Try features in our preferred order

Instead of trying them in source order, which the RFC says is not meant
to be important. This prevents, for example, trying to register on a
server we already have an account and lets us always try authenticating first.

lib/blather/stream/features.rb

@@ -16,36 +16,41 @@ def initialize(stream, succeed, fail)
       @stream, @succeed, @fail = stream, succeed, fail
     end
 
+    # Fetures may appear in the XML in any order, but sometimes
+    # we might prefer to try some first if present
+    FEATURE_SCORES = {
+      "urn:ieft:params:xml:ns:xmpp-tls" => 0,
+      "urn:ieft:params:xml:ns:xmpp-bind" => 1,
+      "urn:ieft:params:xml:ns:xmpp-session" => 1,
+      "urn:ietf:params:xml:ns:xmpp-sasl" => 2
+    }.freeze
+
     def receive_data(stanza)
       if @feature
         @feature.receive_data stanza
       else
         @features ||= stanza
+        @use_next =
+          @features.children
+            .map { |el| el.namespaces['xmlns'] }.compact
+            .sort { |x, y| FEATURE_SCORES.fetch(x, FEATURE_SCORES.length) <=> FEATURE_SCORES.fetch(y, FEATURE_SCORES.length) }
         next!
       end
     end
 
     def next!
-      if starttls = @features.at_xpath("tls:starttls",{"tls" => "urn:ietf:params:xml:ns:xmpp-tls"})
-        @feature = TLS.new(@stream, nil, @fail)
-        @feature.receive_data(starttls)
-        return
-      end
-
       bind = @features.at_xpath('ns:bind', ns: 'urn:ietf:params:xml:ns:xmpp-bind')
       session = @features.at_xpath('ns:session', ns: 'urn:ietf:params:xml:ns:xmpp-session')
       if bind && session && @features.children.last != session
         bind.after session
       end
 
-      @idx = @idx ? @idx+1 : 0
-      if stanza = @features.children[@idx]
+      if (stanza = @features.at_xpath('ns:*', ns: @use_next.shift))
         if stanza.namespaces['xmlns'] && (klass = self.class.from_namespace(stanza.namespaces['xmlns']))
           @feature = klass.new(
             @stream,
             proc {
               if (klass == Blather::Stream::Register && stanza = feature?(:mechanisms))
-                @idx = @features.children.index(stanza)
                 @feature = Blather::Stream::SASL.new @stream, proc { next! }, @fail
                 @feature.receive_data stanza
               else