interface: subscribe to headers in run_fetch_blocks

so that 'monitor_connection' is already running while waiting for first header

electrum/interface.py

@@ -340,7 +340,6 @@ class Interface(PrintError):
         return conn, res['count']
 
     async def open_session(self, sslc, exit_early):
-        header_queue = asyncio.Queue()
         self.session = NotificationSession(self.host, self.port, ssl=sslc, proxy=self.proxy)
         async with self.session as session:
             try:
@@ -350,11 +349,10 @@ class Interface(PrintError):
             if exit_early:
                 return
             self.print_error("connection established. version: {}".format(ver))
-            await session.subscribe('blockchain.headers.subscribe', [], header_queue)
 
             async with self.group as group:
                 await group.spawn(self.ping())
-                await group.spawn(self.run_fetch_blocks(header_queue))
+                await group.spawn(self.run_fetch_blocks())
                 await group.spawn(self.monitor_connection())
                 # NOTE: group.__aexit__ will be called here; this is needed to notice exceptions in the group!
 
@@ -373,7 +371,9 @@ class Interface(PrintError):
         self.fut.cancel()
         asyncio.get_event_loop().create_task(self.group.cancel_remaining())
 
-    async def run_fetch_blocks(self, header_queue):
+    async def run_fetch_blocks(self):
+        header_queue = asyncio.Queue()
+        await self.session.subscribe('blockchain.headers.subscribe', [], header_queue)
         while True:
             self.network.notify('updated')
             item = await header_queue.get()