Compose KeyTransport message correctly

Simply calling omemo_message_create() cannot compose a valid
KeyTransport message, which should at least have an ordinary "message"
node, so we should first make up such message without a "body", then
let omemo_message_prepare_encryption() of libomemo hamdle such case:

gkdr/libomemo#33

Signed-off-by: HardenedVault <root@hardenedvault.net>

src/lurch.c

@@ -801,7 +801,9 @@ static void lurch_pep_bundle_for_keytransport(JabberStream * js_p, const char *
   lurch_addr laddr = {0};
   axc_buf * key_ct_buf_p = (void *) 0;
   char * msg_xml = (void *) 0;
+  int len = 0;
   xmlnode * msg_node_p = (void *) 0;
+  char * msg_id = (void *) 0;
   void * jabber_handle_p = purple_plugins_find_with_id("prpl-jabber");
 
   uname = lurch_util_uname_strip(purple_account_get_username(purple_connection_get_account(js_p->gc)));
@@ -842,9 +844,21 @@ static void lurch_pep_bundle_for_keytransport(JabberStream * js_p, const char *
     goto cleanup;
   }
 
-  ret_val = omemo_message_create(own_id, &crypto, &msg_p);
+  //compose a message without body as template
+  msg_node_p = xmlnode_new("message");
+  xmlnode_set_attrib(msg_node_p, "type", "chat");
+  msg_id = jabber_get_next_id(js_p);
+  xmlnode_set_attrib(msg_node_p, "id", msg_id);
+  xmlnode_set_attrib(msg_node_p, "to", from);
+
+  msg_xml = xmlnode_to_str(msg_node_p, &len);
+  ret_val = omemo_message_prepare_encryption(msg_xml, own_id, &crypto, OMEMO_STRIP_ALL, &msg_p);
+  xmlnode_free(msg_node_p);
+  msg_node_p = (void *) 0;
+  g_free(msg_xml);
+  msg_xml = (void *) 0;
   if (ret_val) {
-    err_msg_dbg = g_strdup_printf("failed to create omemo msg");
+    err_msg_dbg = g_strdup_printf("failed to create omemo key transport msg for %s", from);
     goto cleanup;
   }
 
@@ -891,6 +905,7 @@ static void lurch_pep_bundle_for_keytransport(JabberStream * js_p, const char *
   }
   g_free(laddr.jid);
   g_free(uname);
+  g_free(msg_id);
   axc_context_destroy_all(axc_ctx_p);
   omemo_message_destroy(msg_p);
   axc_buf_free(key_ct_buf_p);