disconnect from servers on exception

electrum/interface.py

@@ -244,6 +244,8 @@ class BlockHeaderInterface(PrintError):
                 could_connect, num_headers = await self.conn.request_chunk(self.height, next_height)
                 self.tip = max(self.height + num_headers, self.tip)
                 if not could_connect:
+                    if self.height <= self.iface.network.max_checkpoint():
+                        raise Exception('server chain conflicts with checkpoints or genesis')
                     last = await self.step()
                     self.tip = max(self.height, self.tip)
                     continue

electrum/network.py

@@ -809,14 +809,16 @@ class Network(PrintError):
                 asyncio.get_event_loop().create_task(self.new_interface(server))
             remove = []
             for k, i in self.interfaces.items():
-                if i.fut.done():
-                    if i.exception:
-                        try:
-                            raise i.exception
-                        except BaseException as e:
-                            self.print_error(i.server, "errored because", str(e), str(type(e)))
-                    else:
-                        assert False, "interface future should not finish without exception"
+                if i.fut.done() and not i.exception:
+                    assert False, "interface future should not finish without exception"
+                if i.exception:
+                    if not i.fut.done():
+                        try: i.fut.cancel()
+                        except Exception as e: self.print_error('exception while cancelling fut', e)
+                    try:
+                        raise i.exception
+                    except BaseException as e:
+                        self.print_error(i.server, "errored because", str(e), str(type(e)))
                     remove.append(k)
             changed = False
             for k in remove: