text: var url = require("url");
  var http = require("http");
  var https = require("https");
  var assert = require("assert");
  var Writable = require("stream").Writable;
  var debug = require("debug")("follow-redirects");
  
  // RFC7231§4.2.1: Of the request methods defined by this specification,
  // the GET, HEAD, OPTIONS, and TRACE methods are defined to be safe.
  var SAFE_METHODS = { GET: true, HEAD: true, OPTIONS: true, TRACE: true };
  
  // Create handlers that pass events from native requests
  var eventHandlers = Object.create(null);
  ["abort", "aborted", "error", "socket", "timeout"].forEach(function (event) {
    eventHandlers[event] = function (arg) {
      this._redirectable.emit(event, arg);
    };
  });
  
  // An HTTP(S) request that can be redirected
  function RedirectableRequest(options, responseCallback) {
    // Initialize the request
    Writable.call(this);
    options.headers = options.headers || {};
    this._options = options;
    this._redirectCount = 0;
    this._redirects = [];
    this._requestBodyLength = 0;
    this._requestBodyBuffers = [];
  
    // Attach a callback if passed
    if (responseCallback) {
      this.on("response", responseCallback);
    }
  
    // React to responses of native requests
    var self = this;
    this._onNativeResponse = function (response) {
      self._processResponse(response);
    };
  
    // Complete the URL object when necessary
    if (!options.pathname && options.path) {
      var searchPos = options.path.indexOf("?");
      if (searchPos < 0) {
        options.pathname = options.path;
      }
      else {
        options.pathname = options.path.substring(0, searchPos);
        options.search = options.path.substring(searchPos);
      }
    }
  
    // Perform the first request
    this._performRequest();
  }
  RedirectableRequest.prototype = Object.create(Writable.prototype);
  
  // Writes buffered data to the current native request
  RedirectableRequest.prototype.write = function (data, encoding, callback) {
    if (!(typeof data === "string" || typeof data === "object" && ("length" in data))) {
      throw new Error("data should be a string, Buffer or Uint8Array");
    }
    // Ignore empty buffers, since writing them doesn't invoke the callback
    // https://github.com/nodejs/node/issues/22066
    if (data.length === 0) {
      callback();
      return;
    }
    // Only write when we don't exceed the maximum body length
    if (this._requestBodyLength + data.length <= this._options.maxBodyLength) {
      this._requestBodyLength += data.length;
      this._requestBodyBuffers.push({ data: data, encoding: encoding });
      this._currentRequest.write(data, encoding, callback);
    }
    // Error when we exceed the maximum body length
    else {
      this.emit("error", new Error("Request body larger than maxBodyLength limit"));
      this.abort();
    }
  };
  
  // Ends the current native request
  RedirectableRequest.prototype.end = function (data, encoding, callback) {
    var currentRequest = this._currentRequest;
    if (!data) {
      currentRequest.end(null, null, callback);
    }
    else {
      this.write(data, encoding, function () {
        currentRequest.end(null, null, callback);
      });
    }
  };
  
  // Sets a header value on the current native request
  RedirectableRequest.prototype.setHeader = function (name, value) {
    this._options.headers[name] = value;
    this._currentRequest.setHeader(name, value);
  };
  
  // Clears a header value on the current native request
  RedirectableRequest.prototype.removeHeader = function (name) {
    delete this._options.headers[name];
    this._currentRequest.removeHeader(name);
  };
  
  // Proxy all other public ClientRequest methods
  [
    "abort", "flushHeaders", "getHeader",
    "setNoDelay", "setSocketKeepAlive", "setTimeout",
  ].forEach(function (method) {
    RedirectableRequest.prototype[method] = function (a, b) {
      return this._currentRequest[method](a, b);
    };
  });
  
  // Proxy all public ClientRequest properties
  ["aborted", "connection", "socket"].forEach(function (property) {
    Object.defineProperty(RedirectableRequest.prototype, property, {
      get: function () { return this._currentRequest[property]; },
    });
  });
  
  // Executes the next native request (initial or redirect)
  RedirectableRequest.prototype._performRequest = function () {
    // Load the native protocol
    var protocol = this._options.protocol;
    var nativeProtocol = this._options.nativeProtocols[protocol];
  
    // If specified, use the agent corresponding to the protocol
    // (HTTP and HTTPS use different types of agents)
    if (this._options.agents) {
      var scheme = protocol.substr(0, protocol.length - 1);
      this._options.agent = this._options.agents[scheme];
    }
  
    // Create the native request
    var request = this._currentRequest =
          nativeProtocol.request(this._options, this._onNativeResponse);
    this._currentUrl = url.format(this._options);
  
    // Set up event handlers
    request._redirectable = this;
    for (var event in eventHandlers) {
      /* istanbul ignore else */
      if (event) {
        request.on(event, eventHandlers[event]);
      }
    }
  
    // End a redirected request
    // (The first request must be ended explicitly with RedirectableRequest#end)
    if (this._isRedirect) {
      // Write the request entity and end.
      var requestBodyBuffers = this._requestBodyBuffers;
      (function writeNext() {
        if (requestBodyBuffers.length !== 0) {
          var buffer = requestBodyBuffers.pop();
          request.write(buffer.data, buffer.encoding, writeNext);
        }
        else {
          request.end();
        }
      }());
    }
  };
  
  // Processes a response from the current native request
  RedirectableRequest.prototype._processResponse = function (response) {
    // Store the redirected response
    if (this._options.trackRedirects) {
      this._redirects.push({
        url: this._currentUrl,
        headers: response.headers,
        statusCode: response.statusCode,
      });
    }
  
    // RFC7231§6.4: The 3xx (Redirection) class of status code indicates
    // that further action needs to be taken by the user agent in order to
    // fulfill the request. If a Location header field is provided,
    // the user agent MAY automatically redirect its request to the URI
    // referenced by the Location field value,
    // even if the specific status code is not understood.
    var location = response.headers.location;
    if (location && this._options.followRedirects !== false &&
        response.statusCode >= 300 && response.statusCode < 400) {
      // RFC7231§6.4: A client SHOULD detect and intervene
      // in cyclical redirections (i.e., "infinite" redirection loops).
      if (++this._redirectCount > this._options.maxRedirects) {
        this.emit("error", new Error("Max redirects exceeded."));
        return;
      }
  
      // RFC7231§6.4: Automatic redirection needs to done with
      // care for methods not known to be safe […],
      // since the user might not wish to redirect an unsafe request.
      // RFC7231§6.4.7: The 307 (Temporary Redirect) status code indicates
      // that the target resource resides temporarily under a different URI
      // and the user agent MUST NOT change the request method
      // if it performs an automatic redirection to that URI.
      var header;
      var headers = this._options.headers;
      if (response.statusCode !== 307 && !(this._options.method in SAFE_METHODS)) {
        this._options.method = "GET";
        // Drop a possible entity and headers related to it
        this._requestBodyBuffers = [];
        for (header in headers) {
          if (/^content-/i.test(header)) {
            delete headers[header];
          }
        }
      }
  
      // Drop the Host header, as the redirect might lead to a different host
      if (!this._isRedirect) {
        for (header in headers) {
          if (/^host$/i.test(header)) {
            delete headers[header];
          }
        }
      }
  
      // Perform the redirected request
      var redirectUrl = url.resolve(this._currentUrl, location);
      debug("redirecting to", redirectUrl);
      Object.assign(this._options, url.parse(redirectUrl));
      this._isRedirect = true;
      this._performRequest();
  
      // Discard the remainder of the response to avoid waiting for data
      response.destroy();
    }
    else {
      // The response is not a redirect; return it as-is
      response.responseUrl = this._currentUrl;
      response.redirects = this._redirects;
      this.emit("response", response);
  
      // Clean up
      this._requestBodyBuffers = [];
    }
  };
  
  // Wraps the key/value object of protocols with redirect functionality
  function wrap(protocols) {
    // Default settings
    var exports = {
      maxRedirects: 21,
      maxBodyLength: 10 * 1024 * 1024,
    };
  
    // Wrap each protocol
    var nativeProtocols = {};
    Object.keys(protocols).forEach(function (scheme) {
      var protocol = scheme + ":";
      var nativeProtocol = nativeProtocols[protocol] = protocols[scheme];
      var wrappedProtocol = exports[scheme] = Object.create(nativeProtocol);
  
      // Executes a request, following redirects
      wrappedProtocol.request = function (options, callback) {
        if (typeof options === "string") {
          options = url.parse(options);
          options.maxRedirects = exports.maxRedirects;
        }
        else {
          options = Object.assign({
            protocol: protocol,
            maxRedirects: exports.maxRedirects,
            maxBodyLength: exports.maxBodyLength,
          }, options);
        }
        options.nativeProtocols = nativeProtocols;
        assert.equal(options.protocol, protocol, "protocol mismatch");
        debug("options", options);
        return new RedirectableRequest(options, callback);
      };
  
      // Executes a GET request, following redirects
      wrappedProtocol.get = function (options, callback) {
        var request = wrappedProtocol.request(options, callback);
        request.end();
        return request;
      };
    });
    return exports;
  }
  
  // Exports
  module.exports = wrap({ http: http, https: https });
  module.exports.wrap = wrap;
  