component: help make client code make more DRY when handling messages

- We now pass subclassed components the stripped resource as a keyword, so they
  don't have to bother doing it themselves.
- If a STANZA-ERROR is signaled during message processing, it gets sent back as
  a response to the message. Yay less boilerplate!

component.lisp

@@ -295,24 +295,31 @@
          (id (dom:get-attribute stanza "id"))
          (children (child-elements stanza))
          (body (get-node-named children "body"))
+         (stripped (strip-resource from))
          (marker (get-node-with-xmlns children +chat-markers-ns+))
          (chat-state (get-node-with-xmlns children +chat-states-ns+)))
-    (cond
-      (body
-       (let* ((child-nodes (dom:child-nodes body))
-              (text (if (> (length child-nodes) 0)
-                        (dom:node-value (elt child-nodes 0))
-                        "")))
-         (emit :text-message comp :from from :to to :body text :id id :stanza stanza)))
-      (marker
-       (let ((marker-type (dom:tag-name marker))
-             (msgid (dom:get-attribute marker "id")))
-         (emit :message-marker comp :from from :to to :type marker-type :marker-id msgid :id id :stanza stanza)))
-      (chat-state
-       (let ((state-type (dom:tag-name chat-state)))
-         (emit :chat-state comp :from from :to to :type state-type :id id :stanza stanza)))
-      (t
-       (emit :message comp :from from :to to :id id :stanza stanza)))))
+    (handler-case
+        (cond
+          (body
+           (let* ((child-nodes (dom:child-nodes body))
+                  (text (if (> (length child-nodes) 0)
+                            (dom:node-value (elt child-nodes 0))
+                            "")))
+             (emit :text-message comp :from from :to to :body text :id id :stanza stanza :stripped stripped)))
+          (marker
+           (let ((marker-type (dom:tag-name marker))
+                 (msgid (dom:get-attribute marker "id")))
+             (emit :message-marker comp :from from :to to :type marker-type :marker-id msgid :id id :stanza stanza :stripped stripped)))
+          (chat-state
+           (let ((state-type (dom:tag-name chat-state)))
+             (emit :chat-state comp :from from :to to :type state-type :id id :stanza stanza :stripped stripped)))
+          (t
+           (emit :message comp :from from :to to :id id :stanza stanza :stripped stripped)))
+      (stanza-error (e)
+        (send-stanza-error comp
+                           :id id :to to :from from
+                           :stanza-type "message"
+                           :e e)))))
 
 (defun handle-connection-complete (comp)
   (format *debug-io* "Connection complete! \\o/")