Added new scheme to allow multiple plugins to share the onsubmit handler for the...

[squirrelmail.git] / doc / Development / plugin.txt

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In addition to this document, please check out the SquirrelMail
development FAQ for more information.  Also, help writing plugins
is easily obtained by posting to the squirrelmail-plugins mailing
list.  (See details about mailing lists on the website)

FAQ -> http://www.squirrelmail.org/wiki/wiki.php?DeveloperFAQ
Plugin Development ->
       http://www.squirrelmail.org/wiki/wiki.php?DevelopingPlugins


A FEW NOTES ON THE PLUGIN ARCHITECTURE
======================================

The plugin architecture of SquirrelMail is designed to make it possible
to add new features without having to patch SquirrelMail itself.
Functionality like password changing, displaying ads and calendars should
be possible to add as plugins.


The Idea
--------

The idea is to be able to run random code at given places in the
SquirrelMail code. This random code should then be able to do whatever
needed to enhance the functionality of SquirrelMail. The places where
code can be executed are called "hooks".

There are some limitations in what these hooks can do. It is difficult
to use them to change the layout and to change functionality that
already is in SquirrelMail.

Some way for the plugins to interact with the help subsystem and
translations will be provided.


The Implementation
------------------

The plugin jumping off point in the main SquirrelMail code is in the
file functions/plugin.php.  In places where hooks are made available,
they are executed by calling the function do_hook('hookname').  The
do_hook function then traverses the array
$squirrelmail_plugin_hooks['hookname'] and executes all the functions
that are named in that array.  Those functions are placed there when
plugins register themselves with SquirrelMail as discussed below.  A
plugin may add its own internal functions to this array under any
hook name provided by the SquirrelMail developers.

A plugin must reside in a subdirectory in the plugins/ directory. The
name of the subdirectory is considered to be the name of the plugin.
(The plugin will not function correctly if this is not the case.)

To start using a plugin, its name must be added to the $plugins array
in config.php like this:

   $plugins[0] = 'plugin_name';

When a plugin is registered, the file plugins/plugin_name/setup.php is
included and the function squirrelmail_plugin_init_plugin_name() is
called with no parameters.  That function is where the plugin may
register itself against any hooks it wishes to take advantage of.


WRITING PLUGINS
===============

All plugins must contain a file called setup.php and must include a
function called squirrelmail_plugin_init_plugin_name() therein.  Since
including numerous plugins can slow SquirrelMail performance
considerably, the setup.php file should contain little else.  Any
functions that are registered against plugin hooks should do little
more than call another function in a different file.

Any other files used by the plugin should also be placed in the
plugin directory (or subdirectory thereof) and should contain the
bulk of the plugin logic.

The function squirrelmail_plugin_init_plugin_name() is called to
initalize a plugin. This function could look something like this (if
the plugin was named "demo" and resided in the directory plugins/demo/):

function squirrelmail_plugin_init_demo ()
{
   global $squirrelmail_plugin_hooks;

   $squirrelmail_plugin_hooks['generic_header']['demo'] = 'plugin_demo_header';
   $squirrelmail_plugin_hooks['menuline']['demo'] = 'plugin_demo_menuline';
}

Please note that as of SquirrelMail 1.5.0, this function will no longer
be called at run time and will instead be called only once at configure-
time.  Thus, the inclusion of any dynamic code (anything except hook
registration) here is strongly discouraged.

In this example, the "demo" plugin should also have two other functions
in its setup.php file called plugin_demo_header() and plugin_demo_menuline().
The first of these might look something like this:

function plugin_demo_header()
{
   include_once(SM_PATH . 'plugins/demo/functions.php');
   plugin_demo_header_do();
}

The function called plugin_demo_header_do() would be in the file called
functions.php in the demo plugin directory and would contain the plugin's
core logic for the "generic_header" hook.


Including Other Files
---------------------

A plugin may need to reference functionality provided in other
files, and therefore need to include those files.  Most of the
core SquirrelMail functions are already available to your plugin
unless it has any files that are requested directly by the client
browser (custom options page, etc.).  In this case, you'll need
to make sure you include the files you need (see below).

Note that as of SquirrelMail 1.4.0, all files are accessed using a
constant called SM_PATH that always contains the relative path to
the main SquirrelMail directory.  This constant is always available
for you to use when including other files from the SquirrelMail core,
your own plugin, or other plugins, should the need arise.  If any of
your plugin files are requested directly from the client browser,
you will need to define this constant before you do anything else:

  define('SM_PATH', '../../');

Files are included like this:

  include_once(SM_PATH . 'include/validate.php');

When including files, please make sure to use the include_once() function
and NOT include(), require(), or require_once(), since these all are much
less efficient than include_once() and can have a cumulative effect on
SquirrelMail performance.

The files that you may need to include in a plugin will vary greatly
depending upon what the plugin is designed to do.  For files that are
requested directly by the client browser, we strongly recommend that
you include the file include/validate.php, since it will set up the
SquirrelMail environment automatically.  It will ensure the the user
has been authenticated and is currently logged in, load all user
preferences, include internationalization support, call stripslashes()
on all incoming data (if magic_quotes_gpc is on), and initialize and
include all other basic SquirrelMail resources and functions.  You may
see other plugins that directly include other SquirrelMail files, but
that is no longer necessary and is a hold-over from older SquirrelMail
versions.

List of files, that are included by include/validate.php (If SquirrelMail
version is not listed, files are included from v.1.3.2.):
   1. class/mime.class.php
      1.1. class/mime/Rfc822Header.class.php
      1.2. class/mime/MessageHeader.class.php
      1.3. class/mime/AddressStructure.class.php
      1.4. class/mime/Message.class.php
      1.5. class/mime/SMimeMessage.class.php
      1.6. class/mime/Disposition.class.php
      1.7. class/mime/Language.class.php
      1.8. class/mime/ContentType.class.php
   2. functions/global.php
   3. functions/strings.php
   4. config/config.php
      4.1. config/config_local.php (from 1.4.0rc1)
   5. functions/i18n.php
      5.1. functions/global.php (from 1.4.0)
   6. functions/auth.php
   7. include/load_prefs.php
      7.1. include/validate.php
      7.2. functions/prefs.php
      7.3. functions/plugin.php
         7.3.1. functions/global.php (from 1.4.0 and 1.5.0)
         7.3.2. functions/prefs.php (from 1.5.1)
      7.4. functions/constants.php
      7.5. do_hook('loading_prefs')
         7.5.1. files loaded by plugins that use 'loading_prefs'
   8. functions/page_header.php
      8.1. functions/strings.php
      8.2. functions/html.php
      8.3. functions/imap_mailbox.php
         8.3.1. functions/imap_utf7_local.php
      8.4. functions/global.php
   9. functions/prefs.php
      9.1. functions/global.php
      9.2. $prefs_backend (only in 1.4.3 and 1.5.0)
           do_hook_function('prefs_backend') (since 1.4.4 and 1.5.1)
           functions/db_prefs.php
           functions/file_prefs.php
         9.2.1. functions/display_messages.php
                (loaded only by file_prefs.php)
         9.2.2. files loaded by plugin that uses 'prefs_backend'

Hook Types:  Parameters and Return Values
-----------------------------------------

Hooks, when executed, are called with differing parameters and may or may
not take return values, all depending on the type of hook being called and
the context in which it is being used.  On the source side (where the hook
call originates), all hooks have at least one parameter, which is the
name of the hook.  After that, things get complicated.

   do_hook
   -------
   Most hook calls don't pass any data and don't ask for anything back.
   These always use the do_hook call.  A limited number of do_hook calls do
   pass some extra parameters, in which case your plugin may modify the
   given data if you do so by reference.  It is not necessary to return
   anything from your function in such a case; modifying the parameter
   data by reference is what does the job (although the hook call itself
   (in the source) must grab the return value for this to work).  Note
   that in this case, the parameter to your hook function will be an array,
   the first element simply being the hook name, followed by any other
   parameters that may have been included in the actual hook call in the
   source.  Modify parameters with care!

   do_hook_function
   ----------------
   This hook type was intended to be the main hook type used when the
   source needs to get something back from your plugin.  It is somewhat
   limited in that it will only use the value returned from the LAST
   plugin registered against the hook.  The source for this hook might
   use the return value for internal purposes, or might expect you to
   provide text or HTML to be sent to the client browser (you'll have to
   look at its use in context to understand how you should return values
   here).  The parameters that your hook function gets will be anything
   you see AFTER the hook name in the actual hook call in the source.
   These cannot be changed in the same way that the do_hook parameters
   can be.

   concat_hook_function
   --------------------
   This is a newer hook type meant to address the shortcomings of
   do_hook_function; specifically in that it uses the return values of
   all plugins registered against the hook.  In order to do so, the
   return value is assumed to be a string, which is just piled on top
   of whatever it got from the other plugins working on the same hook.
   Again, you'll have to inspect the source code to see how such data
   is put to use, but most of the time, it is used to create a string
   of HTML to be inserted into the output page.  The parameters that
   your hook function will get are the same as for the do_hook_function;
   they are anything AFTER the hook name in the actual hook call in the
   source.

   boolean_hook_function
   ---------------------
   The newest of the SquirrelMail hooks, this type is used to let all
   plugins registered against the hook to "vote" for some action.  What
   that action is is entirely dependent on how the hook is used in the
   source (look for yourself).  Plugins make their "vote" by returning
   TRUE or FALSE.  This hook may be configured to "tally votes" in one
   of three ways.  This configuration is done with the third parameter
   in the hook call in the source:
      > 0  --  Any one or more TRUEs will override any FALSEs
      < 0  --  Any one or more FALSEs will override any TRUEs
      = 0  --  Majority wins.  Ties are broken in this case with
               the last parameter in the hook call in the source.
   Your hook function will get the second paramter in the hook call in
   the source as its parameter (this might be an array if multiple values
   need to be passed).

See below for further discussion of special hook types and the values


List of Hooks
-------------

This is a list of all hooks currently available in SquirrelMail, ordered
by file.  Note that this list is accurate as of June 17, 2003 (should be
close to what is contained in release 1.4.1, plus or minus a hook or two),
but may be out of date soon thereafter.  You never know.  ;-)

  Hook Name                      Found In                        Called With(#)
  ---------                      --------                        --------------
  abook_init                     functions/addressbook.php       do_hook
  abook_add_class                functions/addressbook.php       do_hook
  loading_constants              functions/constants.php         do_hook
  logout_error                   functions/display_messages.php  do_hook
  error_box                      functions/display_messages.php  concat_hook
  get_pref_override              functions/file_prefs.php        hook_func
  get_pref                       functions/file_prefs.php        hook_func
& options_identities_process     functions/identity.php          do_hook
&% options_identities_renumber   functions/identity.php          do_hook
  special_mailbox                functions/imap_mailbox.php      hook_func
% rename_or_delete_folder        functions/imap_mailbox.php      hook_func
  mailbox_index_before           functions/mailbox_display.php   do_hook
  mailbox_form_before            functions/mailbox_display.php   do_hook
  mailbox_index_after            functions/mailbox_display.php   do_hook
  check_handleAsSent_result      functions/mailbox_display.php   do_hook
  subject_link                   functions/mailbox_display.php   concat_hook
  mailbox_display_buttons        functions/mailbox_display.php   do_hook
  mailbox_display_button_action  functions/mailbox_display.php   hook_func
  message_body                   functions/mime.php              do_hook
^ attachment $type0/$type1       functions/mime.php              do_hook
  attachments_bottom             functions/mime.php              hook_func
  decode_body                    functions/mime.php              hook_func
  generic_header                 functions/page_header.php       do_hook
  menuline                       functions/page_header.php       do_hook
  prefs_backend                  functions/prefs.php             hook_func
  loading_prefs                  include/load_prefs.php          do_hook
  addrbook_html_search_below     src/addrbook_search_html.php    do_hook
  addressbook_bottom             src/addressbook.php             do_hook
! compose_form                   src/compose.php                 do_hook
  compose_bottom                 src/compose.php                 do_hook
  compose_button_row             src/compose.php                 do_hook
  compose_send                   src/compose.php                 do_hook
  compose_send_after             src/compose.php                 do_hook
  folders_bottom                 src/folders.php                 do_hook
  help_top                       src/help.php                    do_hook
  help_chapter                   src/help.php                    do_hook
  help_bottom                    src/help.php                    do_hook
  left_main_after_each_folder    src/left_main.php               concat_hook
  left_main_before               src/left_main.php               do_hook
  left_main_after                src/left_main.php               do_hook
  login_cookie                   src/login.php                   do_hook
  login_top                      src/login.php                   do_hook
  login_form                     src/login.php                   concat_hook
    (was do_hook before 1.5.1)
  login_bottom                   src/login.php                   do_hook
* optpage_set_loadinfo           src/options.php                 do_hook
* optpage_loadhook_personal      src/options.php                 do_hook
* optpage_loadhook_display       src/options.php                 do_hook
* optpage_loadhook_highlight     src/options.php                 do_hook
* optpage_loadhook_folder        src/options.php                 do_hook
* optpage_loadhook_order         src/options.php                 do_hook
* options_personal_save          src/options.php                 do_hook
* options_display_save           src/options.php                 do_hook
* options_folder_save            src/options.php                 do_hook
* options_save                   src/options.php                 do_hook
* optpage_register_block         src/options.php                 do_hook
* options_link_and_description   src/options.php                 do_hook
* options_personal_inside        src/options.php                 do_hook
* options_display_inside         src/options.php                 do_hook
* options_highlight_inside       src/options.php                 do_hook
* options_folder_inside          src/options.php                 do_hook
* options_order_inside           src/options.php                 do_hook
* options_personal_bottom        src/options.php                 do_hook
* options_display_bottom         src/options.php                 do_hook
* options_highlight_bottom       src/options.php                 do_hook
* options_folder_bottom          src/options.php                 do_hook
* options_order_bottom           src/options.php                 do_hook
* options_highlight_bottom       src/options_highlight.php       do_hook
& options_identities_top         src/options_identities.php      do_hook
& options_identities_table       src/options_identities.php      concat_hook
& options_identities_buttons     src/options_identities.php      concat_hook
  message_body                   src/printer_friendly_bottom.php do_hook
  read_body_header               src/read_body.php               do_hook
  read_body_menu_top             src/read_body.php               hook_func
  read_body_menu_bottom          src/read_body.php               do_hook
  read_body_header_right         src/read_body.php               do_hook
  read_body_top                  src/read_body.php               do_hook
  read_body_bottom               src/read_body.php               do_hook
  login_before                   src/redirect.php                do_hook
  login_verified                 src/redirect.php                do_hook
  right_main_after_header        src/right_main.php              do_hook
  right_main_bottom              src/right_main.php              do_hook
  search_before_form             src/search.php                  do_hook
  search_after_form              src/search.php                  do_hook
  search_bottom                  src/search.php                  do_hook
  logout                         src/signout.php                 do_hook
  webmail_top                    src/webmail.php                 do_hook
  webmail_bottom                 src/webmail.php                 concat_hook
  logout_above_text              src/signout.php                 concat_hook
O info_bottom                    plugins/info/options.php        do_hook

% = This hook is used in multiple places in the given file
# = Called with hook type (see below)
& = Special identity hooks (see below)
^ = Special attachments hook (see below)
* = Special options hooks (see below)
O = Optional hook provided by a particular plugin
! = See below for notes about working with the compose page's <form> tag


(#) Called With
---------------
Each hook is called using the hook type specified in the list above:
   do_hook       do_hook()
   hook_func     do_hook_function()
   concat_hook   concat_hook_function()


(!) Compose Form
----------------
The compose_form hook allows plugins to insert their own code into 
the form tag for the main message composition HTML form.  Usually
plugins will want to insert some kind of code in an onsubmit event
handler.  In order to allow more than one plugin to do so, all plugins
using this hook to add some onsubmit code need to add that code (without
the enclosing attribute name and quotes) as a new array entry to the 
global $compose_onsubmit array.  The code should use "return false"
if the plugin has found a reason to stop form submission, otherwise,
it should DO NOTHING (that is, please do not use "return true", as that
will prevent other plugins from using the onsubmit handler).  SquirrelMail
itself will insert a final "return true".  All onsubmit code will be
enclosed in double quotes by SquirrelMail, so plugins need to quote 
accordingly if needed.  For example:

   global $compose_onsubmit;
   $compose_onsubmit[] = ' if (somevar == \'no\') return false; ';

Note the escaped single quotes.  If you use double quotes, they would have
to be escaped as such:

   global $compose_onsubmit;
   $compose_onsubmit[] = ' if (somevar == \'no\') { alert(\\"Sorry\\"); return false; }';

Any other form tag additions by a plugin (beside onsubmit event code) can 
currently be echoed directly to the browser.


(&) Identity Hooks
------------------
This set of hooks is passed special information in the array of arguments:

options_identities_process

   This hook is called at the top of the Identities page, which is
   most useful when the user has changed any identity settings - this
   is where you'll want to save any custom information you are keeping
   for each identity or catch any custom submit buttons that you may
   have added to the identities page.  The arguments to this hook are:

    (SquirrelMail 1.4.4 or older and 1.5.0)
      [0] = hook name (always "options_identities_process")
      [1] = should I run the SaveUpdateFunction() (alterable)

   Obviously, set the second array element to 1/true if you want to
   trigger SaveUpdateFunction() after the hook is finished - by default,
   it will not be called.

    (SquirrelMail 1.4.6+ or 1.5.1+)
      [0] = hook name (always "options_identities_process")
      [1] = action (hook is used only in 'update' action and any custom 
            action added to form with option_identities_table and 
            option_identities_buttons hooks)
      [2] = processed identity number

   Hook is not available in SquirrelMail 1.4.5.

options_identities_renumber

   This hook is called when one of the identities is being renumbered,
   such as if the user had three identities and deletes the second -
   this hook would be called with an array that looks like this:
   ('options_identities_renumber', 2, 1).  The arguments to this hook
   are:

      [0] = hook name (always "options_identities_renumber")
      [1] = being renumbered from ('default' or 1 through (# idents) - 1)
      [2] = being renumbered to ('default' or 1 through (# idents) - 1)

   Hook is not available in SquirrelMail 1.4.5. Renumbering order differs
   in 1.4.5+ and 1.5.1+.

options_identities_table

   This hook allows you to insert additional rows into the table that
   holds each identity.  The arguments to this hook are:

      [0] = additional html attributes applied to table row.
            use it like this in your plugin:
               <tr "<?php echo $args[0]; ?>">
      [1] = is this an empty section (the one at the end of the list)?
      [2] = what is the 'post' value? (ident # or empty string if default)

   You need to return any HTML you would like to add to the table.
   You could add a table row with code similar to this:

      function demo_identities_table(&$args)
      {
         return '<tr bgcolor="' . $args[0] . '"><td>&nbsp;</td><td>'
              . 'YOUR CODE HERE' . '</td></tr>' . "\n";
      }

   First hook argument was modified in 1.4.5/1.5.1. In SquirrelMail 1.4.1-1.4.4 
   and 1.5.0 argument contains only background color. You should use 
   <tr bgcolor="<?php echo $args[0]; ?>"> in these SquirrelMail versions.

options_identities_buttons

   This hook allows you to add a button (or other HTML) to the row of
   buttons under each identity.  The arguments to this hook are:

      [0] = is this an empty section (the one at the end of the list)?
      [1] = what is the 'post' value? (ident # or empty string if default)

   You need to return any HTML you would like to add here.  You could add
   a button with code similar to this:

      function demo_identities_button(&$args)
      {
         return '<input type="submit" name="demo_button_' . $args[1]
              . '" value="Press Me" />';
      }

   Input element should use 'smaction[action_name][identity_no]' value in 
   'name' attribute, if you want to process your button actions in
   SquirrelMail 1.4.6+ and 1.5.1+ options_identity_process hook.


See sample implementation of identity hooks in SquirrelMail demo plugin.

  cvs -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/squirrelmail \
    co plugins/demo


(^) Attachment Hooks
--------------------
When a message has attachments, this hook is called with the MIME types.  For
instance, a .zip file hook is "attachment application/x-zip".  The hook should
probably show a link to do a specific action, such as "Verify" or "View" for a
.zip file.  Thus, to register your plugin for .zip attachments, you'd do this
in setup.php (assuming your plugin is called "demo"):

   $squirrelmail_plugin_hooks['attachment application/x-zip']['demo']
      = 'demo_handle_zip_attachment';

This is a breakdown of the data passed in the array to the hook that is called:

  [0] = Hook's name ('attachment text/plain')
  [1] = Array of links of actions (see below) (alterable)
  [2] = Used for returning to mail message (startMessage)
  [3] = Used for finding message to display (id)
  [4] = Mailbox name, urlencode()'d (urlMailbox)
  [5] = Entity ID inside mail message (ent)
  [6] = Default URL to go to when filename is clicked on (alterable)
  [7] = Filename that is displayed for the attachment
  [8] = Sent if message was found from a search (where)
  [9] = Sent if message was found from a search (what)

To set up links for actions, you assign them like this:

  $Args[1]['<plugin_name>']['href'] = 'URL to link to';
  $Args[1]['<plugin_name>']['text'] = _("What to display");
  $Args[1]['<plugin_name>']['extra'] = 'extra stuff, such as an <img ...> tag';

Note: _("What to display") is explained in the section about
internationalization.

You can leave the 'text' empty and put an image tag in 'extra' to show an
image-only link for the attachment, or do the opposite (leave 'extra' empty)
to display a text-only link.

It's also possible to specify a hook as "attachment type0/*",
for example "attachment text/*". This hook will be executed whenever there's
no more specific rule available for that type.

Putting all this together, the demo_handle_zip_attachment() function should
look like this (note the argument being passed):

   function demo_handle_zip_attachment(&$Args)
   {
      include_once(SM_PATH . 'plugins/demo/functions.php');
      demo_handle_zip_attachment_do($Args);
   }

And the demo_handle_zip_attachment_do() function in the
plugins/demo/functions.php file would typically (but not necessarily)
display a custom link:

   function demo_handle_zip_attachment_do(&$Args)
   {
      $Args[1]['demo']['href'] = SM_PATH . 'plugins/demo/zip_handler.php?'
         . 'passed_id=' . $Args[3] . '&mailbox=' . $Args[4]
         . '&passed_ent_id=' . $Args[5];
      $Args[1]['demo']['text'] = _("Show zip contents");
   }

The file plugins/demo/zip_handler.php can now do whatever it needs with the
attachment (note that this will hand information about how to retrieve the
source message from the IMAP server as GET varibles).


(*) Options
-----------
Before you start adding user preferences to your plugin, please take a moment
to think about it:  in some cases, more options may not be a good thing.
Having too many options can be confusing.  Thinking from the user's
perspective, will the proposed options actually be used?  Will users
understand what these options are for?

There are two ways to add options for your plugin.  When you only have a few
options that don't merit an entirely new preferences page, you can incorporate
them into an existing section of SquirrelMail preferences (Personal
Information, Display Preferences, Message Highlighting, Folder Preferences or
Index Order).  Or, if you have an extensive number of settings or for some
reason need a separate page for the user to interact with, you can create your
own preferences page.


Integrating Your Options Into Existing SquirrelMail Preferences Pages
---------------------------------------------------------------------

There are two ways to accomplish the integration of your plugin's settings
into another preferences page.  The first method is to add the HTML code
for your options directly to the preferences page of your choice.  Although
currently very popular, this method will soon be deprecated, so avoid it
if you can.  That said, here is how it works.  :)  Look for any of the hooks
named as "options_<pref page>_inside", where <pref page> is "display",
"personal", etc.  For this example, we'll use "options_display_inside" and,
as above, "demo" as our plugin name:

  1.  In setup.php in the squirrelmail_plugin_init_demo() function:

         $squirrelmail_plugin_hooks['options_display_inside']['demo']
            = 'demo_show_options';

      Note that there are also hooks such as "options_display_bottom",
      however, they place your options at the bottom of the preferences
      page, which is usually not desirable (mostly because they also
      come AFTER the HTML FORM tag is already closed).  It is possible
      to use these hooks if you want to create your own FORM with custom
      submission logic.

  2.  Assuming the function demo_show_options() calls another function
      elsewhere called demo_show_options_do(), that function should have
      output similar to this (note that you will be inserting code into
      a table that is already defined with two columns, so please be sure
      to keep this framework in your plugin):

         ------cut here-------
         <tr>
            <td>
               OPTION_NAME
            </td>
            <td>
               OPTION_INPUT
            </td>
         </tr>
         ------cut here-------

      Of course, you can place any text where OPTION_NAME is and any input
      tags where OPTION_INPUT is.

  3.  You will want to use the "options_<pref page>_save" hook (in this case,
      "options_display_save") to save the user's settings after they have
      pressed the "Submit" button.  Again, back in setup.php in the
      squirrelmail_plugin_init_demo() function:

         $squirrelmail_plugin_hooks['options_display_save']['demo']
            = 'demo_save_options';

  4.  Assuming the function demo_save_options() calls another function
      elsewhere called demo_save_options_do(), that function should put
      the user's settings into permanent storage (see the preferences
      section below for more information).  This example assumes that
      in the preferences page, the INPUT tag's NAME attribute was set
      to "demo_option":

         global $data_dir, $username;
         sqgetGlobalVar('demo_option', $demo_option);
         setPref($data_dir, $username, 'demo_option', $demo_option);


The second way to add options to one of the SquirrelMail preferences page is
to use one of the "optpage_loadhook_<pref page>" hooks.  The sent_subfolders
plugin has an excellent example of this method.  Briefly, this way of adding
options consists of adding some plugin-specific information to a predefined
data structure which SquirrelMail then uses to build the HTML input forms
for you.  This is the preferred method of building options lists going forward.

  1.  We'll use the "optpage_loadhook_display" hook to add a new group of
      options to the display preferences page.  In setup.php in the
      squirrelmail_plugin_init_demo() function:

         $squirrelmail_plugin_hooks['optpage_loadhook_display']['demo']
            = 'demo_options';

  2.  Assuming the function demo_options() calls another function elsewhere
      called demo_options_do(), that function needs to add a new key to two
      arrays, $optpage_data['grps'] and $optpage_data['vals'].  The value
      associated with that key should simply be a section heading for your
      plugin on the preferences page for the $optpage_data['grps'] array,
      and yet another array with all of your plugin's options for the
      $optpage_data['vals'] array.  The options are built as arrays (yes,
      that's four levels of nested arrays) that specify attributes that are
      used by SquirrelMail to build your HTML input tags automatically.
      This example includes just one input element, a SELECT (drop-down)
      list:

         global $optpage_data;
         $optpage_data['grps']['DEMO_PLUGIN'] = 'Demo Options';
         $optionValues = array();
         $optionValues[] = array(
            'name'    => 'plugin_demo_favorite_color',
            'caption' => 'Please Choose Your Favorite Color',
            'type'    => SMOPT_TYPE_STRLIST,
            'refresh' => SMOPT_REFRESH_ALL,
            'posvals' => array(0 => 'red',
                               1 => 'blue',
                               2 => 'green',
                               3 => 'orange'),
            'save'    => 'save_plugin_demo_favorite_color'
         );
         $optpage_data['vals']['DEMO_PLUGIN'] = $optionValues;

      The array that you use to specify each plugin option has the following
      possible attributes:

         name           The name of this setting, which is used not only for
                        the INPUT tag name, but also for the name of this
                        setting in the user's preferences
         caption        The text that prefaces this setting on the preferences
                        page
         trailing_text  Text that follows a text input or select list input on
                        the preferences page (useful for indicating units,
                        meanings of special values, etc.)
         type           The type of INPUT element, which should be one of:
                           SMOPT_TYPE_STRING     String/text input
                           SMOPT_TYPE_STRLIST    Select list input
                           SMOPT_TYPE_TEXTAREA   Text area input
                           SMOPT_TYPE_INTEGER    Integer input
                           SMOPT_TYPE_FLOAT      Floating point number input
                           SMOPT_TYPE_BOOLEAN    Boolean (yes/no radio buttons)
                                                 input
                           SMOPT_TYPE_HIDDEN     Hidden input (not actually
                                                 shown on preferences page)
                           SMOPT_TYPE_COMMENT    Text is shown (specified by the
                                                 'comment' attribute), but no
                                                 user input is needed
                           SMOPT_TYPE_FLDRLIST   Select list of IMAP folders
         refresh        Indicates if a link should be shown to refresh part or
                        all of the window (optional).  Possible values are:
                           SMOPT_REFRESH_NONE         No refresh link is shown
                           SMOPT_REFRESH_FOLDERLIST   Link is shown to refresh
                                                      only the folder list
                           SMOPT_REFRESH_ALL          Link is shown to refresh
                                                    the entire window
         initial_value  The value that should initially be placed in this
                        INPUT element
         posvals        For select lists, this should be an associative array,
                        where each key is an actual input value and the
                        corresponding value is what is displayed to the user
                        for that list item in the drop-down list
         value          Specify the default/preselected value for this option
                        input
         save           You may indicate that special functionality needs to be
                        used instead of just saving this setting by giving the
                        name of a function to call when this value would
                        otherwise just be saved in the user's preferences
         size           Specifies the size of certain input items (typically
                        textual inputs).  Possible values are:
                           SMOPT_SIZE_TINY
                           SMOPT_SIZE_SMALL
                           SMOPT_SIZE_MEDIUM
                           SMOPT_SIZE_LARGE
                           SMOPT_SIZE_HUGE
                           SMOPT_SIZE_NORMAL
         comment        For SMOPT_TYPE_COMMENT type options, this is the text
                        displayed to the user
         script         This is where you may add any additional javascript
                        or other code to the user input
         post_script    You may specify some script (usually Javascript) that
                        will be placed after (outside of) the INPUT tag.
         htmlencoded    disables html sanitizing. WARNING - don't use it, if user
                        input is possible in option or use own sanitizing functions.
                        Currently works only with SMOPT_TYPE_STRLIST.
         folder_filter  Controls folder list limits in SMOPT_TYPE_FLDRLIST widget.
                        See $flag argument in sqimap_mailbox_option_list()
                        function. Available since 1.5.1.

      Note that you do not have to create a whole new section on the options
      page if you merely want to add a simple input item or two to an options
      section that already exists.  For example, the Display Options page has
      these groups:

         0  -  General Display Options
         1  -  Mailbox Display Options
         2  -  Message Display and Composition

      To add our previous input drop-down to the Mailbox Display Options,
      we would not have to create our own group; just add it to group
      number one:

         global $optpage_data;
         $optpage_data['vals'][1][] = array(
            'name'    => 'plugin_demo_favorite_color',
            'caption' => 'Please Choose Your Favorite Color',
            'type'    => SMOPT_TYPE_STRLIST,
            'refresh' => SMOPT_REFRESH_ALL,
            'posvals' => array(0 => 'red',
                               1 => 'blue',
                               2 => 'green',
                               3 => 'orange'),
            'save'    => 'save_plugin_demo_favorite_color'
         );

  3.  If you indicated a 'save' attribute for any of your options, you must
      create that function (you'll only need to do this if you need to do
      some special processing for one of your settings).  The function gets
      one parameter, which is an object with mostly the same attributes you
      defined when you made the option above... the 'new_value' (and possibly
      'value', which is the current value for this setting) is the most useful
      attribute in this context:

         function save_plugin_demo_favorite_color($option)
         {
            // if user chose orange, make note that they are really dumb
            if ($option->new_value == 3)
            {
               // more code here as needed
            }

            // don't even save this setting if user chose green (old
            // setting will remain)
            if ($option->new_value == 2)
               return;

            // for all other colors, save as normal
            save_option($option);
         }


Creating Your Own Preferences Page
----------------------------------

It is also possible to create your own preferences page for a plugin.  This
is particularly useful when your plugin has numerous options or needs to
offer special interaction with the user (for things such as changing password,
etc.).  Here is an outline of how to do so (again, using the "demo" plugin
name):

  1.  Add a new listing to the main Options page.  Older versions of
      SquirrelMail offered a hook called "options_link_and_description"
      although its use is deprecated (and it is harder to use in that
      it requires you to write your own HTML to add the option).  Instead,
      you should always use the "optpage_register_block" hook where you
      create a simple array that lets SquirrelMail build the HTML
      to add the plugin options entry automatically.  In setup.php in the
      squirrelmail_plugin_init_demo() function:

         $squirrelmail_plugin_hooks['optpage_register_block']['demo']
            = 'demo_options_block';

  2.  Assuming the function demo_options_block() calls another function
      elsewhere called demo_options_block_do(), that function only needs
      to create a simple array and add it to the $optpage_blocks array:

         global $optpage_blocks;
         $optpage_blocks[] = array(
             'name' => 'Favorite Color Settings',
             'url'  => SM_PATH . 'plugins/demo/options.php',
             'desc' => 'Change your favorite color & find new exciting colors',
             'js'   => FALSE
         );

      The array should have four elements:
         name   The title of the plugin's options as it will be displayed on
                the Options page
         url    The URI that points to your plugin's custom preferences page
         desc   A description of what the preferences page offers the user,
                displayed on the Options page below the title
         js     Indicates if this option page requires the client browser
                to be Javascript-capable.  Should be TRUE or FALSE.

  3.  There are two different ways to create the actual preferences page
      itself.  One is to simply write all of your own HTML and other
      interactive functionality, while the other is to define some data
      structures that allow SquirrelMail to build your user inputs and save
      your data automatically.

      Building your own page is wide open, and for ideas, you should look at
      any of the plugins that currently have their own preferences pages.  If
      you do this, make sure to read step number 4 below for information on
      saving settings.  In order to maintain security, consistant look and
      feel, internationalization support and overall integrity, there are just
      a few things you should always do in this case:  define the SM_PATH
      constant, include the file include/validate.php (see the section about
      including other files above) and make a call to place the standard page
      heading at the top of your preferences page.  The top of your PHP file
      might look something like this:

         define('SM_PATH', '../../');
         include_once(SM_PATH . 'include/validate.php');
         global $color;
         displayPageHeader($color, 'None');

      From here you are on your own, although you are encouraged to do things
      such as use the $color array to keep your HTML correctly themed, etc.

      If you want SquirrelMail to build your preferences page for you,
      creating input forms and automatically saving users' settings, then
      you should change the 'url' attribute in the options block you created
      in step number 2 above to read as follows:

         'url' => SM_PATH . 'src/options.php?optpage=plugin_demo',

      Now, you will need to use the "optpage_set_loadinfo" hook to tell
      SquirrelMail about your new preferences page.  In setup.php in the
      squirrelmail_plugin_init_demo() function:

         $squirrelmail_plugin_hooks['optpage_set_loadinfo']['demo']
            = 'demo_optpage_loadinfo';

      Assuming the function demo_optpage_loadinfo() calls another function
      elsewhere called demo_optpage_loadinfo_do(), that function needs to
      define values for four variables (make sure you test to see that it
      is your plugin that is being called by checking the GET variable you
      added to the url just above):

         global $optpage, $optpage_name, $optpage_file,
                $optpage_loader, $optpage_loadhook;
         if ($optpage == 'plugin_demo')
         {
            $optpage_name = "Favorite Color Preferences";
            $optpage_file = SM_PATH . 'plugins/demo/options.php';
            $optpage_loader = 'load_optpage_data_demo';
            $optpage_loadhook = 'optpage_loadhook_demo';
         }

      Now you are ready to build all of your options.  In the file you
      indicated for the variable $optpage_file above, you'll need to create
      a function named the same as the value you used for $optpage_loader
      above.  In this example, the file plugins/demo/options.php should
      have at least this function in it:

         function load_optpage_data_demo()
         {
            $optpage_data = array();
            $optpage_data['grps']['DEMO_PLUGIN'] = 'Demo Options';
            $optionValues = array();
            $optionValues[] = array(
               'name'    => 'plugin_demo_favorite_color',
               'caption' => 'Please Choose Your Favorite Color',
               'type'    => SMOPT_TYPE_STRLIST,
               'refresh' => SMOPT_REFRESH_ALL,
               'posvals' => array(0 => 'red',
                                  1 => 'blue',
                                  2 => 'green',
                                  3 => 'orange'),
               'save'    => 'save_plugin_demo_favorite_color'
            );
            $optpage_data['vals']['DEMO_PLUGIN'] = $optionValues;
            return $optpage_data;
         }

      For a detailed description of how you build these options, please read
      step number 2 for the second method of adding options to an existing
      preferences page above.  Notice that the only difference here is in the
      very first and last lines of this function where you are actually
      creating and returning the options array instead of just adding onto it.

      That's all there is to it - SquirrelMail will create a preferences page
      titled as you indicated for $optpage_name above, and other plugins
      can even add extra options to this new preferences page.  To do so,
      they should use the hook name you specified for $optpage_loadhook above
      and use the second method for adding option settings to existing
      preferences pages described above.

  4.  Saving your options settings: if you used the second method in step
      number 3 above, your settings will be saved automatically (or you can
      define special functions to save special settings such as the
      save_plugin_demo_favorite_color() function in the example described
      above) and there is probably no need to follow this step.  If you
      created your own preferences page from scratch, you'll need to follow
      this step.  First, you need to register your plugin against the
      "options_save" hook.  In setup.php in the squirrelmail_plugin_init_demo()
      function:

         $squirrelmail_plugin_hooks['options_save']['demo']
            = 'demo_save_options';

      Assuming the function demo_save_options() calls another function
      elsewhere called demo_save_options_do(), that function needs to grab
      all of your POST and/or GET settings values and save them in the user's
      preferences (for more about preferences, see that section below).  Since
      this is a generic hook called for all custom preferences pages, you
      should always set "optpage" as a POST or GET variable with a string that
      uniquely identifies your plugin:

         <input type="hidden" name="optpage" value="plugin_demo" />

      Now in your demo_save_options_do() function, do something like this:

         global $username, $data_dir, $optpage, $favorite_color;
         if ($optpage == 'plugin_demo')
         {
            sqgetGlobalVar('favorite_color', $favorite_color, SQ_FORM);
            setPref($data_dir, $username, 'favorite_color', $favorite_color);
         }

      Note that $favorite_color may not need to be globalized, although
      experience has shown that some versions of PHP don't behave as expected
      unless you do so.  Even when you use SquirrelMail's built-in preferences
      page generation functionality, you may still use this hook, although
      there should be no need to do so.  If you need to do some complex
      validation routines, note that it might be better to do so in the file
      you specified as the "$optpage_file" (in our example, that was the
      plugins/demo/options.php file), since at this point, you can still
      redisplay your preferences page.  You could put code similar to this
      in the plugins/demp/options.php file (note that there is no function;
      this code needs to be executed at include time):

         global $optmode;
         if ($optmode == 'submit')
         {
            // do something here such as validation, etc
            if (you want to redisplay your preferences page)
               $optmode = '';
         }


Preferences
-----------

Saving and retrieving user preferences is very easy in SquirrelMail.
SquirrelMail supports preference storage in files or in a database
backend, however, the code you need to write to manipulate preferences
is the same in both cases.

Setting preferences:

   Setting preferences is done for you if you use the built-in facilities
   for automatic options construction and presentation (see above).  If
   you need to manually set preferences, however, all you need to do is:

      global $data_dir, $username;
      setPref($data_dir, $username, 'pref_name', $pref_value);

   Where "pref_name" is the key under which the value will be stored
   and "pref_value" is a variable that should contain the actual
   preference value to be stored.

Loading preferences:

   There are two approaches to retrieving plugin (or any other) preferences.
   You can grab individual preferences one at a time or you can add your
   plugin's preferences to the routine that loads up user preferences at
   the beginning of each page request.  If you do the latter, making sure
   to place your preference variables into the global scope, they will be
   immediately available in all other plugin code.  To retrieve a single
   preference value at any time, do this:

      global $data_dir, $username;
      $pref_value = getPref($data_dir, $username, 'pref_name', 'default value');

   Where "pref_name" is the preference you are retrieving, "default_value"
   is what will be returned if the preference is not found for this user,
   and, of course, "pref_value" is the variable that will get the actual
   preference value.

   To have all your preferences loaded at once when each page request is
   made, you'll need to register a function against the "loading_prefs" hook.
   For our "demo" plugin, in setup.php in the squirrelmail_plugin_init_demo()
   function:

      $squirrelmail_plugin_hooks['loading_prefs']['demo']
         = 'demo_load_prefs';

   Assuming the function demo_load_prefs() calls another function
   elsewhere called demo_load_prefs_do(), that function just needs to
   pull out any all all preferences you'll be needing elsewhere:

      global $data_dir, $username, $pref_value;
      $pref_value = getPref($data_dir, $username, 'pref_name', 'default value');

   Remember to globalize each preference, or this code is useless.


Internationalization
--------------------

Although this document may only be available in English, we sure hope that you
are thinking about making your plugin useful to the thousands of non-English
speaking SquirrelMail users out there!  It is almost rude not to do so, and
it isn't much trouble, either.  This document will only describe how you can
accomplish the internationalization of a plugin.  For more general information
about PHP and SquirrelMail translation facilities, see:

http://www.squirrelmail.org/wiki/wiki.php?LanguageTranslation

The unofficial way to internationalize a plugin is to put all plugin output
into the proper format but to rely on the SquirrelMail translation facilities
for all the rest.  If the plugin were really to get translated, you'd need
to make sure that all output strings for your plugin are either added to or
already exist in the main SquirrelMail locale files.

The better way to make sure your plugin is translated is to create your own
locale files and what is called a "gettext domain" (see the link above for
more information).

There are three basic steps to getting your plugins internationalized:  put
all output into the proper format, switch gettext domains and create locale
files.

  1.  Putting plugin output into the correct format is quite easy.  The hard
      part is making sure you catch every last echo statement.  You need to
      echo text like this:

         echo _("Hello");

      So, even in the HTML segments of your plugin files, you need to do this:

         <input type="submit" value="<?php echo _("Submit"); ?>" />

      You can put any text you want inside of the quotes (you MUST use double
      quotes!), including HTML tags, etc.  What you should think carefully
      about is that some languages may use different word ordering, so this
      might be problematic:

         echo _("I want to eat a ") . $fruitName . _(" before noon");

      Because some languages (Japanese, for instance) would need to translate
      such a sentence to "Before noon " . $fruitName . " I want to eat", but
      with the format above, they are stuck having to translate each piece
      separately.  You might want to reword your original sentence:

         echo _("This is what I want to eat before noon: ") . $fruitName;

      Note:
      Support for single quotes in gettext was added somewhere along gettext
      0.11.x (release dates 2002-01-31--08-06). This means that strings could
      be written as:

      echo _('Hello');

      However, gettext 0.10.40 is currently the oldest version available at the
      GNU site. It's still used in some Linux and BSD distributions/versions.
      Since it's still in common use and it doesn't support single quoted
      strings, double quoted strings are the preferred way when writing a
      plugin.

  2.  By default, the SquirrelMail gettext domain is always in use.  That
      means that any text in the format described above will be translated
      using the locale files found in the main SquirrelMail locale directory.
      Unless your plugin produces no output or only output that is in fact
      translated under the default SquirrelMail domain, you need to create
      your own gettext domain.  The PHP for doing so is very simple.  At
      the top of any file that produces any output, place the following code
      (again, using "demo" as the plugin name):

         bindtextdomain('demo', SM_PATH . 'plugins/demo/locale');
         textdomain('demo');

      Now all output will be translated using your own custom locale files.
      Please be sure to switch back to the SquirrelMail domain at the end
      of the file, or many of the other SquirrelMail files may misbehave:

         bindtextdomain('squirrelmail', SM_PATH . 'locale');
         textdomain('squirrelmail');

      Note that if, in the middle of your plugin file, you use any
      SquirrelMail functions that send output to the browser, you'll need
      to temporarily switch back to the SquirrelMail domain:

         bindtextdomain('squirrelmail', SM_PATH . 'locale');
         textdomain('squirrelmail');
         displayPageHeader($color, 'None');
         bindtextdomain('demo', SM_PATH . 'plugins/demo/locale');
         textdomain('demo');

      Note that technically speaking, you only need to have one bindtextdomain
      call per file, you should always use it before every textdomain call,
      since PHP installations without gettext compiled into them will not
      function properly if you do not.

  3.  Finally, you just need to create your own locale.  You should create
      a directory structure like this in the plugin directory:

         demo
           |
           ------locale
                    |
                    ------de_DE
                    |       |
                    |       ------LC_MESSAGES
                    |
                    ------ja_JP
                            |
                            ------LC_MESSAGES

      Create a directories such as de_DE for each language (de_DE is German,
      ja_JP is Japanese, etc. - check the SquirrelMail locale directory for
      a fairly comprehensive listing).  Inside of each LC_MESSAGES directory
      you should place two files, one with your translations in it, called
      <plugin name>.po (in this case, "demo.po"), and one that is a compiled
      version of the ".po" file, called <plugin name>.mo (in this case,
      "demo.mo").  On most linux systems, there is a tool you can use to pull
      out most of the strings that you need to have translated from your PHP
      files into a sample .po file:

         xgettext --keyword=_ -d <plugin name> -s -C *.php

         --keyword option tells xgettext what your strings are enclosed in
         -d is the domain of your plugin which should be the plugin's name
         -s tells xgettext to sort the results and remove duplicate strings
         -C means you are translating a file with C/C++ type syntax (ie. PHP)
         *.php is all the files you want translations for

      Note, however, that this will not always pick up all strings, so you
      should double-check manually.  Of course, it's easiest if you just keep
      track of all your strings as you are coding your plugin.  Your .po file
      will now look something like:

         # SOME DESCRIPTIVE TITLE.
         # Copyright (C) YEAR Free Software Foundation, Inc.
         # FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
         #
         #, fuzzy
         msgid ""
         msgstr ""
         "Project-Id-Version: PACKAGE VERSION\n"
         "POT-Creation-Date: 2003-06-18 11:22-0600\n"
         "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
         "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
         "Language-Team: LANGUAGE <LL@li.org>\n"
         "MIME-Version: 1.0\n"
         "Content-Type: text/plain; charset=CHARSET\n"
         "Content-Transfer-Encoding: ENCODING\n"

         #: functions.php:45
         msgid "Hello"
         msgstr ""

         #: functions.php:87
         msgid "Favorite Color"
         msgstr ""

      You should change the header to look something more like:

         # Copyright (c) 1999-2005 The SquirrelMail Project Team
         # Roland Bauerschmidt <rb@debian.org>, 1999.
         # $Id$
         msgid ""
         msgstr ""
         "Project-Id-Version: plugin-name version\n"
         "POT-Creation-Date: 2003-01-21 19:21+0100\n"
         "PO-Revision-Date: 2003-01-21 21:01+0100\n"
         "Last-Translator: Juergen Edner <juergen.edner@epost.de>\n"
         "Language-Team: German <squirrelmail-i18n@lists.sourceforge.net>\n"
         "MIME-Version: 1.0\n"
         "Content-Type: text/plain; charset=ISO-8859-1\n"
         "Content-Transfer-Encoding: 8bit\n"

      The most important thing to change here is the charset on the next to
      last line.  You'll want to keep a master copy of the .po file and make
      a copy for each language you have a translation for.  You'll need to
      translate each string in the .po file:

         msgid "Hello"
         msgstr "Guten Tag"

      After you're done translating, you can create the .mo file very simply
      by running the following command (available on most linux systems):

         msgfmt -o <plugin name>.mo <plugin name>.po

      In the case of the "demo" plugin:

         msgfmt -o demo.mo demo.po

      Please be sure that the .po and .mo files both are named exactly the
      same as the domain you bound in step 2 above and everything else works
      automatically.  In SquirrelMail, go to Options -> Display Preferences
      and change your Language setting to see the translations in action!



Documenting the Code (Optional)
-------------------------------

If you wish, you can use phpdoc (Javadoc-style) comments, when documenting your
code.

If you follow the standards that are followed between SquirrelMail core &
plugin developers, the resulted documentation can be included with the rest of
the SquirrelMail code & API documentation. Specifically, in the page-level
docblock, declare the package to be 'plugins', and the subpackage to be the
name of your plugin. For instance:

/**
 * demo.php
 *
 * Copyright (c) 2005 My Name <my-email-address>
 * Licensed under the GNU GPL. For full terms see the file COPYING.
 *
 * @package plugins
 * @subpackage demo
 */

The rest is up to you. Try to follow some common sense and document what is
really needed. Documenting the code properly can be a big help not only to
yourself, but to those who will take a look at your code, fix the bugs and even
improve it, in the true open-source spirit that SquirrelMail was built upon.

For more information about phpdocumentor and how to write proper-tagged
comments, you are directed at:

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PLUGIN STANDARDS AND REQUIREMENTS
=================================

The SquirrelMail project has some important goals, such as avoiding the
use of JavaScript, avoiding non-standard HTML tags, keeping file sizes
small and providing the fastest webmail client on the Internet.  As such,
we'd like it if plugin authors coded with the same goals in mind that the
core developers do.  Common sense is always a good tool to have in your
programming repertoire, but below is an outline of some standards that we
ask you as a plugin developer to meet.  Depending upon how far you bend
these rules, we may not want to post your plugin on the SquirrelMail
website... and of course, no one really wants your efforts to go to waste
and for the SquirrelMail community to miss out on a potentially useful
plugin, so please try to follow these guidelines as closely as possible.


Small setup.php
---------------

In order for SquirrelMail to remain fast and lean, we are now asking
that all plugin authors remove all unnecessary functionality from setup.php
and refactor it into another file.  There are a few ways to accomplish
this, none of which are difficult.  At a minimum, you'll want to have the
squirrelmail_plugin_init_<plugin name>() function in setup.php, and naturally,
you'll need functions that are merely stubs for each hook that you are using.
One (but not the only) way to do it is:

   function squirrelmail_plugin_init_demo()
   {
      global $squirrelmail_plugin_hooks;
      $squirrelmail_plugin_hooks['generic_header']['demo'] = 'plugin_demo_header';
   }
   function plugin_demo_header()
   {
      include_once(SM_PATH . 'plugins/demo/functions.php');
      plugin_demo_header_do();
   }


Internationalization
--------------------

Q: What is more disappointing to users in France who would make good
   use of your plugin than learning that it is written entirely in English?
A: Learning that they cannot send you a French translation file for your
   plugin.

There are thousands of users out there whose native tongue is not English,
and when you develop your plugin without going through the three simple steps
needed to internationalize it, you are effectively writing them all off.
PLEASE consider internationalizing your plugin!


Developing with E_ALL
---------------------

When you are developing your plugin, you should always have error reporting
turned all the way up.  You can do this by changing two settings in your
php.ini and restarting your web server:

   display_errors = On
   error_reporting  =  E_ALL

This way, you'll be sure to see all Notices, Warnings and Errors that your
code generates (it's OK, really, it happens to the best of us... except me!).
Please make sure to fix them all before you release the plugin.


Compatibility with register_globals=Off
---------------------------------------

Most sensible systems administrators now run their PHP systems with the
setting "register_globals" as OFF.  This is a prudent security setting,
and as the SquirrelMail core code has long since been upgraded to work
in such an environment, we are now requiring that all plugins do the same.
Compatibility with this setting amounts to little more than explicitly
gathering any and all variables you sent from a <form> tag as GET or POST
values instead of just assuming that they will be placed in the global
scope automatically.  There is nothing more to do than this:

   global $favorite_color;
   sqgetGlobalVar('favorite_color', $favorite_color, SQ_FORM);


Security considerations
-----------------------

All plugin authors should consider the security implications of their
plugin. Of course, if you call external programs you have to use great
care, but the following issues are important to nearly every plugin.

- Escape any untrusted data before you output it. This is to prevent
cross site scripting attacks. It means that you have to htmlspecialchars()
every variable that comes in through the URL, a mail message or other
external factors, before outputting it.

- Make sure that your plugin doesn't perform its function when it's not
enabled. If you just call hooks, your hooks won't be called when the
plugin is disabled, but if you also supply extra .php files, you should
check if they perform any function if accessed directly. If they do, you
should check at the start of that file whether the plugin is enabled in the
config, and if not, exit the script. Example:
  global $plugins;
  if ( !in_array('mypluginname', $plugins) ) {
      die("Plugin not enabled in SquirrelMail configuration.");
  }

If you have any questions about this or are unsure, please contact the
mailinglist or IRC channel, because security is very important for a
widely used application like SquirrelMail!


Extra Blank Lines
-----------------

It may seem innocuous, but if you have any blank lines either before the
first <?php tag or after the last ?> tag in any of your plugin files, you
you will break SquirrelMail in ways that may seem entirely unrelated.  For
instance, this will often cause a line feed character to be included with
email attachments when they are viewed or downloaded, rendering them useless!


include_once
------------

When including files, please make sure to use the include_once() function
and NOT include(), require(), or require_once(), since these all are much
less efficient than include_once() and can have a cumulative effect on
SquirrelMail performance.


Version Reporting
-----------------

In order for systems administrators to keep better track of your plugin and
get upgrades more efficiently, you are requested to make version information
available to SquirrelMail in a format that it understands.  There are two
ways to do this.  Presently, we are asking that you do both, since we are
still in a transition period between the two.  This is painless, so please
be sure to include it:

  1.  Create a file called "version" in the plugin directory.  That file
      should have only two lines: the first line should have the name of
      the plugin as named on the SquirrelMail web site (this is often a
      prettified version of the plugin directory name), the second line
      must have the version and nothing more.  So for our "demo" plugin,
      whose name on the web site might be something like "Demo Favorite
      Colors", the file plugins/demo/version should have these two lines:

         Demo Favorite Colors
         1.0

  2.  In setup.php, you should have a function called <plugin name>_version().
      That function should return the version of your plugin.  For the "demo"
      plugin, that should look like this:

         function demo_version()
         {
            return '1.0';
         }


Configuration Files
-------------------

It is common to need a configuration file that holds some variables that
are set up at install time.  For ease of installation and maintenance, you
should place all behavioral settings in a config file, isolated from the
rest of your plugin code.  A typical file name to use is "config.php".  If
you are using such a file, you should NOT include a file called "config.php"
in your plugin distribution, but instead a copy of that file called
"config.php.sample".  This helps systems administrators avoid overwriting
the "config.php" files and losing all of their setup information when they
upgrade your plugin.


Session Variables
-----------------

In the past, there have been some rather serious issues with PHP sessions
and SquirrelMail, and certain people have worked long and hard to ensure
that these problems no longer occur in an extremely wide variety of OS/PHP/
web server environments.  Thus, if you need to place any values into the
user's session, there are some built-in SquirrelMail functions that you are
strongly encouraged to make use of.  Using them also makes your job easier.

  1.  To place a variable into the session:

         global $favorite_color;
         $favoriteColor = 'green';
         sqsession_register($favorite_color, 'favorite_color');

      Strictly speaking, globalizing the variable shouldn't be necessary,
      but certain versions of PHP seem to behave more predictably if you do.

  2.  To retrieve a variable from the session:

         global $favorite_color;
         sqgetGlobalVar('favorite_color', $favorite_color, SQ_SESSION);

  3.  You can also check for the presence of a variable in the session:

         if (sqsession_is_registered('favorite_color'))
            // do something important

  4.  To remove a variable from the session:

         global $favorite_color;
         sqsession_unregister('favorite_color');

      Strictly speaking, globalizing the variable shouldn't be necessary,
      but certain versions of PHP seem to behave more predictably if you do.


Form Variables
--------------

You are also encouraged to use SquirrelMail's built-in facilities to
retrieve variables from POST and GET submissions.  This is also much
easier on you and makes sure that all PHP installations are accounted
for (such as those that don't make the $_POST array automatically
global, etc.):

   global $favorite_color;
   sqgetGlobalVar('favorite_color', $favorite_color, SQ_FORM);


Files In Plugin Directory
-------------------------

There are a few files that you should make sure to include when you build
your final plugin distribution:

  1.  A copy of the file index.php from the main plugins directory.  When
      working in your plugin directory, just copy it in like this:

         $ cp ../index.php .

      This will redirect anyone who tries to browse to your plugin directory
      to somewhere more appropriate.  If you create other directories under
      your plugin directory, you may copy the file there as well to be extra
      safe.  If you are storing sensitive configuration files or other data
      in such a directory, you could even include a .htaccess file with the
      contents "Deny From All" that will disallow access to that directory
      entirely (when the target system is running the Apache web server).
      Keep in mind that not all web servers will honor an .htaccess file, so
      don't depend on it for security. Make sure not to put such a file in
      your main plugin directory!

  2.  A file that describes your plugin and offers detailed instructions for
      configuration or help with troubleshooting, etc.  This file is usually
      entitled "README".  Some useful sections to include might be:

         Plugin Name and Author
         Current Version
         Plugin Features
         Detailed Plugin Description
         How-to for Plugin Configuration
         Change Log
         Future Ideas/Enhancements/To Do List

  3.  A file that explains how to install your plugin.  This file is typically
      called "INSTALL".  If you do not require any special installation
      actions, you can probably copy one from another plugin or use this as
      a template:

         Installing the Demo Plugin
         ==========================

         1) Start with untaring the file into the plugins directory.
            Here is a example for the 1.0 version of the Demo plugin.

           $ cd plugins
           $ tar -zxvf demo-1.0-1.4.0.tar.gz

         2) Change into the demo directory, copy config.php.sample
            to config.php and edit config.php, making adjustments as
            you deem necessary.  For more detailed explanations about
            each of these parameters, consult the README file.

           $ cd demo
           $ cp config.php.sample config.php
           $ vi config.php


         3) Then go to your config directory and run conf.pl.  Choose
            option 8 and move the plugin from the "Available Plugins"
            category to the "Installed Plugins" category.  Save and exit.

           $ cd ../../config/
           $ ./conf.pl


         Upgrading the Demo Plugin
         =========================

         1) Start with untaring the file into the plugins directory.
            Here is a example for the 3.1 version of the demo plugin.

           $ cd plugins
           $ tar -zxvf demo-3.1-1.4.0.tar.gz


         2) Change into the demo directory, check your config.php
            file against the new version, to see if there are any new
            settings that you must add to your config.php file.

           $ diff -Nau config.php config.php.sample

            Or simply replace your config.php file with the provided sample
            and reconfigure the plugin from scratch (see step 2 under the
            installation procedure above).


COMPATIBILITY WITH OLDER VERSIONS OF SQUIRRELMAIL
=================================================

Whenever new versions of SquirrelMail are released, there is always a
considerable lag time before it is widely adopted.  During that transitional
time, especially when the new SquirrelMail version contains any architectural
and/or functional changes, plugin developers are put in a unique and very
difficult position.  That is, there will be people running both the old and
new versions of SquirrelMail who want to use your plugin, and you will
probably want to accomodate them both.

The easiest way to keep both sides happy is to keep two different versions
of your pluign up to date, one that runs under the older SquirrelMail, and
one that requires the newest SquirrelMail.  This is inconvenient, however,
especially if you are continuing to develop the plugin.  Depending on the
changes the SquirrelMail has implemented in the new version, you may be able
to include code that can auto-sense SquirrelMail version and make adjustments
on the fly.  There is a function available to you for determining the
SquirrelMail version called check_sm_version() and it can be used as such:

   check_sm_version(1, 4, 0)

This will return TRUE if the SquirrelMail being used is at least 1.4.0, and
FALSE otherwise.

As this document is written, we are in a transition period between versions
1.2.11 and 1.4.0.  There is a plugin called "Compatibilty" that is intended
for use by plugin authors so they can develop one version of their plugin
and seamlessly support both 1.2.x and 1.4.x SquirrelMail installations.  For
more information about how to use the "Compatibility" plugin, download it and
read its README file or see:

   http://www.squirrelmail.org/wiki/wiki.php?PluginUpgrading


REQUESTING NEW HOOKS
====================

It's impossible to foresee all of the places where hooks might be useful
(it's also impossible to put in hooks everywhere!), so you might need to
negotiate the insertion of a new hook to make your plugin work.  In order
to do so, you should post such a request to the squirrelmail-devel mailing
list.


HOW TO RELEASE YOUR PLUGIN
==========================

As long as you've consulted the list of plugin standards and done your
best to follow them, there's little standing in the way of great fame as an
official SquirrelMail plugin developer.

  1.  Make a distribution file.  There is a convenient Perl script in
      the plugins directory that will help you do this:

         make_archive.pl -v demo 1.0 1.4.0

      -v    is optional and indicates that the script should run in verbose mode
      demo  is the name of your plugin
      1.0   is the version of your plugin
      1.4.0 is the version of SquirrelMail that is required to run your plugin

      You can also create the distribution file manually in most *nix
      environments by running this command from the plugins directory (NOT
      your plugin directory):

         $ tar czvf demo-1.0-1.4.0.tar.gz demo

      Where "demo" is the name of your plugin, "1.0" is the version of
      your plugin, and "1.4.0" is the version of SquirrelMail required
      to use your plugin.

  2.  Consult the SquirrelMail web site for contact information for the
      Plugins Team Leaders, to whom you should make your request.  If they
      do not respond, you should feel free to ask for help contacting them
      on the squirrelmail-plugins mailing list.

         http://www.squirrelmail.org/wiki/wiki.php?SquirrelMailLeadership