NAME

SYNOPSIS

  use LWP::Simple;
  use HTTP::Cache::Transparent;

  HTTP::Cache::Transparent::init( {
    BasePath => '/tmp/cache',
  } );

  my $data = get( 'http://www.sn.no' );

DESCRIPTION

Uses the http-headers If-Modified-Since and ETag to let the server decide if the version in the cache is up-to-date or not.

The cache is implemented by modifying the LWP::UserAgent class to seamlessly cache the result of all requests that can be cached.

INITIALIZING THE CACHE

init

Initialize the HTTP cache. Takes a single parameter which is a hashref containing named arguments to the object.

  HTTP::Cache::Transparent::init( {

    # Directory to store the cache in.
    BasePath  => "/tmp/cache",

    # How many hours should items be kept in the cache
    # after they were last requested?
    # Default is 8*24.
    MaxAge    => 8*24,

    # Print progress-messages to STDERR.
    # Default is 0.
    Verbose   => 1,

    # If a request is made for a url that has been requested
    # from the server less than NoUpdate seconds ago, the
    # response will be generated from the cache without
    # contacting the server.
    # Default is 0.
    NoUpdate  => 15*60,

    # When a url has been downloaded and the response indicates that
    # has been modified compared to the content in the cache,
    # the ApproveContent callback is called with the HTTP::Response.
    # The callback shall return true if the response shall be used and
    # stored in the cache or false if the response shall be discarded
    # and the response in the cache used instead.
    # This mechanism can be used to work around servers that return errors
    # intermittently. The default is to accept all responses.
    ApproveContent => sub { return $_[0]->is_success },
 } );
    

The directory where the cache is stored must be writable. It must also only contain files created by HTTP::Cache::Transparent.

Initializing from use-line

An alternative way of initializing HTTP::Cache::Transparent is to supply parameters in the use-line. This allows you to write

  use HTTP::Cache::Transparent ( BasePath => '/tmp/cache' );
    

which is exactly equivalent to

  use HTTP::Cache::Transparent;
  HTTP::Cache::Transparent::init( BasePath => '/tmp/cache' );
    

The advantage to using this method is that you can do

  perl -MHTTP::Cache::Transparent=BasePath,/tmp/cache myscript.pl
    

or even set the environment variable PERL5OPT

  PERL5OPT=-MHTTP::Cache::Transparent=BasePath,/tmp/cache
  myscript.pl
    

and have all the http-requests performed by myscript.pl go through the cache without changing myscript.pl

INSPECTING CACHE BEHAVIOR

X-Cached

This header is inserted and set to 1 if the response is delivered from the cache instead of from the server.

X-Content-Unchanged

This header is inserted and set to 1 if the content returned is the same as the content returned the last time this url was fetched. This header is always inserted and set to 1 when the response is delivered from the cache.

X-No-Server-Contact

This header is inserted and set to 1 if the content returned has been delivered without any contact with the external server, i.e. no conditional or unconditional HTTP GET request has been sent, the content has been delivered directly from cache. This may be useful when seeking to control loading of the external server.

LIMITATIONS

• There is no upper limit to how much diskspace the cache requires. The only limiting mechanism is that data for urls that haven't been requested in the last MaxAge hours will be removed from the cache the next time the program exits.
• Currently, only get-requests that store the result in memory (i.e. do not use the option to have the result stored directly in a file or delivered via a callback) is cached. I intend to remove this limitation in a future version.
• The support for Ranges is a bit primitive. It creates a new object in the cache for each unique combination of url and range. This will work ok as long as you always request the same range(s) for a url.
• The cache doesn't properly check and store all headers in the HTTP request and response. Therefore, if you request the same url repeatedly with different sets of headers (cookies, accept-encoding etc), and these headers affect the response from the server, the cache may return the wrong response.
• HTTP::Cache::Transparent has not been tested with threads, and will most likely not work if you use them.

CACHE FORMAT

The last modified date of the cache file is set to the time when the cache object was last requested by a user.

AUTHOR

GIT REPOSITORY

COPYRIGHT AND LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of Perl 5 you may have available.