Jeff Garzik wrote:
> Jakub Narebski wrote:
>> Jeff Garzik wrote:
>>> Jakub Narebski wrote:
>>>>
>>>> P.S. Any hints to how to do this with CGI Perl module?
>>>
>>> It's impossible, Apache doesn't supply e-tag info to CGI programs. (it
>>> does supply HTTP_CACHE_CONTROL though apparently)
>>
>> By ETag info you mean access to HTTP headers sent by browser
>> If-Modified-Since:, If-Match:, If-None-Match: do you?
Adn in CGI standard there is a way to access additional HTTP headers
info from CGI script: the envirionmental variables are HTTP_HEADER,
for example if browser sent If-Modified-Since: header it's value
can be found in HTTP_IF_MODIFIED_SINCE environmental variable.
But of course gitweb should rather use mod_perl if possible, so
somewhere in gitweb there would be the following line:
$in_date = $ENV{'MOD_PERL'} ?
$r->header('If-Modified-Since') :
$ENV{'HTTP_IF_MODIFIED_SINCE'};
or something like that...
> You can use this attached shell script as a CGI script, to see precisely
> what information Apache gives you. You can even experiment with passing
> back headers other than Content-type (such as E-tag), to see what sort
> of results are produced. The script currently passes back both E-Tag
> and Last-Modified of a sample file; modify or delete those lines to suit
> your experiments.
It is ETag, not E-tag. Besides, I don't see what the attached script is
meant to do: it does not output the sample file anyway.
>> It's a pity that CGI interface doesn't cover that...
>>
>>> You could probably do it via mod_perl.
>>
>> So the cache verification should be wrapped in if ($ENV{MOD_PERL}) ?
>
> Sorry, I was /assuming/ mod_perl would make this available. The HTTP
> header info is available to all Apache modules, but I confess I have no
> idea how mod_perl passes that info to scripts.
>
> Also, an interesting thing while I was testing the attached shell
> script: even though repeated hits to the script generate a proper 304
> response to the browse, the CGI script and its output run to completion.
> So, it didn't save work on the CGI side; the savings was solely in not
> transmitting the document from server to client. The server still went
> through the work of generating the document (by running the CGI), as one
> would expect.
The idea is of course to stop processing in CGI script / mod_perl script
as soon as possible if cache validates.
I don't know if Apache intercepts and remembers ETag and Last-Modified
headers, adds 304 Not Modified HTTP response on finding that cache validates
and cuts out CGI script output. I.e. if browser provided If-Modified-Since:,
script wrote Last-Modified: header, If-Modified-Since: is no earlier than
Last-Modified: (usually is equal in the case of cache validation), then
Apache provides 304 Not Modified response instead of CGI script output.
--
Jakub Narebski
Poland
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