Namecoin: Allow name_update to use existing value if explicit value o…

…mitted

electrum_nmc/commands.py

@@ -561,13 +561,27 @@ def name_firstupdate(self, identifier, rand, name_new_txid, value, destination=N
         tx = self._mktx([], tx_fee, change_addr, domain, nocheck, unsigned, rbf, password, locktime, name_input_txids=[name_new_txid], name_outputs=[(destination, amount, name_op)])
         return tx.as_dict()
 
-    @command('wp')
-    def name_update(self, identifier, value, destination=None, amount=0.0, fee=None, from_addr=None, change_addr=None, nocheck=False, unsigned=False, rbf=None, password=None, locktime=None):
+    @command('wpn')
+    def name_update(self, identifier, value=None, destination=None, amount=0.0, fee=None, from_addr=None, change_addr=None, nocheck=False, unsigned=False, rbf=None, password=None, locktime=None):
         """Create a name_update transaction. """
 
         tx_fee = satoshis(fee)
         domain = from_addr.split(',') if from_addr else None
 
+        # Allow renewing a name without any value changes by omitting the
+        # value.
+        if value is None:
+            list_results = self.name_list(identifier)[0]
+
+            # This check is in place to prevent an attack where an ElectrumX
+            # server supplies an unconfirmed name_update transaction with a
+            # malicious value and then tricks the wallet owner into signing a
+            # name renewal with that malicious value.
+            if list_results["expires_in"] > 36000 - 12:
+                raise Exception("Name was updated too recently to safely determine current value.  Either wait or specify an explicit value.")
+
+            value = list_results["value"]
+
         # TODO: support non-ASCII encodings
         # TODO: enforce length limits on identifier and value
         identifier_bytes = identifier.encode("ascii")
@@ -947,6 +961,7 @@ def help(self):
     'allow_existing': (None, "Allow pre-registering a name that already is registered.  Your registration fee will be forfeited until you can register the name after it expires."),
     'allow_early': (None, "Allow submitting a name registration while its pre-registration is still pending.  This increases the risk of an attacker stealing your name registration."),
     'identifier':  (None, "The requested name identifier"),
+    'value':       (None, "The value to assign to the name"),
 }