Init logic to receive webmentions

Adds a codepath that would store them as trackback or pingback, depending on the metadata available on the sending page.

comment.php

@@ -129,6 +129,22 @@
         log_pingback('PINGBACK FAILURE');;
         report_pingback_failure();
     }
+} else if ($type == 'webmention') {
+    if (isset($_REQUEST['entry_id'])) {
+        $id = (int)$_REQUEST['entry_id'];;
+    } else if (preg_match('@/(\d+)_[^/]*$@', $uri, $matches)) {
+        $id = (int)$matches[1];
+    }
+
+    // TODO: Check that given $target url matches the $id of this endpoint
+
+    if (add_webmention($id, $_REQUEST['source'], $_REQUEST['target'] )) {
+        log_trackback('WEBMENTION SUCCESS');
+        report_trackback_success();
+    } else {
+        log_trackback('WEBMENTION FAILURE');
+        report_trackback_failure();
+    }
 } else {
     $id = (int)(!empty($serendipity['POST']['entry_id']) ? $serendipity['POST']['entry_id'] : $serendipity['GET']['entry_id']);
     $serendipity['head_subtitle'] = COMMENTS;

include/functions_trackbacks.inc.php

@@ -470,6 +470,65 @@ function add_pingback($id, $postdata) {
     return 0;
 }
 
+/**
+ * Receive a webmention. Converts the webmention to a trackback for internal storage
+ *
+ * @access public
+ * @param   int     The ID of our entry
+ * @param   string  The URL of the foreign blog
+ * @return true
+ */
+function add_webmention($id, $url, $target) {
+    global $serendipity;
+
+    log_trackback('add_trackback:' . print_r(func_get_args(), true));
+
+    // We can't accept a webmention if we don't get any URL
+    // This is a protocol rule.
+    if (empty($url)) {
+        log_trackback('Empty URL.');
+
+        return 0;
+    }
+
+    // We need to get a fallback name. A easy solution would be to fetch the HEAD of the $url and
+    // fetch the title. Alternative and suggestion from indieweb.org: rel-author
+    $sourceHTML = serendipity_request_url($url)
+    $doc = new DOMDocument();
+	$doc->loadHTML($sourceHTML);
+	$xpath = new DOMXPath($doc);
+    $name = $xpath->query('//head/title');
+
+    // We could now already store the webmention like a pingback. The source (in $url) still needs
+    // to be verified, but  he spamblock plugin does that for us later when storing this as
+    // trackback or pingback. 
+    // But we can also try to detect more metadata first by interpreting the microformat on the
+    // source page. See https://indieweb.org/comments#How_to_display
+    $microdata = Mf2\parse($sourceHTML, '$url');
+    if ($microdata) {
+        $title = ''
+        $excerpt = ''
+        // TODO: Check the microdata entry for a $title and an $excerpt, and optionally for a better
+        //       name
+
+        if ($title != '' && $excerpt != '') {
+            // Now we have everything to store the webmention as a trackback
+            return add_trackback($id, $title, $url, $name, $excerpt)
+        }
+    }
+
+    if ($id>0) {
+        $comment['title']   = 'Webmention';
+        $comment['url']     = $url;
+        $comment['comment'] = '';
+        $comment['name']    = $name;
+        serendipity_saveComment($id, $comment, 'PINGBACK');
+        return 1;
+    }
+    return 0; 
+}
+
+
 function evaluateIdByLocalUrl($localUrl) {
     global $serendipity;
 

templates/2k11/index.tpl

@@ -27,6 +27,7 @@
 {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={$entry_id}">
+    <link rel="webmention" href="{$serendipityBaseURL}comment.php?type=webmention&amp;entry_id={$entry_id}" />
 {/if}
 {serendipity_hookPlugin hook="frontend_header"}
     <script src="{$head_link_script}"></script>