==========================
 Horde 4 Coding Standards
==========================

:Authors:       Jon Parise, Chuck Hagenbuch
:Contact:       dev@lists.horde.org

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

Indenting/Whitespace
====================

Use an indent of 4 spaces, with no tabs.  Remove all trailing whitespace.  If
using vim, the following .vimrc code will highlight trailing whitespace in
red::

  highlight WhitespaceEOL ctermbg=red guibg=red
  match WhitespaceEOL /\s\+$/


Language Case
=============

When working with PHP statements, constructs or keywords, lowercase text is
required. This does not apply to classes provided by PHP, which should be
written as they are in the PHP manual (e.g. `DOMDocument::createCDATASection`_)

.. _DOMDocument::createCDATASection: http://us.php.net/manual/en/domdocument.createcdatasection.php


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);

The "@" operator can be used to silence any errors that a function call may
generate. This should be used with caution, as any fatal errors will be
completely transparent to the user. Only use "@" to silence functions that,
e.g., emit warnings when the data input is incorrect (such as unserialize()).


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 or protected)
should begin with a ``_`` character (e.g. ``_exampleLibrary``).  This helps
distinguish these private functions from other, publicly available functions.


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

Class definitions also follow the "BSD/Allman" convention::

  class Some_Class
  {
      /**
       *
       */
      var $_variable;

      public function fooFunction()
      {
          statement;
      }

  }

Note the blank line at the 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.

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 `phpDocumentor conventions`_.

.. _phpDocumentor conventions: http://phpdoc.org/

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.
     *
     * @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.]
     *
     * @since Horde x.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. @since is only needed if the function
     * has been added after the last major point release - e.g. x.0.]
     */


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

You should not explicitly include or require classes. Horde provides an
autoloader library, so the class should be autoloaded. This will allow
maximum flexibility in managing class libraries.

For all other includes (configuration files, data files, etc.) use `include`_.

.. _autoload: http://php.net/autoload
.. _include: http://php.net/include


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.

Files should never end with a closing '?>'. This is redundant and can allow
whitespace added to the end of a file to cause PHP to send headers early.

.. _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.
     *
     * Copyright 2009-2011 The Horde Project (http://www.horde.org/)
     *
     * 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>
     * @category Horde
     * @package  Package
     * @license  http://www.fsf.org/copyleft/lgpl.html LGPL
     * @since    Horde 4.0.1 [only if needed]
     */

.. _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.
     *
     * Copyright 2009-2011 The Horde Project (http://www.horde.org/)
     *
     * 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>
     * @category Horde
     * @package  App
     * @license  http://www.fsf.org/copyleft/gpl.html GPL
     * @since    App 1.0.1 [only if needed]
     */


.. _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.


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

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

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


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

Horde code MUST NOT use global variables set by EGPCS (Environment, GET, POST,
Cookie, Server) data.  Instead, the magic variables ``$_ENV``, ``$_GET``,
``$_POST``, $_COOKIE``, and ``$_SERVER`` must be used instead.

To retrieve posted data (in the global ``$_GET`` and ``$_POST`` variables),
you should normally use `Horde_Util::getFormData()`_ which will automatically
run `Horde_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 `Horde_Util::getFormData()`_ is if you want to directly access
a GET or POST variable instead; in this case, you should use
`Horde_Util::getGet()`_ or `Horde_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.

.. _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
.. _Horde_Util::getFormData(): http://dev.horde.org/api/framework/Horde_Util/Horde_Util.html#methodgetFormData
.. _Horde_Util::dispelMagicQuotes(): http://dev.horde.org/api/framework/Horde_Util/Horde_Util.html#methoddispelMagicQuotes
.. _Horde_Util::getGet(): http://dev.horde.org/api/framework/Horde_Util/Horde_Util.html#methodgetGet
.. _Horde_Util::getPost(): http://dev.horde.org/api/framework/Horde_Util/Horde_Util.html#methodgetPost


HTML 4 Compliance
====================

All Horde libraries and applications that generate content to be sent to a web
browser are expected to generate HTML 4 compliant syntax.  This is a change from
earlier mandates to use XHTML 1.0.

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 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")) ?>

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 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).

Try to use portable data types and avoid RDBMS specific SQL scripts as much as
possible. Portable types are INTEGER, SMALLINT, NUMERIC(4,0) (for TINYINT),
NUMERIC(p,s), VARCHAR(n), CHAR(n), FLOAT, and REAL. See
http://home.fnal.gov/~dbox/SQL_API_Portability.html and
http://articles.techrepublic.com.com/5100-10878_11-1045051.html for more
information.

Other portability guidlines: Always use the database abstraction layer's
capabilities for result set pagination ('LIMIT' is not portable). Also, do not
use the 'AS' keyword for table aliases.

In SQL queries, keywords should be capitalized.

In table creation statements, SQL keywords and datatypes should be
capitalized. Also, 'DEFAULT' constraints should be listed before 'NOT NULL'
constraints for maximum portability. 'NOT NULL' constraints should not use an
empty string for the 'DEFAULT' constraint.

Identifiers should not be longer than 30 characters.


Oracle Database Scripts
-----------------------

For maximum portability with several Oracle versions, Oracle-specific database
scripts are necessary. Coming from MySQL, use the following data types:

* VARCHAR2 for VARCHAR
* NUMBER(16) for INT(EGER)
* NUMBER(8) for SMALLINT
* NUMBER(1) for boolean flags (TINYINT)
* CLOB or VARCHAR2(4000) for TEXT
* DATE for DATETIME

See http://download.oracle.com/docs/html/B10257_01/ch3.htm for more
information.

Identifiers must not be longer than 30 characters. This is easily exceeded
with some of the index names.

'DEFAULT' constraints must always preceed 'NOT NULL' constraints. 'NOT NULL'
constraints must not use an empty string for the 'DEFAULT' constraint.

Instead of using `ALTER TABLE table CHANGE column column spec...` use `ALTER
TABLE table MODIFY column spec...`.


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

Always use the `preg_`_ functions instead of `ereg_`_ (and
`preg_split()`_ instead of `split()`_); they are included in PHP by default
and are faster than `ereg_`_; `ereg_`_ is also deprecated in PHP 5.3+.

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

In addition, when doing replacement or regex matching on large
strings, if you don't know if the target string contains the text to
be matched or replaced, it is often a performance win to use
`strpos()`_ to check first. Then, only if the text to be matched or
replaced is present, go ahead and do the more memory intensive string
manipulation.

.. _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
=================

Parameters should be passed by value wherever semantically possible.
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 unless you are sure you want
          to return an object copy.

If at all possible, the number of optional arguments to a function should be
limited.  If optional arguments are needed, it is usually best to have the
last parameter be an array which contains the list of optional arguments.
This also eases future expansion since new options can be added without
changing the API.

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


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

The optimal line length is 80 characters, including comments. The maximum line
length is 100 characters unless this severely impacts the clarity of the
code. When deciding where to wrap, aim for readability, understanding that
different developers will have different views on this. Always wrap comments
and leave at least 2 spaces at the right margin (in other words, wrap at 78
characters).


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: ``protected
$_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();
    $arrayvar = array('foo1' => 'bar1');


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

Use Horde_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 Horde_String::lower() and Horde_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 Horde_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 throw ``Horde_Exception`` objects (or equivalent Exception
derivatives) to report errors.  The calling code should either explicitly
catch the exception and handle it or else the Horde-wide exception handler
will handle the exception, display an error message, and exit the script.

    try {
        $result = $something->call('may error');
        // Succeeded.
    } catch (Horde_Exception $e) {
        // Handle error condition.
    }

Do NOT return PEAR_Error objects. Any PEAR_Error objects should be converted
to a Horde_Exception before throwing.

When throwing a Horde_Exception the error message provided should not be
localized.

Throwing exceptions is expensive, so use them carefully for logic flow. You
should cache results of Horde::callHook() calls for example, if you expect them
to not exist.


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 want to know if a variable is a non-empty string, including 0, you
   have to use `strlen()`_. This only works with strings or scalars that
   automatically cast to strings without problems::

   // Make sure that $str is a non-empty string. $str must exist, so add an
   // additional check with isset() if necessary.
   if (strlen($str)) {
       // $str has a non-zero length.
   } else {
       // $str is an empty string '', or null.
   }

d. 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.

e. 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)) {
        throw new Horde_Exception('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
.. _strlen(): http://www.php.net/manual/en/function.strlen.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 incorrect::

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

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


define()
========

`define()`_ is a somewhat slow function in PHP (as of PHP 4.3.x) so excessive
use is discouraged.  Every constant created by ``define()`` should be prefixed
with ``HORDE_``, its package name, or the application name.

Class constants should be defined inside the class using the ``const``
keyword.


.. _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 and create_function - 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 Horde_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.

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.

Additionally, for large amounts of data, do not use foreach() loops, as PHP
will make an additional copy in memory of every element of the array when
traversing.  Instead, use either array_shift, a for() loop, or the
next()/each() functions.  (NOTE: As of PHP 5, it is possible to indicate that
the values should be provided to the interior of the loop by reference,
thereby eliminating the need to create a copy of the value.)

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;
    }

Don't use array_unique().  The following is reported to be 20 times faster::

    $unique = array_keys(array_flip($foo));

Even better, if possible rework the algorithm to store the unique data in the
key and then call array_keys($foo) to return the unique list.

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.

Dynamically created functions (eval and create_function)
--------------------------------------------------------
Code executed with eval, and functions created with create_function,
are essentially PHP code that the engine has to parse every time it is
run. This code is impossible to cache with an opcode cache, and even
without one is slower than regular PHP code. Because they also have
security risks, they should be avoided if at all possible.

Disk I/O
--------
Disk read and write operations are slow.  If possible read and write files in
large chunks.  According to the 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
    }
