From 9475423c5918ad5ef7db2ac5db029dc59ce8b355 Mon Sep 17 00:00:00 2001
From: Sam Whited <sam@samwhited.com>
Date: Sat, 14 Nov 2020 08:31:45 -0500
Subject: [PATCH] XEP-0389: error if client selects an invalid flow

---
 xep-0389.xml | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/xep-0389.xml b/xep-0389.xml
index 2ed6b78d..0ed61eb4 100644
--- a/xep-0389.xml
+++ b/xep-0389.xml
@@ -371,7 +371,7 @@
   <register xmlns='urn:xmpp:register:0'/>
 </iq>]]></example>
   </section2>
-  <section2 topic='Issuing Challenges' anchor='challenge'>
+  <section2 topic='Selecting a Flow' anchor='selecting'>
     <p>
       A client selects the registration or recovery feature for negotiation by
       replying with an element of the same name and namespace.
@@ -384,6 +384,19 @@
 <register xmlns='urn:xmpp:register:0'>
   <flow id='1'/>
 </register>]]></example>
+    <p>
+      If during stream initialization the client attempts to select a flow that
+      does not match one of the flows sent by the server, the server MUST
+      respond with an "undefined-condition" stream error containing an
+      "invalid-flow" application error qualified by the 'urn:xmpp:register:0'
+      namespace.
+    </p>
+    <example caption='Server responds to an invalid selection during stream negotiation'><![CDATA[
+<stream:error>
+  <undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
+  <invalid-flow xmlns='urn:xmpp:register:0'/>
+</stream:error>
+</stream:stream>]]></example>
     <p>
       If the client is initiating registration or recovery after a stream has
       already been initiated it uses the same registration element wrapped in an
@@ -396,7 +409,21 @@
   </recovery>
 </iq>]]></example>
     <p>
-      The server then replies to the IQ or feature selection with a challenge.
+      If the client attempts to select a flow that does not match one of the
+      flows sent by the server in response to an IQ after stream initialization
+      the server MUST respond with a stanza error of type "item-not-found".
+    </p>
+    <example caption='Server responds to an invalid selection after stream negotiation'><![CDATA[
+<iq type='error'>
+  <error type='cancel'>
+    <item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
+  </error>
+</iq>]]></example>
+  </section2>
+  <section2 topic='Issuing Challenges' anchor='challenge'>
+    <p>
+      If a valid flow is selected by the client the server then replies to the
+      IQ or feature selection with a challenge.
       If replying to an IQ, the challenge must be wrapped in an IQ of type
       "result".
       Challenges take the form of a &lt;challenge/&gt; element qualified by the