From 18f6429f32faebc6244a9a7176d0fce08bad41c8 Mon Sep 17 00:00:00 2001
From: onli <onli@paskuda.biz>
Date: Sat, 15 Apr 2017 02:19:45 +0200
Subject: [PATCH] Add rel=trackback header and discovery (#438)

---
 include/functions_trackbacks.inc.php | 59 +++++++++++++++-------------
 templates/2k11/index.tpl             |  1 +
 2 files changed, 33 insertions(+), 27 deletions(-)

diff --git a/include/functions_trackbacks.inc.php b/include/functions_trackbacks.inc.php
index 515f2c3e..824b5791 100644
--- a/include/functions_trackbacks.inc.php
+++ b/include/functions_trackbacks.inc.php
@@ -172,42 +172,47 @@ function serendipity_trackback_autodiscover($res, $loc, $url, $author, $title, $
     $is_wp    = false;
     $wp_check = false;
 
-    if (preg_match('@((' . preg_quote($loc, '@') . '|' . preg_quote($loc2, '@') . ')/?trackback/)@i', $res, $wp_loc)) {
-        // We found a WP-blog that may not advertise RDF-Tags!
-        $is_wp = true;
-    }
+    // the new detection method via rel=trackback should have priority
+    if (preg_match('@link\s*rel=["\']trackback["\'].*href=["\'](https?:[^"\']+)["\']@i', $res, $matches)) {
+        $trackURI = trim($matches[1]);
+    } else {
+        if (preg_match('@((' . preg_quote($loc, '@') . '|' . preg_quote($loc2, '@') . ')/?trackback/)@i', $res, $wp_loc)) {
+            // We found a WP-blog that may not advertise RDF-Tags!
+            $is_wp = true;
+        }
 
-    if (!preg_match('@trackback:ping(\s*rdf:resource)?\s*=\s*["\'](https?:[^"\']+)["\']@i', $res, $matches)) {
-        $matches = array();
-        serendipity_plugin_api::hook_event('backend_trackback_check', $matches, $loc);
+        if (!preg_match('@trackback:ping(\s*rdf:resource)?\s*=\s*["\'](https?:[^"\']+)["\']@i', $res, $matches)) {
+            $matches = array();
+            serendipity_plugin_api::hook_event('backend_trackback_check', $matches, $loc);
 
-        // Plugins may say that a URI is valid, in situations where a blog has no valid RDF metadata
-        if (empty($matches[2])) {
-            if ($is_wp) {
-                $wp_check = true;
-            } else {
-                echo '<div>&#8226; ' . sprintf(TRACKBACK_FAILED, TRACKBACK_NOT_FOUND) . '</div>';
-                return false;
+            // Plugins may say that a URI is valid, in situations where a blog has no valid RDF metadata
+            if (empty($matches[2])) {
+                if ($is_wp) {
+                    $wp_check = true;
+                } else {
+                    echo '<div>&#8226; ' . sprintf(TRACKBACK_FAILED, TRACKBACK_NOT_FOUND) . '</div>';
+                    return false;
+                }
             }
         }
-    }
 
-    $trackURI = trim($matches[2]);
+        $trackURI = trim($matches[2]);
 
-    if (preg_match('@dc:identifier\s*=\s*["\'](https?:[^\'"]+)["\']@i', $res, $test)) {
-        if ($loc != $test[1] && $loc2 != $test[1]) {
-            if ($is_wp) {
-                $wp_check = true;
-            } else {
-                echo '<div>&#8226; ' . sprintf(TRACKBACK_FAILED, TRACKBACK_URI_MISMATCH) . '</div>';
-                return false;
+        if (preg_match('@dc:identifier\s*=\s*["\'](https?:[^\'"]+)["\']@i', $res, $test)) {
+            if ($loc != $test[1] && $loc2 != $test[1]) {
+                if ($is_wp) {
+                    $wp_check = true;
+                } else {
+                    echo '<div>&#8226; ' . sprintf(TRACKBACK_FAILED, TRACKBACK_URI_MISMATCH) . '</div>';
+                    return false;
+                }
             }
         }
-    }
 
-    // If $wp_check is set it means no RDF metadata was found, and we simply try the /trackback/ url.
-    if ($wp_check) {
-        $trackURI = $wp_loc[0];
+        // If $wp_check is set it means no RDF metadata was found, and we simply try the /trackback/ url.
+        if ($wp_check) {
+            $trackURI = $wp_loc[0];
+        }
     }
 
     $data = 'url='        . rawurlencode($url)
diff --git a/templates/2k11/index.tpl b/templates/2k11/index.tpl
index 1a96f39c..4c76fcc2 100644
--- a/templates/2k11/index.tpl
+++ b/templates/2k11/index.tpl
@@ -38,6 +38,7 @@
     <link rel="alternate" type="application/rss+xml" title="{$blogTitle} RSS feed" href="{$serendipityBaseURL}{$serendipityRewritePrefix}feeds/index.rss2">
     <link rel="alternate" type="application/x.atom+xml"  title="{$blogTitle} Atom feed"  href="{$serendipityBaseURL}{$serendipityRewritePrefix}feeds/atom.xml">
 {if $entry_id}
+    <link rel="trackback" type="application/x-www-form-urlencoded" href="{$serendipityBaseURL}comment.php?type=trackback&amp;entry_id={$entry_id}">
     <link rel="pingback" href="{$serendipityBaseURL}comment.php?type=pingback&amp;entry_id={$entry_id}">
 {/if}
 {serendipity_hookPlugin hook="frontend_header"}