Add `tractor.query_actor()` an addr looker-upper

Sometimes it's handy to just have a non-`Portal` yielding way
to figure out if a "service" actor is up, so add this discovery
helper for that. We'll prolly just leave it undocumented for
now until we figure out a longer-term/better discovery system.

tractor/__init__.py

@@ -29,7 +29,12 @@ from ._streaming import (
     stream,
     context,
 )
-from ._discovery import get_arbiter, find_actor, wait_for_actor
+from ._discovery import (
+    get_arbiter,
+    find_actor,
+    wait_for_actor,
+    query_actor,
+)
 from ._supervise import open_nursery
 from ._state import current_actor, is_root_process
 from ._exceptions import (
@@ -46,11 +51,15 @@ from ._portal import Portal
 __all__ = [
     'Channel',
     'Context',
-    'ModuleNotExposed',
-    'MultiError',
-    'RemoteActorError',
     'ContextCancelled',
+    'ModuleNotExposed',
+    'MsgStream',
+    'MultiError',
+    'Portal',
+    'ReceiveMsgStream',
+    'RemoteActorError',
     'breakpoint',
+    'context',
     'current_actor',
     'find_actor',
     'get_arbiter',
@@ -59,14 +68,11 @@ __all__ = [
     'open_actor_cluster',
     'open_nursery',
     'open_root_actor',
-    'Portal',
     'post_mortem',
+    'query_actor',
     'run',
     'run_daemon',
     'stream',
-    'context',
-    'ReceiveMsgStream',
-    'MsgStream',
     'to_asyncio',
     'wait_for_actor',
 ]

tractor/_discovery.py

@@ -20,7 +20,7 @@ Actor discovery API.
 """
 import typing
 from typing import Tuple, Optional, Union
-from async_generator import asynccontextmanager
+from contextlib import asynccontextmanager as acm
 
 from ._ipc import _connect_chan, Channel
 from ._portal import (
@@ -31,7 +31,7 @@ from ._portal import (
 from ._state import current_actor, _runtime_vars
 
 
-@asynccontextmanager
+@acm
 async def get_arbiter(
 
     host: str,
@@ -58,7 +58,7 @@ async def get_arbiter(
                 yield arb_portal
 
 
-@asynccontextmanager
+@acm
 async def get_root(
     **kwargs,
 ) -> typing.AsyncGenerator[Portal, None]:
@@ -71,28 +71,56 @@ async def get_root(
             yield portal
 
 
-@asynccontextmanager
-async def find_actor(
+@acm
+async def query_actor(
     name: str,
-    arbiter_sockaddr: Tuple[str, int] = None
-) -> typing.AsyncGenerator[Optional[Portal], None]:
-    """Ask the arbiter to find actor(s) by name.
+    arbiter_sockaddr: Tuple[str, int] = None,
 
-    Returns a connected portal to the last registered matching actor
-    known to the arbiter.
-    """
+) -> tuple[str, int]:
+    '''
+    Simple address lookup for a given actor name.
+
+    Returns the (socket) address or ``None``.
+
+    '''
     actor = current_actor()
-    async with get_arbiter(*arbiter_sockaddr or actor._arb_addr) as arb_portal:
+    async with get_arbiter(
+        *arbiter_sockaddr or actor._arb_addr
+    ) as arb_portal:
 
-        sockaddr = await arb_portal.run_from_ns('self', 'find_actor', name=name)
+        sockaddr = await arb_portal.run_from_ns(
+            'self',
+            'find_actor',
+            name=name,
+        )
 
         # TODO: return portals to all available actors - for now just
         # the last one that registered
         if name == 'arbiter' and actor.is_arbiter:
             raise RuntimeError("The current actor is the arbiter")
 
-        elif sockaddr:
+        yield sockaddr if sockaddr else None
 
+
+@acm
+async def find_actor(
+    name: str,
+    arbiter_sockaddr: Tuple[str, int] = None
+
+) -> typing.AsyncGenerator[Optional[Portal], None]:
+    '''
+    Ask the arbiter to find actor(s) by name.
+
+    Returns a connected portal to the last registered matching actor
+    known to the arbiter.
+
+    '''
+    async with query_actor(
+        name=name,
+        arbiter_sockaddr=arbiter_sockaddr,
+    ) as sockaddr:
+
+        if sockaddr:
             async with _connect_chan(*sockaddr) as chan:
                 async with open_portal(chan) as portal:
                     yield portal
@@ -100,7 +128,7 @@ async def find_actor(
             yield None
 
 
-@asynccontextmanager
+@acm
 async def wait_for_actor(
     name: str,
     arbiter_sockaddr: Tuple[str, int] = None
@@ -111,9 +139,14 @@ async def wait_for_actor(
     """
     actor = current_actor()
 
-    async with get_arbiter(*arbiter_sockaddr or actor._arb_addr) as arb_portal:
-
-        sockaddrs = await arb_portal.run_from_ns('self', 'wait_for_actor', name=name)
+    async with get_arbiter(
+        *arbiter_sockaddr or actor._arb_addr,
+    ) as arb_portal:
+        sockaddrs = await arb_portal.run_from_ns(
+            'self',
+            'wait_for_actor',
+            name=name,
+        )
         sockaddr = sockaddrs[-1]
 
         async with _connect_chan(*sockaddr) as chan: