chunked nor content length. End of body
              // indicated by close.
              _state = _State.BODY;
            }
            _controller.add(_incoming);
            break;

          case _State.CHUNK_SIZE_STARTING_CR:
            _expect(byte, _CharCode.CR);
            _state = _State.CHUNK_SIZE_STARTING_LF;
            break;

          case _State.CHUNK_SIZE_STARTING_LF:
            _expect(byte, _CharCode.LF);
            _state = _State.CHUNK_SIZE;
            break;

          case _State.CHUNK_SIZE:
            if (byte == _CharCode.CR) {
              _state = _State.CHUNK_SIZE_ENDING;
            } else if (byte == _CharCode.SEMI_COLON) {
              _state = _State.CHUNK_SIZE_EXTENSION;
            } else {
              int value = _expectHexDigit(byte);
              _remainingContent = _remainingContent * 16 + value;
            }
            break;

          case _State.CHUNK_SIZE_EXTENSION:
            if (byte == _CharCode.CR) {
              _state = _State.CHUNK_SIZE_ENDING;
            }
            break;

          case _State.CHUNK_SIZE_ENDING:
            _expect(byte, _CharCode.LF);
            if (_remainingContent > 0) {
              _state = _State.BODY;
            } else {
              _state = _State.CHUNKED_BODY_DONE_CR;
            }
            break;

          case _State.CHUNKED_BODY_DONE_CR:
            _expect(byte, _CharCode.CR);
            _state = _State.CHUNKED_BODY_DONE_LF;
            break;

          case _State.CHUNKED_BODY_DONE_LF:
            _expect(byte, _CharCode.LF);
            _reset();
            _closeIncoming();
            break;

          case _State.BODY:
            // The body is not handled one byte at a time but in blocks.
            _index--;
            int dataAvailable = _buffer.length - _index;
            List<int> data;
            if (_remainingContent == null ||
                dataAvailable <= _remainingContent) {
              data = new Uint8List(dataAvailable);
              data.setRange(0, dataAvailable, _buffer, _index);
            } else {
              data = new Uint8List(_remainingContent);
              data.setRange(0, _remainingContent, _buffer, _index);
            }

            _bodyController.add(data);
            if (_remainingContent != null) {
              _remainingContent -= data.length;
            }
            _index += data.length;
            if (_remainingContent == 0) {
              if (!_chunked) {
                _reset();
                _closeIncoming();
              } else {
                _state = _State.CHUNK_SIZE_STARTING_CR;
              }
            }
            break;

          case _State.FAILURE:
            // Should be unreachable.
            assert(false);
            break;

          default:
            // Should be unreachable.
            assert(false);
            break;
        }
      }
    } catch (e, s) {
      _state = _State.FAILURE;
      error(new AsyncError(e, s));
    }

    _parserCalled = false;
    if (_buffer != null && _index == _buffer.length) {
      // If all data is parsed release the buffer and resume receiving
      // data.
      _releaseBuffer();
      if (_state != _State.UPGRADED && _state != _State.FAILURE) {
        _socketSubscription.resume();
      }
    }
  }

  void _onData(List<int> buffer) {
    _socketSubscription.pause();
    assert(_buffer == null);
    _buffer = buffer;
    _index = 0;
    _parse();
  }

  void _onDone() {
    // onDone cancles the subscription.
    _socketSubscription = null;
    if (_state == _State.CLOSED || _state == _State.FAILURE) return;

    if (_incoming != null) {
      if (_state != _State.UPGRADED &&
          !(_state == _State.START && !_requestParser) &&
          !(_state == _State.BODY && !_chunked && _transferLength == -1)) {
        _bodyController.signalError(
            new AsyncError(
                new HttpParserException(
                    "Connection closed while receiving data")));
      }
      _closeIncoming();
      _controller.close();
      return;
    }
    // If the connection is idle the HTTP stream is closed.
    if (_state == _State.START) {
      if (!_requestParser) {
        error(
            new AsyncError(
                new HttpParserException(
                    "Connection closed before full header was received")));
      }
      _controller.close();
      return;
    }

    if (_state == _State.UPGRADED) {
      _controller.close();
      return;
    }

    if (_state < _State.FIRST_BODY_STATE) {
      _state = _State.FAILURE;
      // Report the error through the error callback if any. Otherwise
      // throw the error.
      error(
          new AsyncError(
              new HttpParserException(
                  "Connection closed before full header was received")));
      _controller.close();
      return;
    }

    if (!_chunked && _transferLength == -1) {
      _state = _State.CLOSED;
    } else {
      _state = _State.FAILURE;
      // Report the error through the error callback if any. Otherwise
      // throw the error.
      error(
          new AsyncError(
              new HttpParserException(
                  "Connection closed before full body was received")));
    }
    _controller.close();
  }

  void _onError(e) {
    _controller.signalError(e);
  }

  String get version {
    switch (_httpVersion) {
      case _HttpVersion.HTTP10:
        return "1.0";
      case _HttpVersion.HTTP11:
        return "1.1";
    }
    return null;
  }

  int get messageType => _messageType;
  int get transferLength => _transferLength;
  bool get upgrade => _connectionUpgrade && _state == _State.UPGRADED;
  bool get persistentConnection => _persistentConnection;

  void set responseToMethod(String method) { _responseToMethod = method; }

  _HttpDetachedIncoming detachIncoming() {
    var completer = _pauseCompleter;
    _pauseCompleter = null;
    return new _HttpDetachedIncoming(_socketSubscription,
                                     readUnparsedData(),
                                     completer);
  }

  List<int> readUnparsedData() {
    if (_buffer == null) return null;
    if (_index == _buffer.length) return null;
    var result = _buffer.getRange(_index, _buffer.length - _index);
    _releaseBuffer();
    return result;
  }

  _reset() {
    if (_state == _State.UPGRADED) return;
    _state = _State.START;
    _messageType = _MessageType.UNDETERMINED;
    _headerField = new List();
    _headerValue = new List();
    _method_or_status_code = new List();
    _uri_or_reason_phrase = new List();

    _httpVersion = _HttpVersion.UNDETERMINED;
    _transferLength = -1;
    _persistentConnection = false;
    _connectionUpgrade = false;
    _chunked = false;

    _noMessageBody = false;
    _responseToMethod = null;
    _remainingContent = null;

    _headers = null;
  }

  _releaseBuffer() {
    _buffer = null;
    _index = null;
  }

  bool _isTokenChar(int byte) {
    return byte > 31 && byte < 128 && _Const.SEPARATORS.indexOf(byte) == -1;
  }

  List<String> _tokenizeFieldValue(String headerValue) {
    List<String> tokens = new List<String>();
    int start = 0;
    int index = 0;
    while (index < headerValue.length) {
      if (headerValue[index] == ",") {
        tokens.add(headerValue.substring(start, index));
        start = index + 1;
      } else if (headerValue[index] == " " || headerValue[index] == "\t") {
        start++;
      }
      index++;
    }
    tokens.add(headerValue.substring(start, index));
    return tokens;
  }

  int _toLowerCase(int byte) {
    final int aCode = "A".codeUnitAt(0);
    final int zCode = "Z".codeUnitAt(0);
    final int delta = "a".codeUnitAt(0) - aCode;
    return (aCode <= byte && byte <= zCode) ? byte + delta : byte;
  }

  int _expect(int val1, int val2) {
    if (val1 != val2) {
      throw new HttpParserException("Failed to parse HTTP");
    }
  }

  int _expectHexDigit(int byte) {
    if (0x30 <= byte && byte <= 0x39) {
      return byte - 0x30;  // 0 - 9
    } else if (0x41 <= byte && byte <= 0x46) {
      return byte - 0x41 + 10;  // A - F
    } else if (0x61 <= byte && byte <= 0x66) {
      return byte - 0x61 + 10;  // a - f
    } else {
      throw new HttpParserException("Failed to parse HTTP");
    }
  }

  void _createIncoming(int transferLength) {
    assert(_incoming == null);
    assert(_bodyController == null);
    _bodyController = new StreamController<List<int>>(
        onSubscriptionStateChange: _bodySubscriptionStateChange,
        onPauseStateChange: _updateParsePauseState);
    _incoming = new _HttpIncoming(
        _headers, transferLength, _bodyController.stream);
    _pauseParsing();  // Needed to handle detaching - don't start on the body!
  }

  void _closeIncoming() {
    assert(_incoming != null);
    var tmp = _incoming;
    _incoming = null;
    tmp.close();
    if (_bodyController != null) {
      _bodyController.close();
      _bodyController = null;
    }
    _updateParsePauseState();
  }

  void _continueParsing() {
    _paused = false;
    if (!_parserCalled && _buffer != null) _parse();
  }

  void _pauseParsing() {
    _paused = true;
  }

  void _bodySubscriptionStateChange() {
    if (_incoming != null && !_bodyController.hasSubscribers) {
      _closeIncoming();
    } else {
      _updateParsePauseState();
    }
  }

  void _updateParsePauseState() {
    if (_bodyController != null) {
      if (_bodyController.hasSubscribers && !_bodyController.isPaused) {
        _continueParsing();
      } else {
        _pauseParsing();
      }
    } else {
      if (_controller.hasSubscribers && !_controller.isPaused) {
        _continueParsing();
      } else {
        _pauseParsing();
      }
    }
  }

  void error(error) {
    if (_socketSubscription != null) _socketSubscription.cancel();
    _state = _State.FAILURE;
    _controller.signalError(error);
    _controller.close();
  }

  // State.
  bool _parserCalled = false;

  // The data that is currently being parsed.
  List<int> _buffer;
  int _index;

  final bool _requestParser;
  int _state;
  int _httpVersionIndex;
  int _messageType;
  int _statusCode;
  List _method_or_status_code;
  List _uri_or_reason_phrase;
  List _headerField;
  List _headerValue;

  int _httpVersion;
  int _transferLength;
  bool _persistentConnection;
  bool _connectionUpgrade;
  bool _chunked;

  bool _noMessageBody;
  String _responseToMethod;  // Indicates the method used for the request.
  int _remainingContent;

  _HttpHeaders _headers;

  // The current incoming connection.
  _HttpIncoming _incoming;
  StreamSubscription _socketSubscription;
  bool _paused = false;
  Completer _pauseCompleter;
  StreamController<_HttpIncoming> _controller;
  StreamController<List<int>> _bodyController;
}


class HttpParserException implements Exception {
  const HttpParserException([String this.message = ""]);
  String toString() => "HttpParserException: $message";
  final String message;
}