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

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

    If you have mod_perl2 1.999_21 or earlier, you should instead do:

        mkdir -p /usr/lib/httpd/perl/Interchange
        cp Link.pm.mod_perl-1.999_21_and_before /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
        0660" 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 <directory>".)

        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
    connection:

            <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,
    <interchange-users@icdevgroup.org>.

COPYRIGHT AND LICENSE
    Copyright (C) 1996-2002 Red Hat, Inc.
    Copyright (C) 2002-2007 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.
