Handle network outages

Quote queries will hang indefinitely when the network goes down.
Instead poll for network reestablishment such that roaming on
wifi is supported and real-time feeds will resume once the network is
back.

piker/brokers/core.py

@@ -3,6 +3,8 @@ Core broker-daemon tasks and API.
 """
 import time
 import inspect
+from functools import partial
+import socket
 from types import ModuleType
 from typing import AsyncContextManager
 
@@ -44,6 +46,17 @@ async def quote(brokermod: ModuleType, tickers: [str]) -> dict:
         return results
 
 
+async def wait_for_network(get_quotes, sleep=1):
+    """Wait until the network comes back up.
+    """
+    while True:
+        try:
+            return await get_quotes()
+        except socket.gaierror:
+            log.warn(f"Network is down waiting for reestablishment...")
+            await trio.sleep(sleep)
+
+
 async def poll_tickers(
     client: 'Client',
     quoter: AsyncContextManager,
@@ -64,7 +77,16 @@ async def poll_tickers(
     async with quoter(client, tickers) as get_quotes:
         while True:  # use an event here to trigger exit?
             prequote_start = time.time()
-            quotes = await get_quotes(tickers)
+
+            with trio.move_on_after(3) as cancel_scope:
+                quotes = await get_quotes(tickers)
+
+            cancelled = cancel_scope.cancelled_caught
+            if cancelled:
+                log.warn("Quote query timed out after 3 seconds, retrying...")
+                # handle network outages by idling until response is received
+                quotes = await wait_for_network(partial(get_quotes, tickers))
+
             postquote_start = time.time()
             payload = {}
             for symbol, quote in quotes.items():