From 9638b7e3c6c321793240a0dcd2cca116967c219f Mon Sep 17 00:00:00 2001
From: jrfnl <github_nospam@adviesenzo.nl>
Date: Fri, 4 Dec 2015 16:44:38 +0100
Subject: [PATCH] Only generate pingback url header tag when relevant.

Rationale:
1. The principle of pingbacks is based on articles. Pingbacks are a special kind of comments and the article being 'pinged-back' has to be identifiable (which they're not on archive pages and the like).
2. WP only registers a ping if it can identify the article which is supposed to have been 'pung'. See: https://developer.wordpress.org/reference/classes/wp_xmlrpc_server/pingback_ping/
3. Pingbacks, like comments, can be disabled on a per article basis.

Therefore, having the pingback url auto-discovery header in place, only makes sense on singular pages where pings are open.
---
 header.php     |  1 -
 inc/extras.php | 10 ++++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/header.php b/header.php
index d309fe90dc..0c5a7d43f9 100644
--- a/header.php
+++ b/header.php
@@ -15,7 +15,6 @@
 <meta charset="<?php bloginfo( 'charset' ); ?>">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <link rel="profile" href="http://gmpg.org/xfn/11">
-<link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>">
 
 <?php wp_head(); ?>
 </head>
diff --git a/inc/extras.php b/inc/extras.php
index d3bf8fb160..8475ff8aaf 100644
--- a/inc/extras.php
+++ b/inc/extras.php
@@ -27,3 +27,13 @@ function _s_body_classes( $classes ) {
 	return $classes;
 }
 add_filter( 'body_class', '_s_body_classes' );
+
+/**
+ * Add a pingback url auto-discovery header for singularly identifiable articles.
+ */
+function _s_pingback_header() {
+	if ( is_singular() && pings_open() ) {
+		echo '<link rel="pingback" href="', bloginfo( 'pingback_url' ), '">';
+	}
+}
+add_action( 'wp_head', '_s_pingback_header' );