========================
 Horde Coding Standards
========================

:Last update:   $Date: 2006/09/06 08:02:48 $
:Revision:      $Revision: 1.84.10.16 $
:Authors:       Jon Parise, Chuck Hagenbuch
:Contact:       dev@lists.horde.org

.. contents:: Contents
.. section-numbering::

Indenting
=========

Use an indent of 4 spaces, with no tabs.


Control Structures
==================

These include ``if``, ``for``, ``while``, ``switch``, etc.  Here is an example
``if`` statement, since it is the most complicated of them::

  if ((condition1) || (condition2)) {
      action1;
  } elseif ((condition3) && (condition4)) {
      action2;
  } else {
      defaultaction;
  }

Multi-line if conditions are braced this way::

  if ((condition1) || (condition2) || (condition3) ||
      (condition4)) {
      action1;
  }

Control statements should have one space between the control keyword and
opening parenthesis, to distinguish them from function calls.

Do not omit the curly braces under any circumstance.  In the case of a large
number of short tests and actions, the following is acceptable::

  if (condition)   { action; }
  if (condition 2) { action 2; }
  ...

For switch statements::

  switch (condition) {
  case 1:
      action1;
      break;

  case 2:
      action2;
      break;

  default:
      defaultaction;
      break;
  }


Function Calls
==============

Functions should be called with no spaces between the function name, the
opening parenthesis, and the first parameter; spaces between commas and each
parameter, and no space between the last parameter, the closing parenthesis,
and the semicolon.  Here's an example::

  $var = foo($bar, $baz, $quux);

As displayed above, there should be one space on either side of an equals sign
used to assign the return value of a function to a variable.  In the case of a
block of related assignments, more space may be inserted to promote
readability::

  $short         = foo($bar);
  $long_variable = foo($baz);


Function Definitions
====================

Function declarations follow the "BSD/Allman" convention::

  function fooFunction($arg1, $arg2 = '')
  {
      if (condition) {
          statement;
      }
      return $val;
  }

Arguments with default values go at the end of the argument list.  Always
attempt to return a meaningful value from a function if one is appropriate.

Functions used only in the current script/class (e.g. private member methods)
should begin with a ``_`` character (e.g. ``_exampleLibrary``).  This helps
distinguish these private function calls from other, public function calls.


Class Definitions
=================

Class definitions follow the "K&R/Kernel" convention::

  class Some_Class {

      var $_variable;

      function fooFunction()
      {
          statement;
      }

  }

Note the blank lines at the beginning and end of the class definition.


Naming Libraries
================

Libraries (any file located in the ``lib/`` directory of the application)
should be named with capital letters at the beginning of each word.  Use
studlycaps for naming; a session cache class would be stored in
``lib/SessionCache.php``.

If the library/class is extended, the extending files should be stored in a
directory under ``lib/`` with the same name as the original library.
Subclasses follow the exact same naming requirements, except that if the
subclass is instantiated by a factory method, it should be all lowercase.

Example
-------

The "Example Library" library should be saved as ``lib/ExampleLibrary.php``.
Any file extending the library/class should be stored in the directory
``lib/ExampleLibrary/``.


Comments
========

Inline documentation for classes should follow the `Javadoc convention`_.

.. _Javadoc convention: http://java.sun.com/products/jdk/javadoc/writingdoccomments/index.html

Quick example for private variable definition for Horde::

    /**
     * Variable description.
     *
     * @var datatype
     */

Quick example function definition for Horde::

    /**
     * The description of the function goes here.
     *
     * @access [private | protected]
     * [Don't bother with "public" since it is the default if not specified.]
     *
     * @param datatype $variablename   Description of variable.
     * @param datatype $variable2name  Description of variable2.
     * ...
     * [Insert 2 spaces after the longest $variable definition, and then line
     *  up all descriptions with this description]
     *
     * @return datatype  Description of return value.
     * [Once again, insert 2 spaces after the datatype, and line up all
     *  subsequent lines, if any, with this character.]
     *
     * @abstract [Only if necessary]
     *
     * @since Horde x.x [Only if necessary - use if function is added to the
     * current release versions to indicate that the function has not been
     * available in previous versions.]
     */


Including Code
==============

If you are including a class, function library, or anything else which would
cause a parse error if included twice, always use `include_once`_.  This will
ensure that no matter how many factory methods we use or how much dynamic
inclusion we do, the library will only be included once.

If you are including a static filename, such as a conf file or a template that
is *always* used, use `require`_.

If you are dynamically including a filename, or want the code to only be used
conditionally (an optional template), use `include`_.

.. _include_once: http://www.php.net/manual/en/function.include-once.php
.. _require: http://www.php.net/manual/en/function.require.php
.. _include: http://www.php.net/manual/en/function.include.php


PHP Code Tags
=============

Always use ``<?php ?>`` to delimit PHP code, not the ``<? ?>`` shorthand.
This is required for PEAR compliance and is also the most portable way to
include PHP code on differing operating systems and setups.

In templates, make sure to use this as well (``<?php echo $varname ?>``), as
the shortcut version (``<?= $var ?>``) does not work with `short_open_tag`_
turned off.

.. _short_open_tag: http://www.php.net/manual/en/configuration.directives.php#ini.short-open-tag


Header Comment Blocks
=====================

All source code files in the Horde distribution should contain the following
comment block as the header:

Example for `LGPL`_'ed Horde code::

    /**
     * The Horde_Foo:: class provides an API for various foo
     * techniques that can be used by Horde applications.
     *
     * $Horde
     *
     * Copyright 1999-2001 Original Author <author@example.com>
     * Copyright 2001 Your Name <you@example.com>
     *
     * See the enclosed file COPYING for license information (LGPL). If you
     * did not receive this file, see http://www.fsf.org/copyleft/lgpl.html.
     *
     * @author  Original Author <author@example.com>
     * @author  Your Name <you@example.com>
     * @since   Horde 3.0
     * @package Horde_Package
     */

.. _LGPL: http://www.opensource.org/licenses/lgpl-license.php

Example for `GPL`_'ed application code::

    /**
     * The App_Bar:: class contains all functions related to handling
     * bars in App.
     *
     * $Horde
     *
     * Copyright 1999-2001 Original Author <author@example.com>
     * Copyright 2001 Your Name <you@example.com>
     *
     * See the enclosed file COPYING for license information (GPL). If you
     * did not receive this file, see http://www.fsf.org/copyleft/gpl.html.
     *
     * @author  Original Author <author@example.com>
     * @author  Your Name <you@example.com>
     * @since   App 1.0
     * @package app
     */


.. _GPL: http://www.opensource.org/licenses/gpl-license.php

There's no hard rule to determine when a new code contributer should be added
to the list of authors for a given source file.  In general, their changes
should fall into the "substantial" category (meaning somewhere around 10% to
20% of code changes).  Exceptions could be made for rewriting functions or
contributing new logic.

Simple code reorganization or bug fixes would not justify the addition of a
new individual to the list of authors.


CVS Tags
========

Include the <dollar>Horde: <dollar> CVS vendor tag in each file.  As each file
is edited, add this tag if it's not yet present (or replace existing forms
such as <dollar>Id<dollar>, "Last Modified:", etc.).

EXCEPTION: Don't include these in templates.


Example URLs
============

Use ``example.com`` for all example URLs, per `RFC 2606`_.

.. _RFC 2606: http://www.faqs.org/rfcs/rfc2606.html


php.ini settings
================

All Horde code should work with `register_globals`_ disabled.  This means
using ``$_COOKIE``, ``$_SESSION``, ``$_SERVER`` and ``$_ENV`` to access all
cookie, session, server and environment data, respectively.

To retrieve posted data (in the global ``$_GET`` and ``$_POST`` variables),
you should normally use `Util::getFormData()`_ which will automatically run
`Util::dispelMagicQuotes()`_. This will ensure that all Horde code will work
regardless of the setting of `magic_quotes_gpc`_. The only time you should not
use `Util::getFormData()`_ is if you want to directly access a GET or POST
variable instead; in this case, you should use `Util::getGet()`_ or
`Util::getPost()`_ respectively.

All Horde code should work with `error_reporting`_ = E_ALL. Failure to do so
would result in ugly output, error logs getting filled with lots of warning
messages, or even downright broken scripts.

No Horde code should assume that '.' is in the include path. Always specify
'./' in front of a filename when you are including a file in the same
directory.

.. _register_globals: http://www.php.net/manual/en/security.registerglobals.php
.. _magic_quotes_gpc: http://www.php.net/manual/en/ref.info.php#ini.magic-quotes-gpc
.. _error_reporting: http://www.php.net/manual/en/ref.errorfunc.php#ini.error-reporting
.. _Util::getFormData(): http://dev.horde.org/api/framework/Horde_Util/Util.html#methodgetFormData
.. _Util::dispelMagicQuotes(): http://dev.horde.org/api/framework/Horde_Util/Util.html#methoddispelMagicQuotes
.. _Util::getGet(): http://dev.horde.org/api/framework/Horde_Util/Util.html#methodgetGet
.. _Util::getPost(): http://dev.horde.org/api/framework/Horde_Util/Util.html#methodgetPost


XHTML 1.0 Compliance
====================

All tag names and parameters must be lower case including javascript event
handlers::

    <font color="#FFFFFF">...</font>
    <a href="http://example.com" onmouseover="status=''" onmouseout="status=''">...</a>

All tag parameters must be of a valid parameter="value" form (numeric values
must also be surrounded by quotes).  For parameters that had no value in HTML,
the parameter name is the value.  For example::

    <input type="checkbox" checked="checked" />
    <select name="example">
        <option selected="selected" value="1">Example</option>
    </select>
    <td nowrap="nowrap">Example</td>

All tags must be properly closed.  Tags where closing is forbidden must end
with a space and a slash::

    <br />
    <hr />
    <img src="example.gif" alt="Example" />
    <input type="submit" value="Example" />

All form definitions must be on their own line and either fully defined within
a ``<td></td>`` pair or be outside table tags.  Forms must also always have an
action parameter::

    <form method="post" action="http://example.com/example.cgi">
    <table>
        <tr><td>example</td></tr>
    </table>
    </form>

    <table>
        <tr><td>
            <form action="javascript:void(0)" onsubmit="return false;">
            </form>
        </td></tr>
    </table>

All JavaScript tags must have a valid type parameter::

    <script type="text/javascript">
    <!--
    ...
    // -->
    </script>

Nothing may appear after ``</html>``, therefore include any common footers
after all other output.

All images must have an ``alt`` attribute::

    <img src="example.gif" alt="<?php echo _("Example") ?>" />
    <?php echo Horde::img('example.gif', _("Example")) ?>                  (On the HEAD branch)
    <?php echo Horde::img('example.gif', 'alt="' . _("Example") . '"') ?>  (On the RELENG_2 branch)

Input fields of type "image" do not allow the border attribute and may render
with a border on some browsers.  Use the following instead::

   <a href="" onclick="document.formname.submit(); return false;"><?php echo Horde::img("example.gif", _("Example")) ?></a>


Database Naming Conventions
===========================

All database tables used by Horde resources and Horde applications need to
make sure that their table and field names work in all databases.  Many
databases reserve words like 'uid', 'user', etc. for internal use, and forbid
words that are SQL keywords (select, where, etc.).  Also, all names should be
lowercase, with underscores ('_') to separate words, to avoid case sensitivity
issues.

A good way to do this for field names is to make the field name
tablename_fieldname.

Other general guidelines: Table names should be plural (users); field names
should be singular (user_name).


Regular Expression Use
======================

Always use the `preg_`_ functions if possible instead of `ereg_`_ (and
`preg_split()`_ instead of `split()`_); they are included in PHP by default
and much more efficient and much faster than `ereg_`_.

**NEVER** use a regular expression to match or replace a static string.
`explode()`_ (in place of `split()`_), `str_replace()`_, `strpos()`_, or
`strtr()`_ do the job much more efficiently.

.. _preg_: http://www.php.net/manual/en/ref.pcre.php
.. _ereg_: http://www.php.net/manual/en/ref.regex.php
.. _preg_split(): http://www.php.net/manual/en/function.preg-split.php
.. _split(): http://www.php.net/manual/en/function.split.php
.. _explode(): http://www.php.net/manual/en/function.explode.php
.. _str_replace(): http://www.php.net/manual/en/function.str-replace.php
.. _strpos(): http://www.php.net/manual/en/function.strpos.php
.. _strtr(): http://www.php.net/manual/en/function.strtr.php


Parameter Passing
=================

Objects should be passed by reference.  Everything else, including arrays,
should be passed by value wherever semantically possible.

[Zend Engine 2: objects should also be passed by value]

This practice takes full advantage of reference counting.

.. Note:: The `ternary operator`_ automatically returns a copy of its
          operands, so don't use it with objects, or if you are sure you want
          to return an object copy.

.. _`ternary operator`: http://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary


Long Lines
==========

Wrap lines at 80 characters, including comments, unless this severely impacts
the clarity of the code.  Always wrap comments.


Line Breaks
===========

Only use UNIX style of linebreak (``\n``), not Windows/DOS/Mac style
(``\r\n``).

Using vim, to convert from DOS style type::

    :set ff=unix

Using vi, to convert from DOS style type::

    :g/^M/s///g

(Note that the ``^M`` is a control character, and to reproduce it when you
type in the vi command you have to pad it first using the special ``^V``
character.)


Private Variables
=================

Variables used exclusively within a class should begin with a underscore ('_')
character.  An example class variable definition:  ``var $_variablename;``


Array Definitions
=================

When defining arrays, or nested arrays, use the following format, where
indentation is noted via the closing parenthesis characters::

    $arrayname['index'] = array(
        'name1' => 'value1',
        'name2' => array(
            'subname1' => 'subvalue1',
            'subname2' => 'subvalue2'
        )
    );

The only exception should be for empty or short arrays that fit on one line,
which may be written as::

    $arrayname['index'] = array();


Internationalization (I18n)
===========================

Mark all strings presented to the user as gettext strings by calling the
gettext shortcut function (``_()``)::

    echo _("Hello world");

Don't use the gettext functions for strings that will be written to a log file
or otherwise presented to the administrator.

The String:: class contains several string manipulation methods that are, as
opposed to their PHP equivalents, locale and charset safe.

Use String::convertCharset() if you need to convert between different
character set encodings (for example, between user input and a storage backend
or data from an external source and the user interface).  You don't need to
care if the character sets are really different.

Use the String::lower() and String::upper() methods without a second
parameter if you need to perform a locale-independent string conversion.
That's the case for all strings that are further processed or interpreted by
code.  Use these methods with the second parameter set to true for strings
that need to be converted correctly according to the current (or specified)
character set.

Use the other String:: equivalents of PHP string functions to manipulate
strings correctly according to the current (or specified) character set but
use the PHP functions for code/machine processed strings.


Error checking
==============

Horde code should use `PEAR_Error`_ objects to return most error conditions
from library calls, and many times we will simply pass back a `PEAR_Error`_
object generated by an underlying library (such as Mail or PEAR DB).

For these cases, use the following style of code block to check for success
after any call which could generate an error condition::

    $result = $something->call('may error');
    if (is_a($result, 'PEAR_Error')) {
        // Handle error condition.
    } else {
        // Succeeded.
    }

Note that `is_a()`_ checks for subclasses of the named class, as well, so if
the object you get back is really a `DB_Error`_ object, this will still catch
it (since `DB_Error`_ extends `PEAR_Error`_).

Calling PEAR::isError() results in the same behavior, but is_a()
accomplishes the same result with a single native PHP function call.

.. _PEAR_Error: http://pear.php.net/manual/en/core.pear.pear-error.php
.. _DB_Error: http://pear.php.net/manual/en/package.database.db.db-error.php
.. _is_a(): http://www.php.net/manual/en/function.is-a.php


Existence checking
==================

Often you'll need to check whether or not a variable or property exists.
There are several cases here:

a. If you need to know if a variable exists at all and is not ``null``, use
`isset()`_::

    // Check to see if $param is defined.
    if (isset($param)) {
        // $param may be false, but it's there.
    }

b. If you need to know if a variable exists AND has a non-empty value (not
``null``, 0, ``false``, empty string or undefined), use !`empty()`_::

    // Make sure that $answer exists, is not an empty string, and is
    // not 0:
    if (!empty($answer)) {
        // $answer has some non-false content.
    } else {
        // (bool)$answer would be false.
    }

As pointed out in the comment of the else clause, `empty()`_ essentially does
the same check as `isset()`_ -- is this variable defined in the current scope?
-- and then, if it is, returns what the variable would evaluate to as a
boolean. This means that 0, while potentially valid input, is "empty" - so if
0 is valid data for your case, don't use !`empty()`_.

c. If you know you are working with a mixed variable then using just
`isset()`_ and `empty()`_ could cause unexpected results, for example if
testing for a key and the variable is actually a string::

    $foo = 'bar';
    if (isset($foo['somekey'])) {
        // This will evaluate to TRUE!
    }

If you know that there is a possibility of a mixed type variable the solution
in this case would be to add an `is_array()`_ check in the ``if()`` statement.

d. Use `array_key_exists()`_ when you want to check if an array key is defined
even if it has a value of ``null``::

    // Make sure we have a charset parameter. Value could also be null.
    if (!array_key_exists('charset', $params)) {
        Horde::fatal('Incomplete configuration.');
    }

Please note that `array_key_exists()`_ is a performance hit (25%-100%) and
should only be used when necessary. Instead try to use !`empty()`_ or
`isset()`_ instead.

.. _isset(): http://www.php.net/manual/en/function.isset.php
.. _empty(): http://www.php.net/manual/en/function.empty.php
.. _is_array(): http://www.php.net/manual/en/function.is-array.php
.. _array_key_exists(): http://www.php.net/manual/en/function.array-key-exists.php


Quotes
======

You should always use single quote (') characters around strings, except where
double quote (") characters are required.  All literal strings should be in
single quotes.  A comparison of single and double quote usage follows:

Single Quotes:
  * Variables in the string are not parsed or expanded.
  * New line symbols can be included as literal line ends (not recommended).
  * To include a single quote character, escape it with a ``\`` (backslash)
    character, as in: ``echo 'Here\'s an example';``
  * To specify a ``\`` (backslash) character, double it: ``echo 'c:\\temp';``

Double Quotes:
  * Parses and expands variables in the string.
  * Uses advanced (`sprintf`_-style) escape sequences like ``\n``, ``\$``,
    ``\t``, etc.
  * Should be used in the gettext shortcut ``_("")`` format.
  * Use with care, as many correct looking strings are really invalid.

The following are all incorrect::

    echo "Today is the $date['day'] of $date['month']"
    $_SESSION[index] = $_SESSION["old_index"];

.. _sprintf: http://www.php.net/sprintf


define()
========

Surprisingly enough, `define()`_ is a somewhat slow function in PHP (as of PHP
4.3.x) so excessive use is discouraged.

Using `define()`_ in classes should be OK - we will sacrifice a tiny bit of
speed for readability of code.  `define()`_ should NOT be used for actionIDs -
use a plain old string instead.  For anything else, use your best judgment.

Additionally, every constant should be prefixed with ``HORDE_``, its package
name, or the application name.

.. _define(): http://www.php.net/manual/en/function.define.php


Security Considerations
=======================

The following are a non-exhaustive list of features/functions to take
special care with:

PHP Code Execution:
-------------------

require, include, require_once, include_once - Carefully audit any
variables used in these functions, and check the source of any
constants as well.

eval - Obvious danger if user input is supplied to it in uncontrolled conditions.

preg_replace - The /e modifier causes the replacement string to be
evaluated as PHP code.

Command Execution:
------------------

exec - Executes a specified command and returns the last line of output.

passthru - Executes a specified command and writes the output to STDOUT.

`` (backticks) - Executes the specified command and returns all the
output in an array.

system - Like passthru() but doesn't handle binary data.

popen - Executes a specified command and connects its output or input
stream to a PHP file descriptor.

File Disclosure:
----------------

File functions which can be potentially used to open remote or
unintended files: fopen, readfile, file, file_get_contents.


Optimizations
=============

The following optimizations should be used, if possible:

extension_loaded()
------------------
This appears to be an expensive PHP call.  Use Util::extensionExists()
instead, which will cache the results of the call.

Concatenate strings
-------------------
Building a string with concatenation (the "." operator) using
single-quoted strings and variables is faster than using an
interpolated string (a string inside double quotes with variables
inside the string itself).  In addition, concatenation is easier to
read and audit for logic and security problems.

Pre-increment/decrement
-----------------------
Because of the way compilers/interpreters work, post-incrementing
($var++) requires storing both the original and new values of the
variable in memory because the old value may be used after the
operation in question is complete.  By comparison, pre-incrementing
(++$var) almost never needs to store both values.  It's a marginal
speedup but it's also simply changing the order of a few characters.

Loops
-----
Make sure that you do not continue to define the same variable within a
loop.  Instead, declare the variable a single time before the loop is run.

Array
-----
Avoid frequent array accesses.  If you use an array or an array member in a
loop, assign it to a variable first::

    $a = array('x' => 'y');
    $entries = array(...);

    $length = count($entries);
    $x = $a['x'];
    for ($i = 0; $i < $length; ++$i) {
        echo $x;
    }

User defined functions
----------------------
User defined functions are more expensive than "regular" functions.  Use them
only if they improve the code readability more then regular functions.

Disk I/O
--------
Disk read and write operations are slow.  If possible read and write files in
large chunks.  According to PHP documentation, file_get_contents() is
potentially much faster than using fopen()/fread()/fclose().


STDIN/STDOUT/STDERR
===================

To access either STDIN, STDOUT, or STDERR, the following code should be used::

    while (!feof([STDIN|STDOUT|STDERR])) {
        $line = fgets([STDIN|STDOUT|STDERR]);
        // process $line here
    }
