feat: add S3-compatible storage provider (MinIO, Ceph, R2, etc.)

Adds a new 'S3-Compatible Storage' provider that works with any
S3-API-compatible object storage service, including MinIO, Ceph,
Cloudflare R2, Backblaze B2, and others.

Changes:
- New provider class: classes/providers/storage/s3-compatible-provider.php
  - Provider key: s3compatible
  - Reads user-configured endpoint URL from settings
  - Uses path-style URL access (required by most S3-compatible services)
  - Supports credentials via AS3CF_S3COMPAT_ACCESS_KEY_ID /
    AS3CF_S3COMPAT_SECRET_ACCESS_KEY wp-config.php constants
  - Disables AWS-specific features (Block Public Access, Object Ownership)
- New provider SVG icons (s3compatible.svg, -link.svg, -round.svg)
- Registered provider in main plugin class with endpoint setting support
- Updated StorageProviderSubPage to show endpoint URL input for S3-compatible
- Built pro settings bundle with rollup (Svelte 4.2.19)
- Added package.json and updated rollup.config.mjs for pro-only builds

classes/settings/delivery-check.php

@@ -0,0 +1,300 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings;
+
+use DeliciousBrains\WP_Offload_Media\Items\Provider_Test_Item;
+use DeliciousBrains\WP_Offload_Media\Items\Upload_Handler;
+use DeliciousBrains\WP_Offload_Media\Items\Remove_Provider_Handler;
+use Amazon_S3_And_CloudFront;
+use AS3CF_Utils;
+use Exception;
+use WP_Error as AS3CF_Result;
+
+class Delivery_Check extends Domain_Check {
+	/**
+	 * @var Amazon_S3_And_CloudFront
+	 */
+	private $as3cf;
+
+	/**
+	 * @var string
+	 */
+	private $local_file_path = '';
+
+	/**
+	 * @var string
+	 */
+	private $test_file_name = '';
+
+	/**
+	 * @var Provider_Test_Item|null
+	 */
+	private $as3cf_item;
+
+	/**
+	 * Class constructor.
+	 *
+	 * @param Amazon_S3_And_CloudFront $as3cf
+	 */
+	public function __construct( Amazon_S3_And_CloudFront $as3cf ) {
+		parent::__construct( '' );
+		$this->as3cf = $as3cf;
+	}
+
+	/**
+	 * Class destructor.
+	 */
+	public function __destruct() {
+		$this->remove_test_files();
+	}
+
+	/**
+	 * Create a test file & to upload to the storage provider.
+	 *
+	 * @param bool $is_private
+	 *
+	 * @return AS3CF_Result
+	 */
+	public function setup_test_file( bool $is_private ): AS3CF_Result {
+		if ( empty( $this->as3cf_item ) || $this->as3cf_item->is_private() !== (bool) $is_private ) {
+			$mode = $is_private ? __( 'Private', 'amazon-s3-and-cloudfront' ) : __( 'Public', 'amazon-s3-and-cloudfront' );
+
+			if ( ! $this->create_local_file( $is_private ) ) {
+				return new AS3CF_Result(
+					Validator_Interface::AS3CF_STATUS_MESSAGE_WARNING,
+					sprintf(
+						_x(
+							'Delivery provider status cannot be determined. An error was encountered while attempting to create a temporary file for %1$s delivery.',
+							'amazon-s3-and-cloudfront'
+						),
+						$mode
+					)
+				);
+			}
+
+			if ( ! $this->upload_file( $is_private ) ) {
+				$this->remove_test_files();
+
+				return new AS3CF_Result(
+					Validator_Interface::AS3CF_STATUS_MESSAGE_WARNING,
+					sprintf(
+						_x(
+							'Delivery provider status cannot be determined. An error was encountered while attempting to offload a temporary file for %1$s delivery.',
+							'amazon-s3-and-cloudfront'
+						),
+						$mode
+					)
+				);
+			}
+		}
+
+		return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_SUCCESS );
+	}
+
+	/**
+	 * Access a public file.
+	 *
+	 * @return AS3CF_Result
+	 */
+	public function test_public_file_access(): AS3CF_Result {
+		// Protect against improper use of this method.
+		if ( empty( $this->as3cf_item ) || false !== $this->as3cf_item->is_private() ) {
+			return new AS3CF_Result(
+				Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR,
+				__( 'Internal error', 'amazon-s3-and-cloudfront' )
+			);
+		}
+
+		$url = $this->as3cf_item->get_provider_url();
+
+		if ( is_wp_error( $url ) ) {
+			return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR, $url->get_error_message() );
+		}
+
+		$this->domain = AS3CF_Utils::parse_url( $url, PHP_URL_HOST );
+
+		try {
+			$this->check_dns_resolution();
+			$response = $this->dispatch_request( $url );
+			$this->check_response_code( wp_remote_retrieve_response_code( $response ) );
+		} catch ( Exception $e ) {
+			return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR, $e->getMessage() );
+		}
+
+		return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_SUCCESS );
+	}
+
+	/**
+	 * Access a private file.
+	 *
+	 * @return AS3CF_Result
+	 */
+	public function test_private_file_access(): AS3CF_Result {
+		// Protect against improper use of this method.
+		if ( empty( $this->as3cf_item ) || false === $this->as3cf_item->is_private() ) {
+			return new AS3CF_Result(
+				Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR,
+				__( 'Internal error', 'amazon-s3-and-cloudfront' )
+			);
+		}
+
+		// Attempt to access the file with the standard (signed) URL.
+		$url = $this->as3cf_item->get_provider_url();
+
+		if ( is_wp_error( $url ) ) {
+			return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR, $url->get_error_message() );
+		}
+
+		$this->domain = AS3CF_Utils::parse_url( $url, PHP_URL_HOST );
+
+		try {
+			$this->check_dns_resolution();
+			$response = $this->dispatch_request( $url );
+			$this->check_response_code( (int) wp_remote_retrieve_response_code( $response ) );
+		} catch ( Exception $e ) {
+			return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR, $e->getMessage() );
+		}
+
+		return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_SUCCESS );
+	}
+
+	/**
+	 * Access a private file using an unsigned URL.
+	 *
+	 * @return AS3CF_Result
+	 */
+	public function test_private_file_access_unsigned(): AS3CF_Result {
+		// Protect against improper use of this method.
+		if ( empty( $this->as3cf_item ) || false === $this->as3cf_item->is_private() ) {
+			return new AS3CF_Result(
+				Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR,
+				__( 'Internal error', 'amazon-s3-and-cloudfront' )
+			);
+		}
+
+		// Remove the signing parameters from the URL.
+		$url = $this->as3cf->maybe_remove_query_string( $this->as3cf_item->get_provider_url() );
+
+		if ( is_wp_error( $url ) ) {
+			return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR, $url->get_error_message() );
+		}
+
+		try {
+			$this->check_dns_resolution();
+			$response = $this->dispatch_request( $url );
+
+			// This should throw in an exception.
+			$this->check_response_code( (int) wp_remote_retrieve_response_code( $response ) );
+
+			// If we're still here it's no good.
+			return new AS3CF_Result(
+				Validator_Interface::AS3CF_STATUS_MESSAGE_WARNING,
+				__( 'Private file accessible using an unsigned URL.', 'amazon-s3-and-cloudfront' )
+			);
+		} catch ( Exception $e ) {
+			// Accessing a private file using an unsigned URL failed, this is actually success.
+			return new AS3CF_Result( Validator_Interface::AS3CF_STATUS_MESSAGE_SUCCESS );
+		}
+	}
+
+	/**
+	 * Upload a file to the storage provider.
+	 *
+	 * @param bool $is_private
+	 *
+	 * @return bool
+	 */
+	private function upload_file( bool $is_private ): bool {
+		// Use a bucket key with no dynamic parts.
+		$bucket_path = $this->as3cf->get_object_prefix() . $this->test_file_name;
+
+		$extra_info = array(
+			'objects' => array(
+				Provider_Test_Item::primary_object_key() => array(
+					'source_file' => basename( $this->local_file_path ),
+					'is_private'  => $is_private,
+				),
+			),
+		);
+
+		$this->as3cf_item = new Provider_Test_Item(
+			$this->as3cf->get_storage_provider()->get_provider_key_name(),
+			$this->as3cf->get_setting( 'region' ),
+			$this->as3cf->get_setting( 'bucket' ),
+			$bucket_path,
+			$is_private,
+			0,
+			$this->local_file_path,
+			null,
+			$extra_info
+		);
+
+		$upload_handler = new Upload_Handler( $this->as3cf );
+
+		add_filter( 'upload_mimes', array( $this, 'allow_txt_offload' ) );
+		$upload_result = $upload_handler->handle( $this->as3cf_item );
+		remove_filter( 'upload_mimes', array( $this, 'allow_txt_offload' ) );
+
+		if ( true !== $upload_result ) {
+			$this->remove_test_files();
+
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * Ensure txt files can be offloaded.
+	 *
+	 * @handles upload_mimes
+	 *
+	 * @param array $mime_types
+	 *
+	 * @return array
+	 */
+	public function allow_txt_offload( array $mime_types ): array {
+		if ( empty( $mime_types['txt'] ) ) {
+			$mime_types['txt'] = 'text/plain';
+		}
+
+		return $mime_types;
+	}
+
+	/**
+	 * Remove created test files both locally and on the storage provider.
+	 */
+	public function remove_test_files() {
+		if ( file_exists( $this->local_file_path ) ) {
+			unlink( $this->local_file_path );
+		}
+
+		if ( ! is_null( $this->as3cf_item ) ) {
+			$item_remover = new Remove_Provider_Handler( $this->as3cf );
+			$item_remover->handle( $this->as3cf_item );
+			$this->as3cf_item = null;
+		}
+	}
+
+	/**
+	 * Create local file with unique file name.
+	 *
+	 * @param bool $is_private
+	 *
+	 * @return bool
+	 */
+	private function create_local_file( bool $is_private ): bool {
+		if ( ! empty( $this->local_file_path ) ) {
+			$this->remove_test_files();
+		}
+
+		$uploads_dir = wp_get_upload_dir();
+		$visibility  = $is_private ? 'private' : 'public';
+
+		$this->test_file_name  = "as3cf-delivery-check-$visibility-" . time() . '.txt';
+		$this->local_file_path = $uploads_dir['basedir'] . '/' . $this->test_file_name;
+		$file_contents         = __( 'This is a test file to check delivery. Delete me if found.', 'amazon-s3-and-cloudfront' );
+
+		return (bool) file_put_contents( $this->local_file_path, $file_contents );
+	}
+}

classes/settings/domain-check.php

@@ -0,0 +1,338 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings;
+
+use AS3CF_Utils;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Domain_Check_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\HTTP_Response_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Invalid_Response_Code_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Invalid_Response_Type_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Malformed_Query_String_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Malformed_Response_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\S3_Bucket_Origin_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Ssl_Connection_Exception;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Unresolveable_Hostname_Exception;
+use Exception;
+use InvalidArgumentException;
+use Requests_Utility_CaseInsensitiveDictionary;
+use WP_Error;
+use WP_Http;
+
+class Domain_Check {
+	/**
+	 * @var string domain / hostname
+	 */
+	protected $domain = '';
+
+	/**
+	 * @var bool
+	 */
+	private $dns_checked;
+
+	/**
+	 * @var array Validated domain cache
+	 */
+	private static $validated = array();
+
+	/**
+	 * Domain_Check constructor.
+	 *
+	 * @param string $domain
+	 */
+	public function __construct( string $domain ) {
+		$this->domain = $domain;
+	}
+
+	/**
+	 * Get the domain that was checked.
+	 *
+	 * @return string
+	 */
+	public function domain(): string {
+		return $this->domain;
+	}
+
+	/**
+	 * Validate the domain looks like a real domain.
+	 *
+	 * @throws InvalidArgumentException
+	 */
+	public function validate() {
+		if ( ! is_string( $this->domain ) ) {
+			throw new InvalidArgumentException(
+				sprintf(
+					__( 'Domain must be a string, [%s] given.', 'amazon-s3-and-cloudfront' ),
+					gettype( $this->domain )
+				)
+			);
+		}
+
+		if ( ! trim( $this->domain ) ) {
+			throw new InvalidArgumentException(
+				__( 'Domain cannot be blank.', 'amazon-s3-and-cloudfront' )
+			);
+		}
+
+		if ( preg_match( '/[^a-z0-9-\.]/i', $this->domain ) ) {
+			throw new InvalidArgumentException(
+				__( 'Domain can only contain letters, numbers, hyphens (-), and periods (.)', 'amazon-s3-and-cloudfront' )
+			);
+		}
+
+		if ( $this->domain === parse_url( network_home_url(), PHP_URL_HOST ) ) {
+			throw new InvalidArgumentException(
+				sprintf(
+					__( '<code>%s</code> must not be the same as the site domain. Use a subdomain instead.', 'amazon-s3-and-cloudfront' ),
+					$this->domain
+				)
+			);
+		}
+	}
+
+	/**
+	 * Validate the domain looks like a real domain and return a description of
+	 * any issue found or an empty string if no issue was found.
+	 *
+	 * Convenience function for validate() and check_dns_resolution() that doesn't throw exceptions.
+	 *
+	 * @return string
+	 */
+	public function get_validation_issue(): string {
+		try {
+			$this->validate();
+			$this->check_dns_resolution();
+		} catch ( Exception $e ) {
+			return $e->getMessage();
+		}
+
+		return '';
+	}
+
+	/**
+	 * Check if the given domain passes all validation.
+	 *
+	 * @param string $domain
+	 *
+	 * @return bool
+	 */
+	public static function is_valid( string $domain ): bool {
+		if ( isset( self::$validated[ $domain ] ) ) {
+			return self::$validated[ $domain ];
+		}
+
+		$check = new static( $domain );
+
+		try {
+			$check->validate();
+
+			self::$validated[ $domain ] = true;
+		} catch ( Exception $e ) {
+			self::$validated[ $domain ] = false;
+		}
+
+		return self::$validated[ $domain ];
+	}
+
+	/**
+	 * Test that the given URL works and returns a response that looks like
+	 * a REST response.
+	 *
+	 * @param string $url
+	 *
+	 * @return array
+	 *
+	 * @throws Domain_Check_Exception
+	 */
+	public function test_rest_endpoint( string $url ): array {
+		$this->validate();
+		$this->check_dns_resolution();
+
+		$response = $this->dispatch_request( $url );
+
+		$this->check_response_headers( wp_remote_retrieve_headers( $response ) );
+		$this->check_response_code( wp_remote_retrieve_response_code( $response ) );
+		$this->check_response_type( wp_remote_retrieve_header( $response, 'content-type' ) );
+		$this->check_response_body( wp_remote_retrieve_body( $response ) );
+
+		return $response;
+	}
+
+	/**
+	 * Rewrite the given URL to use the configured domain.
+	 *
+	 * @param string $url
+	 *
+	 * @return string
+	 */
+	protected function prepare_url( string $url ): string {
+		if ( empty( $this->domain() ) ) {
+			return $url;
+		}
+
+		$pull_hostname = AS3CF_Utils::parse_url( $url, PHP_URL_HOST );
+
+		// Force the given domain in the rewritten URL if hostnames do not match.
+		if ( $this->domain !== $pull_hostname ) {
+			$url = str_replace( "//$pull_hostname/", "//$this->domain/", $url );
+		}
+
+		return $url;
+	}
+
+	/**
+	 * Check that the domain is resolvable.
+	 *
+	 * @throws Unresolveable_Hostname_Exception
+	 */
+	protected function check_dns_resolution() {
+		if ( $this->dns_checked ) {
+			return;
+		}
+
+		if ( ! WP_Http::is_ip_address( $this->domain ) && $this->domain === gethostbyname( $this->domain ) ) {
+			throw new Unresolveable_Hostname_Exception(
+				sprintf(
+					__( '<code>%s</code> did not resolve to an IP address.', 'amazon-s3-and-cloudfront' ),
+					$this->domain
+				)
+			);
+		}
+
+		$this->dns_checked = true;
+	}
+
+	/**
+	 * Convert a WP_Error to the appropriate exception.
+	 *
+	 * @param WP_Error $error
+	 *
+	 * @return Domain_Check_Exception
+	 */
+	protected function get_exception_for_wp_error( WP_Error $error ) {
+		if ( preg_match( '/SSL (certificate problem|operation failed)/i', $error->get_error_message() ) ) {
+			return new Ssl_Connection_Exception(
+				sprintf( __( 'An HTTPS connection error was encountered: <code>%s</code>.', 'amazon-s3-and-cloudfront' ), $error->get_error_message() )
+			);
+		}
+
+		return new HTTP_Response_Exception(
+			sprintf( __( 'An HTTP connection error was encountered: <code>%s</code>.', 'amazon-s3-and-cloudfront' ), $error->get_error_message() )
+		);
+	}
+
+	/**
+	 * Check that the given response code is within the acceptable range.
+	 *
+	 * @param int $response_code
+	 *
+	 * @throws Invalid_Response_Code_Exception
+	 */
+	protected function check_response_code( int $response_code ) {
+		if ( $response_code < 200 || $response_code > 399 ) {
+			throw new Invalid_Response_Code_Exception(
+				sprintf(
+					__( 'An error was encountered while testing the domain: <code>Received %d from endpoint</code>.', 'amazon-s3-and-cloudfront' ),
+					$response_code
+				)
+			);
+		}
+	}
+
+	/**
+	 * Check that the response type is the correct type.
+	 *
+	 * @param array|string $content_type
+	 *
+	 * @throws Invalid_Response_Type_Exception
+	 */
+	protected function check_response_type( $content_type ) {
+		if ( is_array( $content_type ) || ! preg_match( '/^application\/json/i', $content_type ) ) {
+			throw new Invalid_Response_Type_Exception(
+				sprintf(
+					__( 'An error was encountered while testing the domain: <code>Invalid response type: %s</code>.', 'amazon-s3-and-cloudfront' ),
+					join( ', ', (array) $content_type )
+				)
+			);
+		}
+	}
+
+	/**
+	 * Send a request to the given URL.
+	 *
+	 * @param string $url
+	 *
+	 * @return array Response data
+	 * @throws Domain_Check_Exception
+	 */
+	protected function dispatch_request( string $url ): array {
+		$request_url = $this->prepare_url( $url );
+		$response    = wp_remote_get( $request_url, array(
+			/**
+			 * CloudFront origin timeout is configurable in Origin settings.
+			 *
+			 * @param int $seconds
+			 */
+			'timeout'   => apply_filters( 'as3cf_assets_pull_test_endpoint_timeout', 15 ),
+
+			/**
+			 * Verify SSL certificates by default.
+			 *
+			 * @param bool   $verify
+			 * @param string $domain
+			 */
+			'sslverify' => apply_filters( 'as3cf_assets_pull_test_endpoint_sslverify', true, $this->domain ),
+
+			// Make sure headers work for various services.
+			'headers'   => array(
+				'accept'     => '*/*',
+				'user-agent' => 'wp-offload-media',
+				'referer'    => home_url(),
+			),
+		) );
+
+		if ( is_wp_error( $response ) ) {
+			throw $this->get_exception_for_wp_error( $response );
+		}
+
+		return $response;
+	}
+
+	/**
+	 * Make assertions about the pull request based on the response body.
+	 *
+	 * @param string $response_body
+	 *
+	 * @throws Malformed_Query_String_Exception
+	 * @throws Malformed_Response_Exception
+	 */
+	protected function check_response_body( string $response_body ) {
+		$raw_body = json_decode( $response_body, true );
+
+		if ( null === $raw_body ) {
+			throw new Malformed_Response_Exception(
+				__( 'An error was encountered while testing the domain: <code>Malformed response from endpoint</code>.', 'amazon-s3-and-cloudfront' )
+			);
+		}
+
+		if ( empty( $raw_body['ver'] ) ) {
+			throw new Malformed_Query_String_Exception(
+				__( 'An error was encountered while testing the domain: <code>Query string missing "ver" parameter</code>.', 'amazon-s3-and-cloudfront' )
+			);
+		}
+	}
+
+	/**
+	 * Checks response headers for possible errors.
+	 *
+	 * @param array|Requests_Utility_CaseInsensitiveDictionary $response_headers
+	 *
+	 * @throws S3_Bucket_Origin_Exception
+	 */
+	public static function check_response_headers( $response_headers ) {
+		if ( ! empty( $response_headers['server'] ) && 'AmazonS3' === $response_headers['server'] ) {
+			throw new S3_Bucket_Origin_Exception(
+				__( 'An error was encountered while testing the domain: <code>S3 bucket set as CDN origin</code>.', 'amazon-s3-and-cloudfront' )
+			);
+		}
+	}
+}

classes/settings/exceptions/domain-check-exception.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+use Exception;
+use ReflectionClass;
+
+class Domain_Check_Exception extends Exception {
+
+	/**
+	 * @var string Relative path for dbrains link
+	 */
+	protected $more_info = '/wp-offload-media/doc/assets-pull-domain-check-errors/';
+
+	/**
+	 * Get the exception name in key form.
+	 */
+	public function get_key(): string {
+		$class = new ReflectionClass( $this );
+
+		return strtolower( $class->getShortName() );
+	}
+
+	/**
+	 * Get the relative URL to a help document for this exception.
+	 *
+	 * @return string
+	 */
+	public function more_info(): string {
+		return $this->more_info;
+	}
+}

classes/settings/exceptions/http-response-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class HTTP_Response_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/invalid-response-code-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Invalid_Response_Code_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/invalid-response-type-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Invalid_Response_Type_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/malformed-query-string-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Malformed_Query_String_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/malformed-response-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Malformed_Response_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/s3-bucket-origin-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class S3_Bucket_Origin_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/signature-verification-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Signature_Verification_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/ssl-connection-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Ssl_Connection_Exception extends Domain_Check_Exception {
+}

classes/settings/exceptions/unresolveable-hostname-exception.php

@@ -0,0 +1,6 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings\Exceptions;
+
+class Unresolveable_Hostname_Exception extends Domain_Check_Exception {
+}

classes/settings/validation-manager.php

@@ -0,0 +1,242 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings;
+
+use Amazon_S3_And_CloudFront;
+use WP_Error;
+
+class Validation_Manager {
+	/**
+	 * @var Amazon_S3_And_CloudFront
+	 */
+	protected $as3cf;
+
+	/**
+	 * @var array
+	 */
+	protected $validation_result = array();
+
+	/**
+	 * The threshold in seconds for the relative time to be considered "just now".
+	 *
+	 * @var int
+	 */
+	protected static $threshold_just_now = 60;
+
+	/**
+	 * @var Validator_Interface[]
+	 */
+	private $settings_validators = array();
+
+	/**
+	 * @var string
+	 */
+	private $base_last_validation_result_key = 'as3cf_last_settings_validation_result';
+
+	/**
+	 * @param Amazon_S3_And_CloudFront $as3cf
+	 */
+	public function __construct( Amazon_S3_And_CloudFront $as3cf ) {
+		$this->as3cf = $as3cf;
+	}
+
+	/**
+	 * Register a validator class for a section key.
+	 *
+	 * @param string              $section
+	 * @param Validator_Interface $settings_validator
+	 */
+	public function register_validator( string $section, Validator_Interface $settings_validator ) {
+		// Only one instance can be responsible for a section, so we just overwrite if called twice.
+		$this->settings_validators[ $section ] = $settings_validator;
+
+		// The validator may know about one or more actions that are fired when its settings are saved.
+		foreach ( $settings_validator->post_save_settings_actions() as $action ) {
+			add_action( $action, array( $this, 'action_post_save_settings' ) );
+		}
+	}
+
+	/**
+	 * Run all registered validator classes and return the result in an array. If the
+	 * force flag is set to true, the validators may run checks that are time-consuming
+	 * or affects the global plugin state (notices).
+	 *
+	 * @param bool $force
+	 *
+	 * @return array
+	 */
+	public function validate( bool $force = false ): array {
+		// Sort the validators by priority.
+		uasort(
+			$this->settings_validators,
+			function ( Validator_Interface $a, Validator_Interface $b ) {
+				return $a->get_validator_priority() <=> $b->get_validator_priority();
+			}
+		);
+
+		$validation_start = time();
+
+		// Run all registered settings validators.
+		foreach ( $this->settings_validators as $section => $settings_validator ) {
+			$transient_key                       = $this->last_validation_result_key( $section );
+			$this->validation_result[ $section ] = get_site_transient( $transient_key );
+
+			if ( ! $force && is_array( $this->validation_result[ $section ] ) ) {
+				continue;
+			}
+
+			// Ensure only one instance of a validator is processing at once unless forced.
+			$this->validation_result[ $section ] = array(
+				'type'      => Validator_Interface::AS3CF_STATUS_MESSAGE_INFO,
+				'message'   => array( _x( 'Processing…', 'Validation in progress', 'amazon-s3-and-cloudfront' ) ),
+				'timestamp' => $validation_start,
+			);
+			set_site_transient( $transient_key, $this->validation_result[ $section ], MINUTE_IN_SECONDS );
+
+			$result = $settings_validator->validate_settings( $force );
+
+			$this->validation_result[ $section ]['type']    = $result->get_error_code();
+			$this->validation_result[ $section ]['message'] = array( $result->get_error_message() );
+
+			$timeout = Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR === $result->get_error_code() ? 5 * MINUTE_IN_SECONDS : DAY_IN_SECONDS;
+
+			/**
+			 * Adjust the transient timeout for the cache of a setting section's validation results.
+			 *
+			 * Min: 3 seconds
+			 * Max: 7 days
+			 *
+			 * The default is 1 day unless the result is an error, in which case it is then 5 minutes.
+			 *
+			 * @param int      $timeout Time until transient expires in seconds.
+			 * @param string   $section The setting section, e.g. storage, delivery or assets.
+			 * @param WP_Error $result  The result to be cached.
+			 */
+			$timeout = min( max( 3, (int) apply_filters( $this->base_last_validation_result_key . '_timeout', $timeout, $section, $result ) ), 7 * DAY_IN_SECONDS );
+
+			set_site_transient( $transient_key, $this->validation_result[ $section ], $timeout );
+		}
+
+		$this->update_relative_time();
+
+		return $this->validation_result;
+	}
+
+	/**
+	 * Get a specific or all registered sections and status messages.
+	 *
+	 * If all sections to be returned, they're in an associative array
+	 * with the sections as the keys.
+	 *
+	 * @param string $section Optional specific section's result only.
+	 *
+	 * @return array|WP_Error
+	 */
+	public function get_validation_result( string $section = '' ) {
+		if ( empty( $this->validation_result ) ) {
+			$this->validate();
+		}
+
+		if ( empty( $section ) ) {
+			return $this->validation_result;
+		} elseif ( ! empty( $this->validation_result[ $section ] ) ) {
+			return $this->validation_result[ $section ];
+		}
+
+		return array();
+	}
+
+	/**
+	 * Return the validation status for a section.
+	 *
+	 * @param string $section
+	 *
+	 * @return string
+	 */
+	public function get_validation_status( string $section ): string {
+		$result = $this->get_validation_result( $section );
+
+		if ( ! isset( $result['type'] ) ) {
+			return Validator_Interface::AS3CF_STATUS_MESSAGE_UNKNOWN;
+		}
+
+		return $result['type'];
+	}
+
+	/**
+	 * Clear the last validation timestamp to force validation on next check.
+	 *
+	 * @param bool $saved Whether settings were successfully saved or not
+	 */
+	public function action_post_save_settings( bool $saved ) {
+		if ( empty( $this->settings_validators ) ) {
+			return;
+		}
+
+		static $deleted = array();
+
+		foreach ( $this->settings_validators as $section => $validator ) {
+			if ( in_array( $section, $deleted ) || ! in_array( current_action(), $validator->post_save_settings_actions() ) ) {
+				continue;
+			}
+
+			delete_site_transient( $this->last_validation_result_key( $section ) );
+			$deleted[] = $section;
+		}
+	}
+
+	/**
+	 * Does the given section currently have a validation error?
+	 *
+	 * @param string $section
+	 *
+	 * @return bool
+	 */
+	public function section_has_error( string $section ): bool {
+		if ( empty( $section ) ) {
+			return false;
+		}
+
+		return Validator_Interface::AS3CF_STATUS_MESSAGE_ERROR === $this->get_validation_status( $section );
+	}
+
+	/**
+	 * Get a correctly formatted validation result transient key.
+	 *
+	 * @param string $section
+	 *
+	 * @return string
+	 */
+	public function last_validation_result_key( string $section ): string {
+		return $this->base_last_validation_result_key . '_' . $section;
+	}
+
+	/**
+	 * Update the relative time for each section's last validation.
+	 */
+	protected function update_relative_time() {
+		foreach ( array_keys( $this->validation_result ) as $key ) {
+			if ( ! isset( $this->validation_result[ $key ]['timestamp'] ) ) {
+				$this->validation_result[ $key ]['last_update'] = _x( 'Unknown', 'Relative time in settings notice', 'amazon-s3-and-cloudfront' );
+				continue;
+			}
+
+			$this->validation_result[ $key ]['last_update'] = $this->get_relative_time( $this->validation_result[ $key ]['timestamp'] );
+		}
+	}
+
+	/**
+	 * Get the relative time display string.
+	 *
+	 * @param int $timestamp
+	 *
+	 * @return string
+	 */
+	protected function get_relative_time( int $timestamp ): string {
+		if ( time() - $timestamp <= static::$threshold_just_now ) {
+			return _x( 'Just now', 'Relative time in settings notice', 'amazon-s3-and-cloudfront' );
+		}
+
+		return sprintf( __( '%s ago', 'amazon-s3-and-cloudfront' ), human_time_diff( $timestamp ) );
+	}
+}

classes/settings/validator-interface.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Settings;
+
+use WP_Error as AS3CF_Result;
+
+interface Validator_Interface {
+	const AS3CF_STATUS_MESSAGE_ERROR   = 'error';
+	const AS3CF_STATUS_MESSAGE_WARNING = 'warning';
+	const AS3CF_STATUS_MESSAGE_INFO    = 'info';
+	const AS3CF_STATUS_MESSAGE_SUCCESS = 'success';
+	const AS3CF_STATUS_MESSAGE_UNKNOWN = 'unknown';
+	const AS3CF_STATUS_MESSAGE_SKIPPED = 'skipped';
+
+	/**
+	 * Validate settings. Set the force flag to true to allow the validators to run
+	 * checks that are time-consuming or affects the global state of the plugin.
+	 *
+	 * @param bool $force A potentially time resource consuming tests to run.
+	 *
+	 * @return AS3CF_Result
+	 */
+	public function validate_settings( bool $force = false ): AS3CF_Result;
+
+	/**
+	 * Get the name of the actions that are fired when the settings that the validator
+	 * is responsible for are saved.
+	 *
+	 * @return array
+	 */
+	public function post_save_settings_actions(): array;
+
+	/**
+	 * Get the validator priority.
+	 *
+	 * @return int
+	 */
+	public function get_validator_priority(): int;
+}