feat: cache is_domain_loopback DNS lookup in a short-lived transient

Co-authored-by: pattonwebz <3902039+pattonwebz@users.noreply.github.com>

Author: 2 people

admin/class-helpers.php

@@ -143,11 +143,22 @@ public static function get_option_as_array( $option_name ) {
 	/**
 	 * Determine if a domain is hosted on a local loopback
 	 *
+	 * Results are cached in a short-lived transient to avoid repeated DNS
+	 * lookups when the same domain is checked multiple times during a scan.
+	 *
 	 * @param string $domain The domain to check.
 	 * @return boolean
 	 */
 	public static function is_domain_loopback( $domain ) {
 
+		// Check the transient cache first to avoid repeated DNS lookups.
+		$cache_key = 'edac_loopback_' . md5( sanitize_text_field( $domain ) );
+		$cached    = get_transient( $cache_key );
+
+		if ( false !== $cached ) {
+			return (bool) $cached;
+		}
+
 		// Check if this is an ipv4 address in the loopback range.
 
 		$record         = gethostbyname( $domain );
@@ -156,6 +167,9 @@ public static function is_domain_loopback( $domain ) {
 		$ip_long        = ip2long( $record );
 
 		if ( $ip_long >= $loopback_start && $ip_long <= $loopback_end ) {
+			// Store as int (1/0) so that a false result is distinguishable from a
+			// cache miss, since get_transient() also returns false on a miss.
+			set_transient( $cache_key, 1, HOUR_IN_SECONDS );
 			return true;
 		}
 
@@ -164,6 +178,7 @@ public static function is_domain_loopback( $domain ) {
 		try {
 			$records = dns_get_record( $domain, DNS_AAAA );
 		} catch ( \Throwable $th ) {
+			set_transient( $cache_key, 0, HOUR_IN_SECONDS );
 			return false;
 		}
 
@@ -179,11 +194,13 @@ public static function is_domain_loopback( $domain ) {
 				$loopback_ipv6 = inet_pton( '::1' );
 
 				if ( $normalized_ipv6 === $loopback_ipv6 ) {
+					set_transient( $cache_key, 1, HOUR_IN_SECONDS );
 					return true;
 				}
 			}
 		}
 
+		set_transient( $cache_key, 0, HOUR_IN_SECONDS );
 		return false;
 	}
 

tests/phpunit/Admin/HelpersLoopbackTest.php

@@ -242,4 +242,65 @@ public function test_performance_multiple_calls() {
 		// Should complete within a reasonable time (5 seconds).
 		$this->assertLessThan( 5.0, $execution_time, 'Method took too long to execute multiple calls' );
 	}
+
+	/**
+	 * Test that the result is cached in a transient after the first call.
+	 */
+	public function test_result_is_cached_in_transient() {
+		$domain    = 'localhost';
+		$cache_key = 'edac_loopback_' . md5( sanitize_text_field( $domain ) );
+
+		// Clear any existing transient.
+		delete_transient( $cache_key );
+
+		// First call performs the DNS lookup and stores the result.
+		$result = Helpers::is_domain_loopback( $domain );
+		$this->assertTrue( $result );
+
+		// The transient should now be set with an integer value.
+		$cached = get_transient( $cache_key );
+		$this->assertNotFalse( $cached, 'Transient should be set after first call.' );
+		$this->assertSame( 1, (int) $cached );
+	}
+
+	/**
+	 * Test that a non-loopback result is also cached correctly.
+	 */
+	public function test_non_loopback_result_is_cached() {
+		$domain    = '8.8.8.8';
+		$cache_key = 'edac_loopback_' . md5( sanitize_text_field( $domain ) );
+
+		// Clear any existing transient.
+		delete_transient( $cache_key );
+
+		// First call performs the DNS lookup.
+		$result = Helpers::is_domain_loopback( $domain );
+		$this->assertFalse( $result );
+
+		// The transient should be set with 0 (not false) so a cache miss can
+		// be distinguished from a cached false result.
+		$cached = get_transient( $cache_key );
+		$this->assertNotFalse( $cached, 'Transient should be set even for non-loopback domains.' );
+		$this->assertSame( 0, (int) $cached );
+	}
+
+	/**
+	 * Test that a cached result is returned without re-doing the DNS lookup.
+	 */
+	public function test_cached_result_is_returned() {
+		$domain    = '127.0.0.1';
+		$cache_key = 'edac_loopback_' . md5( sanitize_text_field( $domain ) );
+
+		// Pre-seed the transient with a value opposite to the real DNS answer.
+		// If the cache is respected, this value will be returned as-is.
+		set_transient( $cache_key, 0, HOUR_IN_SECONDS );
+
+		$result = Helpers::is_domain_loopback( $domain );
+
+		// The seeded value (0 / false) should be returned from cache.
+		$this->assertFalse( $result );
+
+		// Clean up.
+		delete_transient( $cache_key );
+	}
 }