NAME
Apache2::Translation - Configuring Apache dynamically
SYNOPSIS
LoadModule perl_module /path/to/mod_perl.so
PerlLoadModule Apache2::Translation
PerlTransHandler Apache2::Translation
PerlMapToStorageHandler Apache2::Translation
TranslationEvalCache 1000
TranslationKey MyKey
Database dbi:mysql:dbname:host
User username
Password password
Singleton 1
Table tablename
Key keycolumn
Uri uricolumn
Block blockcolumn
Order ordercolumn
Action actioncolumn
Cachetbl cachetablename
Cachecol cachecolumn
Cachesize 1000
# another provider
Configfile /path/to/config
# export our provider parameters
SetHandler modperl
PerlResponseHandler Apache2::Translation::Config
# configuring the WEB interface
PerlModule Apache2::Translation::Admin
SetHandler modperl
PerlResponseHandler Apache2::Translation::Admin
INSTALLATION
perl Makefile.PL
make
make test
make install
DESCRIPTION
As the name implies "Apache2::Translation" lives mostly in the URI
Translation Phase. It is somehow similar to "mod_rewrite" but
configuration statements are read at runtime, thus, allowing to
reconfigure a server without restarting it.
The actual configuration statements are read by means of a *Translation
Provider*, a Perl class offering a particular interface, see below.
Currently there are 3 providers implemented, Apache2::Translation::DB,
Apache2::Translation::BDB, and Apache2::Translation::File.
There is also a WEB interface (Apache2::Translation::Admin).
An Example
Let's begin with an example. Given some database table:
id key uri blk ord action
1 front :PRE: 0 0 Cond: $HOSTNAME !~ /^(?:www\.)xyz\.(?:com|de)$/
2 front :PRE: 0 1 Redirect: 'http://xyz.com'.$URI, 301
3 front :PRE: 1 0 Do: $ctx->{lang}='en'
4 front :PRE: 1 1 Cond: $HOSTNAME =~ /de$/
5 front :PRE: 1 2 Do: $ctx->{lang}='de'
6 front /static 0 0 File: $DOCROOT.'/'.$ctx->{lang}.$MATCHED_PATH_INFO
7 front /appl1 0 0 Proxy: 'http://backend/'.$ctx->{lang}.$URI
8 front /appl2 0 0 Proxy: 'http://backend/'.$URI.'?l='.$ctx->{lang}
9 front / 0 0 Config: ['AuthName "secret"'], ['AuthType Basic']
10 back :PRE: 0 0 Cond: $r->connection->remote_ip ne '127.0.0.1'
11 back :PRE: 0 1 Error: 403, 'Forbidden by Apache2::Translation(11)'
12 back /appl1 0 0 PerlHandler: 'My::Application1'
13 back /appl2 0 0 PerlHandler: 'My::Application2'
The "id" column in this table is not really necessary for
"Apache2::Translation". But if you want to deploy
Apache2::Translation::Admin you need it.
Well, here we have a frontend/backend configuration. The frontend
records are labeled with the key "front", the backend records with
"back".
When a request comes in first the records with ":PRE:" in the
"uri"-field are examined. Suppose, a request for
"http://abc.com/static/img.png" comes in. Record 1 (id=1) checks the
"Host" header. The expression after "Cond:" is evaluated as Perl code.
It obviously returns true. "Cond" stands for *condition*. But how does
it affect the further workflow? Here "blk" and "ord" come in. All
records with the same "key", "uri" and "blk" form a block. "ord" gives
an order within this block. Within a block all actions are executed up
to the first condition that is false.
Now, because our condition in record 1 is true the action in record 2
(within the same block) is executed. It redirects the browser with a
HTTP code of 301 (MOVED PERMANENTLY) to "http://xyz.com/static/img.png".
When the redirected request comes back the condition in record 1 is
false. Hence, the next block (key=front, uri=:PRE:, blk=1) is evaluated.
First a "lang" member of a context hash is set to "en". A "Do" action is
similar to a condition, only its value is ignored. Record 4 then checks
if the "Host" header matches "/de$/". If so, then record 5 sets the
*language* to "de".
Now, the records labeled with ":PRE:" are finished. The handler starts
looking for blocks labeled with the request uri. That is, it looks for a
block with key=front, uri=/static/img.png. None is found.
Then it cuts off the last part of the uri (/img.png), repeats the lookup
and finds record 6. The "File" action sets "$r->filename" to
"$DOCROOT/en/img.png". "Apache2::Translation" provides some convenience
variables. They are tied to members of the request record or to elements
of $ctx. $MATCHED_PATH_INFO contains the uri part cut off ("/img.png").
More on them below.
Now another round is started and the next uri part is cut off. Record 9
matches. We see a "Config" action that sets "AuthName" and "AuthType".
At the end the translation handler checks if "$r->filename" was set and
returns "Apache2::Const::OK" or "Apache2::Const::DECLINED" respectively.
I think that example gives a general idea, what "Apache2::Translation"
does.
Processing States
Internally "Apache2::Translation" is implemented as a state machine. It
starts in the *START* state, where some variables are initialized. From
there it shifts immediately to the *PREPOC* state. Here all ":PRE:"
rules are evaluated. From *PREPROC* it shifts to *PROC*. Now the rules
with real uris are examined. When the *DONE* state is reached processing
is finished.
There is a special state named *LOOKUPFILE*. It is only used for
subrequests that don't have an URI. For such requests the URI
translation phase of the request cycle is skipped. Hence a
*PerlTransHandler* would never be called. Such requests are results of
calling "$r->lookup_file" for example.
To catch also such requests install "Apache2::Translation" both as
*PerlTransHandler* as well as *PerlMapToStorageHandler*. Then if such a
subrequest occures the handler enters the *LOOKLUPFILE* state instead of
*PREPROC*. From *LOOKLUPFILE* it normally shifts to *PROC* unless it
executes a "Restart" action. In that case it shifts to *PREPROC*.
You have to set $MATCHED_URI to some initial value if you want to hop
through the *PROC* phase. A still empty $MATCHED_URI shifts from *PROC*
immediately to *DONE*.
Note: The *LOOKUPFILE* stuff is still somewhat experimental.
You can control the current state by means of the "State", "Done" and
"Restart" actions.
Blocks and Lists of Blocks
Above, we have defined a block as all records with the same "key", "uri"
and "block". The actions within a block are ordered by the "order"
field.
A list of blocks is then an ordered list of all blocks with the same
"key" and "uri". The order is given by the "block" number.
Actions
An action starts with a key word optionally followed by a colon and some
arguments. The key words are case insensitive.
"Apache2::Translation" provides some environment for code snippets in
actions. They are compiled into perl functions. The compiled result is
cached. 2 variables, $r and $ctx, are provided plus a few convenience
variables. $r is the current "Apache2::RequestRec". $ctx points to a
hash that can be used to store arbitrary data. All keys beginning with a
space character in that hash are reserved for "Apache2::Translation".
Do: perl_code
Fixup: perl_code
"Do" is the simplest action. The Perl code is evaluated in scalar
context. The return value is ignored. "Fixup" is just the same save
it is run in the *Fixup* phase
Cond: perl_code
This is almost the same as "Do". The return value is taken as
boolean. If it is false, the current block is finished. Processing
continues with the next block.
Done
"Done" finishes the current block list and transfers control to the
next state. That means if encountered in *PREPROC* state it switches
to *PROC*. If the current state is *PROC* then the translation
handler ends here.
This action is a combination of "State: next_state" and "Last", see
below.
Don't try to use "Done" to return from a subroutine. Use "Last"
instead.
File: string
This action sets "$r->filename" to string. It is equivalent to
Do: $FILENAME=do{ string }
Doc: ?content_type?, string
"string" is evaluated as well as "content_type" if given. Then a
special "moperl" handler is installed that simply sets the given
content type and prints out the string to the client. "content_type"
is "text/plain" if omitted.
Proxy: ?url?
This tells Apache to forward the request to "url" as a proxy. "url"
is optional. If ommitted "$r->unparsed_uri" is used. That means
Apache must be used as a proxy by the browser.
CgiScript: ?string?
is equivalent to
Do: $r->handler( 'cgi-script' );
FixupConfig: ['Options ExecCGI']
If "string" is given it is evaluated and the result is assigned to
"$r->filename".
PerlScript: ?string?
is equivalent to
Do: $r->handler( 'perl-script' );
FixupConfig: ['Options ExecCGI'], ['PerlOptions +ParseHeaders']
If "string" is given it is evaluated and the result is assigned to
"$r->filename".
PerlHandler: string
In short this action tries to figure out what "string" means and
calls it as "modperl" handler.
In detail it installs a "Apache2::Translation::response" as
"PerlResponseHandler". When called the handler evaluates "string"
which results either in a subroutine name, a package name, a
subroutine reference or an object or class that implements the
"handler" method. If a package name is given it must implement a
"handler" subroutine.
If the given package is not yet loaded it is "require"ed.
Then the resulting subroutine or method is called and $r is passed.
Further, a "PerlMapToStorageHandler" is installed that skips the
handling of "Directory" containers and ".htaccess" files. If not
set, this handler also sets "path_info". Assumed,
#uri blk ord action
/some/path 0 0 PerlHandler: ...
and a request comes in for "/some/path/foo/bar". Then "path_info" is
set to "/foo/bar".
Config: list_of_strings_or_arrays
FixupConfig: list_of_strings_or_arrays
Surprisingly, these are the most complex actions of all.
"Config" adds Apache configuration directives to the request in the
*Map To Storage* phase before the default "MapToStorage" handler.
Think of it as a kind of ".htaccess". "FixupConfig" does the same in
the *Fixup* phase. While "Config" is used quite often "FixupConfig"
is seldom required. It is used mainly to mend configurations that
are spoiled by the default "MapToStorage" handler.
Arguments to both actions are strings or arrays of one or two
elements:
Config: 'AuthName "secret"',
['AuthType Basic'],
['ProxyPassReverse http://...', '/path']
To understand the different meaning, you have to know about how
Apache applies its configuration to a request. Hence, let's digress
a little.
Each Apache directive is used in certain contexts. Some for example
can occur only in server config context, that means outside any
"Directory", "Location" or even "VirtualHost" container. "Listen" or
"PidFile" are examples. Other directives insist on being placed in a
container.
Also, the point in time when a directive takes effect differs for
different directives. "PidFile" is clearly applied during server
startup before any request is processed. Hence, our "Config" action
cannot apply "PidFile". It's simply too late. "AllowOverride" is
applied to single requests. But since it affects the processing of
".htaccess" files it must be applied before that processing takes
place. To make things even more confusing some directives take
effect at several points in time. Consider
Options FollowSymLinks ExecCGI
"FollowSymLinks" is applied when Apache looks up a file in the file
system, while "ExecCGI" influences the way the response is generated
ages later.
Apache solves this complexity by computing a configuration for each
single request. As a starting point it uses the server default
configuration. That is the configuration outside any "Location" or
"Directory" for a virtual host. This basic configuration is assigned
to the request just between the *Uri Translation Phase* and *Map to
Storage*. At the very end of *Map to Storage* Apache's core *Map to
Storage* handler incorporates matching "Directory" containers and
".htaccess" files into the request's current configuration.
"Location" containers are merged after *Map to Storage* is finished.
Our "Config" action is applied early in *Map to Storage*. That means
it affects the way Apache maps the request file name computed to the
file system, because that comes later. But it also means, your
static configuration (config file based) overrides our "Config"
actions. This limitation can be partly overcome using "FixupConfig"
instead of "Config".
Now, what does the various syntaxes mean? The simplest one:
#uri blk ord action
/uri 0 0 Config: 'ProxyPassReverse http://my.backend.org'
is very close to
ProxyPassReverse http://my.backend.org
Only, it is applied before any "Directory" container takes effect.
Note, the uri-argument to the "Location" container is the value of
$MATCHED_URI, see below. This is also valid if the "Config" action
is used from a "Call"ed block.
The location uri is sometimes important. "ProxyPassReverse", for
example, uses the path given to the location container for its own
purpose.
All other forms of "Config" are not influenced by $MATCHED_URI.
These two:
Config: ['ProxyPassReverse http://my.backend.org']
Config: ['ProxyPassReverse /path http://my.backend.org', '']
are equivalent to
ProxyPassReverse http://my.backend.org
Note, the location container uri differs.
The first one of them is also the only form of "Config" available
with mod_perl before 2.0.3.
The next one:
Config: ['ProxyPassReverse http://my.backend.org', '/path']
is equivalent to
ProxyPassReverse http://my.backend.org
I have chosen "ProxyPassReverse" for this example because the
"Location" container uri matters for this directive, see httpd docs.
The following form of applying "ProxyPassReverse" outside of any
container is not possible with "Apache2::Translation":
ProxyPassReverse /path http://my.backend.org
Now let's look at another example to see how "Directory" containers
and ".htaccess" files are applied. "AllowOverride" controls which
directives are allowed in ".htaccess" files. As said before Apache
applies "Directory" containers and ".htaccess" files after our
"Config" directives. Unfortunately, they are both applied in the
same step. That means we can say:
Config: 'AllowOverride Options'
But if at least one "Directory" container from our "httpd.conf" is
applied that says for example "AllowOverride AuthConfig" it will
override our "Config" statement. So, if you want to control which
directives are allowed in ".htaccess" files with
"Apache2::Translation" then avoid "AllowOverride" in your
"httpd.conf", especially the often seen:
AllowOverride None
Put it instead in a *PREPROC* rule:
#uri blk ord action
:PRE: 0 0 Config: 'AllowOverride None'
So subsequent rules can override it.
A similar problem exists with "Options FollowSymlinks". This option
affects directly the phase when "Directory" containers are applied.
Hence, any such option from the "httpd.conf" cannot be overridden by
a "Config" rule.
In Apache 2.2 at least up to 2.2.4 there is a bug that prevents
"Config: AllowOverride Options" from working properly. The reason is
an uninitialized variable that is by cause 0, see
Call: string, ?@params?
Well, the name suggests it is calling a subroutine. Assume you have
several WEB applications running on the same server, say one
application for each department. Each department needs of course
some kind of authorization:
#uri blk ord action
AUTH 0 0 Config: "AuthName \"$ARGV[0]\""
AUTH 0 1 Config: 'AuthType Basic'
AUTH 0 2 Config: 'AuthUserFile /etc/htaccess/user/'.$ARGV[1]
/dep1 0 0 Call: qw/AUTH Department_1 dep1/
/dep2 0 0 Call: qw/AUTH Department_2 dep2/
The "AUTH" in the "Call" actions refer to the "AUTH" block list in
the "uri" column. An optional parameter list is passed via @ARGV.
"Call" fetches the block list for a given uri and processes it. If a
"Last" action is executed the processing of that block list is
finished.
Redirect: url, ?http_code?
The "Redirect" action sends a HTTP redirect response to the client
and abort the current request. The optional "http_code" specifies
the HTTP response code. Default is 302 (MOVED TEMPORARILY).
"Redirect" tries to make the outgoing "Location" header RFC2616
conform. That means if the schema part is ommitted it figures out if
it has to be "http" or "https". If a relative url is given an
appropriate url is computed based on the current value of $URI.
If the current request is the result of an internal redirect the
redirecting request's status is changed to "http_code". Thus,
"Redirect" works also for "ErrorDocument"s.
Error: ?http_code?, ?message?
"Error" aborts the entire request. A HTTP response is sent to the
client. The optional "http_code" specifies the HTTP response code.
The optional "message" is logged as reason to the "error_log".
"http_code" defaults to 500 (INTERNAL SERVER ERROR), "message" to
"unspecified error".
Uri: string
This action sets "$r->uri" to string. It is equivalent to
Do: $URI=do{ string }
Key: string
"string" is evaluated in scalar context. The result is assigned to
the current key. The new key takes effect if the list of blocks
matching the current uri is finished.
For example:
id key uri blk ord action
1 dflt :PRE: 0 0 Cond: $CLIENTIP eq '192.168.0.1'
2 dflt :PRE: 0 1 Key: 'spec'
3 dflt :PRE: 0 2 Do: $DEBUG=3
4 dflt :PRE: 1 0 Config: 'Options None'
5 dflt / 0 0 File: $DOCROOT.$URI
6 spec / 0 0 File: '/very/special'.$URI
Here an entirely different directory tree is shown to a client with
the IP address 192.168.0.1. In record 2 the current key is set to
"spec" if the condition in record 1 matches. Also, $DEBUG is set in
this case (record 3).
The next block in record 4 is executed for all clients, because the
key change is not in effect, yet.
Records 5 and 6 are new lists of blocks. Hence, record 6 is executed
only for 192.168.0.1 and record 5 for the rest.
The action "Key: 'string'" is equivalent to "Do: $KEY='string'".
Restart: ?newuri?, ?newkey?, ?newpathinfo?
"Restart" restarts the processing from the *PREPROC* phase. The
optional arguments ar evaluated and assumed to result in strings.
"newuri" is then assigned to "$r->uri" and $MATCHED_URI. "newkey" is
assigned to $KEY and "newpathinfo" to $MATCHED_PATH_INFO.
State: string
If you look for a premature exit from the current block list take
the "Done" action.
This action affects the current state directly. Thus, you can loop
back to the *PREPROC* state from *PROC*. It is mostly used the
prematurely finish the translation handler from the *PREPROC* state.
As the "Key" action it takes effect, when the current list of blocks
is finished.
"string" is evaluated as perl code. It is expected to result in one
of the following strings. If not, a warning is printed in the
"error_log". State names are case insensitive:
start
preproc
proc
done
The "State" action is similar to setting the convenience variable
$STATE. Only in the latter case you must use the state constants,
e.g. "$STATE=DONE".
Last
If you look for a premature exit from the current block list take
the "Done" action.
This action finishes the current list of blocks (just like a false
condition finishes the current block). It is used together with
"State" to finish the translation handler from a conditional block
in the *PREPROC* state:
:PRE: 0 0 Cond: $finish
:PRE: 0 1 State: 'done'
:PRE: 0 2 Last
Another application of "Last" is to return from a "Call" action.
Convenience Variables and Data Structures
These variables are tied to elements of the current request ($r) or the
current context hash ($ctx). Reading them returns the current value,
setting changes it.
$URI = "$r->uri"
$REAL_URI = "$r->unparsed_uri"
$METHOD = "$r->method"
$QUERY_STRING = "$r->args"
$FILENAME = "$r->filename"
$DOCROOT = "$r->document_root"
$HOSTNAME = "$r->hostname"
$PATH_INFO = "$r->path_info"
$REQUEST = "$r->the_request"
$HEADERS = "$r->headers_in"
$C = "$r->connection"
$CLIENTIP = "$r->connection->remote_ip"
$KEEPALIVE = "$r->connection->keepalive"
for more information see Apache2::RequestRec.
$MATCHED_URI = "$ctx->{' uri'}"
$MATCHED_PATH_INFO = "$ctx->{' pathinfo'}"
While in "PROC" state the incoming uri is split in 2 parts. The
first part is matching the "uri" field of a database record. The
second part is the rest. They can be accessed as $MATCHED_URI and
$MATCHED_PATH_INFO.
$KEY = "$ctx->{' key'}"
the current key.
$STATE = "$ctx->{' state'}"
the current processing state.
$RC = "$ctx->{' rc'}"
Normally, "Apache2::Translation" checks at the end if "$r->filename"
is set. If so, it returns "Apache2::Const::OK" to its caller. If
not, "Apache2::Const::DECLINED" is returned. The first alternative
signals that the *Uri Translation Phase* is done and no further
handlers are called in this phase. The second alternative signals
that subsequent handlers are to be called. Thus, "mod_alias" or even
the core translation handler see the request.
Setting $RC your action decide what is returned.
$RC is also set by the "PerlHandler" action. Modperl generated
responses are normally not associated with a single file on disk.
$DEBUG = "$r->notes->{'Apache2::Translation:: debug'}"
If set to 1 or 2 debugging output is sent to the "error_log".
APACHE CONFIGURATION DIRECTIVES
After installed and loaded by
PerlLoadModule Apache2::Translation
in your "httpd.conf" "Apache2::Translation" is configured with the
following directives:
...
Currently there are 3 provider classes implemented,
Apache2::Translation::DB, Apache2::Translation::File and
Apache2::Translation::BDB.
The ellipsis represents configuration lines formatted as
NAME VALUE
These lines are passed as parameters to the provider. "NAME" is case
insensitive and is converted to lowercase before passed to the
provider object. Spaces round "VALUE" are stripped off. If "VALUE"
begins and ends with the same quotation character (double quote or
single quote) they are also stripped off.
The provider object is then created by:
$Apache2::Translation::class->new( NAME1=>VALUE1, NAME2=>VALUE2, ... );
where "class" is exchanged by the actual provider name.
TranslationProvider class param1 param2 ...
This is an alternative way to specify translation provider
parameters.
Each parameter is expected to be a string formatted as
NAME=VALUE
There must be no spaces around the equal sign. The list is passed to
the constructor of the provider class as named parameters:
$Apache2::Translation::class->new( NAME1=>VALUE1, NAME2=>VALUE2, ... );
TranslationKey initial-key
This sets the initial value for the key. Default is the string
"default".
TranslationEvalCache number
"Apache2::Translation" compiles all code snippets into functions and
caches these functions. Normally, an ordinary hash is used for this.
Strictly speaking this is a memory hole if your translation table
changes. I think that can be ignored, if the number of requests per
worker is limited, see "MaxRequestsPerChild". If you think this is
too lax, put a number here.
If set the cache is tied to Tie::Cache::LRU. The number of cached
code snippets will then be limited by "number".
WHICH PROVIDER TO CHOOSE
Unless you want to implement your own provider you can choose from these
3:
* DB
This is the provider implemented first. It uses a cache to store
lookup results but at least one read (to fetch the version) is made
for each request. Use it if you already have a DB engine at your
site and if you don't mind the additional lookups.
* File
This provider is very fast. It reads the complete config file into
memory and refreshes it when modified. Hence come the greatest
drawback. Each perl interpreter reads the file and needs all the
memory to hold every rule. So with many rules and a high
"MaxClients" directive it eats up much memory.
* BDB
Choose this provider if you have many rules and a high "MaxClients"
directive. Since most of the database is stored in shared memory by
BerkeleyDB it is almost as fast as the "File" provider but its
resource hunger is limited.
EXPORTING OUR PROVIDER PARAMETERS
A WEB server can export its provider parameters by means of the
Apache2::Translation::Config module. That can then be used by the admin
interface to connect to that provider.
THE WEB ADMINISTRATION INTERFACE
The simplest way to configure the WEB interface is this:
PerlModule Apache2::Translation::Admin
SetHandler modperl
PerlResponseHandler Apache2::Translation::Admin
Note, here an extra PerlModule statement is necessary. If nothing else
specified the provider that has handled the current request is used.
Note, there is a slash at the end of the location statement. It is
necessary to be specified. Also, the URL given to the browser to reach
the WEB interface must end with a slash or with "/index.html".
Another provider is given by creating an "Apache2::Translation::Admin"
object:
$My::Transadmin=Apache2::Translation::Admin->new
(provider_spec=>[File,
ConfigFile=>'/path/to/config']);
SetHandler modperl
PerlResponseHandler $My::Transadmin->handler
Here the provider is specified in a way similar to the
"TranslationProvider" statement above.
Also, an URL can be given that links to an exported parameter set:
$My::Transadmin=Apache2::Translation::Admin->new
(provider_url=>'http://host/config');
In this case "LWP::UserAgent" is used to fetch the parameters.
Or you can create the provider object by yourself and pass it:
use Apache2::Translation::File;
$My::Transadmin=Apache2::Translation::Admin->new
(provider=>Apache2::Translation::File->new
(configfile=>'/path/to/config'));
IMPLEMENTING A NEW PROVIDER
A provider implements a certain interface that is documented in
Apache2::Translation::_base.
SEE ALSO
Apache2::Translation::DB
Apache2::Translation::BDB
Apache2::Translation::File
Apache2::Translation::Admin
Apache2::Translation::_base
Apache2::Translation::Config
mod_perl: http://perl.apache.org
TODO / WHISHLIST
* UI improvements
Help system that provides a short explanation to the actions and
perhaps convenience variables.
Action selection box.
More and better keyboard control.
* cleaning up the javascript code
my.js could use redesign.
* auto-Done mode
In this mode the the translation handler finishes the current state
after processing the first block list. Most of my block lists have a
"Done" action at the end. This would also require an "Continue"
action that to go to the next block list thus overruling the
auto-Done.
* user identities + access rights
* domain specific mode
to delegate responsibility for certain domains to different user
groups.
* some kind of *run-once* actions
To initialize things.
* error_log hook
Apache implements an "error_log" hook. If there were a perl
interface to it one could direct error messages to separate files
with "Apache2::Translation".
AUTHOR
Torsten Foertsch,
SPONSORING
Sincere thanks to Arvato Direct Services (http://www.arvato.com/) for
sponsoring the initial version of this module.
COPYRIGHT AND LICENSE
Copyright (C) 2005-2008 by Torsten Foertsch
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.