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<html>
<head>
<title>AOLserver</title>
</head>
<body>
<h1>AOLserver Tcl Libraries</h1>
<p>
<small>
$Header: /cvsroot/aolserver/aolserver.com/docs/devel/tcl/tcl-libraries.html,v 1.1 2002/03/07 19:15:35 kriston Exp $
</small>
<p>
<a href=#1>What Are Tcl Libraries?</a>
<p>
<a href=#2>When to Use Tcl Libraries</a>
<p>
<a href=#3>Tcl Libraries</a>
<p>
<a href=#4>Tcl Script Order of Evaluation</a>
<p>
<a href=#5>Tcl-only Modules</a>
<p>
<a href=#6>Configuration for Tcl Libraries</a>
<p>
<a href=#7>How to Build and Debug Tcl Scripts</a>
<p>
<p>
<h2><a name=1>What Are Tcl Libraries?</a></h2>
<p>
A Tcl library is simply a directory containing Tcl scripts that are
sourced at startup by a virtual server. You can create private
libraries for individual virtual servers and public libraries that
affect all or some of an installation's virtual servers.
<p>
Each Tcl file in a library often contains one or more calls to
ns_register_proc, ns_schedule_proc, or ns_register_filter to bind a
script to a specific URL or URL hierarchy, plus the Tcl scripts that
will handle the URL(s). This example shows the ns_register_proc
function being used to bind the Tcl procedure "hello" to handle a GET
request for /example/hello, plus the "hello" procedure itself:
ns_register_proc GET /example/hello hello
<p>
<pre>
proc hello {conn context} {
ns_return $conn 200 text/plain "Hello World"
}
</pre>
<p>
Tcl libraries can also be created that contain no registration
functions; they may just contain Tcl scripts that are called from
ADPs.
<p>
When AOLserver processes a method/URL request, it checks to see if
there is a Tcl script in the virtual server's private or shared
library to handle the method and URL. A private Tcl script registered
to handle a URL overrides a shared Tcl script registered to handle the
same URL.
<p>
<p>
<p>
<p>
<p>
<h2><a name=1>When to Use Tcl Libraries</a></h2>
<p>
The alternative to embedding Tcl scripts in HTML pages using ADPs (see
Chapter 2), is to store Tcl scripts in Tcl libraries. The situations
listed below are well-suited to the Tcl libraries approach.
<p>
* Inheritance: If you want one Tcl script to handle an URL and all
of its sub-URLs, it's better to store the script in a Tcl library
and register it using ns_register_proc to handle an URL hierarchy.
For example, you may want to manage a server domain name change by
redirecting every response to the corresponding domain name on
another server.
<p>
* Special Extensions: If you want one Tcl script to handle all files
with a specific extension, like /*.csv, you would register the
script with ns_register_proc to handle those files.
<p>
* Scheduled Procedures: If you want a Tcl script to be run at
specific intervals, you can use the ns_schedule_* functions to run
a script from the Tcl library at scheduled intervals. These
procedures do not normally involve returning HTML pages and so are
not well suited to ADPs.
<p>
* Filters: If you want a Tcl script to be called at
pre-authorization, post-authorization, or trace time for a group
of URLs, you would register a filter using the ns_register_filter
function.
<p>
* Re-using Tcl Scripts: If there are Tcl scripts that you want to
use in multiple situations, you can store them in a Tcl library
and invoke them from within any ADP or Tcl script.
<p>
<h2><a name=3>Tcl Libraries</a></h2>
<p>
Tcl libraries are initialized from a Tcl directory specified for each
server. The Tcl directory is specified with the Library configuration
parameter. It defaults to /servers/servername/modules/tcl.You can
specify a Tcl directory for each server.
<p>
Note that the directories you specify need not reside under the
AOLserver installation directory. This allows you to keep user-defined
scripts physically separate from the scripts supplied by AOLserver.
<p>
<h2><a name=4>Tcl Script Order of Evaluation</a></h2>
<p>
At server startup time, Tcl initialization is performed in the
following steps for the server:
<p>
1. If a Tcl directory is specified, the init.tcl file in that
directory is sourced first (if it exists), and then all the
remaining .tcl files are sourced alphabetically.
<p>
2. For each module (including any Tcl-only modules as described on
page 25) in the server: If a private Tcl directory is specified,
the init.tcl file in the module-name subdirectory of the private
directory is sourced first (if it exists), and then all the
remaining .tcl files are sourced alphabetically.
<p>
<h2><a name=5>Tcl-only Modules</a></h2>
<p>
As described in the "Tcl Libraries" section, you can define a Tcl
directory for each server. However, none of the subdirectories under
the Tcl directories will be initialized unless you load a
corresponding module. For example, if the ServerA server has a Tcl
directory defined as /home/mydir/tcl/a, and the nsdb and perm modules
are loaded, then the following directories will be initialized as
server start-up:
<br>
/home/mydir/tcl/a
<br>
/home/mydir/tcl/a/nsdb
<br>
/home/mydir/tcl/a/perm
<br>
<p>
If you want another directory under /home/tcl/a that contains Tcl
scripts to be initialized also, you must load a Tcl-only module for it
into the server using the "Tcl" keyword.
<p>
<h2><a name=6>Configuration for Tcl-only Modules</a></h2>
<p>
To load a Tcl-only module, add the following line to your
configuration file:
<br>
ns_section "ns/server/servername/modules"
<br>
ns_param mytcl Tcl
<br>
<p>
Then, at server start-up, the /home/mydir/tcl/a/mytcl directory will
be initialized too. You can load any number of Tcl-only modules into a
virtual server to have the Tcl scripts in the corresponding
directories initialized.
<p>
For Tcl-only modules, no C module file is loaded. Only the
corresponding Tcl directories are initialized.
<p>
Example of Tcl Initialization with Tcl-only Modules
<p>
This example shows demonstrates the order in which Tcl scripts are
initialized at startup time for a server. The Library parameter is not
set, so the library for S1 defaults to /servers/S1/modules/tcl. A
Tcl-only module called M1 is loaded for S1 as follows:
ns_section "ns/server/S1/modules"
ns_param M1 Tcl
<p>
The library for server S1 (/servers/S1/modules/tcl) contains these
files:
<br>
abc.tcl
<p>
The library for module M1 (/servers/S1/modules/tcl/M1) contains these
files:
<br>
init.tcl
<br>
priv.tcl
<br>
script1.tcl
<br>
<p>
The Tcl files will be sourced in this order:
<br>
/servers/S1/module/tcl/abc.tcl
<br>
/servers/S1/module/tcl/M1/init.tcl
<br>
/servers/S1/module/tcl/M1/priv.tcl
<br>
/servers/S1/module/tcl/M1/script1.tcl
<br>
<p>
<p>
Configuration for Tcl Libraries
<p>
Configuration for Tcl libraries is handled in the
ns/server/server-name/tcl section of the configuration file. The
parameters in that section are described in detail on page 61 of the
AOLserver Administrator's Guide. Some parameters to note are:
<p>
* Debug, which prints the names of files sourced at server startup
to the log file
<p>
* Library, which defines the Tcl library for the server
<p>
To configure Tcl-only modules, see page 25.
<p>
<h2><a name=7>How to Build and Debug Tcl Scripts</a></h2>
<p>
Follow these steps to build and debug your Tcl scripts:
<p>
1. Create a .tcl file containing a Tcl script in the directory
specified by the Library parameter (see page 26) for your server.
Include a call to ns_register_proc to register your script to an
URL or URL hierarchy.
<p>
2. Test your script by accessing an URL that it is registered for.
For example, if you registered the hello script to the
/example/hello URL as follows:
<br>
ns_register_proc GET /example/hello hello
<p>
Then you would test the script by visiting the URL
<br>
http://yourserver/example/hello.
<p>
3. After testing your script, you may want to make changes to it.
Edit the script file and open the URL associated with the script
(such as the /example/hello URL in the above example) again in
your browser and perform a Reload to see the new results.
<p>
</body>
</html>
|
