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POHow to correctly write http response so as to use XHR progress event listener
 

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  1. POHow to correctly write http response so as to use XHR progress event listener
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    <p>I would like to use XHR object's "progress" event to get the progress of download. </p> <p>Here's example code from <a href="https://developer.mozilla.org/en/using_xmlhttprequest#Monitoring_progress" rel="nofollow">MDN</a></p> <pre><code>var req = new XMLHttpRequest(); req.addEventListener("progress", updateProgress, false); req.addEventListener("load", transferComplete, false); req.addEventListener("error", transferFailed, false); req.addEventListener("abort", transferCanceled, false); req.open(); ... // progress on transfers from the server to the client (downloads) function updateProgress(evt) { if (evt.lengthComputable) { var percentComplete = evt.loaded / evt.total; ... } else { // Unable to compute progress information since the total size is unknown } } function transferComplete(evt) { alert("The transfer is complete."); } function transferFailed(evt) { alert("An error occurred while transferring the file."); } function transferCanceled(evt) { alert("The transfer has been canceled by the user."); } </code></pre> <p>I've written similar code, but <code>lengthComputable</code> field of the progress event turns out to be false. The <code>loaded</code> field is some finite value, but <code>total</code> is set to zero.</p> <p>From the comment in the code example above, I can see that the browser doesn't get enough information in the HTTP response to calculate a meaningful download progress.</p> <p>What is the correct way to write the response to make this work? The response I see in my testing has <code>Transfer-encoding: chunked</code> and <code>Content-Length: 8</code>. I am generating it from Tornado Web server.</p>
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    1. USJayesh
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      1. USJimmy Sawczuk
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