qt "open channel" dialog: detect invalid remote node id sooner

and avoid the "please wait" text to be interpreted as a node id

related #6705

electrum/gui/qt/channels_list.py

@@ -357,8 +357,9 @@ class ChannelsList(MyTreeView):
             self.parent.wallet.network.start_gossip()
             nodeid = bh2u(lnworker.lnrater.suggest_peer() or b'')
             if not nodeid:
-                remote_nodeid.setText(
+                remote_nodeid.setText("")
-                    "Please wait until the graph is synchronized to 30%.")
+                remote_nodeid.setPlaceholderText(
+                    "Please wait until the graph is synchronized to 30%, and then try again.")
             else:
                 remote_nodeid.setText(nodeid)
             remote_nodeid.repaint()  # macOS hack for #6269

electrum/gui/qt/main_window.py

@@ -74,7 +74,7 @@ from electrum.network import Network, TxBroadcastError, BestEffortRequestFailed,
 from electrum.exchange_rate import FxThread
 from electrum.simple_config import SimpleConfig
 from electrum.logging import Logger
-from electrum.lnutil import ln_dummy_address
+from electrum.lnutil import ln_dummy_address, extract_nodeid, ConnStringFormatError
 from electrum.lnaddr import lndecode, LnDecodeException
 
 from .exception_window import Exception_Hook
@@ -1757,6 +1757,11 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         return make_tx
 
     def open_channel(self, connect_str, funding_sat, push_amt):
+        try:
+            extract_nodeid(connect_str)
+        except ConnStringFormatError as e:
+            self.main_window.show_error(str(e))
+            return
         # use ConfirmTxDialog
         # we need to know the fee before we broadcast, because the txid is required
         make_tx = self.mktx_for_open_channel(funding_sat)

electrum/lnutil.py

@@ -1203,7 +1203,8 @@ def extract_nodeid(connect_contents: str) -> Tuple[bytes, str]:
         raise ConnStringFormatError(_('At least a hostname must be supplied after the at symbol.'))
     try:
         node_id = bfh(nodeid_hex)
-        assert len(node_id) == 33, len(node_id)
+        if len(node_id) != 33:
+            raise Exception()
     except:
         raise ConnStringFormatError(_('Invalid node ID, must be 33 bytes and hexadecimal'))
     return node_id, rest