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| {{Moodle_2.0}} | | {{Template:Migrated|newDocId=/docs/apis/subsystems/external/writing-a-service}} |
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| = Quick start =
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| == Example ==
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| Have a look to the [https://github.com/moodlehq/moodle-local_wstemplate web service plugin template]. This plugin contains a web service hello_world function. To make testing easy for you, the plugin is distributed with a test client in the folder /client.
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| == File structure ==
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| The file structure is explained in these two documents:
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| * [[Web_services_API|Web services API]]
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| * [[External_functions_API|External function API]]
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| = Tutorial =
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| We will create a web service into a local plugin. This service will contain one ''local_myplugin_create_groups($groups)'' web service function. This web service function will create a group into a Moodle course.
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| == Write the specification documentation ==
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| Before starting coding, let's identify our needs writing some short specification documents.
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| === functional specification===
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| ''local_myplugin_create_groups($groups)'' will take a list of groups as parameters and it will return the same groups with their newly created id. If ever one group creation fails, the function will throw an exception, and no creation will happen.
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| === technical specification ===
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| * '''the core function the external function will call''': ''groups_create_group()'' from [http://cvs.moodle.org/moodle/group/ /group/lib.php].
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| * '''the parameter types''': a list of object. This object are groups, with id/name/courseid.
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| * '''the returned value types''': a list of objects (groups) with their id.
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| * '''the user capabilities to check''': ''moodle/course:managegroups''
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| == Write a simple test client ==
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| The first thing you should code is a web service test client. You will often discover use cases that you didn't think about. We are not showing any test client code here, see [[Creating_a_web_service_client|How to create a web service client]].
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| == Declare the service ==
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| This step is optional. You can pre-build a service including any web service functions, so the Moodle administrator doesn't need to do it. Add into /local/myplugin/db/services.php:
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| <code php>
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| $services = array(
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| 'mypluginservice' => array( //the name of the web service
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| 'functions' => array ('local_myplugin_create_groups'), //web service functions of this service
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| 'requiredcapability' => '', //if set, the web service user need this capability to access
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| //any function of this service. For example: 'some/capability:specified'
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| 'restrictedusers' =>0, //if enabled, the Moodle administrator must link some user to this service
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| //into the administration
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| 'enabled'=>1, //if enabled, the service can be reachable on a default installation
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| )
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| );
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| </code>
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| Note: it is not possible for an administrator to add/remove any function from a pre-built service.
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| == Declare the web service function ==
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| Following the [[Web_services_API|Web service API]], you must declare the web service function in the ''local/myplugin/db/services.php'' file.
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| <code php>
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| $functions = array(
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| 'local_myplugin_create_groups' => array( //web service function name
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| 'classname' => 'local_myplugin_external', //class containing the external function
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| 'methodname' => 'create_groups', //external function name
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| 'classpath' => 'local/myplugin/externallib.php', //file containing the class/external function
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| 'description' => 'Creates new groups.', //human readable description of the web service function
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| 'type' => 'write', //database rights of the web service function (read, write)
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| ),
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| );
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| </code>
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| Web service functions should match the [https://docs.moodle.org/dev/Web_services_Roadmap#Naming_convention naming convention].
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| == Write the external function descriptions ==
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| Every web service function is mapped to an external function. External function are described in the [[External_functions_API|External functions API]].
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| Each external function is written with two other functions describing the parameters and the return values. These description functions are used by web service servers to:
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| * validate the web service function parameters
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| * validate the web service function returned values
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| * build WSDL files or other protocol documents
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| These two description functions are located in the same file and the same class mentioned in local/myplugin/db/services.php.
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| Thus for the web service function '''local_myplugin_create_groups()''', we need write a class named '''local_myplugin_external''' in the file '''local/myplugin/externallib.php'''. The class will contain:
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| * create_groups(...)
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| * create_groups_parameters()
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| * create_groups_return()
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| === create_groups_parameters() ===
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| <code php>
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| require_once("$CFG->libdir/externallib.php");
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| class local_myplugin_external extends external_api {
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| /**
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| * Returns description of method parameters
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| * @return external_function_parameters
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| */
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| public static function create_groups_parameters() {
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| return new external_function_parameters(
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| array(
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| 'groups' => new external_multiple_structure(
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| new external_single_structure(
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| array(
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| 'courseid' => new external_value(PARAM_INT, 'id of course'),
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| 'name' => new external_value(PARAM_TEXT, 'multilang compatible name, course unique'),
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| 'description' => new external_value(PARAM_RAW, 'group description text'),
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| 'enrolmentkey' => new external_value(PARAM_RAW, 'group enrol secret phrase'),
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| )
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| )
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| )
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| )
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| );
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| }
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| </code>
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| A web service function without parameters will have a parameter description function like that:
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| <code php>
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| /**
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| * Returns description of method parameters
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| * @return external_function_parameters
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| */
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| public static function functionname_parameters() {
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| return new external_function_parameters(
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| array(
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| //if I had any parameters, they would be described here. But I don't have any, so this array is empty.
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| )
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| );
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| }
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| </code>
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| A parameter can be described as:
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| * a list => external_multiple_structure
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| * an object => external_single_structure
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| * a primary type => external_value
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| Our create_groups() function expects one parameter named ''groups'', so we will first write:
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| <code php>
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| /**
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| * Returns description of method parameters
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| * @return external_function_parameters
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| */
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| public static function create_groups_parameters() {
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| return new external_function_parameters(
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| array(
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| 'groups' => ...
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|
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| )
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| );
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| }
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| </code>
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| This ''groups'' parameter is a list of group. So we will write :
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| <code php>
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| 'groups' => new external_multiple_structure(
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| ...
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| )
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| </code>
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| An external_multiple_structure object (list) can be constructed with:
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| * ''external_multiple_structure'' (list)
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| * ''external_single_structure'' (object)
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| * ''external_value'' (primary type).
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| For our function it will be a ''external_single_structure'':
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| <code php>
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| new external_single_structure(
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| array(
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| 'courseid' => ...,
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| 'name' => ...,
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| 'description' => ...,
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| 'enrolmentkey' => ...,
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| )
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| )
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| </code>
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| Thus we obtain :
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| <code php>
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| 'groups' => new external_multiple_structure(
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| new external_single_structure(
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| array(
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| 'courseid' => ...,
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| 'name' => ...,
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| 'description' => ...,
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| 'enrolmentkey' => ...,
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| )
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| )
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| )
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| </code>
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| Each group values is a ''external_value'' (primary type):
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| * ''courseid'' is an integer
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| * ''name'' is a string (text only, not tag)
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| * ''description'' is a string (can be anything)
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| * ''enrolmentkey'' is also a string (can be anything)
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| We add them to the description :
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| <code php>
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| 'groups' => new external_multiple_structure(
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| new external_single_structure(
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| array(
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| 'courseid' => new external_value(PARAM_INT, 'id of course'), //the second argument is a human readable description text. This text is displayed in the automatically generated documentation.
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| 'name' => new external_value(PARAM_TEXT, 'multilang compatible name, course unique'),
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| 'description' => new external_value(PARAM_RAW, 'group description text'),
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| 'enrolmentkey' => new external_value(PARAM_RAW, 'group enrol secret phrase'),
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| )
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| )
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| )
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| </code>
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| === create_groups_returns() ===
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| It's similar to create_groups_parameters(), but instead of describing the parameters, it describes the return values.
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| <code php>
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| public static function create_groups_returns() {
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| return new external_multiple_structure(
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| new external_single_structure(
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| array(
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| 'id' => new external_value(PARAM_INT, 'group record id'),
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| 'courseid' => new external_value(PARAM_INT, 'id of course'),
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| 'name' => new external_value(PARAM_TEXT, 'multilang compatible name, course unique'),
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| 'description' => new external_value(PARAM_RAW, 'group description text'),
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| 'enrolmentkey' => new external_value(PARAM_RAW, 'group enrol secret phrase'),
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| )
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| )
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| );
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| }
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| </code>
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| === Required, Optional or Default value ===
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| A value can be VALUE_REQUIRED, VALUE_OPTIONAL, or VALUE_DEFAULT. If not mentioned, a value is VALUE_REQUIRED by default.
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| <code php>
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| 'yearofstudy' => new external_value(PARAM_INT, 'year of study',VALUE_DEFAULT, 1979),
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| </code>
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| * VALUE_REQUIRED - if the value is not supplied => the server throws an error message
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| * VALUE_OPTIONAL - if the value is not supplied => the value is ignored. Note that VALUE_OPTIONAL can't be used in parameters, it must be used only in array/objects key definition. If you need Optional parameters you should use VALUE_DEFAULT instead.
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| * VALUE_DEFAULT - if the value is not supplied => the default value is used
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| Note: Because some web service protocols are strict about the number and types of arguments - it is not possible to specify an optional parameter as one of the top-most parameters for a function. Examples:
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| Not cool:
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| <code php>
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| public static function get_biscuit_parameters() {
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| return new external_function_parameters(
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| array(
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| 'chocolatechips' => new external_value(PARAM_BOOL, PARAM_REQUIRED),
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| 'glutenfree' => new external_value(PARAM_BOOL, PARAM_DEFAULT, false),
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| 'icingsugar' => new external_value(PARAM_BOOL, VALUE_OPTIONAL), // ERROR! top level optional parameter!!!
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| )
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| );
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| }
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|
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| </code>
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| Cool:
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| <code php>
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| public static function get_biscuit_parameters() {
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| return new external_function_parameters(
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| array(
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| 'ifeellike' => new external_single_structure(
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| array(
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| 'chocolatechips' => new external_value(PARAM_BOOL, VALUE_REQUIRED),
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| 'glutenfree' => new external_value(PARAM_BOOL, PARAM_DEFAULT, false),
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| 'icingsugar' => new external_value(PARAM_BOOL, VALUE_OPTIONAL), // ALL GOOD!! We have nested the params in a external_single_structure.
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| )
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| )
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| )
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| );
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| }
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|
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| </code>
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| == Implement the external function ==
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| We declared our web service function and we defined the external function parameters and return values. We will now implement the external function:
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| <code php>
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| /**
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| * Create groups
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| * @param array $groups array of group description arrays (with keys groupname and courseid)
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| * @return array of newly created groups
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| */
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| public static function create_groups($groups) { //Don't forget to set it as static
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| global $CFG, $DB;
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| require_once("$CFG->dirroot/group/lib.php");
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| $params = self::validate_parameters(self::create_groups_parameters(), array('groups'=>$groups));
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| $transaction = $DB->start_delegated_transaction(); //If an exception is thrown in the below code, all DB queries in this code will be rollback.
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| $groups = array();
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| foreach ($params['groups'] as $group) {
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| $group = (object)$group;
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| if (trim($group->name) == '') {
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| throw new invalid_parameter_exception('Invalid group name');
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| }
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| if ($DB->get_record('groups', array('courseid'=>$group->courseid, 'name'=>$group->name))) {
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| throw new invalid_parameter_exception('Group with the same name already exists in the course');
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| }
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| // now security checks
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| $context = get_context_instance(CONTEXT_COURSE, $group->courseid);
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| self::validate_context($context);
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| require_capability('moodle/course:managegroups', $context);
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| // finally create the group
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| $group->id = groups_create_group($group, false);
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| $groups[] = (array)$group;
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| }
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| $transaction->allow_commit();
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| return $groups;
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| }
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| </code>
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| === Parameter validation ===
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| <code php>
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| $params = self::validate_parameters(self::create_groups_parameters(), array('groups'=>$groups));
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| </code>
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| This ''validate_parameters'' function validates the external function parameters against the description. It will return an exception if some required parameters are missing, if parameters are not well-formed, and check the parameters validity. It is essential that you do this call to avoid potential hack.
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| '''Important:''' the parameters of the external function and their declaration in the description '''must be the same order'''. In this example we have only one parameter named $groups, so we don't need to worry about the order.
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| === Context and Capability checks ===
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| <code php>
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| /// now security checks
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| $context = context_course::instance($group->courseid);
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| self::validate_context($context);
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| require_capability('moodle/course:managegroups', $context);
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| </code>
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| Note: validate_context() is required in all external functions before operating on any data belonging to a context. This function does sanity and security checks on the context that was passed to the external function - and sets up the global $PAGE and $OUTPUT for rendering return values. Do NOT use require_login(), or $PAGE->set_context() in an external function.
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| === Exceptions===
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| You can throw exceptions. There are automatically handle by Moodle web service servers.
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| <code php>
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| //Note: it is good practice to add detailled information in $debuginfo,
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| // and only send back a generic exception message when Moodle DEBUG mode < NORMAL.
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| // It's what we do here throwing the invalid_parameter_exception($debug) exception
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| throw new invalid_parameter_exception('Group with the same name already exists in the course');
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| </code>
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| === Correct return values ===
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| The return values will be validated by the Moodle web service servers:
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| * return values contain some values not described => these values will be skipped.
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| * return values miss some required values (VALUE_REQUIRED) => the server will return an error.
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| * return values types don't match the description (int != PARAM_ALPHA) => the server will return an error
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| '''Note:''' cast all your returned objects into arrays.
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| == Making web service accessible through Apache Thrift ==
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| This step is optional. If you wish to generate SDK for different programming languages and platforms using [http://thrift.apache.org Apache Thrift framework] then [https://bitbucket.org/hhteam/moodle_thrift_tools/wiki/Home Moodle Thrift tools] can help you.
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| Two steps should be performed:
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| * Generate .thrift files for Moodle API using thriftgenerator script.
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| * Generate thrift handlers for PHP and copy the php files generated to your plugin source tree.
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| It is also recommended to include thrift files into the distribution of your plugin in order to simplify creation of client bindings for the users of your API.
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| That's it. Now the web API of your plugin is accessible through Apache Thrift Framework.
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| == Bump the plugin version ==
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| Edit your local/myplugin/version.php and increase the plugin version. This should trigger a Moodle upgrade and the new web service should be available in the administration (''Administration > Plugins > Web Services > Manage services'')
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| =See also=
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| * [[Web_services|Web services developer documentation]]
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| * [[:en:Web_services|Web services user documentation]]
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| * [[Creating_a_web_service_client|Implement a web service client]]
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| Specification:
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| * [[External services security]]
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| * [[External services description]]
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| [[Category:Web Services]]
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| [[Category:Plugins]]
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