Interchange::Link(3)  User Contributed Perl Documentation Interchange::Link(3)



NAME
       Interchange::Link -- mod_perl 1.99/2.0 module for linking to Inter-
       change

VERSION
       $Revision: 1.2 $

SYNOPSIS
	 <Location /foundation>
	   SetHandler perl-script
	    PerlResponseHandler	 Interchange::Link
	    PerlOptions +GlobalRequest
	    PerlSetVar InterchangeServer /var/run/interchange/socket
	    PerlSetVar OrdinaryFileList "/foundation/images/ /foundation/dl/"
	 </Location>

DESCRIPTION
       Interchange::Link is designed to replace the vlink and tlink programs
       that come with Interchange. The Interchange link protocol has been
       implemented via an Apache mod_perl modules which saves us the (small)
       overhead of the execution of a CGI program.

       In addition, it will deliver downloadable files in a streaming fashion
       without keeping Interchange open, which cuts overhead dramatically for
       large downloadable files. See FileDeliveryBase.

       Note that this module is not compatible with Apache 1.

PREREQUISITES
       You must have mod_perl 1.99 or higher installed on your Apache. On a
       Red Hat-style Linux system, it is as simple as:

	   rpm -i mod_perl-1.99.XX-X.rpm
	   service httpd restart

       Installation of mod_perl will vary from system to system. Consult the
       mod_perl documentation. Sometimes it is as easy as

	   perl -MCPAN -e 'install ModPerl::Registry'

       but often it is not.

       Usually you can download the package from http://perl.apache.org/ and
       follow those instructions.

INSTALLATION
       You must specify that Apache use mod_perl, and you must tell it where
       to find the Perl modules you want to use.

       On a Red Hat Linux system you might copy this file to
       /usr/lib/httpd/perl/ via this procedure:

	   mkdir -p /usr/lib/httpd/perl/Interchange
	   cp Link.pm /usr/lib/httpd/perl/Interchange

       Then you provide a startup script that tells mod_perl where its
       libraries are:

	   cd /usr/lib/httpd/perl
	   echo "use lib qw(/usr/lib/httpd/perl);1;" > startup.pl

       Then you can put in your /etc/httpd/conf/httpd.conf:

	   PerlModule Apache2
	   PerlRequire /usr/lib/httpd/perl/startup.pl

       Finally, you specify a location like:

	 <Location /foundation>
	   SetHandler perl-script
	    PerlResponseHandler	 Interchange::Link
	    PerlOptions +GlobalRequest
		# Make sure you set SocketPerms to 0666 (or 0660 with appropriate
		# setgid group ownership of the directory)
	    PerlSetVar InterchangeServer /var/run/interchange/socket
	    PerlSetVar OrdinaryFileList "/foundation/images/ /foundation/dl/"
	 </Location>

       Note: The Apache <Location> path should not contain a dot (.) or any
       other characters except A-Z, a-z, 0-9 or a hyphen (-), so:

	   <Location /shop.name> is invalid, whereas:
	   <Location /shop-name> is valid.

       The specifics of the configuration are discussed in the next section.

CONFIGURATION
       The module understands directives set via the mod_perl "PerlSetVar"
       directive.

       InterchangeServer
	   This specifies the way to contact the primary and possibly additio-
	   nial Interchange servers. The InterchangeServer directive takes
	   either a pathname to the Interchange UNIX socket or a host:port
	   specification if you want to use INET mode.

	   Normally this takes the form of:

		PerlSetVar InterchangeServer /var/run/interchange/socket

	   Note that your file permissions for the socket file need to allow
	   the Apache User uid to read and write it. This usually means "Sock-
	   etPerms 0666" or in interchange.cfg.	 You can also do "SocketPerms
	   0666" if you set the group of the containing directory to the
	   Apache Group value, and change the directory permissions to enable
	   the setgid bit. (That is accomplished with "chmod g+s <direc-
	   tory>".)

	   If you want to specify more than one so that a backup server can
	   provide request support in case of failure:

	       PerlSetVar InterchangeServer  "/var/run/interchange/socket 10.1.1.1:7786"

	   The optional InterchangeServerBackup directive takes the same argu-
	   ments, but should obviously point to a different Interchange server
	   than the primary.  The InterchangeServerBackup directive is only of
	   any use if you have multiple Interchange servers configured in a
	   clustered environment.

	   If you want to randomly select from a series of clustered servers,
	   do:

	       PerlSetVar InterchangeServer "10.1.1.1:7786 10.1.1.2:7786 10.1.1.3:7786"
	       PerlSetVar RandomServer 1

	   Note: The Apache <Location> path should not contain a dot (.) or
	   any other characters except A-Z, a-z, 0-9 or a hyphen (-), so:

	       <Location /shop.name> is invalid, whereas:
	       <Location /shop-name> is valid.

	   Example of a UNIX mode local connection:

	       <Location /shop>
	       SetHandler perl-script
	       PerlResponseHandler Interchange::Link
	       PerlSetVar InterchangeServer /opt/interchange/etc/socket
	       </Location>

	   Example of INET mode local connection:

	       <Location /shop>
	       SetHandler perl-script
	       PerlResponseHandler Interchange::Link
	       PerlSetVar InterchangeServer localhost:7786
	       </Location>

	   UNIX mode local primary connection and INET mode remote backup con-
	   nection:

	       <Location /shop>
	       SetHandler perl-script
	       PerlResponseHandler Interchange::Link
	       PerlSetVar InterchangeServer /opt/interchange/etc/socket
	       PerlSetVar InterchangeServerBackup another.server.com:7786
	       </Location>

	   The default if not set is "127.0.0.1:7786".

       ConnectTries and ConnectRetryDelay
	   The ConnectTries parameter specifies the number of connection
	   attempts to make before giving up.  ConnectRetryDelay specifies the
	   delay, in seconds, between each retry attempt.

	   The ConnectTries default is 10 and the ConnectRetryDelay default is
	   2 seconds.  Here is an example:

	       <Location /shop>
	       SetHandler perl-script
	       PerlResponseHandler Interchange::Link
	       PerlSetVar ConnectTries 10
	       PerlSetVar ConnectRetryDelay 1
	       </Location>

       DropRequestList
	   The DropRequestList allows a list of space-separated URI components
	   to be specified.  If one of the list entries is found anywhere in
	   the requested URI, the request will be dropped with a 404 (not
	   found) error, without the request being passed to Interchange.
	   This parameter is useful for blocking known Microsoft IIS attacks
	   like "Code Red", so that we don't waste any more time processing
	   the (bogus) requests than we have to.

	       <Location /shop>
	       SetHandler perl-script
	       PerlResponseHandler Interchange::Link
	       PerlSetVar DropRequestList "/default.ida /x.ida /cmd.exe /root.exe"
	       </Location>

       OrdinaryFileList
	   The OrdinaryFileList allows a list of space-separated URI path com-
	   ponents to be specified.  If one of the list entries is found at
	   the start of any request then that request will not be passed to
	   Interchange.	 Instead, the file will be directly served by Apache.
	   For example:

	       <Location />
	       SetHandler perl-script
	       PerlResponseHandler Interchange::Link
	       PerlSetVar OrdinaryFileList "/foundation/ /interchange-5/ /robots.txt"
	       </Location>

	   This will result in the following:

	       www.example.com/index.html	   (handled by Interchange)
	       www.example.com/ord/basket.html	   (handled by Interchange)
	       www.example.com/foundation/images/somefile.gif (served by Apache)
	       www.example.com/robots.txt	   (served by Apache)

	   You should add a trailing slash to directory names to prevent, for
	   instance, "/images/foo.gif" from being confused with the likes of
	   "/images.html".  If OrdinaryFileList was set to "/images" then both
	   of those requests would be handled by Apache.  If OrdinaryFileList
	   was set to "/images/" then "/images/foo.gif" would be handled by
	   Apache and "/images.html" would be handled by Interchange.

	   If you're using "<Location />" then you will need a dummy
	   "index.html" file in your VirtualHost's DocumentRoot directory to
	   avoid permission problems assocated with the Apache directory index
	   creation code.

       InterchangeScript
	   The InterchangeScript parameter allows the SCRIPT_NAME to be dif-
	   ferent from the <Location>.	For example:

	       <Location /shop>
		   ...
	       </Location>

	   The above will set the SCRIPT_NAME to "/shop".

	       <Location /shop>
		   ...
	       PerlSetVar InterchangeScript /foo
	       </Location>

	   The above will set the SCRIPT_NAME to "/foo", instead of "/shop"
	   before passing the request to Interchange.

	   The appropriate SCRIPT_NAME must be configured into the "Catalog"
	   directive in your interchange.cfg file.

       FileDeliveryBase
	   Interchange::Link can deliver files without needing to keep Inter-
	   change open. To do this, you set the HTTP Status: header to
	   "httpd_deliver".  In Interchange 5.0 or higher you can do this by
	   putting in a page:

	       [deliver
		   status=httpd_deliver
		   location=directory/file.ext
		   type=application/octet-stream
		  ]

	   The "FileDeliveryBase" setting determines where the file will be
	   relative to. While you can set it to "/", that is not recommended
	   as files like "/etc/passwd" could be delivered.

	   The default is the document root of the Apache server. To protect
	   files from being served directly by Apache, you can either put them
	   under a directory at the Interchange location, or you can use nor-
	   mal Apache exclusions.

BUGS
       Send bug reports and suggestions to the Interchange users list, <inter-
       change-users@icdevgroup.org>.

COPYRIGHT AND LICENSE
	Copyright (C) 1996-2002 Red Hat, Inc.
	Copyright (C) 2002-2004 Interchange Development Group

       This program is free software.  You can redistribute it and/or modify
       it under the terms of the GNU General Public License as published by
       the Free Software Foundation.  You may refer to either version 2 of the
       License or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of MER-
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
       Public License for more details.



perl v5.8.4			  2004-06-29		  Interchange::Link(3)
