Ticket #52536: 52536-poc.diff

src/wp-includes/class-wp.php

@@ -547 +547 @@
                         }
                 }
 
+                $x_robots_tag_value = wp_x_robots_tag_header_string();
+                if ( is_string( $x_robots_tag_value ) ) {
+                        $headers['X-Robots-Tag'] = $x_robots_tag_value;
+                }
+
                 /**
                  * Filters the HTTP headers before they're sent to the browser.
                  *

src/wp-includes/robots-template.php

@@ -49 +49 @@
         echo "<meta name='robots' content='" . esc_attr( implode( ', ', $robots_strings ) ) . "' />\n";
 }
 
+/**
+ * Returns the necessary X-Robots-Tag value.
+ *
+ * Gathers robots directives to include for the current context, using the
+ * {@see 'wp_robots'} filter. The directives are then sanitized, and the
+ * X-Robots-Tag header is output if there is at least one relevant directive.
+ *
+ * @since x.x.x
+ *
+ * @return string|null The X-Robots-Tag header value, or null if no relevant directives.
+ */
+function wp_x_robots_tag_header_string() {
+        /** This filter is documented in wp-includes/robots-template.php */
+        $robots = apply_filters( 'wp_robots', array() );
+
+        $robots_strings = array();
+        foreach ( $robots as $directive => $value ) {
+                if ( is_string( $value ) ) {
+                        // If a string value, include it as value for the directive.
+                        $robots_strings[] = "{$directive}={$value}";
+                } elseif ( $value ) {
+                        // Otherwise, include the directive if it is truthy.
+                        $robots_strings[] = $directive;
+                }
+        }
+
+        if ( empty( $robots_strings ) ) {
+                return null;
+        }
+
+        return implode( ', ', $robots_strings );
+}
+
 /**
  * Adds `noindex` to the robots meta tag if required by the site configuration.
  *