diff --git a/src/wormhole/twisted/demo.py b/src/wormhole/twisted/demo.py
index 790440d..4236cbf 100644
--- a/src/wormhole/twisted/demo.py
+++ b/src/wormhole/twisted/demo.py
@@ -5,11 +5,11 @@ from twisted.internet import reactor
 from .transcribe import Wormhole
 from .. import public_relay
 
-APPID = "lothar.com/wormhole/text-xfer"
+APPID = b"lothar.com/wormhole/text-or-file-xfer"
 
 w = Wormhole(APPID, public_relay.RENDEZVOUS_RELAY)
 
-if sys.argv[1] == "send-text":
+if sys.argv[1] == "send":
     message = sys.argv[2]
     data = json.dumps({"message": message}).encode("utf-8")
     d = w.get_code()
@@ -22,12 +22,12 @@ if sys.argv[1] == "send-text":
     d.addCallback(_sent)
     def _got_data(them_bytes):
         them_d = json.loads(them_bytes.decode("utf-8"))
-        if them_d["message"] == "ok":
+        if them_d["message_ack"] == "ok":
             print("text sent")
         else:
             print("error sending text: %r" % (them_d,))
     d.addCallback(_got_data)
-elif sys.argv[1] == "receive-text":
+elif sys.argv[1] == "receive":
     code = sys.argv[2]
     w.set_code(code)
     d = w.get_data()
@@ -35,14 +35,37 @@ elif sys.argv[1] == "receive-text":
         them_d = json.loads(them_bytes.decode("utf-8"))
         if "error" in them_d:
             print("ERROR: " + them_d["error"], file=sys.stderr)
-            return 1
+            raise RuntimeError
+        if "file" in them_d:
+            print("they're trying to send us a file, which I don't handle")
+            data = json.dumps({"error": "not capable of receiving files"})
+            d1 = w.send_data(data.encode("utf-8"))
+            d1.addCallback(lambda _: RuntimeError())
+            return d1
+        if not "message" in them_d:
+            print("I don't know what they're offering\n")
+            print(them_d)
+            data = json.dumps({"error": "huh?"})
+            d1 = w.send_data(data.encode("utf-8"))
+            d1.addCallback(lambda _: RuntimeError())
+            return d1
         print(them_d["message"])
-        data = json.dumps({"message": "ok"}).encode("utf-8")
-        return w.send_data(data)
+        data = json.dumps({"message_ack": "ok"})
+        d1 = w.send_data(data.encode("utf-8"))
+        d1.addCallback(lambda _: 0)
+        return d1
     d.addCallback(_got_data)
 else:
     raise ValueError("bad command")
-d.addCallback(w.close)
+
+d.addBoth(w.close)
+rc = []
+def _success(res):
+    rc.append(res)
+def _fail(f):
+    log.err(f)
+    rc.append(1)
+d.addCallbacks(_success, _fail)
 d.addCallback(lambda _: reactor.stop())
-d.addErrback(log.err)
 reactor.run()
+sys.exit(rc[0])