NAME

Apache::Dynagzip - mod_perl extension for Apache-1.3.X to compress the response with gzip format.

ABSTRACT

This Apache handler provides dynamic content compression of the response data stream for HTTP/1.0 and HTTP/1.1 requests. Standard gzip compression is optionally combined with an extra light compression that eliminates leading blank spaces and/or blank lines within the source document. An extra light compression could be applied even when the client (browser) is not capable to decompress gzip format.

Handler helps to compress the outbound HTML content usually by 3 to 20 times, and provides a list of useful features. This is particularly useful for compressing outgoing web content that is dynamically generated on the fly (using templates, DB data, XML, etc.), when at the time of the request it is impossible to determine the length of the document to be transmitted. Support for Perl, Java, and C source generators is provided.

Besides the benefits of reduced document size, this approach gains efficiency from being able to overlap the various phases of data generation, compression, transmission, and decompression. In fact, the browser can start to decompress a document, which has not yet been completely generated.

SYNOPSIS

There is more then one way to configure Apache to use this handler...

Compress regular (static) HTML files

 ======================================================
 Static html file (size=149208) no light compression:
 ======================================================
 httpd.conf:

  PerlModule Apache::Dynagzip
  <Files ~ "*\.html">
      SetHandler perl-script
      PerlHandler Apache::Dynagzip
  </Files>

 client-side log:

  C05 --> S06 GET /html/wowtmovie.html HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Referer: http://devl4.outlook.net/html/
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Pragma: no-cache
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==

  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Fri, 31 May 2002 17:36:57 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Expires: Friday, 31-May-2002 17:41:57 GMT
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 9411 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  1314 (hex) = 4884 (dec)
  3ed (hex) = 1005 (dec)
  354 (hex) = 852 (dec)
  450 (hex) = 1104 (dec)
  5e6 (hex) = 1510 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.170 seconds, Extra Delay = 0.440 seconds
  == Restored Body was 149208 bytes ==

 ======================================================
 Static html file (size=149208) with light compression:
 ======================================================
 httpd.conf:

  PerlModule Apache::Dynagzip
  <Files ~ "*\.html">
        SetHandler perl-script
        PerlHandler Apache::Dynagzip
        PerlSetVar LightCompression On
  </Files>

 client-side log:

  C05 --> S06 GET /html/wowtmovie.html HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Referer: http://devl4.outlook.net/html/
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Pragma: no-cache
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==

  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Fri, 31 May 2002 17:49:06 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Expires: Friday, 31-May-2002 17:54:06 GMT
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 8515 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  119f (hex) = 4511 (dec)
  3cb (hex) = 971 (dec)
  472 (hex) = 1138 (dec)
  736 (hex) = 1846 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.280 seconds, Extra Delay = 0.820 seconds
  == Restored Body was 128192 bytes ==

Default values for the minChunkSizeSource and minChunkSize will be in effect in this case. In order to overwrite them one can try for example

        <IfModule mod_perl.c>
                PerlModule Apache::Dynagzip
                <Files ~ "*\.html">
                        SetHandler perl-script
                        PerlHandler Apache::Dynagzip
                        PerlSetVar minChunkSizeSource 36000
                        PerlSetVar minChunkSize 9
                </Files>
        </IfModule>

Compress the output stream of the Perl scripts

 ===============================================================================
 GET dynamically generated (by perl script) html file with no light compression:
 ===============================================================================
 httpd.conf:

 PerlModule Apache::Filter
 PerlModule Apache::Dynagzip
 <Directory /var/www/perl/>
      SetHandler perl-script
      PerlHandler Apache::RegistryFilter Apache::Dynagzip
      PerlSetVar Filter On
      PerlSendHeader Off
      PerlSetupEnv On
      AllowOverride None
      Options ExecCGI FollowSymLinks
      Order allow,deny
      Allow from all
 </Directory>

 client-side log:

  C05 --> S06 GET /perl/start_example.cgi HTTP/1.1
  C05 --> S06 Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/msword, */*
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==

  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Sat, 01 Jun 2002 16:59:47 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Expires: Saturday, 01-June-2002 17:04:47 GMT
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 758 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  2db (hex) = 731 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.220 seconds, Extra Delay = 0.050 seconds
  == Restored Body was 1434 bytes ==

 ============================================================================
 GET dynamically generated (by perl script) html file with light compression:
 ============================================================================
 httpd.conf:

  PerlModule Apache::Filter
  PerlModule Apache::Dynagzip
 <Directory /var/www/perl/>
        SetHandler perl-script
        PerlHandler Apache::RegistryFilter Apache::Dynagzip
        PerlSetVar Filter On
        PerlSetVar LightCompression On
        PerlSendHeader Off
        PerlSetupEnv On
        AllowOverride None
        Options ExecCGI FollowSymLinks
        Order allow,deny
        Allow from all
 </Directory>

 client-side log:

  C05 --> S06 GET /perl/start_example.cgi HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Pragma: no-cache
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==

  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Sat, 01 Jun 2002 17:09:13 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Expires: Saturday, 01-June-2002 17:14:14 GMT
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 750 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  2d3 (hex) = 723 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.280 seconds, Extra Delay = 0.000 seconds
  == Restored Body was 1416 bytes ==

Compress the outgoing stream from the CGI binary

 ====================================================================================
 GET dynamically generated (by C-written binary) html file with no light compression:
 ====================================================================================
 httpd.conf:

 PerlModule Apache::Dynagzip
 <Directory /var/www/cgi-bin/>
     SetHandler perl-script
     PerlHandler Apache::Dynagzip
     AllowOverride None
     Options +ExecCGI
     PerlSetupEnv On
     PerlSetVar BinaryCGI On
     Order allow,deny
     Allow from all
 </Directory>

 client-side log:

  C05 --> S06 GET /cgi-bin/mylook.cgi HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Pragma: no-cache
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==

  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Fri, 31 May 2002 23:18:17 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Expires: Friday, 31-May-2002 23:23:17 GMT
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 1002 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  3cf (hex) = 975 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.110 seconds, Extra Delay = 0.110 seconds
  == Restored Body was 1954 bytes ==

 =================================================================================
 GET dynamically generated (by C-written binary) html file with light compression:
 =================================================================================
  httpd.conf:

   PerlModule Apache::Dynagzip
   <Directory /var/www/cgi-bin/>
       SetHandler perl-script
       PerlHandler Apache::Dynagzip
       AllowOverride None
       Options +ExecCGI
       PerlSetupEnv On
       PerlSetVar BinaryCGI On
       PerlSetVar LightCompression On
       Order allow,deny
       Allow from all
   </Directory>

 client-side log:

  C05 --> S06 GET /cgi-bin/mylook.cgi HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Pragma: no-cache
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==

  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Fri, 31 May 2002 23:37:45 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Expires: Friday, 31-May-2002 23:42:45 GMT
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 994 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  3c7 (hex) = 967 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.170 seconds, Extra Delay = 0.110 seconds
  == Restored Body was 1862 bytes ==

INTRODUCTION

From a historical point of view this package was developed primarily in order to compress the output of a proprietary CGI binary written in C that was widely used by Outlook Technologies, Inc. in order to deliver uncompressed dynamically generated HTML content over the Internet using HTTP/1.0 since the mid-'90s. We were then presented with the challenge of using the content compression features over HTTP/1.1 on busy production servers, especially those serving heavy traffic on virtual hosts of popular American broadcasting companies.

The very first our attempts to implement a static gzip approach in order to compress the dynamic content helped us to scale effectively the bandwidth at the cost of significantly increased latency of the content delivery.

That was why I came up with an idea to use chunked data transmission of the gzipped content, sharing a real time between the server side data creation/compression, media data transmission, and the client side data decompression/presentation in order to provide end users with the partially displayed content as soon as it's possible in particular conditions of the user's connection.

At the time we decided to go for dynamic compression there were no appropriate software on the market. Even later in February 2002 Nicholas Oxhøj wrote to the mod_perl mailing list about his experience of finding Apache gzipper for the streaming outgoing content:

"... I have been experimenting with all the different Apache compression modules I have been able to find, but have not been able to get the desired result. I have tried Apache::GzipChain, Apache::Compress, mod_gzip and mod_deflate, with different results. One I cannot get to work at all. Most work, but seem to collect all the output before compressing it and sending it to the browser...

... Wouldn't it be nice to have some option to specify that the handler should flush and send the currently compressed output every time it had received a certain amount of input or every time it had generated a certain amount of output?..

... So I am basically looking for anyone who has had any success in achieving this kind of "streaming" compression, who could direct me at an appropriate Apache module."

Unfortunately for him, Apache::Dynagzip has not yet been publicly available at that time...

Since relesed this handler is especially useful when one needs to compress the outgoing web content that is dynamically generated on the fly using templates, DB data, XML, etc., and when at the time of the request it is impossible to determine the length of the response.

Content provider can benefit additionally from the fact that handler begins the transmission of compressed data concurent to further document creation. On the other hand, the internal buffer inside the handler prevents Apache from the creation of too short chunks over HTTP/1.1.

In order to simplify the use of this handler on public/open-source sites, the capability of content compression over HTTP/1.0 was added to this handler since the version 0.06. This helps to avoid dynamic invocation of other Apache handlers for the content generation phase.

Acknowledgments

Thanks to Tom Evans, Valerio Paolini, and Serge Bizyayev for their valuable idea contributions and multiple testing. Thanks to Igor Sysoev and Henrik Nordstrom those helped me to understand better the HTTP/1.0 compression features. Thanks to Vlad Jebelev for the patch that helps to survive possible dynamical Apache downgrade from HTTP/1.1 to HTTP/1.0 (especially serving MSIE requests over SSL). Thanks to Rob Bloodgood and Damyan Ivanov for the patches those help to eliminate some unnecessary warnings. Thanks to John Siracusa for the hint that helps to control the content type properly. Thanks to Richard Chen for the bug report concerning some uncompressed responses.

Obviously, I hold a full responsibility for how all those contributions are implemented.

DESCRIPTION

The main pupose of this package is to serve the content generation phase within the mod_perl enabled Apache 1.3.X, providing dynamic on the fly compression of outgoing web content. This is done through the use of zlib library via the Compress::Zlib perl interface to serve both HTTP/1.0 and HTTP/1.1 requests from clients/browsers, capable to understand gzip format and decompress it on the fly. This handler does never gzip content for clients/browsers those do not declare the ability to decompress gzip format.

In fact, this handler mainly serves as a kind of customizable filter of outbound web content for Apache 1.3.X.

This handler is supposed to be used within Apache::Filter chain mostly in order to serve the outgoing content that is dynamically generated on the fly by Perl and/or Java. It is featured to serve the regular CGI binaries (C-written for examle) as a standalong handler out of Apache::Filter chain. As an extra option, this handler can be used to compress dynamically the huge static files, and to transfer gzipped content in the form of a stream back to the client browser. For the last purpose Apache::Dynagzip handler should be configured as a standalong handler out of Apache::Filter chain too.

Working over HTTP/1.0 this handler indicates the end of data stream by closing connection. Indeed, over HTTP/1.1 the outgoing data is compressed within a chunked outgoing stream, keeping the connection alive. Resonable control over the chunk-size is provided in this case.

In order to serve better the older web clients, an extra light compression is provided independently in order to remove unnecessary leading blank spaces and/or blank lines from the outgoing web content. This extra light compression could be combined with the main gzip compression, when necessary.

The list of features of this handler includes:

· Support for both HTTP/1.0 and HTTP/1.1 requests.
· Reasonable control over the size of content chunks for HTTP/1.1.
· Support for Perl, Java, or C/C++ CGI applications in order to provide dynamic on-the-fly compression of outbound content.
· Optional extra light compression for all browsers, including older ones that incapable to decompress gzipped content.
· Optional control over the duration of the content's life in client/proxy local cache.
· Limited control over the proxy caching.
· Optional support for server-side caching of dynamically generated content.

Compression Features

Apache::Dynagzip provides content compression for both HTTP/1.0 and HTTP/1.1 in accordance with the type of the initial request.

There are two types of compression, which could be applied to outgoing content by this handler:

  - extra light compression
  - gzip compression

These compressions could be applied independently, or in combination.

An extra light compression is provided in order to remove leading blank spaces and/or blank lines from the outgoing web content. It is supposed to serve the ASCII data types like html, JavaScript, css, etc. The implementation of extra light compression is turned off by default. It could be turned on with the statement

  PerlSetVar LightCompression On

in httpd.conf. The value "On" is case-insensitive. Any other value turns the extra light compression off.

The main gzip format is described in rfc1952. This type of compression is applied when the client is recognized as one capable to decompress gzip format on the fly. In this version the decision is under the control of whether the client sends the Accept-Encoding: gzip HTTP header within the request, or not.

On HTTP/1.1, when the gzip compression is in effect, handler keeps the resonable control over the size of the chunks and over the compression ratio using the combination of two internal variables (those could be set in httpd.conf):

  minChunkSizeSource
  minChunkSize

minChunkSizeSource defines the minimum length of the source stream that zlib may accumulate in its internal buffer.

Note:: The compression ratio depends on the length of the data accumulated in that buffer; More data we keep -- better ratio will be achieved...

When the length defined by the minChunkSizeSource is exceeded, the handler flushes the internal buffer of zlib and transfers the accumulated portion of the compressed data into the own internal buffer in order to create a chunk when appropriate.

This buffer is not necessarily be fransfered to Appache immediately. The decision is under the control of the minChunkSize internal variable. When the size of the buffer exceeds the value of minChunkSize the handler chunks the internal buffer and transfers the accumulated data to the Client.

This approach helps to create the effective compression combined with the limited latency.

For example, when I use

  PerlSetVar minChunkSizeSource 16000
  PerlSetVar minChunkSize 8

in my httpd.conf in order to compress the dynamically generated content of the size of some 54,000 bytes, the client side log

  C05 --> S06 GET /pipe/pp-pipe.pl/big.html?try=chunkOneMoreTime HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==
  
  ## Sockets 6 of 4,5,6 need checking ##
  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Thu, 21 Feb 2002 20:01:47 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Vary: Accept-Encoding
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 6034 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  949 (hex) = 2377 (dec)
  5e6 (hex) = 1510 (dec)
  5c5 (hex) = 1477 (dec)
  26e (hex) = 622 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.990 seconds, Extra Delay = 0.110 seconds
  == Restored Body was 54655 bytes ==

shows that the first chunk consists of the gzip header only (10 bytes). This chunk was sent back to web client as soon as the handler received the first portion of the data generated by the CGI script. The data itself at that moment has been storied in the zlib's internal buffer, because the minChunkSizeSource is big enough.

Note:: Longer we allow zlib to keep its internal buffer -- better compression ratio it makes for us...

So far, in this example we have obtained the compression ratio at about 9 times.

In this version the handler provides defaults:

  minChunkSizeSource = 32768
  minChunkSize = 8

In case of gzip compressed response to HTTP/1.0 request, handler uses minChunkSize and minChunkSizeSource values in order to limit the minimum size of internal buffers providing appropriate compression ratio and avoiding multiple short outputs to the core Apache.

Chunking Features

On HTTP/1.1 this handler overwrites the default Apache behavior, and keeps own control over the chunk-size when it is possible. In fact, handler provides the soft control over the chunk-size only: It does never cut the incoming string in order to create a chunk of a particular size. Instead, it controls the minimum size of the chunk only. I consider this approach reasonable, because to date the HTTP chunk-size is not coordinated with the packet-size on transport level.

In case of gzipped output the minimum size of the chunk is under the control of internal variable

  minChunkSize

In case of uncompressed output, or the extra light compression only, the minimum size of the chunk is under the control of internal variable

  minChunkSizePP

In this version handler provides defaults:

  minChunkSize = 8
  minChunkSizePP = 8192

You may overwrite the default values of these variables in your httpd.conf if necessary.

Note:

The internal variable minChunkSize should be treated carefully together with the minChunkSizeSource (see Compression Features).

In this version handler does not keep control over the chunk-size when it serves the internally redirected request. An appropriate warning is placed to error_log in this case.

Filter Chain Features

As a member of Apache::Filter chain, Apache::Dynagzip handler is supposed to be the last executable filter in the chain due to the features of it's functions.

CGI Compatibility

When serving CGI binary this version of the handler is CGI/1.1 compatible. It accepts CGI headers from the binary and produces a set of required HTTP headers followed by gzipped content.

POST Request Features

I have to serve the POST requests for CGI binary with special care, because in this case the handler is standing along and have to serve all data flow in both directions at the time when stdin is tied into Apache, and could not be exposed to CGI binary transparently.

To solve the problem I alter POST with GET request internally doing the required incoming data transformations on the fly.

This could cause a problem, when you have a huge incoming stream from your client (more than 4K bytes). Another problem could appear if your CGI binary is capable to distinguish POST and GET requests internally.

Control over the Client Cache

The control over the lifetime of the response in client's cache is provided through implementation of Expires HTTP header:

The Expires entity-header field gives the date/time after which the response should be considered stale. A stale cache entry may not normally be returned by a cache (either a proxy cache or an user agent cache) unless it is first validated with the origin server (or with an intermediate cache that has a fresh copy of the entity). The format is an absolute date and time as defined by HTTP-date in section 3.3; it MUST be in rfc1123-date format:

Expires = "Expires" ":" HTTP-date

This handler creates the Expires HTTP header, adding the pageLifeTime to the date-time of the request. The internal variable pageLifeTime has default value

  pageLifeTime = 300 # sec.

that could be overwriten in httpd.conf for example as:

  PerlSetVar pageLifeTime 1800

to make the pageLifeTime = 30 minutes.

During the lifetime the client (browser) will not even try to access the server when user requests the same URL again. Instead, it restarts the page from the local cache.

It's important to point out here, that all initial JavaScripts will be restarted indeed, so you can rotate your advertisements and dynamic content when needed.

The second important point should be mentioned here: when user clicks the "Refresh" button, the browser will reload the page from the server unconditionally. This is right behavior, because it is exactly what the human user expects from "Refresh" button.

Notes:

The lifetime defined by Expires depends on accuracy of time settings on client machine. If the client's local clock is running 1 hour back, the cached copy of the page will be alive 60 minutes longer on that machine.

Apache::Dynagzip never overwrites Expires header set by earlier handler inside the filter-chain.

Support for the Server-Side Cache

In order to support the Server-Side Cache I place a reference to the dynamically generated document to the notes() when the Server-Side Cache Support is ordered. The referenced document could be already compressed with an extra light compression (if an extra light compression is in effect for the current request).

In this case the regular dynamic gzip compression takes place as usual and the effective gzip compression is supposed to take place within the log stage of the request processing flow.

You usually should not care about this feature of Apache::Dynagzip unless you use it in your own chain of handlers for the various phases of the request processing.

Control over the Proxy Cache.

Control over the (possible) proxy cache is provided through the implementation of Vary HTTP header. Within Apache::Dynagzip this header is under the control of few simple rules:

Apache::Dynagzip does never generate this header unless gzip compression is provided.
The value of Accept-Encoding is always provided for this header, accompanying gzip compression.

Advanced control over the proxy cache is provided since the version 0.07 with optional extension of Vary HTTP header. This extension could be placed into your configuration file, using directive

PerlSetVar Vary <value>

Particularly, it might be helpful to indicate the content, which depends on some conditions, other than just compression features. For example, when the content is personalized, someone might wish to use the "*" Vary extension in order to prevent any proxy caching.

When the outgoing content is gzipped, this extension will be appended to the regular Vary header, like in the following example:

Using the following fragment within the httpd.conf:

  PerlModule Apache::Dynagzip
  <Files ~ "*\.html">
    SetHandler perl-script
    PerlHandler Apache::Dynagzip
    PerlSetVar LightCompression On
    PerlSetVar Vary *
  </Files>

We can observe the client-side log in the form of:

  C05 --> S06 GET /devdoc/Dynagzip/Dynagzip.html HTTP/1.1
  C05 --> S06 Accept: */*
  C05 --> S06 Referer: http://devl4.outlook.net/devdoc/Dynagzip/
  C05 --> S06 Accept-Language: en-us
  C05 --> S06 Accept-Encoding: gzip, deflate
  C05 --> S06 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)
  C05 --> S06 Host: devl4.outlook.net
  C05 --> S06 Pragma: no-cache
  C05 --> S06 Accept-Charset: ISO-8859-1
  == Body was 0 bytes ==
  
  C05 <-- S06 HTTP/1.1 200 OK
  C05 <-- S06 Date: Sun, 11 Aug 2002 21:28:43 GMT
  C05 <-- S06 Server: Apache/1.3.22 (Unix) Debian GNU/Linux mod_perl/1.26
  C05 <-- S06 X-Module-Sender: Apache::Dynagzip
  C05 <-- S06 Expires: Sunday, 11-August-2002 21:33:43 GMT
  C05 <-- S06 Vary: Accept-Encoding,*
  C05 <-- S06 Transfer-Encoding: chunked
  C05 <-- S06 Content-Type: text/html; charset=iso-8859-1
  C05 <-- S06 Content-Encoding: gzip
  C05 <-- S06 == Incoming Body was 11311 bytes ==
  == Transmission: text gzip chunked ==
  == Chunk Log ==
  a (hex) = 10 (dec)
  1c78 (hex) = 7288 (dec)
  f94 (hex) = 3988 (dec)
  0 (hex) = 0 (dec)
  == Latency = 0.160 seconds, Extra Delay = 0.170 seconds
  == Restored Body was 47510 bytes ==

Simple form

Vary: Accept-Encoding

is provided as a default for the gzipped content.

CUSTOMIZATION

Apache::Dynagzip can be used in order

to compress dynamic web content generated in Apache::Filter chain;
to compress the output of CGI-compatible binary program;
to stream huge static files providing on the fly compression of the stream.

These are the main regims, wich one can implement through the appropriate configuration of the handler. Every main regim can be tuned with some specific settings and can be accomplished with various control features. All these specific settings and control features could be addressed through additional configuration parameters unless provided defaults are sufficient.

Note:

Do your best in order to avoid the implementation of this handler in internally redirected requests. It does not help much in this case. Read your error_log carefully in order to find appropriate warnings. Tune your httpd.conf carefully in order to take the most from opportunities offered by this handler.

Always use accomplishing Apache::CompressClientFixup handler in order to avoid gzip compression for known buggy web clients.

Apache::Filter Chain

If your application is initially configured something like

  PerlModule HTML::Mason::ApacheHandler
  <Directory /path/to/subdirectory>
    <FilesMatch "\.html$">
      SetHandler perl-script
      PerlHandler HTML::Mason::ApacheHandler
    </FilesMatch>
  </Directory>

you might want just to replace it with the following:

  PerlModule HTML::Mason::ApacheHandler
  PerlModule Apache::Dynagzip
  PerlModule Apache::CompressClientFixup
  <Directory /path/to/subdirectory>
    <FilesMatch "\.html$">
      SetHandler perl-script
      PerlHandler HTML::Mason::ApacheHandler Apache::Dynagzip
      PerlSetVar Filter On
      PerlFixupHandler Apache::CompressClientFixup
      PerlSetVar LightCompression On
    </FilesMatch>
  </Directory>

in order to provide gzip compression of your content. You should be all set safely after that.

In more common cases you need to replace the line

    PerlHandler HTML::Mason::ApacheHandler

in your initial configuration file with the set of the following lines:

    PerlHandler HTML::Mason::ApacheHandler Apache::Dynagzip
    PerlSetVar Filter On
    PerlFixupHandler Apache::CompressClientFixup

You might want to add optionally

    PerlSetVar LightCompression On

to reduce the size of the stream even for clients incapable to speak gzip (like Microsoft Internet Explorer over HTTP/1.0).

Finally, make sure you have somewhere declared

  PerlModule Apache::Dynagzip
  PerlModule Apache::CompressClientFixup

Outgoing Content-Type will be set to default text/html unless you have another value defined by core Apache or generated by another perl handler included in the chain.

In order to control the compression ratio and the minimum size of the chunk/buffer for gzipped content you can optionally use directives

    PerlSetVar minChunkSizeSource <value>
    PerlSetVar minChunkSize <value>

for example you can try

    PerlSetVar minChunkSizeSource 32768
    PerlSetVar minChunkSize 8

which are the defaults in this version.

Note:: You can improve the compression ratio when you increase the value of minChunkSizeSource.

In order to control the minimum size of the chunk for uncompressed content over HTTP/1.1 you can optionally use the directive

    PerlSetVar minChunkSizePP <value>

Default value is 8192 bytes in this version.

In order to control the pageLifeTime in client's local cache you can optionally use the directive

    PerlSetVar pageLifeTime <value>

where the value stands for the life-length in seconds.

    PerlSetVar pageLifeTime 300

is default in this version. Apache::Dynagzip does not overwrite any existent Expires HTTP header, whether one is set by core Apache, or by the previous perl handler.

You might wish to place

    PerlSetVar Vary User-Agent

in your httpd.conf file in order to notify possible proxies that you distinguish browsers in your content. Alternatively, you might want to place

    PerlSetVar Vary *

in order to prevent all proxies from caching your content.

you may use Apache::Filter chain to serve another sources, when you know what you are doing. You might wish to write your own handler and include it into Apache::Filter chain, preprocessing the outgoing stream if necessary.

In order to use your own handler (that might be generating its own HTTP headers) inside the Apache::Filter chain, make sure to register your handler with the Apache::Filter chain like

  $r->filter_register();

when necessary. See Apache::Filter documentation for details.

CGI-Compatible Binary

Use the directives like

  PerlModule Apache::Dynagzip
  PerlModule Apache::CompressClientFixup
  <Directory /path/to/subdirectory>
      SetHandler perl-script
      PerlHandler Apache::Dynagzip
      PerlSetVar BinaryCGI On
      Options +ExecCGI
      PerlFixupHandler Apache::CompressClientFixup
      PerlSetVar LightCompression On
  </Directory>

in order to indicate that the source-generator is supposed to be a CGI binary. Don't use Apache::Filter chain in this case. Support for CGI/1.1 headers defaults to "On" for this type of source generators.

Outgoing Content-Type will be set to default text/html unless you have another value defined by core Apache for this binary, or binary itself generates appropriate CGI header.

When your source is a very old CGI-application that fails to provide correct Content-Type CGI header, use

    PerlSetVar UseCGIHeadersFromScript Off

in your httpd.conf in order to overwrite the document's Content-Type to text/html. All other CGI headers generated by the binary will be disregarded in this case too.

Make sure that your POST requests do never exceed 4K bytes in body length. Longer POST body is not supported in this version of Apache::Dynagzip.

In order to control the compression ratio and the minimum size of the chunk/buffer for gzipped content you can optionally use directives

    PerlSetVar minChunkSizeSource <value>
    PerlSetVar minChunkSize <value>

For example you can try

    PerlSetVar minChunkSizeSource 32768
    PerlSetVar minChunkSize 8

which are the defaults in this version.

Note:: You can improve the compression ratio when you increase the value of minChunkSizeSource.

In order to control the minimum size of the chunk for uncompressed content over HTTP/1.1 you can optionally use the directive

    PerlSetVar minChunkSizePP <value>

Default value is 8192 bytes in this version.

In order to control the extra light compression you can optionally use the directive

    PerlSetVar LightCompression <On/Off>

In order to turn "On" the extra light compression, use the directive

    PerlSetVar LightCompression On

Any other value turns the extra light compression "Off" (default).

In order to control the pageLifeTime in client's local cache you can optionally use the directive

    PerlSetVar pageLifeTime <value>

where the value stands for the life-length in seconds.

    PerlSetVar pageLifeTime 300

is default in this version.

You might wish to place

    PerlSetVar Vary User-Agent

in your httpd.conf file in order to notify possible proxies that you distinguish browsers in your content. Alternatively, you might place

    PerlSetVar Vary *

in order to prevent all proxies from caching your content.

Stream Compression of Static File

It will be assumed the plain file transfer, when you use the standing-along handler with no BinaryCGI directive:

  PerlModule Apache::Dynagzip
  PerlModule Apache::CompressClientFixup
  <Directory /path/to/subdirectory>
      SetHandler perl-script
      PerlHandler Apache::Dynagzip
      PerlFixupHandler Apache::CompressClientFixup
      PerlSetVar LightCompression On
  </Directory>

The Content-Type is determined by Apache in this case.

In order to control the compression ratio and the minimum size of the chunk/buffer for gzipped content you can optionally use directives

    PerlSetVar minChunkSizeSource <value>
    PerlSetVar minChunkSize <value>

For example you can try

    PerlSetVar minChunkSizeSource 32768
    PerlSetVar minChunkSize 8

which are the defaults in this version.

Note:: You can improve the compression ratio when you increase the value of minChunkSizeSource.

In order to control the minimum size of the chunk for uncompressed content over HTTP/1.1 you can optionally use the directive

    PerlSetVar minChunkSizePP <value>

In order to control the extra light compression you can optionally use the directive

    PerlSetVar LightCompression <On/Off>

In order to turn "On" the extra light compression, use the directive

    PerlSetVar LightCompression On

Any other value turns the extra light compression "Off" (default).

In order to control the pageLifeTime in client's local cache you can optionally use the directive

    PerlSetVar pageLifeTime <value>

where the value stands for the life-length in seconds.

    PerlSetVar pageLifeTime 300

is default in this version.

You might wish to place

    PerlSetVar Vary *

in order to prevent all proxies from caching your content.

Dynamic Setup/Configuration from the Perl Code

Alternatively, one can control this handler from the own perl-written handler serving the earlier phase of the request processing flow. For example, I'm using dynamic installation of Apache::Dynagzip from my PerlTransHandler in order to serve the server-side content cache appropriately.

  use Apache::RegistryFilter;
  use Apache::Dynagzip;

  . . .

  $r->handler("perl-script");
  $r->push_handlers(PerlHandler => \&Apache::RegistryFilter::handler);
  $r->push_handlers(PerlHandler => \&Apache::Dynagzip::handler);

In your perl code you can even extend the main config settings (for the current request) with:

  $r->dir_config->set(minChunkSizeSource => 36000);
  $r->dir_config->set(minChunkSize => 6);

for example...

TROUBLESHOOTING

This handler fails to keep control over the chunk-size when it serves the internally redirected request. At the same time it fails to provide gzip compression. A corresponding warning is placed to error_log in this case. Make the appropriate configuration tunings in order to avoid the implementation of this handler for internally redirected request(s).

The handler logs error, warn, info, and debug messages to the Apache error_log file. Please, read it first in case of any trouble.

DEPENDENCIES

This module requires these other modules and libraries:

   Apache::Constants;
   Apache::File;
   Apache::Filter 1.019;
   Apache::Log;
   Apache::URI;
   Apache::Util;
   Fcntl;
   FileHandle;

   Compress::LeadingBlankSpaces;
   Compress::Zlib 1.16;
       
  Note 1: the Compress::Zlib 1.16 requires the Info-zip zlib 1.0.2 or better
        (it is NOT compatible with versions of zlib <= 1.0.1).
        The zlib compression library is available at http://www.gzip.org/zlib/
        
  note 2: it is recommended to have a mod_perl compiled with the EVERYTHING=1
        switch. However, Apache::Dynagzip uses just fiew phases of the request
        processing flow:
              Content generation phase
              Logging phase

It is strongly recommended to use Apache::CompressClientFixup handler in order to avoid compression for known buggy browsers. Apache::CompressClientFixup package can be found on CPAN at http://search.cpan.org/author/SLAVA/.

AUTHOR

Slava Bizyayev <slava@cpan.org> - Freelance Software Developer & Consultant.

COPYRIGHT AND LICENSE

This package is free software. You can use it, redistribute it, and/or modify it under the same terms as Perl itself.

The latest version of this module can be found on CPAN.

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NAME

ABSTRACT

SYNOPSIS

Compress regular (static) HTML files

Compress the output stream of the Perl scripts

Compress the outgoing stream from the CGI binary

INTRODUCTION

Acknowledgments

DESCRIPTION

Compression Features

Chunking Features

Filter Chain Features

CGI Compatibility

POST Request Features

Control over the Client Cache

Support for the Server-Side Cache

Control over the Proxy Cache.

CUSTOMIZATION

Apache::Filter Chain

CGI-Compatible Binary

Stream Compression of Static File

Dynamic Setup/Configuration from the Perl Code

TROUBLESHOOTING

DEPENDENCIES

AUTHOR

COPYRIGHT AND LICENSE

SEE ALSO

Module Install Instructions