moodle-web-services

Moodle Web Services

Overview

Moodle exposes plugin functions as web services via db/services.php + classes/external/<fn>.php. Same function is callable as REST, AJAX, SOAP, or XMLRPC. Authentication is token-based for external clients, session-based for AJAX. All inputs/outputs are typed via external_value / external_single_structure / external_multiple_structure.

When to Use

• Adding a function callable from mobile app, AMD JS, or external system
• Defining a service (bundle of functions) for an external client
• Issuing/managing tokens
• Returning files via web service
• Debugging "Invalid response value" or "Missing required parameter"

Skip when: building UI-only PHP (no remote callers) — use moodle-plugin-development.

File layout

<plugin>/
  db/services.php                                # function + service definitions
  classes/external/get_items.php                 # one file per external function
  classes/external/get_items_returns.php         # (optional) split returns
  lang/en/<component>.php                        # service descriptions

db/services.php

<?php
defined('MOODLE_INTERNAL') || die();

$functions = [
    'local_example_get_items' => [
        'classname'    => 'local_example\external\get_items',
        'methodname'   => 'execute',                // default: 'execute'
        'description'  => 'Return items in a course',
        'type'         => 'read',                   // 'read' or 'write'
        'ajax'         => true,                     // callable from core/ajax
        'capabilities' => 'local/example:view',     // checked in addition to per-method checks
        'services'     => [MOODLE_OFFICIAL_MOBILE_SERVICE], // expose to mobile
    ],
    'local_example_mark_present' => [
        'classname'    => 'local_example\external\mark_present',
        'description'  => 'Mark a user present',
        'type'         => 'write',
        'ajax'         => true,
        'capabilities' => 'local/example:mark',
    ],
];

$services = [
    'Example REST API' => [
        'functions'         => array_keys($functions),
        'restrictedusers'   => 1,        // require explicit user assignment
        'enabled'           => 1,
        'shortname'         => 'local_example_api',
        'downloadfiles'     => 1,
        'uploadfiles'       => 0,
    ],
];

After editing: bump version.php, run php admin/cli/upgrade.php.

External function class

<?php
namespace local_example\external;
defined('MOODLE_INTERNAL') || die();

use core_external\external_api;
use core_external\external_function_parameters;
use core_external\external_value;
use core_external\external_single_structure;
use core_external\external_multiple_structure;

class get_items extends external_api {

    public static function execute_parameters(): external_function_parameters {
        return new external_function_parameters([
            'courseid' => new external_value(PARAM_INT, 'Course ID'),
            'limit'    => new external_value(PARAM_INT, 'Max items', VALUE_DEFAULT, 50),
        ]);
    }

    public static function execute(int $courseid, int $limit = 50): array {
        global $DB, $USER;

        // 1. Validate params (re-runs schema, normalizes types)
        $params = self::validate_parameters(self::execute_parameters(), [
            'courseid' => $courseid,
            'limit'    => $limit,
        ]);

        // 2. Validate context + capability
        $context = \context_course::instance($params['courseid']);
        self::validate_context($context);
        require_capability('local/example:view', $context);

        // 3. Business logic
        $rows = $DB->get_records('local_example_items',
            ['courseid' => $params['courseid']], 'timecreated DESC', '*', 0, $params['limit']);

        return array_values(array_map(fn($r) => [
            'id'   => (int)$r->id,
            'name' => format_string($r->name, true, ['context' => $context]),
            'time' => (int)$r->timecreated,
        ], $rows));
    }

    public static function execute_returns(): external_multiple_structure {
        return new external_multiple_structure(
            new external_single_structure([
                'id'   => new external_value(PARAM_INT, 'ID'),
                'name' => new external_value(PARAM_TEXT, 'Name'),
                'time' => new external_value(PARAM_INT, 'Created timestamp'),
            ])
        );
    }
}

Required ordering inside execute():

1. validate_parameters()
2. validate_context()
3. require_capability()
4. business logic
5. format output (format_string, format_text with context)

Skipping any of (1)-(3) is a security bug.

Moodle version notes

Moodle	Namespace
4.2+	core_external\external_api (etc.)
≤ 4.1	bare external_api (no namespace)

For 4.2+ compatibility wrappers, see lib/classes/external/.

Parameter types (PARAM_*)

Constant	Use
PARAM_INT	Integers
PARAM_FLOAT	Decimals
PARAM_BOOL	true/false
PARAM_TEXT	Plain text (strips tags)
PARAM_RAW	Untrusted text — use only if you re-format on output
PARAM_NOTAGS	Strips tags, keeps entities
PARAM_CLEANHTML	Sanitized HTML
PARAM_ALPHANUM	a-zA-Z0-9
PARAM_ALPHA	a-zA-Z
PARAM_USERNAME	Validates Moodle username
PARAM_EMAIL	Validates email
PARAM_URL	Validates URL
PARAM_FILE	Filename (no path)
PARAM_PATH	Path (no ..)
PARAM_COMPONENT	frankenstyle (local_example)
PARAM_CAPABILITY	local/example:view
PARAM_PLUGIN	<name> part
PARAM_AREA	File area names
PARAM_BASE64	Base64

VALUE_REQUIRED (default), VALUE_OPTIONAL (omit from response if null), VALUE_DEFAULT (with default).

Calling from REST

TOKEN=abcdef0123456789
SITE=https://moodle.example.com

curl -X POST "$SITE/webservice/rest/server.php" \
  -d "wstoken=$TOKEN" \
  -d "moodlewsrestformat=json" \
  -d "wsfunction=local_example_get_items" \
  -d "courseid=5" \
  -d "limit=10"

Response on error:

{"exception":"invalid_parameter_exception","errorcode":"invalidparameter","message":"..."}

Calling from AJAX (browser)

import Ajax from 'core/ajax';

const [items] = await Ajax.call([{
    methodname: 'local_example_get_items',
    args: {courseid: 5, limit: 10},
}]);

Requires 'ajax' => true in db/services.php. Session cookie auths; no token needed.

Token issuance

# Site admin > Server > Web services > Manage tokens
# or programmatically:

$service = $DB->get_record('external_services', ['shortname' => 'local_example_api']);
$token = \core_external\util::generate_token(
    EXTERNAL_TOKEN_PERMANENT,
    $service,
    $userid,
    \context_system::instance()
);

File uploads via web service

1. Upload to draft area: POST /webservice/upload.php?token=$T&filearea=draft&itemid=0
2. Returns itemid
3. Pass that itemid to your function via a PARAM_INT param
4. In execute(), move from draft to plugin area:

file_save_draft_area_files($params['draftitemid'], $context->id,
    'local_example', 'attachments', $itemid,
    ['subdirs' => 0, 'maxfiles' => 5]);

Service must have uploadfiles => 1.

File downloads

Set downloadfiles => 1 on service, serve via pluginfile.php. Token-authed clients append ?token=$T to pluginfile URLs.

Rate limiting

No built-in per-token rate limit. Options:

• \core\session\manager::is_loggedinas() checks
• Custom middleware via lib/setuplib.php hook
• Reverse-proxy rate limit (nginx limit_req)

Common Mistakes

Mistake	Fix
Skipping validate_parameters()	Always call first — ensures types match schema
Skipping validate_context()	Required for capability + permission scoping
Returning unformatted user text	Run through format_string() / format_text() with context
Schema mismatch in returns	Wrap response with clean_returnvalue in tests
Wrong namespace pre-4.2	Use external_api bare; for 4.2+ use core_external\external_api
'ajax' => true missing for browser calls	Calls fail with accessexception
Not bumping version.php after db/services.php change	Service won't register — bump + upgrade
Token user lacks required capability	require_capability fails — assign user to service or grant cap
restrictedusers => 1 but no users assigned	Site admin > Server > Web services > Authorised users
MOODLE_OFFICIAL_MOBILE_SERVICE exposes more than intended	Audit — only add functions safe for mobile app

Testing

// tests/external/get_items_test.php
$this->setUser($user);
$result = get_items::execute($course->id, 10);
$result = external_api::clean_returnvalue(get_items::execute_returns(), $result);
$this->assertCount(2, $result);

clean_returnvalue is mandatory — catches return schema bugs.

References

• Web services overview: https://moodledev.io/docs/apis/subsystems/external/services
• Writing a function: https://moodledev.io/docs/apis/subsystems/external/writing-a-function
• Calling from JS: https://moodledev.io/docs/apis/subsystems/external/writing-a-service#calling-from-javascript
• File uploads: https://moodledev.io/docs/apis/subsystems/external/files
• Token API: https://moodledev.io/docs/apis/subsystems/external/security