<?php
final class Example extends PhabricatorApplication {
	public function getName() {
		return pht('My Example');
	}
	public function getBaseURI() {
		return '/example/';
	}
	public function getIcon() {
		return 'fa-star';
	}
	public function getShortDescription() {
		return pht('Example extension');
	}
	public function getTitleGlyph() {
		return '\xE2\x98\x85';
	}
	public function getApplicationGroup() {
		return self::GROUP_UTILITIES;
	}
	public function getRoutes() {
		return array(
			'/example/' => array(
				'.*' => 'exampleController'
			)
		);
	}
}

<?php
final class ExampleController extends PhabricatorController {
  public function handleRequest(AphrontRequest $request) {
    $request = $this->getRequest();
    $viewer = $request->getViewer();
    $user = $request->getUser();
    $viewer_spaces = PhabricatorSpacesNamespaceQuery::getViewerSpaces($user);

    $base64_data = base64_decode('iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==');

    // Set the options for the new file
    $options = array(
      'name' => 'my_image.png',
      'viewPolicy' => PhabricatorPolicies::POLICY_USER,
      'mime-type' => 'image/png',
    );

    // Create the new file object
    $file = PhabricatorFile::newFromFileData($base64_data, $options);

    $response = new AphrontFileResponse();
    $response->setCacheDurationInSeconds(60*60*24*30);
    $response->setContent($base64_data);
    $response->setMimeType('image/png');
    return $response;
  }
}

[Sun Jun 11 11:19:55.205192 2023] [php:notice] [::1:45810] [2023-06-11 09:19:55] EXCEPTION: (RuntimeException) strncmp(): Passing null to parameter #1 ($string1) of type string is deprecated at [<arcanist>/src/error/PhutilErrorHandler.php:261]
[Sun Jun 11 11:19:55.205432 2023] [php:notice] [::1:45810] arcanist(head=master, ref.master=b325304b6e52), diagramsnet(), example(), phorge(head=master, ref.master=7b57ba2b982f, custom=1)
[Sun Jun 11 11:19:55.205438 2023] [php:notice] [::1:45810]   #0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer) called at [<arcanist>/src/error/PhutilErrorHandler.php:261]
[Sun Jun 11 11:19:55.205441 2023] [php:notice] [::1:45810]   #1 <#2> strncmp(NULL, string, integer) called at [<phorge>/src/applications/auth/engine/PhabricatorAuthCSRFEngine.php:50]
[Sun Jun 11 11:19:55.205443 2023] [php:notice] [::1:45810]   #2 <#2> PhabricatorAuthCSRFEngine::isValidToken(NULL) called at [<phorge>/src/applications/people/storage/PhabricatorUser.php:985]
[Sun Jun 11 11:19:55.205445 2023] [php:notice] [::1:45810]   #3 <#2> PhabricatorUser::validateCSRFToken(NULL) called at [<phorge>/src/aphront/AphrontRequest.php:348]
[Sun Jun 11 11:19:55.205447 2023] [php:notice] [::1:45810]   #4 <#2> AphrontRequest::validateCSRF() called at [<phorge>/src/aphront/writeguard/AphrontWriteGuard.php:167]
[Sun Jun 11 11:19:55.205449 2023] [php:notice] [::1:45810]   #5 <#2> AphrontWriteGuard::willWrite() called at [<phorge>/src/infrastructure/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:305]
[Sun Jun 11 11:19:55.205451 2023] [php:notice] [::1:45810]   #6 <#2> AphrontBaseMySQLDatabaseConnection::checkWrite(string) called at [<phorge>/src/infrastructure/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:193]
[Sun Jun 11 11:19:55.205462 2023] [php:notice] [::1:45810]   #7 <#2> AphrontBaseMySQLDatabaseConnection::executeQuery(PhutilQueryString) called at [<phorge>/src/infrastructure/storage/xsprintf/queryfx.php:8]
[Sun Jun 11 11:19:55.205465 2023] [php:notice] [::1:45810]   #8 <#2> queryfx(AphrontMySQLiDatabaseConnection, string, PhutilQueryString, PhabricatorFileStorageBlob, array, array) called at [<phorge>/src/infrastructure/storage/connection/AphrontDatabaseConnection.php:58]
[Sun Jun 11 11:19:55.205467 2023] [php:notice] [::1:45810]   #9 <#2> AphrontDatabaseConnection::query(string, PhutilQueryString, PhabricatorFileStorageBlob, array, array) called at [<phorge>/src/infrastructure/storage/lisk/LiskDAO.php:1117]
[Sun Jun 11 11:19:55.205469 2023] [php:notice] [::1:45810]   #10 <#2> LiskDAO::insertRecordIntoDatabase(string) called at [<phorge>/src/infrastructure/storage/lisk/LiskDAO.php:954]
[Sun Jun 11 11:19:55.205471 2023] [php:notice] [::1:45810]   #11 <#2> LiskDAO::insert() called at [<phorge>/src/infrastructure/storage/lisk/LiskDAO.php:923]
[Sun Jun 11 11:19:55.205473 2023] [php:notice] [::1:45810]   #12 <#2> LiskDAO::save() called at [<phorge>/src/applications/files/engine/PhabricatorMySQLFileStorageEngine.php:55]
[Sun Jun 11 11:19:55.205475 2023] [php:notice] [::1:45810]   #13 <#2> PhabricatorMySQLFileStorageEngine::writeFile(string, array) called at [<phorge>/src/applications/files/storage/PhabricatorFile.php:553]
[Sun Jun 11 11:19:55.205478 2023] [php:notice] [::1:45810]   #14 <#2> PhabricatorFile::writeToEngine(PhabricatorMySQLFileStorageEngine, string, array) called at [<phorge>/src/applications/files/storage/PhabricatorFile.php:380]
[Sun Jun 11 11:19:55.205480 2023] [php:notice] [::1:45810]   #15 phlog(RuntimeException) called at [<phorge>/src/applications/files/storage/PhabricatorFile.php:395]
[Sun Jun 11 11:19:55.205482 2023] [php:notice] [::1:45810]   #16 PhabricatorFile::buildFromFileData(string, array) called at [<phorge>/src/applications/files/storage/PhabricatorFile.php:449]
[Sun Jun 11 11:19:55.205484 2023] [php:notice] [::1:45810]   #17 PhabricatorFile::newFromFileData(string, array) called at [<phorge>/src/extensions/example/src/controller/ExampleController.php:18]
[Sun Jun 11 11:19:55.205486 2023] [php:notice] [::1:45810]   #18 ExampleController::handleRequest(AphrontRequest) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:284]
[Sun Jun 11 11:19:55.205488 2023] [php:notice] [::1:45810]   #19 AphrontApplicationConfiguration::processRequest(AphrontRequest, PhutilDeferredLog, AphrontPHPHTTPSink, MultimeterControl) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:203]
[Sun Jun 11 11:19:55.205490 2023] [php:notice] [::1:45810]   #20 AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phorge>/webroot/index.php:35]

public function handleRequest(AphrontRequest $request) {
  $viewer = $request->getViewer();

  // NOTE: Throws if valid CSRF token is not present in the request.
  $request->validateCSRF();