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copied!<p>Nope, it's a vestigial header nowadays; that is to say, it was put there to work around a bug in a browser which is obsolete (several generations older than IE6 - the bug was reported fixed as of 1997, 15 years ago!) and nobody uses it any more.</p> <p><a href="http://mail-archives.apache.org/mod_mbox/httpd-cvs/200812.mbox/%3C20081205051015.456402388879@eris.apache.org%3E" rel="noreferrer">The patch to remove it</a> is in Apache's SVN since 2008, but it apparently still hasn't propagated to all distributions (plus some sites may use non-updated versions of Apache).</p> <p>Here's the comment for the header, picked up <a href="http://svn.apache.org/viewvc/httpd/httpd/trunk/modules/http/http_filters.c?r1=722081&r2=723585" rel="noreferrer">from the source</a>:</p> <pre><code>/* Navigator versions 2.x, 3.x and 4.0 betas up to and including 4.0b2 * have a header parsing bug. If the terminating \r\n occur starting * at offset 256, 257 or 258 of output then it will not properly parse * the headers. Curiously it doesn't exhibit this problem at 512, 513. * We are guessing that this is because their initial read of a new request * uses a 256 byte buffer, and subsequent reads use a larger buffer. * So the problem might exist at different offsets as well. * * This should also work on keepalive connections assuming they use the * same small buffer for the first read of each new request. * * At any rate, we check the bytes written so far and, if we are about to * tickle the bug, we instead insert a bogus padding header. Since the bug * manifests as a broken image in Navigator, users blame the server. :( * It is more expensive to check the User-Agent than it is to just add the * bytes, so we haven't used the BrowserMatch feature here. */ </code></pre>

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