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Member "mod_gzip-1.3.26.1a/docs/manual/english/browser.htm" (30 Sep 2002, 10414 Bytes) of package /linux/www/apache_httpd_modules/old/mod_gzip-1.3.26.1a.tgz:


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    1 <?xml version="1.0" encoding="iso-8859-1" ?>
    2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
    3 <html xmlns="http://www.w3.org/1999/xhtml">
    4 
    5 <head>
    6  <title>Which browsers can handle 'Content-Encoding:'?</title>
    7  <meta name="author"      content="Michael Schr&ouml;pl" />
    8  <meta name="description" content="A description of the behaviour of the most popular web browsers regarding compressed page contents" />
    9  <meta name="keywords"    content="browsers, HTTP, encoding, gzip, compression" />
   10  <style type="text/css">
   11 body{font-family:sans-serif;margin:0px 30px 0px 30px;}
   12 h1{font-size:22px;margin-top:20px;}
   13 h2{font-size:18px;margin-top:14px;}
   14 small{font-size:80%;}
   15 td{vertical-align:top;}
   16 tt{font-weight:bold;}
   17 code,tt{font-family:"Courier New",monospace;}
   18 h1,h2{margin-bottom:1px;}
   19 p,td{margin-top:3px;margin-bottom:3px;}
   20 p,ul,ol,li{font-size:17px;line-height:22px;}
   21 ul,ol,li{margin-top:0px;margin-bottom:0px;}
   22 img{border-width:0;}
   23 
   24 #nav{position:absolute;top:30px;left:0px;font-size:14px;width:170px;font-weight:bold;margin:2px 2px 2px 30px;}
   25 #nav[id]{position:fixed;}
   26 #nav img{margin:5px;}
   27 #nav p, #nav a:hover, #nav a{display:block;padding:3px;margin:2px;width:150px;font-size:15px;line-height:18px;}
   28 #content{position:absolute;left:220px;right:30px;}
   29 #mail{text-align:right;}
   30 #icon{width:190px;float:left;}
   31 #mail,#icon{margin-top:30px;}
   32 
   33 @media screen {
   34 body{color:#000;background-color:#f8ebd9;}
   35 h1{color:#666;}
   36 h2{color:#840;}
   37 code{color:#333;}
   38 em{color:#900;}
   39 tt{color:#909;}
   40 h1,h2,code,em,tt{background-color:inherit;}
   41 .new13192a{color:#inherit;background-color:#ffd;}
   42 .new13261a{color:#inherit;background-color:#eff;}
   43 .bugfix{color:#fff;background-color:#f00;font-weight:bold;padding:0px 4px;}
   44 #nav a{color:#530;background-color:transparent;}
   45 #nav a{text-decoration:none;}
   46 #nav p, #nav a:hover{color:#000;background-color:#fff;}
   47 #nav p {border:1px #660 solid;}
   48 #nav a {border:1px #666 dotted;}
   49 }
   50 
   51 @media print {
   52 #icon,#nav{display:none;}
   53 #content{position:absolute;left:0px;right:0px;}
   54 }
   55  </style>
   56 </head>
   57 
   58 <body>
   59 
   60 <div id="nav">
   61 
   62 <img src="mod_gzip_logo.gif" height="47" width="102" alt="mod_gzip logo" />
   63 
   64 
   65 <a title="mod_gzip - what's that, anyway?" href="index.htm">mod_gzip</a>
   66 
   67 
   68 
   69 <a title="Compression of HTTP content using Content-Encoding" href="encoding.htm">Content-Encoding</a>
   70 
   71 
   72 
   73 <p>Browsers</p>
   74 
   75 
   76 
   77 <a title="How do Firewalls handle 'Content-Encoding:'?" href="firewalls.htm">Firewalls</a>
   78 
   79 
   80 
   81 <a title="An example configuration for mod_gzip" href="config.htm">Configuration</a>
   82 
   83 
   84 
   85 <a title="Complete description of mod_gzip status codes" href="status.htm">Status Codes</a>
   86 
   87 
   88 
   89 <a title="Possible enhancements in future versions of mod_gzip" href="enhancements.htm">Enhancements</a>
   90 
   91 
   92 
   93 <a title="Caching of negotiated HTTP responses" href="cache.htm">Caching</a>
   94 
   95 
   96 
   97 <a title="Version history and change log for mod_gzip" href="versions.htm">Versions</a>
   98 
   99 
  100 
  101 <a title="Other ressources about mod_gzip" href="links.htm">Links</a>
  102 
  103 
  104 </div>
  105 
  106 <div id="content">
  107 
  108 <h1>Which browsers can handle <code>Content-Encoding: gzip</code> ?</h1>
  109 
  110 <h2><a id="Netscape3"></a>Netscape 3</h2>
  111 <p>This browser uses HTTP/1.0. It doesn't send an <code>Accept-Encoding</code> header, thus doesn't request compressed content from a server.</p>
  112 <p>The browser <strong>does not yet support the processing of compressed page content</strong>. If it receives gzip compressed content, it recognizes that there is an encoding <code>gzip</code> unknown to it <small>(and displays a corresponding message to the user)</small>, but after that it displays the compressed page content within the browser windows. Serving compressed content unconditionally <small>(like in statically precompressed documents)</small> this browser isn't good for.</p>
  113 <p>A web server correctly evaluating the <code>Accept-Encoding</code> header is able to serve usable, uncompressed data to the browser.</p>
  114 
  115 <h2><a id="Netscape4"></a>Netscape 4</h2>
  116 <p>This browser uses HTTP/1.0. From version 4.06 on it is sending the header <code>Accept-Encoding: gzip</code>.</p>
  117 <p>Nevertheless the implementation of handling compressed content contains a number of <strong>bad errors</strong>:</p>
  118 <ul>
  119  <li>In many 4.x versions <strong>Cascading Style Sheets</strong> that are loaded from a separate file by use of the HTML tag<br />
  120  <code>&lt;link rel=&quot;stylesheet&quot; type=&quot;text/css&quot; href=&quot;</code><i>file name</i><code>&quot; /&gt;</code><br />
  121  will <em>not</em> be decompressed and thus not evaluated.</li>
  122  <li>In many 4.x versions <strong>JavaScript code</strong> that is loaded from a separate file by use of the HTML tag<br />
  123  <code>&lt;script type=&quot;text/javascript&quot; src=&quot;</code><i>file name</i><code>&quot; /&gt;</code><br />
  124  will be decompressed and evaluated <em>only</em> if a <strong>cache is activated</strong> in the browser.<br />
  125  <small>(In case of activated JavaScript in the browser this problem may additionally cause JavaScript error messages if the HTML source code references definitions of the included JavaScript code.)</small></li>
  126  <li>In many 4.x versions the HTML code of the document will be decompressed before <strong>printing the page content</strong> <em>only</em> if a <strong>cache is activated</strong> in the browser; the same applies to the <strong>display of the page content in print preview mode</strong>.</li>
  127  <li>In many 4.x versions the <strong>display of HTML source code</strong> of the current documents works correctly <em>only</em> if a <strong>cache is activated</strong> in the browser. Otherwise an empty screen will be displayed instead of the source code.</li>
  128  <li>In many 4.x versions the correct handling of <strong>gzip compressed images</strong> may fail in the browser, under circumstances that don't seem to be easily reproducable. <small>(Anyway, images should be optimized manually by using chosing the correct file type, using a minimal color depth for GIF and the like - gzipping an already compressed file format won't lead to an additional gain worth mentioning.)</small></li>
  129  <li>In the versions 4.06 to 4.08 there are even problems with the processing of JavaScript code inside the <code>&lt;head&gt;</code> section of compressed HTML pages.</li>
  130 </ul>
  131 <p>In all these cases Netscape 4 seems to use the received, yet uncompressed version; obviously the invocation of a <small>(surely available)</small> function for content compression simply has been forgotten at the decisive positions.</p>
  132 <p>And some part of the errors described above may only be in effect if the browser's cache has been set to 0 MB and/or switched off - so it seems Netscape 4 is somehow using the browser cache as temporary storage for decompressing ...</p>
  133 
  134 <h2><a id="Mozilla"></a>Netscape 6 &amp; 7 and Mozilla 0.9.x &amp; 1.x</h2>
  135 <p>This browser uses HTTP/1.1. From Netscape 6.2 on <small>(= Mozilla 0.9.4)</small>, it is sending the header <code>Accept-Encoding: gzip, deflate, compress;q=0.9</code>.</p>
  136 <p>Mozilla 0.9.9+ und Netscape 7.0PR1 allow the user to define the HTTP version as well as the content of this headers in its configuration; in Mozilla 1.1alpha this function is no longer visible in the preferences but can be defined in the configuration file <code>defaults/pref/all.js</code> <small>(under the name <code>network.http.accept-encoding</code>)</small>.</p>
  137 <p>Processing compressed content works <em>if the browser has requested compressed content</em>; otherwise it ignores the HTTP header <code>Content-Encoding: gzip</code> although it would be able to decompress the content.</p>
  138 
  139 <h2><a id="Microsoft"></a>Microsoft Internet Explorer 4.0, 5.0, 5.5 and 6.0</h2>
  140 <p>This browser uses either HTTP/1.0 or HTTP/1.1, depending upon the settings in the internet options. It is sending the header <code>Accept-Encoding: gzip, deflate</code> - but only if using HTTP/1.1.</p>
  141 <p>Processing compressed content works <em>if the browser has requested compressed content</em>; otherwise it ignores the HTTP header <code>Content-Encoding: gzip</code> although it would be able to decompress the content.</p>
  142 <p>Some older versions of the Internet Explorer seem to fire the JavaScript event <code>onLoad</code> already when they have successfully <em>received</em> a JavaScript file referenced within the <code>&lt;head&gt;</code> section instead of waiting for the successful completion of <em>decompressing</em> its content.</p>
  143 
  144 <h2><a id="Opera-old"></a>Opera 3 and 4</h2>
  145 <p>Opera 3.5 does <em>not yet</em> understand compressed content.</p>
  146 <p>From version 4 on Opera is using HTTP/1.1. Opera 4.0beta3 did already try to communicate in compressed form but sent the header <code>TE: deflate, gzip, x-gzip, identity, trailers</code>, i.&nbsp;e. it expected gzip compression to be applied as <em>Transfer Encoding</em>, not as <em>Content Encoding</em>.</p>
  147 
  148 <h2><a id="Opera"></a>Opera 5 and 6</h2>
  149 <p>Starting with version 5.12 <small>(or a bit earlier)</small> Opera is sending the header <code>Accept-Encoding: deflate, gzip, x-gzip, identity, *;q=0</code>. Processing compressed content works without known problems in versions 5 and up.</p>
  150 <p>Opera 6 <small>(as the single known browser up to now)</small> decompresses gzip-compressed document content even if the server did <em>not</em> call its attention to it by serving the HTTP header <code>Content-Encoding: gzip</code>.</p>
  151 
  152 <h2><a id="Lynx"></a>Lynx</h2>
  153 <p>Lynx supports gzip-compressed communikation since version 2.6.</p>
  154 <p>The first Lynx versions had to start a separate process using an external <code>gzip -d</code> command for decompressing. This of course leads into problems in case of no <code>gzip</code> command being available.</p>
  155 <p>More recent versions of Lynx <small>(since 1997-08-14, see Lynx 2.8.0 <code>CHANGES</code> file)</small> use the <code>zlib</code> library for decompressing and don't have these problems any more.</p>
  156 
  157 <div id="icon">
  158  <a href="http://validator.w3.org/check/referer"><img alt="" title="valid XHTML 1.1" height="31" width="88" src="valid-xhtml11.png" /></a><a href="http://jigsaw.w3.org/css-validator/check/referer"><img alt="" title="valid CSS" height="31" width="88" src="valid-css.png" /></a>
  159 </div>
  160 
  161 
  162 <p id="mail">(<a href="mailto:michael.schroepl&#x40;gmx.de?subject=mod_gzip">Michael Schr&ouml;pl</a>, 2002-09-16)</p>
  163 
  164 </div>
  165 
  166 </body>
  167 </html>