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Any collaborative project needs consistency and stability to stay strong.
This page is the top-level page describing Moodle's coding guidelines.  It's the place to start if you want to know how to write code for Moodle.


These '''coding guidelines''' are to provide a goal for all Moodle code to strive to. It's true that some of the older existing code falls short in a few areas, but it will all be fixed eventually. All new code definitely must adhere to these standards as closely as possible.
<p class="note">WARNING: Under construction RIGHT NOW!</p>


==General rules==


# All code files should use the .php extension.
 
# All template files should use the .html extension.
==Moodle architecture==
# All text files should use Unix-style text format (most text editors have this as an option).
 
# All php tags must be 'full' tags like <?php ?> ... not 'short' tags like <? ?>.
Moodle tries to run on the widest possible range of platforms, for the widest possible number of people, while remaining easy to install, use, upgrade and integrate with other systems.
# All existing copyright notices must be retained. You can add your own if necessary.
 
# Each file should include the main config.php file.
For more about this, see: [[Moodle architecture]].
# Each file should check that the user is authenticated correctly, using require_login() and isadmin(), isteacher(), iscreator() or isstudent().
 
# All access to databases should use the functions in ''lib/datalib.php'' whenever possible - this allows compatibility across a wide range of databases. You should find that almost anything is possible using these functions. If you must write SQL code then make sure it is: cross-platform; restricted to specific functions within your code (usually a lib.php file); and clearly marked.
==Plugins==
# Don't create or use global variables except for the standard $CFG, $SESSION, $THEME and $USER.
 
# All variables should be initialised or at least tested for existence using isset() or empty() before they are used.
Moodle has a general philosophy of modularity.  There are over 25 different types of plugins, however many of these plugin types work the same way.
# All strings should be translatable - create new texts in the "lang/en" files with concise English lowercase names and retrieve them from your code using get_string() or print_string().
 
# All help files should be translatable - create new texts in the "en/help" directory and call them using helpbutton(). If you need to update a help file:
For more about the structure of plugins, see [[Development:Plugins|Moodle plugins]].
#* with a minor change, where an old translation of the file would still make sense, then it's OK to make the change but you should notify translation AT moodle DOT org.
 
#* for a major change you should create a new file by adding an incrementing number (eg filename2.html) so that translators can easily see it's a new version of the file. Obviously the new code and the help index files should also be modified to point to the newest versions.
# Incoming data from the browser (sent via GET or POST) automatically has magic_quotes applied (regardless of the PHP settings) so that you can safely insert it straight into the database. All other raw data (from files, or from databases) must be escaped with addslashes() before inserting it into the database.
# IMPORTANT: All texts within Moodle, especially those that have come from users, should be printed using the format_text() function. This ensures that text is filtered and cleaned correctly.
==Coding style==
==Coding style==


I know it can be a little annoying to change your style if you're used to something else, but balance that annoyance against the annoyance of all the people trying later on to make sense of Moodle code with mixed styles. There are obviously many good points for and against any style that people use, but the current style just is, so please stick to it.
Consistent coding style is important in any development project, and particularly so when many developers are involved. A standard style helps to ensure that the code is easier to read and understand, which helps overall quality.
 
Writing your code in this way is an important step to having your code accepted by the Moodle community.
 
Our [[Development:Coding_style|Moodle coding style]] document explains this standard.
 
==Security==
 
Security is about protecting the interests and data of all our users.  Moodle may not be banking software, but it is still protecting a lot of sensitive and important data such as private discussions and grades from outside eyes (or student hackers!) as well as protecting our users from spammers and other internet predators.
 
It's also a script running on people's servers, so Moodle needs to be a responsible Internet citizen and not introduce vulnerabilities that could allow crackers to gain unlawful access to the server it runs on.
 
Any single script (in Moodle core or a third party module) can introduce a vulnerability to thousands of sites, so it's important that all developers strictly follow our [[Development:Security|Moodle security guidelines]].
 
==XHTML and CSS==
 
It's important that Moodle produces strict, well-formed XHTML code, compliant with all common accessibility guidelines (such as W3C WAG).
 
CSS should be used for layout. Moodle comes with several themes installed. The 'standard' theme, which should be a plain theme suitable to act as a building block for other themes. That should contain the minimal styling to make Moodle look OK and be function. Then Moodle comes with several other default themes that look good and demonstrate various techniques for building themes.
 
This helps consistency across browsers in a nicely-degrading way (especially those using non-visual or mobile browsers), as well as improving life for theme designers.
 
Full information is here:  [[Development:XHTML|Moodle XHTML]]
 
==JavaScript==
 
In general, everything in Moodle should work with JavaScript turned off in your browser.  If you do have JavaScript enabled it should only improve usability (not add features).
 
This is important for accessibility, and in line with the principles of unobtrusive JavaScript and progressive enhancement.
 
See the [[Development:JavaScript guidelines|Moodle JavaScript guidelines]] for more information.
 
==Internationalisation==
 
Moodle works in over 84 languages because we pay great attention to keeping the language strings and locale information separate from the code, in language packs.
 
The default language for all code, comments and documentation, however, is English (AU).
 
Full details:  [[Development:Internationalisation|Moodle Internationalisation]]
 
==Accessibility==
 
Moodle should work well for the widest possible range of people.


1. Indenting should be consistently 4 spaces. Don't use tabs AT ALL.
See: [[Development:Accessibility|Moodle Accessibility]]


2. Variable names should always be easy-to-read, meaningful lowercase English words. If you really need more than one word then run them together, but keep them short as possible. Use plural names for arrays of objects.
==Usability==


      GOOD: $quiz
See [[Development:Interface_guidelines| Interface Guidelines]] (under construction)
      GOOD: $errorstring
      GOOD: $assignments (for an array of objects)
      GOOD: $i (but only in little loops)


      BAD: $Quiz
==Performance==
      BAD: $aReallyLongVariableNameWithoutAGoodReason
      BAD: $error_string


3. Constants should always be in upper case, and always start with the name of the module. They should have words separated by underscores.
The load any Moodle site can cope with will, of course, depend on the server and network hardware that it is running on.


      define("FORUM_MODE_FLATOLDEST", 1);
The most important property is scalability, so a small increase in the number of users, courses, activities in a course, and so on, only causes a correspondingly small increase in server load.
4. Function names should be simple English lowercase words, and start with the name of the module to avoid conflicts between modules. Words should be separated by underscores. Parameters should always have sensible defaults if possible. Note there is no space between the function name and the following (brackets).


      function forum_set_display_mode($mode=0) {
For more information and advice, see [[Development:Performance and scalability|Performance and scalability]].
          global $USER, $CFG;


          if ($mode) {
==Database==
              $USER->mode = $mode;
          } else if (empty($USER->mode)) {
              $USER->mode = $CFG->forum_displaymode;
          }
      }


5. Blocks must always be enclosed in curly braces (even if there is only one line). Moodle uses this style:
Moodle has a powerful database abstraction layer that we wrote ourselves, called [[Development:XMLDB_Documentation|XMLDB]]. This lets the same Moodle code work on MySQL, PostgreSQL, Oracle and MSSQL.


      if ($quiz->attempts) {
We have tools and API for [[Development:DDL functions|defining and modifying tables]] as well as [[Development:DML functions|methods for getting data in and out]] of the database.
          if ($numattempts > $quiz->attempts) {
              error($strtoomanyattempts, "view.php?id=$cm->id");
          }
      }


6. Strings should be defined using single quotes where possible, for increased speed.
Overview: [[Development:Database|Moodle Database]] guidelines


      $var = 'some text without any variables';
==Events==
      $var = "with special characters like a new line \n";
      $var = 'a very, very long string with a '.$single.' variable in it';
      $var = "some $text with $many variables $within it";


7. Comments should be added as much as is practical, to explain the code flow and the purpose of functions and variables.
Moodle allows inter-module communication via '''events'''. Modules can '''trigger''' specific events and other modules can choose to '''handle''' those events.


* Every function (and class) should use the popular [http://www.phpdoc.org/ phpDoc format]. This allows code documentation to be generated automatically.
Full information:  [[Development:Events_API|Moodle Events API]]
* Inline comments should use the // style, laid out neatly so that it fits among the code and lines up with it.


      /**
==Unit tests==
      * The description should be first, with asterisks laid out exactly
      * like this example. If you want to refer to a another function,
      * do it like this: {@link clean_param()}. Then, add descriptions
      * for each parameter as follows.
      *
      * @param int $postid The PHP type is followed by the variable name
      * @param array $scale The PHP type is followed by the variable name
      * @param array $ratings The PHP type is followed by the variable name
      * @return mixed
      */
      function forum_get_ratings_mean($postid, $scale, $ratings=NULL) {
          if (!$ratings) {
              $ratings = array();    // Initialize the empty array
              if ($rates = get_records("forum_ratings", "post", $postid)) {
                  // Process each rating in turn
                  foreach ($rates as $rate) {
      ....etc


8. Space should be used liberally - don't be afraid to spread things out a little to gain some clarity. Generally, there should be one space between brackets and normal statements, but no space between brackets and variables or functions:
[http://en.wikipedia.org/wiki/Unit_testing Unit testing] is not simply a technique but a philosophy of software development.


      foreach ($objects as $key => $thing) {
The idea is to create automatable tests for each bit of functionality that you are developing (at the same time you are developing it).  This not only helps everyone later test that the software works, but helps the development itself, because it forces you to work in a modular way with very clearly defined structures and goals.
          process($thing);
      }


      if ($x == $y) {
Moodle uses a library called simpletest (not very extensively yet though!) that makes writing unit tests fairly simple.  Our unit testing is currently not deep but we want to improve this.
          $a = $b;
      } else if ($x == $z) {
          $a = $c;
      } else {
          $a = $d;
      }


==Database structures==
Full information here:  [[Development:Unit_tests|Moodle Unit Tests]]


# Every table must have an auto-incrementing id field (INT10) as primary index. (see [[IdColumnReasons]])
== See also ==
# The main table containing instances of each module must have the same name as the module (eg widget) and contain the following minimum fields:
* [http://doku.clausvb.de/php_coding_standard.htm General PHP coding standards]
#* id - as described above
* [http://pear.php.net/manual/en/standards.php PEAR coding standards]
#* course - the id of the course that each instance belongs to
#* name - the full name of each instance of the module
# Other tables associated with a module that contain information about 'things' should be named widget_things (note the plural).
# Column names should be simple and short, following the same rules as for variable names.
# Where possible, columns that contain a reference to the id field of another table (eg widget) should be called widgetid. (Note that this convention is newish and not followed in some older tables)
# Boolean fields should be implemented as small integer fields (eg INT4) containing 0 or 1, to allow for later expansion of values if necessary.
# Most tables should have a timemodified field (INT10) which is updated with a current timestamp obtained with the PHP time() function.


==Security issues (and handling form and URL data)==


# Do not rely on 'register_globals'. Every variable must be properly initialised in every code file. It must be obvious where the variable came from
[[Category:Coding guidelines|Coding]]
# Initialise all arrays and objects, even if empty. $a = array() or $obj = new stdClass();.
# Do not use the optional_variable() function (this function is now deprecated). Use the optional_param() function instead. Pick the correct PARAM_XXXX value for the data type you expect.
# Do not use the require_variable() function (this function is now deprecated). Use the required_param() function instead. Pick the correct PARAM_XXXX value for the data type you expect.
# Use data_submitted(), with care. Data must still be cleaned before use.
# Do not use $_GET, $_POST or $_REQUEST. Use the appropriate required_param() or optional_param() appropriate to your need.
# Do not check for an action using something like if (isset($_GET['something'])). Use, e.g., $something = optional_param( 'something',-1,PARAM_INT ) and then perform proper test for it being in its expected range of values e.g., if ($something>=0) {....
# Wherever possible group all your required_param(), optional_param() and other variables initialisation at the beginning of each file to make them easy to find.
# Use 'sesskey' mechanism to protect form handling routines from attack. Basic example of use: when form is generated, include <input type="hidden" name="sesskey" value="<?php echo sesskey(); ?>" />. When you process the form check with if (!confirm_sesskey()) {error('Bad Session Key');}.
# All filenames must be 'cleaned' using the clean_filename() function, if this has not been done already by appropriate use of required_param() or optional_param()
# Any data read from the database must have addslashes() applied to it before it can be written back. A whole object of data can be hit at once with addslashes_object().
# Wherever possible, data to be stored in the database must come from POST data (from a form with method="POST") as opposed to GET data (ie, data from the URL line).
# Do not use data from $_SERVER if you can avoid it. This has portability issues.
# If it hasn't been done somewhere else, make sure all data written to the database has been through the clean_param() function using the appropriate PARAM_XXXX for the datatype.
# If you write custom SQL code, make very sure it is correct. In particular watch out for missing quotes around values. Possible SQL 'injection' exploit.
# Check all data (particularly that written to the database) in every file it is used. Do not expect or rely on it being done somewhere else.
# Blocks of code to be included should contain a definite PHP structure (e.g, a class declaration, function definition(s) etc.) - straight blocks of code promote uninitialised variable usage.


[[Category:Core]]
[[es:Manual de Estilo de Código]]
[[Category:Developer]]
[[ja:コーディング]]
[[zh:代码指南]]
[[pl:Kodowanie]]
[[pt:manual_de_codigo]]
[[fr:Développement:Directives_de_codage]]

Latest revision as of 08:00, 14 May 2010

This page is the top-level page describing Moodle's coding guidelines. It's the place to start if you want to know how to write code for Moodle.

WARNING: Under construction RIGHT NOW!


Moodle architecture

Moodle tries to run on the widest possible range of platforms, for the widest possible number of people, while remaining easy to install, use, upgrade and integrate with other systems.

For more about this, see: Moodle architecture.

Plugins

Moodle has a general philosophy of modularity. There are over 25 different types of plugins, however many of these plugin types work the same way.

For more about the structure of plugins, see Moodle plugins.

Coding style

Consistent coding style is important in any development project, and particularly so when many developers are involved. A standard style helps to ensure that the code is easier to read and understand, which helps overall quality.

Writing your code in this way is an important step to having your code accepted by the Moodle community.

Our Moodle coding style document explains this standard.

Security

Security is about protecting the interests and data of all our users. Moodle may not be banking software, but it is still protecting a lot of sensitive and important data such as private discussions and grades from outside eyes (or student hackers!) as well as protecting our users from spammers and other internet predators.

It's also a script running on people's servers, so Moodle needs to be a responsible Internet citizen and not introduce vulnerabilities that could allow crackers to gain unlawful access to the server it runs on.

Any single script (in Moodle core or a third party module) can introduce a vulnerability to thousands of sites, so it's important that all developers strictly follow our Moodle security guidelines.

XHTML and CSS

It's important that Moodle produces strict, well-formed XHTML code, compliant with all common accessibility guidelines (such as W3C WAG).

CSS should be used for layout. Moodle comes with several themes installed. The 'standard' theme, which should be a plain theme suitable to act as a building block for other themes. That should contain the minimal styling to make Moodle look OK and be function. Then Moodle comes with several other default themes that look good and demonstrate various techniques for building themes.

This helps consistency across browsers in a nicely-degrading way (especially those using non-visual or mobile browsers), as well as improving life for theme designers.

Full information is here: Moodle XHTML

JavaScript

In general, everything in Moodle should work with JavaScript turned off in your browser. If you do have JavaScript enabled it should only improve usability (not add features).

This is important for accessibility, and in line with the principles of unobtrusive JavaScript and progressive enhancement.

See the Moodle JavaScript guidelines for more information.

Internationalisation

Moodle works in over 84 languages because we pay great attention to keeping the language strings and locale information separate from the code, in language packs.

The default language for all code, comments and documentation, however, is English (AU).

Full details: Moodle Internationalisation

Accessibility

Moodle should work well for the widest possible range of people.

See: Moodle Accessibility

Usability

See Interface Guidelines (under construction)

Performance

The load any Moodle site can cope with will, of course, depend on the server and network hardware that it is running on.

The most important property is scalability, so a small increase in the number of users, courses, activities in a course, and so on, only causes a correspondingly small increase in server load.

For more information and advice, see Performance and scalability.

Database

Moodle has a powerful database abstraction layer that we wrote ourselves, called XMLDB. This lets the same Moodle code work on MySQL, PostgreSQL, Oracle and MSSQL.

We have tools and API for defining and modifying tables as well as methods for getting data in and out of the database.

Overview: Moodle Database guidelines

Events

Moodle allows inter-module communication via events. Modules can trigger specific events and other modules can choose to handle those events.

Full information: Moodle Events API

Unit tests

Unit testing is not simply a technique but a philosophy of software development.

The idea is to create automatable tests for each bit of functionality that you are developing (at the same time you are developing it). This not only helps everyone later test that the software works, but helps the development itself, because it forces you to work in a modular way with very clearly defined structures and goals.

Moodle uses a library called simpletest (not very extensively yet though!) that makes writing unit tests fairly simple. Our unit testing is currently not deep but we want to improve this.

Full information here: Moodle Unit Tests

See also

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