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POWhy does this XMLHttpRequest POST fail to even connect to the server?
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copied!<p>I have an XMLHttpRequest opened with the POST method, to a URL that I know exists because I've just done a GET on it. However, the send() call on the XHR doesn't actually open any connection to the server or send any data -- I've verified this with WireShark. Instead, it just fails the request, calls the onreadystatechange event handler, setting status to 0 (meaning, according to the spec, that the "error flag" is set).</p> <p>But... there's no way for me to inspect WHAT is going wrong. I've tried this in FireBug, and the headers and body look OK; there is no response body or response headers. The line in the console output is a POST /url (x) where the (x) is a red circle with an X in it. No error reason is visible anywhere. That same line is not in the NET panel at all. This is probably a clue, but I don't know of what.</p> <pre><code>function save_edits(url, txt, cb) { var xhr = new XMLHttpRequest(); console.log("'POST' " + url); xhr.open('POST', url, true); xhr.onreadystatechange = function(ev) { if (xhr.readyState == 4) { console.log('post complete status:' + xhr.status); cb(); } } xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); var text = "&" + edit_what + "=" + escape(txt.replace(/\r/g, '\n')); try { xhr.send(text); } catch (e) { console.log('send() error: ' + e.toString()); } </code></pre> <p>This outputs in the FireBug console:</p> <ol> <li>'POST' <a href="http://mydomain.com/srv.json.section-xna.latest" rel="nofollow">http://mydomain.com/srv.json.section-xna.latest</a></li> <li>POST <a href="http://mydomain.com/srv.json.section-xna.latest" rel="nofollow">http://mydomain.com/srv.json.section-xna.latest</a> source.js (line 70)</li> <li>post complete status:0</li> </ol> <p>Line 1) is my console log statement.</p> <p>Line 2) is the POST XHR request, which is red, with the circle-X showing failure.</p> <p>Line 3) is the console log statement from the onreadystatechange handler.</p> <p>There is no exception raised (I put that check in there just for paranoia) -- even if I make the open() be synchronous instead of asynchronous.</p> <p>Again, this is not a server-side problem, because the request doesn't even make it onto the wire, and I don't know how to figure out why that is.</p>

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