Bittrex tries to access this._subCount when sub/unsub but its undefined, throws error

ccxws v 0.27.2

Exchange Bittrex

Subscription type level2 orderbook updates

Describe the bug It looks like the Bittrex client is trying to access the internal this._subCount property but it’s undefined (perhaps it needs to be bound for the correct this).

Bittrex ccxws websocket error: No Hub
Cannot read property 'BTC-EOS' of undefined
    at BittrexClient._sendSub (/home/evan/devel/coygo/webapp/.meteor/desktop-build/node_modules/ccxws/src/exchanges/bittrex-client.js:126:48)
    at BittrexClient._subscribe (/home/evan/devel/coygo/webapp/.meteor/desktop-build/node_modules/ccxws/src/exchanges/bittrex-client.js:108:14)
    at BittrexClient.subscribeLevel2Updates (/home/evan/devel/coygo/webapp/.meteor/desktop-build/node_modules/ccxws/src/exchanges/bittrex-client.js:82:10)
    at classDefinition.(anonymous function).registerOrderBookListener (/home/evan/devel/coygo/webapp/.meteor/desktop-build/desktop.asar/trading/exchange-clients/ExchangeClientCcxtCcxwsCommon.js:177:16)
    at process._tickCallback (internal/process/next_tick.js:68:7)

TypeError: Cannot read property 'BTC-EOS' of undefined
    at BittrexClient._sendUnsub (/home/evan/devel/coygo/webapp/.meteor/desktop-build/node_modules/ccxws/src/exchanges/bittrex-client.js:150:20)
    at BittrexClient._unsubscribe (/home/evan/devel/coygo/webapp/.meteor/desktop-build/node_modules/ccxws/src/exchanges/bittrex-client.js:119:14)
    at BittrexClient.unsubscribeLevel2Updates (/home/evan/devel/coygo/webapp/.meteor/desktop-build/node_modules/ccxws/src/exchanges/bittrex-client.js:90:10)
    at classDefinition.(anonymous function).deregisterOrderBookListener (/home/evan/devel/coygo/webapp/.meteor/desktop-build/desktop.asar/trading/exchange-clients/ExchangeClientCcxtCcxwsCommon.js:363:16)
(node:10161) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)

The problem lines are:

 _sendSub(remote_id) {
    // increment market counter
    this._subCount[remote_id] = (this._subCount[remote_id] || 0) + 1;

_sendUnsub(remote_id) {
    // decrement market count
    this._subCount[remote_id] -= 1;
  }

To Reproduce Subscribe to l2 updates on Bittrex BTC-EOS market.

This happened once but I can’t reproduce it since then, so I just grabbed the logs to place them here in hopes that it’s enough details.

Expected behavior Connection is successful and doesn’t throw error.

Additional context Add any other context about the problem here.

[bmancini55]

Two fixes are now available in release v0.27.3:

1. Reordered connection logic to match logic in other clients
2. Fixed a race condition on subscribe.

Most likely the second is the culprit of your issues. The calls to subscribe were checking for the existence of the websocket variable _wss https://github.com/altangent/ccxws/blob/22eafc7fc5330a7fac75be7cf62a4602a390f7c0/src/exchanges/bittrex-client.js#L118 to determine if it is ok to immediately send a subscription to the server.

_wss is created in _connect https://github.com/altangent/ccxws/blob/22eafc7fc5330a7fac75be7cf62a4602a390f7c0/src/exchanges/bittrex-client.js#L191

However, _subCount does not get set until a valid connection is established with the handler _onConnected.

This opened a window where a subscription would think the websocket was open when it was not actually open yet and when the call stack subscribeLevel2Update > _subscribe > _sendSub > occurred without actually be connected it would abend.

A new flag has been added _isConnected that gets set when the connection handler _onConnected is fired and is unset when disconnected event is fired in _onDisconnected. This flag is now checked in the subscribe method to determine if an immediate subscription can be performed.

I’m going to close this issue for now, if you’re still seeing the issue after this fix then we can reopen it.

[bmancini55]

@evan-coygo v0.27.3 should be live on NPM now