Factor out all `maybe_open_context()` guff

piker/clearing/_ems.py

@@ -1275,13 +1275,48 @@ async def maybe_open_trade_relays(
 
 ) -> tuple:
 
-    relay, feed, client_ready = await _router.nursery.start(
-        _router.open_trade_relays,
-        fqsn,
-        exec_mode,
-        loglevel,
-    )
-    yield relay, feed, client_ready
+    def cache_on_fqsn_unless_paper(
+        router: Router,
+        fqsn: str,
+        exec_mode: str,  # ('paper', 'live')
+        loglevel: str = 'info',
+    ) -> Hashable:
+        if exec_mode == 'paper':
+            return f'paper_{fqsn}'
+        else:
+            return fqsn
+
+    # XXX: closure to enable below use of
+    # ``tractor.trionics.maybe_open_context()``
+    @acm
+    async def cached_mngr(
+        router: Router,
+        fqsn: str,
+        exec_mode: str,  # ('paper', 'live')
+        loglevel: str = 'info',
+    ):
+        relay, feed, client_ready = await _router.nursery.start(
+            _router.open_trade_relays,
+            fqsn,
+            exec_mode,
+            loglevel,
+        )
+        yield relay, feed, client_ready
+
+    async with tractor.trionics.maybe_open_context(
+        acm_func=cached_mngr,
+        kwargs={
+            'router': _router,
+            'fqsn': fqsn,
+            'exec_mode': exec_mode,
+            'loglevel': loglevel,
+        },
+        key=cache_on_fqsn_unless_paper,
+    ) as (
+        cache_hit,
+        (relay, feed, client_ready)
+    ):
+        yield relay, feed, client_ready
 
 
 @tractor.context
@@ -1351,31 +1386,13 @@ async def _emsd_main(
     # NOTE: open a stream with the brokerd backend for order flow
     # dialogue and dark clearing but only open one: we try to keep as
     # few duplicate streams as necessary per ems actor.
-    def cache_on_fqsn_unless_paper(
-        router: Router,
-        fqsn: str,
-        exec_mode: str,  # ('paper', 'live')
-        loglevel: str = 'info',
-    ) -> Hashable:
-        if exec_mode == 'paper':
-            return f'paper_{fqsn}'
-        else:
-            return fqsn
+    async with maybe_open_trade_relays(
+        _router,
+        fqsn,
+        exec_mode,
+        loglevel,
+    ) as (relay, feed, client_ready):
 
-    async with tractor.trionics.maybe_open_context(
-        acm_func=maybe_open_trade_relays,
-        kwargs={
-            'router': _router,
-            'fqsn': fqsn,
-            'exec_mode': exec_mode,
-            'loglevel': loglevel,
-        },
-        key=cache_on_fqsn_unless_paper,
-
-    ) as (
-        cache_hit,
-        (relay, feed, client_ready)
-    ):
         brokerd_stream = relay.brokerd_stream
         dark_book = _router.get_dark_book(broker)
 
@@ -1412,7 +1429,6 @@ async def _emsd_main(
                     dark_book,
                     _router,
                 )
-
             finally:
                 # try to remove client from subscription registry
                 _router.subscribers[fqsn].remove(client_stream)