readmongo/node_modules/engine.io-client/lib/transports/polling.js

const Transport = require("../transport");
const parseqs = require("parseqs");
const parser = require("engine.io-parser");
const yeast = require("yeast");

const debug = require("debug")("engine.io-client:polling");

class Polling extends Transport {
  /**
   * Transport name.
   */
  get name() {
    return "polling";
  }

  /**
   * Opens the socket (triggers polling). We write a PING message to determine
   * when the transport is open.
   *
   * @api private
   */
  doOpen() {
    this.poll();
  }

  /**
   * Pauses polling.
   *
   * @param {Function} callback upon buffers are flushed and transport is paused
   * @api private
   */
  pause(onPause) {
    const self = this;

    this.readyState = "pausing";

    function pause() {
      debug("paused");
      self.readyState = "paused";
      onPause();
    }

    if (this.polling || !this.writable) {
      let total = 0;

      if (this.polling) {
        debug("we are currently polling - waiting to pause");
        total++;
        this.once("pollComplete", function() {
          debug("pre-pause polling complete");
          --total || pause();
        });
      }

      if (!this.writable) {
        debug("we are currently writing - waiting to pause");
        total++;
        this.once("drain", function() {
          debug("pre-pause writing complete");
          --total || pause();
        });
      }
    } else {
      pause();
    }
  }

  /**
   * Starts polling cycle.
   *
   * @api public
   */
  poll() {
    debug("polling");
    this.polling = true;
    this.doPoll();
    this.emit("poll");
  }

  /**
   * Overloads onData to detect payloads.
   *
   * @api private
   */
  onData(data) {
    const self = this;
    debug("polling got data %s", data);
    const callback = function(packet, index, total) {
      // if its the first message we consider the transport open
      if ("opening" === self.readyState && packet.type === "open") {
        self.onOpen();
      }

      // if its a close packet, we close the ongoing requests
      if ("close" === packet.type) {
        self.onClose();
        return false;
      }

      // otherwise bypass onData and handle the message
      self.onPacket(packet);
    };

    // decode payload
    parser.decodePayload(data, this.socket.binaryType).forEach(callback);

    // if an event did not trigger closing
    if ("closed" !== this.readyState) {
      // if we got data we're not polling
      this.polling = false;
      this.emit("pollComplete");

      if ("open" === this.readyState) {
        this.poll();
      } else {
        debug('ignoring poll - transport state "%s"', this.readyState);
      }
    }
  }

  /**
   * For polling, send a close packet.
   *
   * @api private
   */
  doClose() {
    const self = this;

    function close() {
      debug("writing close packet");
      self.write([{ type: "close" }]);
    }

    if ("open" === this.readyState) {
      debug("transport open - closing");
      close();
    } else {
      // in case we're trying to close while
      // handshaking is in progress (GH-164)
      debug("transport not open - deferring close");
      this.once("open", close);
    }
  }

  /**
   * Writes a packets payload.
   *
   * @param {Array} data packets
   * @param {Function} drain callback
   * @api private
   */
  write(packets) {
    this.writable = false;

    parser.encodePayload(packets, data => {
      this.doWrite(data, () => {
        this.writable = true;
        this.emit("drain");
      });
    });
  }

  /**
   * Generates uri for connection.
   *
   * @api private
   */
  uri() {
    let query = this.query || {};
    const schema = this.opts.secure ? "https" : "http";
    let port = "";

    // cache busting is forced
    if (false !== this.opts.timestampRequests) {
      query[this.opts.timestampParam] = yeast();
    }

    if (!this.supportsBinary && !query.sid) {
      query.b64 = 1;
    }

    query = parseqs.encode(query);

    // avoid port if default for schema
    if (
      this.opts.port &&
      (("https" === schema && Number(this.opts.port) !== 443) ||
        ("http" === schema && Number(this.opts.port) !== 80))
    ) {
      port = ":" + this.opts.port;
    }

    // prepend ? to query
    if (query.length) {
      query = "?" + query;
    }

    const ipv6 = this.opts.hostname.indexOf(":") !== -1;
    return (
      schema +
      "://" +
      (ipv6 ? "[" + this.opts.hostname + "]" : this.opts.hostname) +
      port +
      this.opts.path +
      query
    );
  }
}

module.exports = Polling;