source/posts/sending_pingback_oldskool_indieweb.org

   1 #+title: About sending pingbacks, webmentions and some thoughts on how to improve on them.
   2 #+filetags: indieweb blogging open_web
   3 #+date: 2023-10-31T20:41:30+08:00
   4
   5 In a 'blast from the past', I sent my first
   6 [[https://www.hixie.ch/specs/pingback/pingback][pingback]] after writing
   7 the [[file:agent_based_models_digital_twins.org][previous post]]. A pingback is a
   8 way for a blogger to send a message to another blogger, informing them
   9 they've written a post that refers to theirs, e.g. as a reply or an
  10 extension of the ideas raised.
  11
  12 The process is a bit more involved than using a
  13 [[https://www.w3.org/TR/webmention/][webmention]], which I've used
  14 before and [[file:Implementing_Webmention_on_my_blog.org][implemented support for]] a while back, due to requiring an XML message to be created
  15 rather than a simple exchange of URLs.
  16
  17 First, I created a file =pingback.xml= containing the URLs of the blog
  18 post I wrote and the one I made reference to within my post. The
  19 standard defines the schema, resulting in the following:
  20
  21 #+BEGIN_SRC XML
  22 <?xml version="1.0" encoding="UTF-8"?>
  23 <methodCall>
  24     <methodName>pingback.ping</methodName>
  25     <params>
  26         <param>
  27             <value><string>https://www.vanrenterghem.biz/blog/posts/agent_based_models_digital_twins/</string></value>
  28         </param>
  29         <param>
  30             <value><string>https://johncarlosbaez.wordpress.com/2023/10/25/software-for-compositional-modeling-in-epidemiology/</string></value>
  31         </param>
  32     </params>
  33 </methodCall>
  34 #+END_SRC
  35
  36 Next, I used =curl= on the command-line to send this file in a POST
  37 request to Wordpress's pingback service. I had to use the =-k= option to
  38 make this work - bypassing verification of the TLS certificate.
  39
  40 #+BEGIN_SRC sh
  41 curl -k https://johncarlosbaez.wordpress.com/xmlrpc.php -d @pingback.xml
  42 #+END_SRC
  43
  44 In a sign things were going well, I saw the following appear in my
  45 website's access log:
  46
  47 #+BEGIN_SRC txt
  48 192.0.112.141 - - [29/Oct/2023:09:35:06 +0100] "GET /blog/posts/agent_based_models_digital_twins/ HTTP/1.1" 200 2676
  49 "https://www.vanrenterghem.biz/blog/posts/agent_based_models_digital_twins/"
  50 "WordPress.com; https://johncarlosbaez.wordpress.com; verifying pingback
  51 from 139.216.235.49"
  52 #+END_SRC
  53
  54 Finally, I received the following response to my =curl= request on the
  55 command-line:
  56
  57 #+BEGIN_SRC XML
  58 <?xml version="1.0" encoding="UTF-8"?>
  59 <methodResponse>
  60   <params>
  61     <param>
  62       <value>
  63       <string>Pingback from https://www.vanrenterghem.biz/blog/posts/agent_based_models_digital_twins/ to https://johncarlosbaez.wordpress.com/2023/10/25/software-for-compositional-modeling-in-epidemiology/ registered. Keep the web talking! :-)</string>
  64       </value>
  65     </param>
  66   </params>
  67 </methodResponse>
  68 #+END_SRC
  69
  70 That "Keep the web talking! :-)" message made me smile.
  71
  72 In order to understand a bit better how things were being processed, I
  73 checked the Wordpress code for its pingback service, and it appears they
  74 [[https://core.trac.wordpress.org/browser/trunk/src/wp-includes/class-wp-xmlrpc-server.php?rev=56637#L7040][take
  75 the title of the linked article as the author]], which seems a bit odd.
  76 The pingback standard didn't allow for anything but the swapping out of
  77 links though. How your reference is summarized on the referred site is
  78 entirely left to recipient - who may process pingbacks manually or use a
  79 service automating (parts of) the processing.
  80
  81 Wordpress processes pingbacks automatically, turning them into comments
  82 on the original post. As the comment text,
  83 [[https://core.trac.wordpress.org/browser/trunk/src/wp-includes/class-wp-xmlrpc-server.php?rev=56637#L7036][Wordpress
  84 uses the link text in the anchor element]] with a horizontal ellipsis
  85 around it, and some filtering to prevent the comment from being too
  86 long. It's odd how the standard didn't define further approaches to make
  87 this a bit easier. A pingback attribute in the anchor element would have
  88 been helpful for instance, as we could put some text in there to
  89 summarise our page when the pingback is processed automatically. Most
  90 surprisingly maybe, with the benefit of hindsight, it would have been
  91 interesting had the subsequent standard that emerged, Webmention,
  92 implemented some further enhancements.
  93 [[https://aaronparecki.com/][Aaron Parecki]], author of the Webmention
  94 W3C Recommendation, might know if that was ever considered, or just not
  95 within the use case for pingbacks / webmentions? There seemed to have
  96 been [[https://aaronparecki.com/2019/10/15/26/][some thought put into it
  97 in 2019]] at least.