[thelist] [evolt] Is server-side browser-sniffing a bad idea? (was RE: js include error in IE 3)

[George Dillon <> Evolt!]

I intended to send nate this reply offlist, but it reminded me of a
question which has been troubling me for a little while...

I've read recently that using server-side browser-sniffing to keep code lean
by tailoring it for each browser's quirks is NOT a good idea because of web
caches.  The undesirable scenario is that a web cache stores the page
designed for WinMSIE5 (e.g.) and then delivers THAT verison when requested
by a user with MacNN4... resulting in a layout mess for that particular
user.

Is this a real issue or have I misunderstood how web caches work?

[Note: I am not talking about client browser caches but the server caches
created by some ISPs.]

TIA

George Dillon


===============================

nate wrote:

> i've run across a silly problem with IE 3. does anyone know if IE3/pc does
> or doesn't support included js files?

If your server allows you to use XSSI this 'feature' of IE3 is not a problem
and can easily be overcome. All you need to do is sniff for IE3 and if found
include it between style tags rather than call it as a linked .js a bit like
this:

<!--#if expr="($VAR_jssrc=/yes/)"
  --><SCRIPT LANGUAGE="JavaScript" SRC="/path/myfile.js"
  TYPE="text/javascript"></SCRIPT><!--#else

  --><SCRIPT LANGUAGE="JavaScript" TYPE="text/javascript"><!--#include
  virtual="/path/myfile.js" --></SCRIPT><!--#endif
  -->

The sniffing part might go a bit like this (slightly pruned version of the
real code, but any suggestions to improve my sloppy code would be welcome :)

<!--#set var="VAR_browser" value="msie"
 --><!--#set var="VAR_version" value="4"
 --><!--#set var="VAR_jssrc" value="yes"

 --><!--#if expr="($HTTP_USER_AGENT=/Mozilla.*.*/)
              && ($HTTP_USER_AGENT !=/compatible/)
              && ($HTTP_USER_AGENT !=/Spoofer/)
              && ($HTTP_USER_AGENT !=/Opera/)
              && ($HTTP_USER_AGENT !=/WebTV/)"
 --><!--#set var="VAR_browser" value="nav"
 --><!--#endif
 --><!--#if expr="($HTTP_USER_AGENT=/Opera/)"
 --><!--#set var="VAR_browser" value="opera"
 --><!--#endif
 --><!--#if expr="($HTTP_USER_AGENT=/AOL/)"
 --><!--#set var="VAR_browser" value="aol"
 --><!--#endif

 --><!--#if expr="($HTTP_USER_AGENT=//1/)
 || ($HTTP_USER_AGENT=/ 1/)"
 --><!--#set var="VAR_version" value="1"
 --><!--#endif
 --><!--#if expr="($HTTP_USER_AGENT=//2/)
 || ($HTTP_USER_AGENT=/ 2/)"
 --><!--#set var="VAR_version" value="2"
 --><!--#endif
 --><!--#if expr="($HTTP_USER_AGENT=//3/)
 || ($HTTP_USER_AGENT=/ 3/)"
 --><!--#set var="VAR_version" value="3"
 --><!--#endif
 --><!--#if expr="($HTTP_USER_AGENT=//5/)
 || ($HTTP_USER_AGENT=/ 5/)"
 --><!--#set var="VAR_version" value="5"
 --><!--#endif
 --><!--#if expr="($HTTP_USER_AGENT=//6/)
 || ($HTTP_USER_AGENT=/ 6/)"
 --><!--#set var="VAR_version" value="6"
 --><!--#endif

 --><!--#if expr="($HTTP_USER_AGENT=/Gecko/)"
 --><!--#set var="VAR_browser" value="gecko"
 --><!--#set var="VAR_version" value="6"
 --><!--#endif

 --><!--#if expr="($VAR_version=/1/)
 || ($VAR_version=/2/)
 || (($VAR_version=/3/) && ($VAR_browser=/msie/))"
 --><!--#set var="VAR_jssrc" value="no"
 --><!--#endif

 -->


HTH

George Dillon