So far, people have reported a few variants of this error:

Unexpected token c in JSON at position 90
Unexpected token R in JSON at position 0
Unexpected token � in JSON at position 0"

I'm not sure how to reproduce those exact errors, but I found a way to reproduce a similar error. If we force the requests to last more than 30 seconds, Heroku will terminate the request and respond with the following error:

Response Headers

HTTP/1.1 503 Service Unavailable
Connection: keep-alive
Server: Cowboy
Date: Mon, 22 Jan 2018 19:28:37 GMT
Content-Length: 506
Content-Type: text/html; charset=utf-8
Cache-Control: no-cache, no-store

Response Body

<!DOCTYPE html>
	<html>
	  <head>
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<meta charset="utf-8">
		<title>Application Error</title>
		<style media="screen">
		  html,body,iframe {
			margin: 0;
			padding: 0;
		  }
		  html,body {
			height: 100%;
			overflow: hidden;
		  }
		  iframe {
			width: 100%;
			height: 100%;
			border: 0;
		  }
		</style>
	  </head>
	  <body>
		<iframe src="//www.herokucdn.com/error-pages/application-error.html"></iframe>
	  </body>
	</html>

Because the response is HTML instead of JSON, Teletype experiences an error attempting to parse the response as JSON:

Unexpected token < in JSON at position 0

Now that we have a way to reproduce some form of this issue, hopefully we can use this info to teach Teletype to gracefully handle non-JSON responses. 🤞

Teletype "unexpected token" error #266

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