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POIssues with long polling XMLHttpRequests and intermittent network connections
 

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  1. POIssues with long polling XMLHttpRequests and intermittent network connections
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    <p>I've implemented a long polling connection to allow me to do server-side push (comet) using a Tomcat web server and standard javascript on the frontend. To keep the connection going, I have a simple keep-alive loop that initiates a new request as soon as the last one completes/fails.</p> <p>The vast majority of the time, this connection works perfectly fine and keeps alive as I expect. But, I've noticed that when a user's internet connection drops out (e.g. they disconnect from a VPN, unplug their ethernet, etc.) AND I have a pending XMLHttpRequest out to the server, I get no indication of failure. Because of this, the connection dies silently, and I can't know that it's happened unless I constantly send requests to the server to test the connection (which seems to defeat the purpose of using long polling).</p> <p>Here's the request object that I see in Chrome when it dies this silent death:</p> <pre><code>request: XMLHttpRequest onabort: function () onerror: function () onload: null onloadend: null onloadstart: null onprogress: null onreadystatechange: function () readyState: 1 response: "" responseText: "" responseType: "" responseXML: null status: [Exception: DOMException] statusText: [Exception: DOMException] upload: XMLHttpRequestUpload withCredentials: false </code></pre> <p>I have the three listeners (onabort, onerror, onreadystatechange) setup to alert a message if they ever get fired, but I get nothing whenever I take my connection to the server down. Here's how I'm forming the request:</p> <pre><code>var request = new XMLHttpRequest(); //url is just the url to my servlet to handle this request.open("GET", url, true); //handlestatechange is just my standard handling code //that I've put an alert at the top of request.onreadystatechange = handleStateChange; request.onerror = function() { alert("We encountered an error"); } request.onabort = function() { alert("I've had an abortion"); } request.send(null); </code></pre> <p>It seems like this would be a pretty standard situation, but I've not seen any conversations on how to allow a long polling connection to recover from this sort of disconnection.</p> <p>Am I doing something wrong? Is there some other more standard approach to doing long polling/comet that circumvents this issue?</p> <p>Any help with this would be appreciated, Thanks</p>
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