mod_dtcl Documentation

1) Installation

1. Check dependencies
   To install mod_dtcl, you will need Tcl 8.2 or greater and Apache 1.3.xx. It is known to run on Linux, FreeBSD, OpenBSD, and Solaris and HPUX. NT is also possible - please see the directions in the distribution.
2. Get mod_dtcl
   If you are running a Debian or FreeBSD system, there are pre-built packages available at: http://www.debian.org/Packages/unstable/web/libapache-mod-dtcl.html or http://www.freebsd.org/ports/www.html#mod_dtcl-0.8.1.1.
   Otherwise, download the sources at http://tcl.apache.org/mod_dtcl/download/.
   
3. Uncompress the sources
   gunzip apache-1.3.X.tar.gz
tar -xvf apache-1.3.X.tar.gz
You don't need the Apache sources if you are building a shared object module. gunzip mod_dtcl-X.X.X.tar.gz
tar -xvf mod_dtcl-X.X.X.tar.gz

4. Configure, Edit builddtcl.sh and Make
   cd apache-1.3.X/
./configure

cd ../mod_dtcl/
Now edit the builddtcl.sh script. The 3 variables you may need to change are:
   • TCLSH
     Name of the tclsh program on your computer.
   • APACHE
     Location of the Apache sources (for static builds only).
   • INC
     Location of the Apache headers (you will need this even for building shared objects).
   ./builddtcl.sh static (shared in place of static if you are building a shared object module
   ./builddtcl.sh install (Not necessary if it is a shared object build)
   cd ../apache-1.3.X
./configure --activate-module=src/modules/mod_dtcl/mod_dtcl.a [ other configure options ]
export EXTRA_LIBS="-ltcl8.X -lm"
make -e
make install

5. Configure Apache
   
   • http.conf
     LoadModule dtcl_module /usr/lib/apache/1.3/mod_dtcl.so
     This points Apache to the shared object if mod_dtcl is being used as a loadable module.
   • srm.conf
     AddType application/x-httpd-tcl .ttml
AddType application/x-dtcl-tcl .tcl (optional)
     These add the .ttml and .tcl (if desired) types to Apache, so that they are processed by mod_dtcl.

2) Apache Directives

• Dtcl_Script GlobalInitScript "script"
  Tcl script that is run when each interpreter is initialized. "script" is actual Tcl script, so to run a file, you would do Dtcl_Script GlobalInitScript "source /var/www/foobar.tcl".
• Dtcl_Script ChildInitScript "script"
  Script to be evaluated when each apache child is initialized. This is the best place to load modules.
• Dtcl_Script ChildExitScript "script"
  Script to be evaluated when each apache child exits.
• Dtcl_Script BeforeScript "script"
  Script to be evaluated before each .ttml page. Note that you cannot use hputs in the BeforeScript, but must instead use buffer_add.
• Dtcl_Script AfterScript "script"
  Script to be called after each .ttml page.
• Dtcl_CacheSize cachesize
  Number of ttml scripts to cache as Tcl Objects. Default is MaxRequestsPerChild / 2, or 50, if MaxRequestsPerChild is 0.

3) mod_dtcl specific Tcl commands

• buffer_add string
  Add text to output_buffer for later printing. Used internally.
• hputs ?-error? text
  The mod_dtcl version of "puts". Outputs to the client, instead of to stdout. The error option permits you to send an 'error message' to the apache log file, at the NOTICE level.
• hgetvars
  Get environmental, CGI and Cookie variables. This is in a seperate command so as not to make the server do this every time you load a .ttml file. ENVS, VARS, and COOKIES are the associative arrays created. ENVS contains environmental variables, VARS contains all the 'cgi' variables, and COOKIES, any cookies recieved from the client.
• include filename
  Include a file without parsing it. This is the best way to include an HTML file or any other static content.
• parse filename
  "Source" a .ttml file. This is the way to include other .ttml files.
• hflush
  Flush the output buffers to the client. Use this if you want to incrementally update a page.
• headers redirect uri
  Redirect from the current page to a new URI. Must be done in the first block of TCL code.
• headers setcookie cookie-name cookie-value ?-expires date/time? ?-domain domain? ?-path path? ?-secure?
  This command is for setting cookies. Cookie-name is the name of the cookie, cookie-value is the data associated with the variable. Expires sets an expiration date for the cookie, and must be in the format 'DD-Mon-YY HH:MM:SS', path sets the path for which the cookie is valid, and secure specifies that the cookie is only to be transmitted if the connection is secure (HTTPS).
• headers type content-type
  This command sets the "Content-type:" header returned by the script, which is useful if you wish to create a PNG (image), for example, with mod_dtcl.
• headers set headername value
  Set arbitrary header names and values.
• dtcl_info
  Prints information on the internals of the module in HTML. Currently, only the PID and size of the object cache are reported.

4) Internals

• Read the code!
• Initialization
  When Apache is started, (or when child Apache processes are started if a threaded Tcl is used), tcl_init_stuff is called, which creates a new interpreter, and initializes various things, like the apache_channel channel system. The caching system is also set up, and if there is a GlobalScript, it is run.
• Achan/apache_channel
  The "Apache Channel" system was created so that it is possible to have an actual Tcl channel that we could redirect standard output to. This lets us use, for instance, the regular "puts" command in .ttml pages. It works by creating commands that write to memory that is slated to be sent to the client.
• Page parsing/execution
  In send_parsed_file Each .ttml file is loaded and run within its own namespace. No new interpreter is created for each page. This lets you share variables, and most importantly, loaded modules, from a common parent (such as one of the InitScripts). When a file is loaded, it is transformed into a Tcl script by putting everything outside of <+ and +> into large hputs statements. When the script is complete, it is then inserted into the cache, for future use. In fact, if the file modification information doesn't change, mod_dtcl will execute the cached version of the script the next time it is encountered.
• Binary data
  mod_dtcl is capable of outputing binary data, such as images, or loading binary data with 'include'.