twit/lib/streaming-api-connection.js

var EventEmitter = require('events').EventEmitter;
var util = require('util');

var helpers = require('./helpers')
var Parser = require('./parser');
var request = require('request');
var STATUS_CODES_TO_ABORT_ON = require('./settings').STATUS_CODES_TO_ABORT_ON

var StreamingAPIConnection = function (reqOpts, twitOptions) {
  this.reqOpts = reqOpts
  this.twitOptions = twitOptions
  EventEmitter.call(this)
}

util.inherits(StreamingAPIConnection, EventEmitter)

/**
 * Resets the connection.
 * - clears request, response, parser
 * - removes scheduled reconnect handle (if one was scheduled)
 * - stops the stall abort timeout handle (if one was scheduled)
 */
StreamingAPIConnection.prototype._resetConnection = function () {
  if (this.request) {
    // clear our reference to the `request` instance
    this.request.removeAllListeners();
    this.request.destroy();
    delete this.request;
  }

  if (this.response) {
    // clear our reference to the http.IncomingMessage instance
    this.response.removeAllListeners();
    this.response.destroy();
    delete this.response;
  }

  if (this.parser) {
    this.parser.removeAllListeners()
    delete this.parser
  }

  // ensure a scheduled reconnect does not occur (if one was scheduled)
  // this can happen if we get a close event before .stop() is called
  clearTimeout(this._scheduledReconnect)
  delete this._scheduledReconnect

  // clear our stall abort timeout
  this._stopStallAbortTimeout()
}

/**
 * Resets the parameters used in determining the next reconnect time
 */
StreamingAPIConnection.prototype._resetRetryParams = function () {
  // delay for next reconnection attempt
  this._connectInterval = 0
  // flag indicating whether we used a 0-delay reconnect
  this._usedFirstReconnect = false
}

StreamingAPIConnection.prototype._startPersistentConnection = function () {
  var self = this;
  self._resetConnection();
  self._setupParser();
  self._resetStallAbortTimeout();
  self.request = request.post(this.reqOpts);
  self.emit('connect', self.request);
  self.request.on('response', function (response) {
    // reset our reconnection attempt flag so next attempt goes through with 0 delay
    // if we get a transport-level error
    self._usedFirstReconnect = false;
    // start a stall abort timeout handle
    self._resetStallAbortTimeout();
    self.response = response
    self.response.setEncoding('utf8');

    if (STATUS_CODES_TO_ABORT_ON.indexOf(self.response.statusCode) !== -1) {
      // We got a status code telling us we should abort the connection.
      // Read the body from the response and return an error to the user.
      var body = ''
      self.response.on('data', function (chunk) {
        body += chunk.toString('utf8')
      })

      self.response.on('end', function () {
        try {
          body = JSON.parse(body)
        } catch (jsonDecodeError) {
          // Twitter may send an HTML body
          // if non-JSON text was returned, we'll just attach it to the error as-is
        }
        // surface the error to the user
        var error = helpers.makeTwitError('Bad Twitter streaming request: ' + self.response.statusCode)
        error.statusCode = response ? response.statusCode: null;
        helpers.attachBodyInfoToError(error, body)
        self.emit('error', error);
        // stop the stream explicitly so we don't reconnect
        self.stop()
        delete body
      })
      return
    } else if (self.response.statusCode === 420) {
      // close the connection forcibly so a reconnect is scheduled by `self.onClose()`
      self._scheduleReconnect();
      return
    }

    //pass all response data to parser
    self.response.on('data', function (chunk) {
      self._connectInterval = 0
      // stop stall timer, and start a new one
      self._resetStallAbortTimeout();
      self.parser.parse(chunk);
    });

    self.response.on('close', self._onClose.bind(self))
    self.response.on('error', function (err) {
      // expose response errors on twit instance
      self.emit('error', err)
    })

    // connected without an error response from Twitter, emit `connected` event
    // this must be emitted after all its event handlers are bound
    // so the reference to `self.response` is not interfered-with by the user until it is emitted
    self.emit('connected', self.response);
  });
  self.request.on('close', self._onClose.bind(self));
  self.request.on('error', self._scheduleReconnect.bind(self));
  return self;
}

/**
 * Handle when the request or response closes.
 * Schedule a reconnect according to Twitter's reconnect guidelines
 *
 */
StreamingAPIConnection.prototype._onClose = function () {
  var self = this;
  self._stopStallAbortTimeout();

  // We closed it explicitly - don't reconnect
  if (self._abortedBy === 'twit-client')
    return

  // we got disconnected by twitter - reconnect according to their guidelines
  self._abortedBy = 'twitter';

  if (self._scheduledReconnect) {
    // if we already have a reconnect scheduled, don't schedule another one.
    // this race condition can happen if the http.ClientRequest and http.IncomingMessage both emit `close`
    return
  }

  self._scheduleReconnect()
}

/**
 * Kick off the http request, and persist the connection
 *
 */
StreamingAPIConnection.prototype.start = function () {
  this._resetRetryParams();
  this._startPersistentConnection();
  return this;
}

/**
 * Abort the http request, stop scheduled reconnect (if one was scheduled) and clear state
 *
 */
StreamingAPIConnection.prototype.stop = function () {
  this._abortedBy = 'twit-client';
  // clear connection variables and timeout handles
  this._resetConnection();
  return this;
}

/**
 * Stop and restart the stall abort timer (called when new data is received)
 *
 * If we go 90s without receiving data from twitter, we abort the request & reconnect.
 */
StreamingAPIConnection.prototype._resetStallAbortTimeout = function () {
  var self = this;
  // stop the previous stall abort timer
  self._stopStallAbortTimeout();
  //start a new 90s timeout to trigger a close & reconnect if no data received
  self._stallAbortTimeout = setTimeout(function () {
    self._scheduleReconnect()
  }, 90000);
  return this;
}

/**
 * Stop stall timeout
 *
 */
StreamingAPIConnection.prototype._stopStallAbortTimeout = function () {
  clearTimeout(this._stallAbortTimeout);
  // mark the timer as `null` so it is clear via introspection that the timeout is not scheduled
  delete this._stallAbortTimeout;
  return this;
}

/**
 * Computes the next time a reconnect should occur (based on the last HTTP response received)
 * and starts a timeout handle to begin reconnecting after `self._connectInterval` passes.
 *
 * @return {Undefined}
 */
StreamingAPIConnection.prototype._scheduleReconnect = function () {
  var self = this;
  if (self.response && self.response.statusCode === 420) {
    // we are being rate limited
    // start with a 1 minute wait and double each attempt
    if (!self._connectInterval) {
      self._connectInterval = 60000;
    } else {
      self._connectInterval *= 2;
    }
  } else if (self.response && String(self.response.statusCode).charAt(0) === '5') {
    // twitter 5xx errors
    // start with a 5s wait, double each attempt up to 320s
    if (!self._connectInterval) {
      self._connectInterval = 5000;
    } else if (self._connectInterval < 320000) {
      self._connectInterval *= 2;
    } else {
      self._connectInterval = 320000;
    }
  } else {
    // we did not get an HTTP response from our last connection attempt.
    // DNS/TCP error, or a stall in the stream (and stall timer closed the connection)
    if (!self._usedFirstReconnect) {
      // first reconnection attempt on a valid connection should occur immediately
      self._connectInterval = 0;
      self._usedFirstReconnect = true;
    } else if (self._connectInterval < 16000) {
      // linearly increase delay by 250ms up to 16s
      self._connectInterval += 250;
    } else {
      // cap out reconnect interval at 16s
      self._connectInterval = 16000;
    }
  }

  // schedule the reconnect
  self._scheduledReconnect = setTimeout(function () {
    self._startPersistentConnection();
  }, self._connectInterval);
  self.emit('reconnect', self.request, self.response, self._connectInterval);
}

StreamingAPIConnection.prototype._setupParser = function () {
  var self = this
  self.parser = new Parser()

  // handle twitter objects as they come in - emit the generic `message` event
  // along with the specific event corresponding to the message
  self.parser.on('element', function (msg) {
    self.emit('message', msg)

    if      (msg.delete)          { self.emit('delete', msg) }
    else if (msg.disconnect)      { self.handleDisconnect(msg) }
    else if (msg.limit)           { self.emit('limit', msg) }
    else if (msg.scrub_geo)       { self.emit('scrub_geo', msg) }
    else if (msg.warning)         { self.emit('warning', msg) }
    else if (msg.status_withheld) { self.emit('status_withheld', msg) }
    else if (msg.user_withheld)   { self.emit('user_withheld', msg) }
    else if (msg.friends)         { self.emit('friends', msg) }
    else if (msg.direct_message)  { self.emit('direct_message', msg) }
    else if (msg.event)           {
      self.emit('user_event', msg)
      // reference: https://dev.twitter.com/docs/streaming-apis/messages#User_stream_messages
      var ev = msg.event

      if      (ev === 'blocked')                { self.emit('blocked', msg) }
      else if (ev === 'unblocked')              { self.emit('unblocked', msg) }
      else if (ev === 'favorite')               { self.emit('favorite', msg) }
      else if (ev === 'unfavorite')             { self.emit('unfavorite', msg) }
      else if (ev === 'follow')                 { self.emit('follow', msg) }
      else if (ev === 'unfollow')               { self.emit('unfollow', msg) }
      else if (ev === 'user_update')            { self.emit('user_update', msg) }
      else if (ev === 'list_created')           { self.emit('list_created', msg) }
      else if (ev === 'list_destroyed')         { self.emit('list_destroyed', msg) }
      else if (ev === 'list_updated')           { self.emit('list_updated', msg) }
      else if (ev === 'list_member_added')      { self.emit('list_member_added', msg) }
      else if (ev === 'list_member_removed')    { self.emit('list_member_removed', msg) }
      else if (ev === 'list_user_subscribed')   { self.emit('list_user_subscribed', msg) }
      else if (ev === 'list_user_unsubscribed') { self.emit('list_user_unsubscribed', msg) }
      else                                      { self.emit('unknown_user_event', msg) }
    } else                                      { self.emit('tweet', msg) }
  })

  self.parser.on('error', function (err) {
    self.emit('error', err)
  })
}

module.exports = StreamingAPIConnection