title: Why is Connection: keep-alive still being specified in http headers (isn't it deprecated)?
body: <p>According to "HTTP: The Definitive Guide", using</p>
  
  <pre><code>Connection: keep-alive
  </code></pre>
  
  <p>to specify a persistent connection is deprecated in HTTP/1.1, since HTTP/1.1 specifies that connections are persistent by default and must be closed manually by sending </p>
  
  <pre><code>Connection: close
  </code></pre>
  
  <p><br>
  Thus, my simple assumption is that "Connection: keep-alive" shouldn't really be used anymore. However, it still seems alive and well. For example, keep-alive is being returned in the following query:</p>
  
  <pre><code>curl -I https://foursquare.com
  
  HTTP/1.1 200 OK
  Server: nginx/0.8.52
  Date: Thu, 11 Aug 2011 21:15:45 GMT
  Content-Type: text/html; charset=utf-8
  Connection: keep-alive
  Expires: Thu, 11 Aug 2011 21:15:45 UTC
  Set-Cookie: XSESSIONID=w19~kqtn4bpqmfq51p8qolstpk6ti;Path=/;Secure;HttpOnly
  Set-Cookie: LOCATION=49.25::-123.13330078125::Hockeytown::CA;Path=/;Secure
  Set-Cookie: bbhive=OQ32XATE0OQAEVCY0IVSWUDPQ1A2GT
  Content-Length: 38815
  Cache-Control: no-cache, private, no-store
  Pragma: no-cache
  </code></pre>
  
  <p>My question is: <strong>Why is Connection: keep-alive still being specified in HTTP headers?</strong> </p>
  
  <p>A corollary question is: <strong>Are there still (clients, servers, proxies, etc) that still only speak HTTP/1.0 and its variants, or are most such entities on HTTP/1.1 as of 2011?</strong></p>
  
  <p>Here are my working hypotheses:</p>
  
  <p>1) HTTP/1.0 is no longer in use, b/c that was "many years" ago</p>
  
  <p>2) Given (1), keep-alive <em>shouldn't</em> be used anymore, but <em>is</em> purely for vestigial reasons (that is, certain technologies haven't bothered to remove it, or keep it around as voodoo code, etc.)</p>
  
  <p>If (1) is incorrect, and HTTP/1.0 is still in use, then sure it seems plausible to keep using keep-alive, despite follow-up questions on HTTP 1.0-1.1 interop.</p>
  
  <p>Thanks in advance for any insights shared!</p>