Tell (Google)bots not to index short URLs

Should fix YOURLS#2202

includes/functions.php

@@ -719,6 +719,34 @@ function yourls_redirect( $location, $code = 301 ) {
 	die();
 }
 
+/**
+ * Redirect to an existing short URL
+ *
+ * Redirect client to an existing short URL (no check performed) and execute misc tasks: update
+ * clicks for short URL, update logs, and send a nocache header to prevent bots indexing short
+ * URLS (see #2202)
+ *
+ * @since  1.7.3
+ * @param  string $url
+ * @param  string $keyword
+ */
+function yourls_redirect_shorturl($url, $keyword) {
+    yourls_do_action('redirect_shorturl', $url, $keyword);
+
+    // Update click count in main table
+    $update_clicks = yourls_update_clicks($keyword);
+
+    // Update detailed log for stats
+    $log_redirect = yourls_log_redirect($keyword);
+
+    // Tell (Google)bots not to index this short URL, see #2202
+    if( !headers_sent() ) {
+        header("X-Robots-Tag: noindex", true);
+    }
+
+    yourls_redirect($url, 301);
+}
+
 /**
  * Set HTTP status header
  *

yourls-go.php

@@ -18,15 +18,7 @@
 
 // URL found
 if( !empty( $url ) ) {
-	yourls_do_action( 'redirect_shorturl', $url, $keyword );
-
-	// Update click count in main table
-	$update_clicks = yourls_update_clicks( $keyword );
-
-	// Update detailed log for stats
-	$log_redirect = yourls_log_redirect( $keyword );
-
-	yourls_redirect( $url, 301 );
+    yourls_redirect_shorturl($url, $keyword);
 
 // URL not found. Either reserved, or page, or doesn't exist
 } else {
@@ -38,7 +30,7 @@
 	// Either reserved id, or no such id
 	} else {
 		yourls_do_action( 'redirect_keyword_not_found', $keyword );
-		
+
 		yourls_redirect( YOURLS_SITE, 302 ); // no 404 to tell browser this might change, and also to not pollute logs
 	}
 }