lib/http.js

// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.

var util = require('util');
var net = require('net');
var Stream = require('stream');
var url = require('url');
var EventEmitter = require('events').EventEmitter;
var FreeList = require('freelist').FreeList;
var HTTPParser = process.binding('http_parser').HTTPParser;
var assert = require('assert').ok;

var debug;
if (process.env.NODE_DEBUG && /http/.test(process.env.NODE_DEBUG)) {
  debug = function(x) { console.error('HTTP: %s', x); };
} else {
  debug = function() { };
}

function readStart(socket) {
  if (!socket || !socket._handle || !socket._handle.readStart) return;
  socket._handle.readStart();
}

function readStop(socket) {
  if (!socket || !socket._handle || !socket._handle.readStop) return;
  socket._handle.readStop();
}

// Only called in the slow case where slow means
// that the request headers were either fragmented
// across multiple TCP packets or too large to be
// processed in a single run. This method is also
// called to process trailing HTTP headers.
function parserOnHeaders(headers, url) {
  // Once we exceeded headers limit - stop collecting them
  if (this.maxHeaderPairs <= 0 ||
      this._headers.length < this.maxHeaderPairs) {
    this._headers = this._headers.concat(headers);
  }
  this._url += url;
}

// info.headers and info.url are set only if .onHeaders()
// has not been called for this request.
//
// info.url is not set for response parsers but that's not
// applicable here since all our parsers are request parsers.
function parserOnHeadersComplete(info) {
  var parser = this;
  var headers = info.headers;
  var url = info.url;

  if (!headers) {
    headers = parser._headers;
    parser._headers = [];
  }

  if (!url) {
    url = parser._url;
    parser._url = '';
  }

  parser.incoming = new IncomingMessage(parser.socket);
  parser.incoming.httpVersionMajor = info.versionMajor;
  parser.incoming.httpVersionMinor = info.versionMinor;
  parser.incoming.httpVersion = info.versionMajor + '.' + info.versionMinor;
  parser.incoming.url = url;

  var n = headers.length;

  // If parser.maxHeaderPairs <= 0 - assume that there're no limit
  if (parser.maxHeaderPairs > 0) {
    n = Math.min(n, parser.maxHeaderPairs);
  }

  for (var i = 0; i < n; i += 2) {
    var k = headers[i];
    var v = headers[i + 1];
    parser.incoming._addHeaderLine(k, v);
  }


  if (info.method) {
    // server only
    parser.incoming.method = info.method;
  } else {
    // client only
    parser.incoming.statusCode = info.statusCode;
    // CHECKME dead code? we're always a request parser
  }

  parser.incoming.upgrade = info.upgrade;

  var skipBody = false; // response to HEAD or CONNECT

  if (!info.upgrade) {
    // For upgraded connections and CONNECT method request,
    // we'll emit this after parser.execute
    // so that we can capture the first part of the new protocol
    skipBody = parser.onIncoming(parser.incoming, info.shouldKeepAlive);
  }

  return skipBody;
}

// XXX This is a mess.
// TODO: http.Parser should be a Writable emits request/response events.
function parserOnBody(b, start, len) {
  var parser = this;
  var stream = parser.incoming;

  // if the stream has already been removed, then drop it.
  if (!stream)
    return;

  var socket = stream.socket;

  // pretend this was the result of a stream._read call.
  if (len > 0 && !stream._dumped) {
    var slice = b.slice(start, start + len);
    var ret = stream.push(slice);
    if (!ret)
      readStop(socket);
  }
}

function parserOnMessageComplete() {
  var parser = this;
  var stream = parser.incoming;

  if (stream) {
    stream.complete = true;
    // Emit any trailing headers.
    var headers = parser._headers;
    if (headers) {
      for (var i = 0, n = headers.length; i < n; i += 2) {
        var k = headers[i];
        var v = headers[i + 1];
        parser.incoming._addHeaderLine(k, v);
      }
      parser._headers = [];
      parser._url = '';
    }

    if (!stream.upgrade)
      // For upgraded connections, also emit this after parser.execute
      stream.push(null);
  }

  if (stream && !parser.incoming._pendings.length) {
    // For emit end event
    stream.push(null);
  }

  if (parser.socket.readable) {
    // force to read the next incoming message
    readStart(parser.socket);
  }
}


var parsers = new FreeList('parsers', 1000, function() {
  var parser = new HTTPParser(HTTPParser.REQUEST);

  parser._headers = [];
  parser._url = '';

  // Only called in the slow case where slow means
  // that the request headers were either fragmented
  // across multiple TCP packets or too large to be
  // processed in a single run. This method is also
  // called to process trailing HTTP headers.
  parser.onHeaders = parserOnHeaders;
  parser.onHeadersComplete = parserOnHeadersComplete;
  parser.onBody = parserOnBody;
  parser.onMessageComplete = parserOnMessageComplete;

  return parser;
});
exports.parsers = parsers;


var CRLF = '\r\n';
var STATUS_CODES = exports.STATUS_CODES = {
  100 : 'Continue',
  101 : 'Switching Protocols',
  102 : 'Processing',                 // RFC 2518, obsoleted by RFC 4918
  200 : 'OK',
  201 : 'Created',
  202 : 'Accepted',
  203 : 'Non-Authoritative Information',
  204 : 'No Content',
  205 : 'Reset Content',
  206 : 'Partial Content',
  207 : 'Multi-Status',               // RFC 4918
  300 : 'Multiple Choices',
  301 : 'Moved Permanently',
  302 : 'Moved Temporarily',
  303 : 'See Other',
  304 : 'Not Modified',
  305 : 'Use Proxy',
  307 : 'Temporary Redirect',
  400 : 'Bad Request',
  401 : 'Unauthorized',
  402 : 'Payment Required',
  403 : 'Forbidden',
  404 : 'Not Found',
  405 : 'Method Not Allowed',
  406 : 'Not Acceptable',
  407 : 'Proxy Authentication Required',
  408 : 'Request Time-out',
  409 : 'Conflict',
  410 : 'Gone',
  411 : 'Length Required',
  412 : 'Precondition Failed',
  413 : 'Request Entity Too Large',
  414 : 'Request-URI Too Large',
  415 : 'Unsupported Media Type',
  416 : 'Requested Range Not Satisfiable',
  417 : 'Expectation Failed',
  418 : 'I\'m a teapot',              // RFC 2324
  422 : 'Unprocessable Entity',       // RFC 4918
  423 : 'Locked',                     // RFC 4918
  424 : 'Failed Dependency',          // RFC 4918
  425 : 'Unordered Collection',       // RFC 4918
  426 : 'Upgrade Required',           // RFC 2817
  428 : 'Precondition Required',      // RFC 6585
  429 : 'Too Many Requests',          // RFC 6585
  431 : 'Request Header Fields Too Large',// RFC 6585
  500 : 'Internal Server Error',
  501 : 'Not Implemented',
  502 : 'Bad Gateway',
  503 : 'Service Unavailable',
  504 : 'Gateway Time-out',
  505 : 'HTTP Version Not Supported',
  506 : 'Variant Also Negotiates',    // RFC 2295
  507 : 'Insufficient Storage',       // RFC 4918
  509 : 'Bandwidth Limit Exceeded',
  510 : 'Not Extended',               // RFC 2774
  511 : 'Network Authentication Required' // RFC 6585
};


var connectionExpression = /Connection/i;
var transferEncodingExpression = /Transfer-Encoding/i;
var closeExpression = /close/i;
var chunkExpression = /chunk/i;
var contentLengthExpression = /Content-Length/i;
var dateExpression = /Date/i;
var expectExpression = /Expect/i;
var continueExpression = /100-continue/i;

var dateCache;
function utcDate() {
  if (!dateCache) {
    var d = new Date();
    dateCache = d.toUTCString();
    setTimeout(function() {
      dateCache = undefined;
    }, 1000 - d.getMilliseconds());
  }
  return dateCache;
}


/* Abstract base class for ServerRequest and ClientResponse. */
function IncomingMessage(socket) {
  Stream.Readable.call(this);

  // XXX This implementation is kind of all over the place
  // When the parser emits body chunks, they go in this list.
  // _read() pulls them out, and when it finds EOF, it ends.

  this.socket = socket;
  this.connection = socket;

  this.httpVersion = null;
  this.complete = false;
  this.headers = {};
  this.trailers = {};

  this.readable = true;

  this._pendings = [];
  this._pendingIndex = 0;

  // request (server) only
  this.url = '';
  this.method = null;

  // response (client) only
  this.statusCode = null;
  this.client = this.socket;

  // flag for backwards compatibility grossness.
  this._consuming = false;

  // flag for when we decide that this message cannot possibly be
  // read by the user, so there's no point continuing to handle it.
  this._dumped = false;
}
util.inherits(IncomingMessage, Stream.Readable);


exports.IncomingMessage = IncomingMessage;


IncomingMessage.prototype.setTimeout = function(msecs, callback) {
  if (callback)
    this.on('timeout', callback);
  this.socket.setTimeout(msecs);
};


IncomingMessage.prototype.read = function(n) {
  this._consuming = true;
  this.read = Stream.Readable.prototype.read;
  return this.read(n);
};


IncomingMessage.prototype._read = function(n) {
  // We actually do almost nothing here, because the parserOnBody
  // function fills up our internal buffer directly.  However, we
  // do need to unpause the underlying socket so that it flows.
  if (!this.socket.readable)
    this.push(null);
  else
    readStart(this.socket);
};


IncomingMessage.prototype.destroy = function(error) {
  this.socket.destroy(error);
};


// Add the given (field, value) pair to the message
//
// Per RFC2616, section 4.2 it is acceptable to join multiple instances of the
// same header with a ', ' if the header in question supports specification of
// multiple values this way. If not, we declare the first instance the winner
// and drop the second. Extended header fields (those beginning with 'x-') are
// always joined.
IncomingMessage.prototype._addHeaderLine = function(field, value) {
  var dest = this.complete ? this.trailers : this.headers;

  field = field.toLowerCase();
  switch (field) {
    // Array headers:
    case 'set-cookie':
      if (dest[field] !== undefined) {
        dest[field].push(value);
      } else {
        dest[field] = [value];
      }
      break;

    // Comma separate. Maybe make these arrays?
    case 'accept':
    case 'accept-charset':
    case 'accept-encoding':
    case 'accept-language':
    case 'connection':
    case 'cookie':
    case 'pragma':
    case 'link':
    case 'www-authenticate':
    case 'proxy-authenticate':
    case 'sec-websocket-extensions':
    case 'sec-websocket-protocol':
      if (dest[field] !== undefined) {
        dest[field] += ', ' + value;
      } else {
        dest[field] = value;
      }
      break;


    default:
      if (field.slice(0, 2) == 'x-') {
        // except for x-
        if (dest[field] !== undefined) {
          dest[field] += ', ' + value;
        } else {
          dest[field] = value;
        }
      } else {
        // drop duplicates
        if (dest[field] === undefined) dest[field] = value;
      }
      break;
  }
};


// Call this instead of resume() if we want to just
// dump all the data to /dev/null
IncomingMessage.prototype._dump = function() {
  if (!this._dumped) {
    this._dumped = true;
    if (this.socket.parser) this.socket.parser.incoming = null;
    this.push(null);
    readStart(this.socket);
    this.read();
  }
};


function OutgoingMessage() {
  Stream.call(this);

  this.output = [];
  this.outputEncodings = [];

  this.writable = true;

  this._last = false;
  this.chunkedEncoding = false;
  this.shouldKeepAlive = true;
  this.useChunkedEncodingByDefault = true;
  this.sendDate = false;

  this._hasBody = true;
  this._trailer = '';

  this.finished = false;
  this._hangupClose = false;

  this.socket = null;
  this.connection = null;
}
util.inherits(OutgoingMessage, Stream);


exports.OutgoingMessage = OutgoingMessage;


OutgoingMessage.prototype.setTimeout = function(msecs, callback) {
  if (callback)
    this.on('timeout', callback);
  if (!this.socket) {
    this.once('socket', function(socket) {
      socket.setTimeout(msecs);
    });
  } else
    this.socket.setTimeout(msecs);
};


OutgoingMessage.prototype.destroy = function(error) {
  this.socket.destroy(error);
};


// This abstract either writing directly to the socket or buffering it.
OutgoingMessage.prototype._send = function(data, encoding) {
  // This is a shameful hack to get the headers and first body chunk onto
  // the same packet. Future versions of Node are going to take care of
  // this at a lower level and in a more general way.
  if (!this._headerSent) {
    if (typeof data === 'string') {
      data = this._header + data;
    } else {
      this.output.unshift(this._header);
      this.outputEncodings.unshift('ascii');
    }
    this._headerSent = true;
  }
  return this._writeRaw(data, encoding);
};


OutgoingMessage.prototype._writeRaw = function(data, encoding) {
  if (data.length === 0) {
    return true;
  }

  if (this.connection &&
      this.connection._httpMessage === this &&
      this.connection.writable &&
      !this.connection.destroyed) {
    // There might be pending data in the this.output buffer.
    while (this.output.length) {
      if (!this.connection.writable) {
        this._buffer(data, encoding);
        return false;
      }
      var c = this.output.shift();
      var e = this.outputEncodings.shift();
      this.connection.write(c, e);
    }

    // Directly write to socket.
    return this.connection.write(data, encoding);
  } else if (this.connection && this.connection.destroyed) {
    // The socket was destroyed.  If we're still trying to write to it,
    // then something bad happened, but it could be just that we haven't
    // gotten the 'close' event yet.
    //
    // In v0.10 and later, this isn't a problem, since ECONNRESET isn't
    // ignored in the first place.  We'll probably emit 'close' on the
    // next tick, but just in case it's not coming, set a timeout that
    // will emit it for us.
    if (!this._hangupClose) {
      this._hangupClose = true;
      var socket = this.socket;
      var timer = setTimeout(function() {
        socket.emit('close');
      });
      socket.once('close', function() {
        clearTimeout(timer);
      });
    }
    return false;
  } else {
    // buffer, as long as we're not destroyed.
    this._buffer(data, encoding);
    return false;
  }
};


OutgoingMessage.prototype._buffer = function(data, encoding) {
  if (data.length === 0) return;

  var length = this.output.length;

  if (length === 0 || typeof data != 'string') {
    this.output.push(data);
    this.outputEncodings.push(encoding);
    return false;
  }

  var lastEncoding = this.outputEncodings[length - 1];
  var lastData = this.output[length - 1];

  if ((encoding && lastEncoding === encoding) ||
      (!encoding && data.constructor === lastData.constructor)) {
    this.output[length - 1] = lastData + data;
    return false;
  }

  this.output.push(data);
  this.outputEncodings.push(encoding);

  return false;
};


OutgoingMessage.prototype._storeHeader = function(firstLine, headers) {
  // firstLine in the case of request is: 'GET /index.html HTTP/1.1\r\n'
  // in the case of response it is: 'HTTP/1.1 200 OK\r\n'
  var state = {
    sentConnectionHeader: false,
    sentContentLengthHeader: false,
    sentTransferEncodingHeader: false,
    sentDateHeader: false,
    sentExpect: false,
    messageHeader: firstLine
  };

  var field, value;
  var self = this;

  if (headers) {
    var keys = Object.keys(headers);
    var isArray = (Array.isArray(headers));
    var field, value;

    for (var i = 0, l = keys.length; i < l; i++) {
      var key = keys[i];
      if (isArray) {
        field = headers[key][0];
        value = headers[key][1];
      } else {
        field = key;
        value = headers[key];
      }

      if (Array.isArray(value)) {
        for (var j = 0; j < value.length; j++) {
          storeHeader(this, state, field, value[j]);
        }
      } else {
        storeHeader(this, state, field, value);
      }
    }
  }

  // Date header
  if (this.sendDate == true && state.sentDateHeader == false) {
    state.messageHeader += 'Date: ' + utcDate() + CRLF;
  }

  // Force the connection to close when the response is a 204 No Content or
  // a 304 Not Modified and the user has set a "Transfer-Encoding: chunked"
  // header.
  //
  // RFC 2616 mandates that 204 and 304 responses MUST NOT have a body but
  // node.js used to send out a zero chunk anyway to accommodate clients
  // that don't have special handling for those responses.
  //
  // It was pointed out that this might confuse reverse proxies to the point
  // of creating security liabilities, so suppress the zero chunk and force
  // the connection to close.
  var statusCode = this.statusCode;
  if ((statusCode == 204 || statusCode === 304) &&
      this.chunkedEncoding === true) {
    debug(statusCode + ' response should not use chunked encoding,' +
          ' closing connection.');
    this.chunkedEncoding = false;
    this.shouldKeepAlive = false;
  }

  // keep-alive logic
  if (state.sentConnectionHeader === false) {
    var shouldSendKeepAlive = this.shouldKeepAlive &&
        (state.sentContentLengthHeader ||
         this.useChunkedEncodingByDefault ||
         this.agent);
    if (shouldSendKeepAlive) {
      state.messageHeader += 'Connection: keep-alive\r\n';
    } else {
      this._last = true;
      state.messageHeader += 'Connection: close\r\n';
    }
  }

  if (state.sentContentLengthHeader == false &&
      state.sentTransferEncodingHeader == false) {
    if (this._hasBody) {
      if (this.useChunkedEncodingByDefault) {
        state.messageHeader += 'Transfer-Encoding: chunked\r\n';
        this.chunkedEncoding = true;
      } else {
        this._last = true;
      }
    } else {
      // Make sure we don't end the 0\r\n\r\n at the end of the message.
      this.chunkedEncoding = false;
    }
  }

  this._header = state.messageHeader + CRLF;
  this._headerSent = false;

  // wait until the first body chunk, or close(), is sent to flush,
  // UNLESS we're sending Expect: 100-continue.
  if (state.sentExpect) this._send('');
};

function storeHeader(self, state, field, value) {
  // Protect against response splitting. The if statement is there to
  // minimize the performance impact in the common case.
  if (/[\r\n]/.test(value))
    value = value.replace(/[\r\n]+[ \t]*/g, '');

  state.messageHeader += field + ': ' + value + CRLF;

  if (connectionExpression.test(field)) {
    state.sentConnectionHeader = true;
    if (closeExpression.test(value)) {
      self._last = true;
    } else {
      self.shouldKeepAlive = true;
    }

  } else if (transferEncodingExpression.test(field)) {
    state.sentTransferEncodingHeader = true;
    if (chunkExpression.test(value)) self.chunkedEncoding = true;

  } else if (contentLengthExpression.test(field)) {
    state.sentContentLengthHeader = true;
  } else if (dateExpression.test(field)) {
    state.sentDateHeader = true;
  } else if (expectExpression.test(field)) {
    state.sentExpect = true;
  }
}


OutgoingMessage.prototype.setHeader = function(name, value) {
  if (arguments.length < 2) {
    throw new Error('`name` and `value` are required for setHeader().');
  }

  if (this._header) {
    throw new Error('Can\'t set headers after they are sent.');
  }

  var key = name.toLowerCase();
  this._headers = this._headers || {};
  this._headerNames = this._headerNames || {};
  this._headers[key] = value;
  this._headerNames[key] = name;
};


OutgoingMessage.prototype.getHeader = function(name) {
  if (arguments.length < 1) {
    throw new Error('`name` is required for getHeader().');
  }

  if (!this._headers) return;

  var key = name.toLowerCase();
  return this._headers[key];
};


OutgoingMessage.prototype.removeHeader = function(name) {
  if (arguments.length < 1) {
    throw new Error('`name` is required for removeHeader().');
  }

  if (this._header) {
    throw new Error('Can\'t remove headers after they are sent.');
  }

  if (!this._headers) return;

  var key = name.toLowerCase();
  delete this._headers[key];
  delete this._headerNames[key];
};


OutgoingMessage.prototype._renderHeaders = function() {
  if (this._header) {
    throw new Error('Can\'t render headers after they are sent to the client.');
  }

  if (!this._headers) return {};

  var headers = {};
  var keys = Object.keys(this._headers);
  for (var i = 0, l = keys.length; i < l; i++) {
    var key = keys[i];
    headers[this._headerNames[key]] = this._headers[key];
  }
  return headers;
};


Object.defineProperty(OutgoingMessage.prototype, 'headersSent', {
  configurable: true,
  enumerable: true,
  get: function() { return !!this._header; }
});


OutgoingMessage.prototype.write = function(chunk, encoding) {
  if (!this._header) {
    this._implicitHeader();
  }

  if (!this._hasBody) {
    debug('This type of response MUST NOT have a body. ' +
          'Ignoring write() calls.');
    return true;
  }

  if (typeof chunk !== 'string' && !Buffer.isBuffer(chunk)) {
    throw new TypeError('first argument must be a string or Buffer');
  }

  if (chunk.length === 0) return false;

  var len, ret;
  if (this.chunkedEncoding) {
    if (typeof(chunk) === 'string') {
      len = Buffer.byteLength(chunk, encoding);
      chunk = len.toString(16) + CRLF + chunk + CRLF;
      ret = this._send(chunk, encoding);
    } else {
      // buffer
      len = chunk.length;
      this._send(len.toString(16) + CRLF);
      this._send(chunk);
      ret = this._send(CRLF);
    }
  } else {
    ret = this._send(chunk, encoding);
  }

  debug('write ret = ' + ret);
  return ret;
};


OutgoingMessage.prototype.addTrailers = function(headers) {
  this._trailer = '';
  var keys = Object.keys(headers);
  var isArray = (Array.isArray(headers));
  var field, value;
  for (var i = 0, l = keys.length; i < l; i++) {
    var key = keys[i];
    if (isArray) {
      field = headers[key][0];
      value = headers[key][1];
    } else {
      field = key;
      value = headers[key];
    }

    this._trailer += field + ': ' + value + CRLF;
  }
};


var zero_chunk_buf = new Buffer('\r\n0\r\n');
var crlf_buf = new Buffer('\r\n');


OutgoingMessage.prototype.end = function(data, encoding) {
  if (this.finished) {
    return false;
  }
  if (!this._header) {
    this._implicitHeader();
  }

  if (data && !this._hasBody) {
    debug('This type of response MUST NOT have a body. ' +
          'Ignoring data passed to end().');
    data = false;
  }

  var ret;

  var hot = this._headerSent === false &&
            (data && data.length > 0) &&
            this.output.length === 0 &&
            this.connection &&
            this.connection.writable &&
            this.connection._httpMessage === this;

  // The benefits of the hot-path optimization below start to fall
  // off when the buffer size gets up near 128KB, because the cost
  // of the copy is more than the cost of the extra write() call.
  // Switch to the write/end method at that point.  Heuristics and
  // magic numbers are awful, but slow http responses are worse.
  if (hot && Buffer.isBuffer(data) && data.length > 120 * 1024)
    hot = false;

  if (hot) {
    // Hot path. They're doing
    //   res.writeHead();
    //   res.end(blah);
    // HACKY.

    if (typeof data === 'string') {
      if (this.chunkedEncoding) {
        var l = Buffer.byteLength(data, encoding).toString(16);
        ret = this.connection.write(this._header + l + CRLF +
                                    data + '\r\n0\r\n' +
                                    this._trailer + '\r\n', encoding);
      } else {
        ret = this.connection.write(this._header + data, encoding);
      }
    } else if (Buffer.isBuffer(data)) {
      if (this.chunkedEncoding) {
        var chunk_size = data.length.toString(16);

        // Skip expensive Buffer.byteLength() calls; only ISO-8859-1 characters
        // are allowed in HTTP headers. Therefore:
        //
        //   this._header.length == Buffer.byteLength(this._header.length)
        //   this._trailer.length == Buffer.byteLength(this._trailer.length)
        //
        var header_len = this._header.length;
        var chunk_size_len = chunk_size.length;
        var data_len = data.length;
        var trailer_len = this._trailer.length;

        var len = header_len +
                  chunk_size_len +
                  2 + // '\r\n'.length
                  data_len +
                  5 + // '\r\n0\r\n'.length
                  trailer_len +
                  2;  // '\r\n'.length

        var buf = new Buffer(len);
        var off = 0;

        buf.write(this._header, off, header_len, 'ascii');
        off += header_len;

        buf.write(chunk_size, off, chunk_size_len, 'ascii');
        off += chunk_size_len;

        crlf_buf.copy(buf, off);
        off += 2;

        data.copy(buf, off);
        off += data_len;

        zero_chunk_buf.copy(buf, off);
        off += 5;

        if (trailer_len > 0) {
          buf.write(this._trailer, off, trailer_len, 'ascii');
          off += trailer_len;
        }

        crlf_buf.copy(buf, off);

        ret = this.connection.write(buf);
      } else {
        var header_len = this._header.length;
        var buf = new Buffer(header_len + data.length);
        buf.write(this._header, 0, header_len, 'ascii');
        data.copy(buf, header_len);
        ret = this.connection.write(buf);
      }
    } else {
      throw new TypeError('first argument must be a string or Buffer');
    }
    this._headerSent = true;

  } else if (data) {
    // Normal body write.
    ret = this.write(data, encoding);
  }

  if (!hot) {
    if (this.chunkedEncoding) {
      ret = this._send('0\r\n' + this._trailer + '\r\n'); // Last chunk.
    } else {
      // Force a flush, HACK.
      ret = this._send('');
    }
  }

  this.finished = true;

  // There is the first message on the outgoing queue, and we've sent
  // everything to the socket.
  debug('outgoing message end.');
  if (this.output.length === 0 && this.connection._httpMessage === this) {
    this._finish();
  }

  return ret;
};


OutgoingMessage.prototype._finish = function() {
  assert(this.connection);
  if (this instanceof ServerResponse) {
    DTRACE_HTTP_SERVER_RESPONSE(this.connection);
    COUNTER_HTTP_SERVER_RESPONSE();
  } else {
    assert(this instanceof ClientRequest);
    DTRACE_HTTP_CLIENT_REQUEST(this, this.connection);
    COUNTER_HTTP_CLIENT_REQUEST();
  }
  this.emit('finish');
};


OutgoingMessage.prototype._flush = function() {
  // This logic is probably a bit confusing. Let me explain a bit:
  //
  // In both HTTP servers and clients it is possible to queue up several
  // outgoing messages. This is easiest to imagine in the case of a client.
  // Take the following situation:
  //
  //    req1 = client.request('GET', '/');
  //    req2 = client.request('POST', '/');
  //
  // When the user does
  //
  //   req2.write('hello world\n');
  //
  // it's possible that the first request has not been completely flushed to
  // the socket yet. Thus the outgoing messages need to be prepared to queue
  // up data internally before sending it on further to the socket's queue.
  //
  // This function, outgoingFlush(), is called by both the Server and Client
  // to attempt to flush any pending messages out to the socket.

  if (!this.socket) return;

  var ret;
  while (this.output.length) {

    if (!this.socket.writable) return; // XXX Necessary?

    var data = this.output.shift();
    var encoding = this.outputEncodings.shift();

    ret = this.socket.write(data, encoding);
  }

  if (this.finished) {
    // This is a queue to the server or client to bring in the next this.
    this._finish();
  } else if (ret) {
    // This is necessary to prevent https from breaking
    this.emit('drain');
  }
};


function ServerResponse(req) {
  OutgoingMessage.call(this);

  if (req.method === 'HEAD') this._hasBody = false;

  this.sendDate = true;

  if (req.httpVersionMajor < 1 || req.httpVersionMinor < 1) {
    this.useChunkedEncodingByDefault = chunkExpression.test(req.headers.te);
    this.shouldKeepAlive = false;
  }
}
util.inherits(ServerResponse, OutgoingMessage);


exports.ServerResponse = ServerResponse;

ServerResponse.prototype.statusCode = 200;

function onServerResponseClose() {
  // EventEmitter.emit makes a copy of the 'close' listeners array before
  // calling the listeners. detachSocket() unregisters onServerResponseClose
  // but if detachSocket() is called, directly or indirectly, by a 'close'
  // listener, onServerResponseClose is still in that copy of the listeners
  // array. That is, in the example below, b still gets called even though
  // it's been removed by a:
  //
  //   var obj = new events.EventEmitter;
  //   obj.on('event', a);
  //   obj.on('event', b);
  //   function a() { obj.removeListener('event', b) }
  //   function b() { throw "BAM!" }
  //   obj.emit('event');  // throws
  //
  // Ergo, we need to deal with stale 'close' events and handle the case
  // where the ServerResponse object has already been deconstructed.
  // Fortunately, that requires only a single if check. :-)
  if (this._httpMessage) this._httpMessage.emit('close');
}

ServerResponse.prototype.assignSocket = function(socket) {
  assert(!socket._httpMessage);
  socket._httpMessage = this;
  socket.on('close', onServerResponseClose);
  this.socket = socket;
  this.connection = socket;
  this.emit('socket', socket);
  this._flush();
};

ServerResponse.prototype.detachSocket = function(socket) {
  assert(socket._httpMessage == this);
  socket.removeListener('close', onServerResponseClose);
  socket._httpMessage = null;
  this.socket = this.connection = null;
};

ServerResponse.prototype.writeContinue = function() {
  this._writeRaw('HTTP/1.1 100 Continue' + CRLF + CRLF, 'ascii');
  this._sent100 = true;
};

ServerResponse.prototype._implicitHeader = function() {
  this.writeHead(this.statusCode);
};

ServerResponse.prototype.writeHead = function(statusCode) {
  var reasonPhrase, headers, headerIndex;

  if (typeof arguments[1] == 'string') {
    reasonPhrase = arguments[1];
    headerIndex = 2;
  } else {
    reasonPhrase = STATUS_CODES[statusCode] || 'unknown';
    headerIndex = 1;
  }
  this.statusCode = statusCode;

  var obj = arguments[headerIndex];

  if (obj && this._headers) {
    // Slow-case: when progressive API and header fields are passed.
    headers = this._renderHeaders();

    if (Array.isArray(obj)) {
      // handle array case
      // TODO: remove when array is no longer accepted
      var field;
      for (var i = 0, len = obj.length; i < len; ++i) {
        field = obj[i][0];
        if (headers[field] !== undefined) {
          obj.push([field, headers[field]]);
        }
      }
      headers = obj;

    } else {
      // handle object case
      var keys = Object.keys(obj);
      for (var i = 0; i < keys.length; i++) {
        var k = keys[i];
        if (k) headers[k] = obj[k];
      }
    }
  } else if (this._headers) {
    // only progressive api is used
    headers = this._renderHeaders();
  } else {
    // only writeHead() called
    headers = obj;
  }

  var statusLine = 'HTTP/1.1 ' + statusCode.toString() + ' ' +
                   reasonPhrase + CRLF;

  if (statusCode === 204 || statusCode === 304 ||
      (100 <= statusCode && statusCode <= 199)) {
    // RFC 2616, 10.2.5:
    // The 204 response MUST NOT include a message-body, and thus is always
    // terminated by the first empty line after the header fields.
    // RFC 2616, 10.3.5:
    // The 304 response MUST NOT contain a message-body, and thus is always
    // terminated by the first empty line after the header fields.
    // RFC 2616, 10.1 Informational 1xx:
    // This class of status code indicates a provisional response,
    // consisting only of the Status-Line and optional headers, and is
    // terminated by an empty line.
    this._hasBody = false;
  }

  // don't keep alive connections where the client expects 100 Continue
  // but we sent a final status; they may put extra bytes on the wire.
  if (this._expect_continue && !this._sent100) {
    this.shouldKeepAlive = false;
  }

  this._storeHeader(statusLine, headers);
};

ServerResponse.prototype.writeHeader = function() {
  this.writeHead.apply(this, arguments);
};


// New Agent code.

// The largest departure from the previous implementation is that
// an Agent instance holds connections for a variable number of host:ports.
// Surprisingly, this is still API compatible as far as third parties are
// concerned. The only code that really notices the difference is the
// request object.

// Another departure is that all code related to HTTP parsing is in
// ClientRequest.onSocket(). The Agent is now *strictly*
// concerned with managing a connection pool.

function Agent(options) {
  EventEmitter.call(this);

  var self = this;
  self.options = options || {};
  self.requests = {};
  self.sockets = {};
  self.maxSockets = self.options.maxSockets || Agent.defaultMaxSockets;
  self.on('free', function(socket, host, port, localAddress) {
    var name = host + ':' + port;
    if (localAddress) {
      name += ':' + localAddress;
    }

    if (!socket.destroyed &&
        self.requests[name] && self.requests[name].length) {
      self.requests[name].shift().onSocket(socket);
      if (self.requests[name].length === 0) {
        // don't leak
        delete self.requests[name];
      }
    } else {
      // If there are no pending requests just destroy the
      // socket and it will get removed from the pool. This
      // gets us out of timeout issues and allows us to
      // default to Connection:keep-alive.
      socket.destroy();
    }
  });
  self.createConnection = net.createConnection;
}
util.inherits(Agent, EventEmitter);
exports.Agent = Agent;

Agent.defaultMaxSockets = 5;

Agent.prototype.defaultPort = 80;
Agent.prototype.addRequest = function(req, host, port, localAddress) {
  var name = host + ':' + port;
  if (localAddress) {
    name += ':' + localAddress;
  }
  if (!this.sockets[name]) {
    this.sockets[name] = [];
  }
  if (this.sockets[name].length < this.maxSockets) {
    // If we are under maxSockets create a new one.
    req.onSocket(this.createSocket(name, host, port, localAddress, req));
  } else {
    // We are over limit so we'll add it to the queue.
    if (!this.requests[name]) {
      this.requests[name] = [];
    }
    this.requests[name].push(req);
  }
};
Agent.prototype.createSocket = function(name, host, port, localAddress, req) {
  var self = this;
  var options = util._extend({}, self.options);
  options.port = port;
  options.host = host;
  options.localAddress = localAddress;

  options.servername = host;
  if (req) {
    var hostHeader = req.getHeader('host');
    if (hostHeader) {
      options.servername = hostHeader.replace(/:.*$/, '');
    }
  }

  var s = self.createConnection(options);
  if (!self.sockets[name]) {
    self.sockets[name] = [];
  }
  this.sockets[name].push(s);
  var onFree = function() {
    self.emit('free', s, host, port, localAddress);
  }
  s.on('free', onFree);
  var onClose = function(err) {
    // This is the only place where sockets get removed from the Agent.
    // If you want to remove a socket from the pool, just close it.
    // All socket errors end in a close event anyway.
    self.removeSocket(s, name, host, port, localAddress);
  }
  s.on('close', onClose);
  var onRemove = function() {
    // We need this function for cases like HTTP 'upgrade'
    // (defined by WebSockets) where we need to remove a socket from the pool
    //  because it'll be locked up indefinitely
    self.removeSocket(s, name, host, port, localAddress);
    s.removeListener('close', onClose);
    s.removeListener('free', onFree);
    s.removeListener('agentRemove', onRemove);
  }
  s.on('agentRemove', onRemove);
  return s;
};
Agent.prototype.removeSocket = function(s, name, host, port, localAddress) {
  if (this.sockets[name]) {
    var index = this.sockets[name].indexOf(s);
    if (index !== -1) {
      this.sockets[name].splice(index, 1);
      if (this.sockets[name].length === 0) {
        // don't leak
        delete this.sockets[name];
      }
    }
  }
  if (this.requests[name] && this.requests[name].length) {
    var req = this.requests[name][0];
    // If we have pending requests and a socket gets closed a new one
    this.createSocket(name, host, port, localAddress, req).emit('free');
  }
};

var globalAgent = new Agent();
exports.globalAgent = globalAgent;


function ClientRequest(options, cb) {
  var self = this;
  OutgoingMessage.call(self);

  self.agent = options.agent === undefined ? globalAgent : options.agent;

  var defaultPort = options.defaultPort || 80;

  var port = options.port || defaultPort;
  var host = options.hostname || options.host || 'localhost';

  if (options.setHost === undefined) {
    var setHost = true;
  }

  self.socketPath = options.socketPath;

  var method = self.method = (options.method || 'GET').toUpperCase();
  self.path = options.path || '/';
  if (cb) {
    self.once('response', cb);
  }

  if (!Array.isArray(options.headers)) {
    if (options.headers) {
      var keys = Object.keys(options.headers);
      for (var i = 0, l = keys.length; i < l; i++) {
        var key = keys[i];
        self.setHeader(key, options.headers[key]);
      }
    }
    if (host && !this.getHeader('host') && setHost) {
      var hostHeader = host;
      if (port && +port !== defaultPort) {
        hostHeader += ':' + port;
      }
      this.setHeader('Host', hostHeader);
    }
  }

  if (options.auth && !this.getHeader('Authorization')) {
    //basic auth
    this.setHeader('Authorization', 'Basic ' +
                   new Buffer(options.auth).toString('base64'));
  }

  if (method === 'GET' || method === 'HEAD' || method === 'CONNECT') {
    self.useChunkedEncodingByDefault = false;
  } else {
    self.useChunkedEncodingByDefault = true;
  }

  if (Array.isArray(options.headers)) {
    self._storeHeader(self.method + ' ' + self.path + ' HTTP/1.1\r\n',
                      options.headers);
  } else if (self.getHeader('expect')) {
    self._storeHeader(self.method + ' ' + self.path + ' HTTP/1.1\r\n',
                      self._renderHeaders());
  }
  if (self.socketPath) {
    self._last = true;
    self.shouldKeepAlive = false;
    if (options.createConnection) {
      self.onSocket(options.createConnection(self.socketPath));
    } else {
      self.onSocket(net.createConnection(self.socketPath));
    }
  } else if (self.agent) {
    // If there is an agent we should default to Connection:keep-alive.
    self._last = false;
    self.shouldKeepAlive = true;
    self.agent.addRequest(self, host, port, options.localAddress);
  } else {
    // No agent, default to Connection:close.
    self._last = true;
    self.shouldKeepAlive = false;
    if (options.createConnection) {
      options.port = port;
      options.host = host;
      var conn = options.createConnection(options);
    } else {
      var conn = net.createConnection({
        port: port,
        host: host,
        localAddress: options.localAddress
      });
    }
    self.onSocket(conn);
  }

  self._deferToConnect(null, null, function() {
    self._flush();
    self = null;
  });

}
util.inherits(ClientRequest, OutgoingMessage);

exports.ClientRequest = ClientRequest;

ClientRequest.prototype._implicitHeader = function() {
  this._storeHeader(this.method + ' ' + this.path + ' HTTP/1.1\r\n',
                    this._renderHeaders());
};

ClientRequest.prototype.abort = function() {
  if (this.socket) {
    // in-progress
    this.socket.destroy();
  } else {
    // haven't been assigned a socket yet.
    // this could be more efficient, it could
    // remove itself from the pending requests
    this._deferToConnect('destroy', []);
  }
};


function createHangUpError() {
  var error = new Error('socket hang up');
  error.code = 'ECONNRESET';
  return error;
}

// Free the parser and also break any links that it
// might have to any other things.
// TODO: All parser data should be attached to a
// single object, so that it can be easily cleaned
// up by doing `parser.data = {}`, which should
// be done in FreeList.free.  `parsers.free(parser)`
// should be all that is needed.
function freeParser(parser, req) {
  if (parser) {
    parser._headers = [];
    parser.onIncoming = null;
    if (parser.socket) {
      parser.socket.onend = null;
      parser.socket.ondata = null;
      parser.socket.parser = null;
    }
    parser.socket = null;
    parser.incoming = null;
    parsers.free(parser);
    parser = null;
  }
  if (req) {
    req.parser = null;
  }
}


function socketCloseListener() {
  var socket = this;
  var parser = socket.parser;
  var req = socket._httpMessage;
  debug('HTTP socket close');
  req.emit('close');
  if (req.res && req.res.readable) {
    // Socket closed before we emitted 'end' below.
    req.res.emit('aborted');
    var res = req.res;
    res.on('end', function() {
      res.emit('close');
    });
    res.push(null);
  } else if (!req.res && !req._hadError) {
    // This socket error fired before we started to
    // receive a response. The error needs to
    // fire on the request.
    req.emit('error', createHangUpError());
    req._hadError = true;
  }

  // Too bad.  That output wasn't getting written.
  // This is pretty terrible that it doesn't raise an error.
  // Fixed better in v0.10
  if (req.output)
    req.output.length = 0;
  if (req.outputEncodings)
    req.outputEncodings.length = 0;

  if (parser) {
    parser.finish();
    freeParser(parser, req);
  }
}

function socketErrorListener(err) {
  var socket = this;
  var parser = socket.parser;
  var req = socket._httpMessage;
  debug('HTTP SOCKET ERROR: ' + err.message + '\n' + err.stack);

  if (req) {
    req.emit('error', err);
    // For Safety. Some additional errors might fire later on
    // and we need to make sure we don't double-fire the error event.
    req._hadError = true;
  }

  if (parser) {
    parser.finish();
    freeParser(parser, req);
  }
  socket.destroy();
}

function socketOnEnd() {
  var socket = this;
  var req = this._httpMessage;
  var parser = this.parser;

  if (!req.res) {
    // If we don't have a response then we know that the socket
    // ended prematurely and we need to emit an error on the request.
    req.emit('error', createHangUpError());
    req._hadError = true;
  }
  if (parser) {
    parser.finish();
    freeParser(parser, req);
  }
  socket.destroy();
}

function socketOnData(d, start, end) {
  var socket = this;
  var req = this._httpMessage;
  var parser = this.parser;

  var ret = parser.execute(d, start, end - start);
  if (ret instanceof Error) {
    debug('parse error');
    freeParser(parser, req);
    socket.destroy();
    req.emit('error', ret);
    req._hadError = true;
  } else if (parser.incoming && parser.incoming.upgrade) {
    // Upgrade or CONNECT
    var bytesParsed = ret;
    var res = parser.incoming;
    req.res = res;

    socket.ondata = null;
    socket.onend = null;
    parser.finish();

    // This is start + byteParsed
    var bodyHead = d.slice(start + bytesParsed, end);

    var eventName = req.method === 'CONNECT' ? 'connect' : 'upgrade';
    if (EventEmitter.listenerCount(req, eventName) > 0) {
      req.upgradeOrConnect = true;

      // detach the socket
      socket.emit('agentRemove');
      socket.removeListener('close', socketCloseListener);
      socket.removeListener('error', socketErrorListener);

      req.emit(eventName, res, socket, bodyHead);
      req.emit('close');
    } else {
      // Got Upgrade header or CONNECT method, but have no handler.
      socket.destroy();
    }
    freeParser(parser, req);
  } else if (parser.incoming && parser.incoming.complete &&
             // When the status code is 100 (Continue), the server will
             // send a final response after this client sends a request
             // body. So, we must not free the parser.
             parser.incoming.statusCode !== 100) {
    freeParser(parser, req);
  }
}


// client
function parserOnIncomingClient(res, shouldKeepAlive) {
  var parser = this;
  var socket = this.socket;
  var req = socket._httpMessage;


  // propogate "domain" setting...
  if (req.domain && !res.domain) {
    debug('setting "res.domain"');
    res.domain = req.domain;
  }

  debug('AGENT incoming response!');

  if (req.res) {
    // We already have a response object, this means the server
    // sent a double response.
    socket.destroy();
    return;
  }
  req.res = res;

  // Responses to CONNECT request is handled as Upgrade.
  if (req.method === 'CONNECT') {
    res.upgrade = true;
    return true; // skip body
  }

  // Responses to HEAD requests are crazy.
  // HEAD responses aren't allowed to have an entity-body
  // but *can* have a content-length which actually corresponds
  // to the content-length of the entity-body had the request
  // been a GET.
  var isHeadResponse = req.method == 'HEAD';
  debug('AGENT isHeadResponse ' + isHeadResponse);

  if (res.statusCode == 100) {
    // restart the parser, as this is a continue message.
    delete req.res; // Clear res so that we don't hit double-responses.
    req.emit('continue');
    return true;
  }

  if (req.shouldKeepAlive && !shouldKeepAlive && !req.upgradeOrConnect) {
    // Server MUST respond with Connection:keep-alive for us to enable it.
    // If we've been upgraded (via WebSockets) we also shouldn't try to
    // keep the connection open.
    req.shouldKeepAlive = false;
  }


  DTRACE_HTTP_CLIENT_RESPONSE(socket, req);
  COUNTER_HTTP_CLIENT_RESPONSE();
  req.res = res;
  res.req = req;

  // add our listener first, so that we guarantee socket cleanup
  res.on('end', responseOnEnd);
  var handled = req.emit('response', res);

  // If the user did not listen for the 'response' event, then they
  // can't possibly read the data, so we ._dump() it into the void
  // so that the socket doesn't hang there in a paused state.
  if (!handled)
    res._dump();

  return isHeadResponse;
}

// client
function responseOnEnd() {
  var res = this;
  var req = res.req;
  var socket = req.socket;

  if (!req.shouldKeepAlive) {
    if (socket.writable) {
      debug('AGENT socket.destroySoon()');
      socket.destroySoon();
    }
    assert(!socket.writable);
  } else {
    debug('AGENT socket keep-alive');
    if (req.timeoutCb) {
      socket.setTimeout(0, req.timeoutCb);
      req.timeoutCb = null;
    }
    socket.removeListener('close', socketCloseListener);
    socket.removeListener('error', socketErrorListener);
    // Mark this socket as available, AFTER user-added end
    // handlers have a chance to run.
    process.nextTick(function() {
      socket.emit('free');
    });
  }
}

ClientRequest.prototype.onSocket = function(socket) {
  var req = this;

  process.nextTick(function() {
    var parser = parsers.alloc();
    req.socket = socket;
    req.connection = socket;
    parser.reinitialize(HTTPParser.RESPONSE);
    parser.socket = socket;
    parser.incoming = null;
    req.parser = parser;

    socket.parser = parser;
    socket._httpMessage = req;

    // Setup "drain" propogation.
    httpSocketSetup(socket);

    // Propagate headers limit from request object to parser
    if (typeof req.maxHeadersCount === 'number') {
      parser.maxHeaderPairs = req.maxHeadersCount << 1;
    } else {
      // Set default value because parser may be reused from FreeList
      parser.maxHeaderPairs = 2000;
    }

    socket.on('error', socketErrorListener);
    socket.ondata = socketOnData;
    socket.onend = socketOnEnd;
    socket.on('close', socketCloseListener);
    parser.onIncoming = parserOnIncomingClient;
    req.emit('socket', socket);
  });

};

ClientRequest.prototype._deferToConnect = function(method, arguments_, cb) {
  // This function is for calls that need to happen once the socket is
  // connected and writable. It's an important promisy thing for all the socket
  // calls that happen either now (when a socket is assigned) or
  // in the future (when a socket gets assigned out of the pool and is
  // eventually writable).
  var self = this;
  var onSocket = function() {
    if (self.socket.writable) {
      if (method) {
        self.socket[method].apply(self.socket, arguments_);
      }
      if (cb) { cb(); }
    } else {
      self.socket.once('connect', function() {
        if (method) {
          self.socket[method].apply(self.socket, arguments_);
        }
        if (cb) { cb(); }
      });
    }
  }
  if (!self.socket) {
    self.once('socket', onSocket);
  } else {
    onSocket();
  }
};

ClientRequest.prototype.setTimeout = function(msecs, callback) {
  if (callback) this.once('timeout', callback);

  var self = this;
  function emitTimeout() {
    self.emit('timeout');
  }

  if (this.socket && this.socket.writable) {
    if (this.timeoutCb)
      this.socket.setTimeout(0, this.timeoutCb);
    this.timeoutCb = emitTimeout;
    this.socket.setTimeout(msecs, emitTimeout);
    return;
  }

  // Set timeoutCb so that it'll get cleaned up on request end
  this.timeoutCb = emitTimeout;
  if (this.socket) {
    var sock = this.socket;
    this.socket.once('connect', function() {
      sock.setTimeout(msecs, emitTimeout);
    });
    return;
  }

  this.once('socket', function(sock) {
    sock.setTimeout(msecs, emitTimeout);
  });
};

ClientRequest.prototype.setNoDelay = function() {
  this._deferToConnect('setNoDelay', arguments);
};
ClientRequest.prototype.setSocketKeepAlive = function() {
  this._deferToConnect('setKeepAlive', arguments);
};

ClientRequest.prototype.clearTimeout = function(cb) {
  this.setTimeout(0, cb);
};

exports.request = function(options, cb) {
  if (typeof options === 'string') {
    options = url.parse(options);
  }

  if (options.protocol && options.protocol !== 'http:') {
    throw new Error('Protocol:' + options.protocol + ' not supported.');
  }

  return new ClientRequest(options, cb);
};

exports.get = function(options, cb) {
  var req = exports.request(options, cb);
  req.end();
  return req;
};


function ondrain() {
  if (this._httpMessage) this._httpMessage.emit('drain');
}


function httpSocketSetup(socket) {
  socket.removeListener('drain', ondrain);
  socket.on('drain', ondrain);
}


function Server(requestListener) {
  if (!(this instanceof Server)) return new Server(requestListener);
  net.Server.call(this, { allowHalfOpen: true });

  if (requestListener) {
    this.addListener('request', requestListener);
  }

  // Similar option to this. Too lazy to write my own docs.
  // http://www.squid-cache.org/Doc/config/half_closed_clients/
  // http://wiki.squid-cache.org/SquidFaq/InnerWorkings#What_is_a_half-closed_filedescriptor.3F
  this.httpAllowHalfOpen = false;

  this.addListener('connection', connectionListener);

  this.addListener('clientError', function(err, conn) {
    conn.destroy(err);
  });

  this.timeout = 2 * 60 * 1000;
}
util.inherits(Server, net.Server);


Server.prototype.setTimeout = function(msecs, callback) {
  this.timeout = msecs;
  if (callback)
    this.on('timeout', callback);
};


exports.Server = Server;


exports.createServer = function(requestListener) {
  return new Server(requestListener);
};


function connectionListener(socket) {
  var self = this;
  var outgoing = [];
  var incoming = [];

  function abortIncoming() {
    while (incoming.length) {
      var req = incoming.shift();
      req.emit('aborted');
      req.emit('close');
    }
    // abort socket._httpMessage ?
  }

  function serverSocketCloseListener() {
    debug('server socket close');
    // mark this parser as reusable
    if (this.parser)
      freeParser(this.parser);

    abortIncoming();
  }

  debug('SERVER new http connection');

  httpSocketSetup(socket);

  // If the user has added a listener to the server,
  // request, or response, then it's their responsibility.
  // otherwise, destroy on timeout by default
  if (self.timeout)
    socket.setTimeout(self.timeout);
  socket.on('timeout', function() {
    var req = socket.parser && socket.parser.incoming;
    var reqTimeout = req && !req.complete && req.emit('timeout', socket);
    var res = socket._httpMessage;
    var resTimeout = res && res.emit('timeout', socket);
    var serverTimeout = self.emit('timeout', socket);

    if (!reqTimeout && !resTimeout && !serverTimeout)
      socket.destroy();
  });

  var parser = parsers.alloc();
  parser.reinitialize(HTTPParser.REQUEST);
  parser.socket = socket;
  socket.parser = parser;
  parser.incoming = null;

  // Propagate headers limit from server instance to parser
  if (typeof this.maxHeadersCount === 'number') {
    parser.maxHeaderPairs = this.maxHeadersCount << 1;
  } else {
    // Set default value because parser may be reused from FreeList
    parser.maxHeaderPairs = 2000;
  }

  socket.addListener('error', function(e) {
    self.emit('clientError', e, this);
  });

  socket.ondata = function(d, start, end) {
    var ret = parser.execute(d, start, end - start);
    if (ret instanceof Error) {
      debug('parse error');
      socket.destroy(ret);
    } else if (parser.incoming && parser.incoming.upgrade) {
      // Upgrade or CONNECT
      var bytesParsed = ret;
      var req = parser.incoming;

      socket.ondata = null;
      socket.onend = null;
      socket.removeListener('close', serverSocketCloseListener);
      parser.finish();
      freeParser(parser, req);

      // This is start + byteParsed
      var bodyHead = d.slice(start + bytesParsed, end);

      var eventName = req.method === 'CONNECT' ? 'connect' : 'upgrade';
      if (EventEmitter.listenerCount(self, eventName) > 0) {
        self.emit(eventName, req, req.socket, bodyHead);
      } else {
        // Got upgrade header or CONNECT method, but have no handler.
        socket.destroy();
      }
    }
  };

  socket.onend = function() {
    var ret = parser.finish();

    if (ret instanceof Error) {
      debug('parse error');
      socket.destroy(ret);
      return;
    }

    if (!self.httpAllowHalfOpen) {
      abortIncoming();
      if (socket.writable) socket.end();
    } else if (outgoing.length) {
      outgoing[outgoing.length - 1]._last = true;
    } else if (socket._httpMessage) {
      socket._httpMessage._last = true;
    } else {
      if (socket.writable) socket.end();
    }
  };

  socket.addListener('close', serverSocketCloseListener);

  // The following callback is issued after the headers have been read on a
  // new message. In this callback we setup the response object and pass it
  // to the user.
  parser.onIncoming = function(req, shouldKeepAlive) {
    incoming.push(req);

    var res = new ServerResponse(req);

    res.shouldKeepAlive = shouldKeepAlive;
    DTRACE_HTTP_SERVER_REQUEST(req, socket);
    COUNTER_HTTP_SERVER_REQUEST();

    if (socket._httpMessage) {
      // There are already pending outgoing res, append.
      outgoing.push(res);
    } else {
      res.assignSocket(socket);
    }

    // When we're finished writing the response, check if this is the last
    // respose, if so destroy the socket.
    res.on('finish', function() {
      // Usually the first incoming element should be our request.  it may
      // be that in the case abortIncoming() was called that the incoming
      // array will be empty.
      assert(incoming.length == 0 || incoming[0] === req);

      incoming.shift();

      // if the user never called req.read(), and didn't pipe() or
      // .resume() or .on('data'), then we call req._dump() so that the
      // bytes will be pulled off the wire.
      if (!req._consuming)
        req._dump();

      res.detachSocket(socket);

      if (res._last) {
        socket.destroySoon();
      } else {
        // start sending the next message
        var m = outgoing.shift();
        if (m) {
          m.assignSocket(socket);
        }
      }
    });

    if (req.headers.expect !== undefined &&
        (req.httpVersionMajor == 1 && req.httpVersionMinor == 1) &&
        continueExpression.test(req.headers['expect'])) {
      res._expect_continue = true;
      if (EventEmitter.listenerCount(self, 'checkContinue') > 0) {
        self.emit('checkContinue', req, res);
      } else {
        res.writeContinue();
        self.emit('request', req, res);
      }
    } else {
      self.emit('request', req, res);
    }
    return false; // Not a HEAD response. (Not even a response!)
  };
}
exports._connectionListener = connectionListener;

// Legacy Interface

function Client(port, host) {
  if (!(this instanceof Client)) return new Client(port, host);
  EventEmitter.call(this);

  host = host || 'localhost';
  port = port || 80;
  this.host = host;
  this.port = port;
  this.agent = new Agent({ host: host, port: port, maxSockets: 1 });
}
util.inherits(Client, EventEmitter);
Client.prototype.request = function(method, path, headers) {
  var self = this;
  var options = {};
  options.host = self.host;
  options.port = self.port;
  if (method[0] === '/') {
    headers = path;
    path = method;
    method = 'GET';
  }
  options.method = method;
  options.path = path;
  options.headers = headers;
  options.agent = self.agent;
  var c = new ClientRequest(options);
  c.on('error', function(e) {
    self.emit('error', e);
  });
  // The old Client interface emitted 'end' on socket end.
  // This doesn't map to how we want things to operate in the future
  // but it will get removed when we remove this legacy interface.
  c.on('socket', function(s) {
    s.on('end', function() {
      if (self._decoder) {
        var ret = self._decoder.end();
        if (ret)
          self.emit('data', ret);
      }
      self.emit('end');
    });
  });
  return c;
};

exports.Client = util.deprecate(Client,
    'http.Client will be removed soon. Do not use it.');

exports.createClient = util.deprecate(function(port, host) {
  return new Client(port, host);
}, 'http.createClient is deprecated. Use `http.request` instead.');