Base class for all WebDriver request classes. This class wraps up an URL prefix (host, port, and initial path), and provides a client function for doing HTTP requests with JSON payloads.

class WebDriverBase {

  String _host;
  int _port;
  String _path;
  String _url;

  String get path => _path;
  String get url => _url;

  /**
   * The default URL for WebDriver remote server is
   * http://localhost:4444/wd/hub.
   */
  WebDriverBase.fromUrl([this._url = 'http://localhost:4444/wd/hub']) {
    // Break out the URL components.
    var re = const RegExp('[^:/]+://([^/]+)(/.*)');
    var matches = re.firstMatch(_url);
    _host = matches[1];
    _path = matches[2];
    var idx = _host.indexOf(':');
    if (idx >= 0) {
      _port = parseInt(_host.substring(idx+1));
      _host = _host.substring(0, idx);
    } else {
      _port = 80;
    }
  }

  WebDriverBase([
      this._host = 'localhost',
      this._port = 4444,
      this._path = '/wd/hub']) {
    _url = 'http://$_host:$_port$_path';
  }

  /**
   * Execute a request to the WebDriver server. [http_method] should be
   * one of 'GET', 'POST', or 'DELETE'. [command] is the text to append
   * to the base URL path to get the full URL. [params] are the additional
   * parameters. If a [List] or [Map] they will be posted as JSON parameters.
   * If a number or string, "/params" is appended to the URL.
   */
  void _serverRequest(String http_method, String command, Completer completer,
                      [List successCodes, Map params, Function customHandler]) {
    var status = 0;
    var results = null;
    var message = null;
    if (successCodes == null) {
      successCodes = [ 200, 204 ];
    }
    try {
      if (params != null && params is List && http_method != 'POST') {
        throw new Exception(
          'The http method called for ${command} is ${http_method} but it has '
          'to be POST if you want to pass the JSON params '
          '${JSON.stringify(params)}');
      }

      var path = command;
      if (params != null && (params is num || params is String)) {
        path = '$path/$params';
      }

      var client = new HttpClient();
      var connection = client.open(http_method, _host, _port, path);

      connection.onRequest = (r) {
        r.headers.add(HttpHeaders.ACCEPT, "application/json");
        r.headers.add(
            HttpHeaders.CONTENT_TYPE, 'application/json;charset=UTF-8');
        OutputStream s = r.outputStream;
        if (params != null && params is Map) {
          s.writeString(JSON.stringify(params));
        }
        s.close();
      };
      connection.onError = (e) {
        if (completer != null) {
          completer.completeException(new WebDriverError(-1, e));
          completer = null;
        }
      };
      connection.followRedirects = false;
      connection.onResponse = (r) {
        StringInputStream s = new StringInputStream(r.inputStream);
        StringBuffer sbuf = new StringBuffer();
        s.onData = () {
          var data = s.read();
          if (data != null) {
            sbuf.add(data);
          }
        };
        s.onClosed = () {
          var value = null;
          results  = sbuf.toString().trim();
          // For some reason we get a bunch of NULs on the end
          // of the text and the JSON parser blows up on these, so
          // strip them. We have to do this the hard way as
          // replaceAll('\0', '') does not work.
          // These NULs can be seen in the TCP packet, so it is not
          // an issue with character encoding; it seems to be a bug
          // in WebDriver stack.
          for (var i = results.length; --i >= 0;) {
            var code = results.charCodeAt(i);
            if (code != 0) {
              results = results.substring(0, i+1);
              break;
            }
          }
          if (successCodes.indexOf(r.statusCode) < 0) {
            throw 'Unexpected response ${r.statusCode}';
          }
          if (status == 0 && results.length > 0) {
            // 4xx responses send plain text; others send JSON.
            if (r.statusCode < 400) {
              results = JSON.parse(results);
              status = results['status'];
            }
            if (results is Map && (results as Map).containsKey('value')) {
              value = results['value'];
            }
            if (value is Map && value.containsKey('message')) {
              message = value['message'];
            }
          }
          if (status == 0) {
            if (customHandler != null) {
              customHandler(r, value);
            } else if (completer != null) {
              completer.complete(value);
            }
          }
        };
      };
    } catch (e, s) {
      completer.completeException(
          new WebDriverError(-1, e), s);
      completer = null;
    }
  }

  Future _simpleCommand(method, extraPath, [successCodes, params]) {
    var completer = new Completer();
    _serverRequest(method, '${_path}/$extraPath', completer,
          successCodes, params: params);
    return completer.future;
  }

  Future _get(extraPath, [successCodes]) =>
      _simpleCommand('GET', extraPath, successCodes);

  Future _post(extraPath, [successCodes, params]) =>
      _simpleCommand('POST', extraPath, successCodes, params);

  Future _delete(extraPath, [successCodes]) =>
      _simpleCommand('DELETE', extraPath, successCodes);
}