protocol: fail gracefully on cancellation

trezor_agent/client.py

@@ -81,7 +81,7 @@ class Client(object):
         except self.call_exception as e:
             code, msg = e.args
             log.warning('%s error #%s: %s', self.device_name, code, msg)
-            raise IOError(msg)
+            raise IOError(msg)  # close current connection, keep server open
 
         verifying_key = formats.decompress_pubkey(pubkey=result.public_key,
                                                   curve_name=self.curve)

trezor_agent/protocol.py

@@ -139,7 +139,10 @@ class Handler(object):
 
         log.debug('signing %d-byte blob', len(blob))
         label = key['name'].decode('ascii')  # label should be a string
-        signature = self.signer(label=label, blob=blob)
+        try:
+            signature = self.signer(label=label, blob=blob)
+        except IOError:
+            return _fail()
         log.debug('signature: %s', binascii.hexlify(signature))
 
         try:

trezor_agent/server.py

@@ -55,8 +55,6 @@ def handle_connection(conn, handler):
             msg = util.read_frame(conn)
             reply = handler.handle(msg=msg)
             util.send(conn, reply)
-    except IOError as e:
-        log.error('I/O error: %s', e)
     except EOFError:
         log.debug('goodbye agent')
     except Exception as e:  # pylint: disable=broad-except