API Add AbsoluteLink method to RequestHandler

This is a method that is commonly implemented on controllers, but
it really doesn't need to be.

src/Control/RequestHandler.php

@@ -551,10 +551,13 @@ public function setRequest(HTTPRequest $request): static
     }
 
     /**
-     * Returns a link to this controller. Overload with your own Link rules if they exist.
+     * Returns a link to this controller.
+     * Returns null if no link could be generated.
+     *
+     * Overload with your own Link rules if they exist.
      *
      * @param string $action Optional action
-     * @return string
+     * @return ?string
      */
     public function Link($action = null)
     {
@@ -576,6 +579,22 @@ public function Link($action = null)
         return null;
     }
 
+    /**
+     * Get the absolute URL for this controller, including protocol and host.
+     * Returns null if no link could be generated.
+     *
+     * @param string $action See {@link Link()}
+     * @return ?string
+     */
+    public function AbsoluteLink($action = '')
+    {
+        $link = $this->Link($action);
+        if ($link === null) {
+            return null;
+        }
+        return Director::absoluteURL((string) $link);
+    }
+
     /**
      * Redirect to the given URL.
      */

tests/php/Control/RequestHandlerTest.php

@@ -0,0 +1,97 @@
+<?php
+
+namespace SilverStripe\Control\Tests;
+
+use SilverStripe\Control\Controller;
+use SilverStripe\Control\Director;
+use SilverStripe\Control\RequestHandler;
+use SilverStripe\Dev\SapphireTest;
+
+/**
+ * Tests for the RequestHandler class
+ */
+class RequestHandlerTest extends SapphireTest
+{
+    protected $usesDatabase = false;
+
+    public function provideTestLink(): array
+    {
+        return [
+            // If there's no url segment, there's no link
+            [
+                'urlSegment' => null,
+                'action' => null,
+                'expected' => null,
+            ],
+            [
+                'urlSegment' => null,
+                'action' => 'some-action',
+                'expected' => null,
+            ],
+            // The action is just addeed on after the url segment
+            [
+                'urlSegment' => 'my-controller',
+                'action' => null,
+                'expected' => 'my-controller',
+            ],
+            [
+                'urlSegment' => 'my-controller',
+                'action' => 'some-action',
+                'expected' => 'my-controller/some-action',
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider provideTestLink
+     */
+    public function testLink(?string $urlSegment, ?string $action, ?string $expected)
+    {
+        if ($urlSegment === null) {
+            $this->expectWarning();
+            $this->expectWarningMessage('Request handler SilverStripe\Control\RequestHandler does not have a url_segment defined. Relying on this link may be an application error');
+        }
+
+        $handler = new RequestHandler();
+        RequestHandler::config()->set('url_segment', $urlSegment);
+        Controller::config()->set('add_trailing_slash', false);
+
+        $this->assertEquals($expected, $handler->Link($action));
+
+        // Validate that trailing slash config is respected
+        Controller::config()->set('add_trailing_slash', true);
+        if (is_string($expected)) {
+            $expected .= '/';
+        }
+
+        $this->assertEquals($expected, $handler->Link($action));
+    }
+
+    /**
+     * @dataProvider provideTestLink
+     */
+    public function testAbsoluteLink(?string $urlSegment, ?string $action, ?string $expected)
+    {
+        if ($urlSegment === null) {
+            $this->expectWarning();
+            $this->expectWarningMessage('Request handler SilverStripe\Control\RequestHandler does not have a url_segment defined. Relying on this link may be an application error');
+        }
+
+        $handler = new RequestHandler();
+        RequestHandler::config()->set('url_segment', $urlSegment);
+        Controller::config()->set('add_trailing_slash', false);
+
+        if ($expected !== null) {
+            $expected = Director::absoluteURL($expected);
+        }
+        $this->assertEquals($expected, $handler->AbsoluteLink($action));
+
+        // Validate that trailing slash config is respected
+        Controller::config()->set('add_trailing_slash', true);
+        if (is_string($expected)) {
+            $expected = Director::absoluteURL($expected . '/');
+        }
+
+        $this->assertEquals(Director::absoluteURL($expected), $handler->AbsoluteLink($action));
+    }
+}

tests/php/Control/RequestHandlingTest.php

@@ -17,7 +17,7 @@
 use SilverStripe\Security\SecurityToken;
 
 /**
- * Tests for RequestHandler and HTTPRequest.
+ * Tests for functionality related to handling requests - not unit tests for RequestHandler.
  * We've set up a simple URL handling model based on
  */
 class RequestHandlingTest extends FunctionalTest