fix: improve error when exiting before running Nitric.run() (#145)

Author: jyecusch

.gitignore

@@ -149,3 +149,5 @@ cython_debug/
 .vscode/
 
 contracts/
+
+testproj/

nitric/application.py

@@ -28,6 +28,8 @@
 class Nitric:
     """Represents a nitric app."""
 
+    _has_run = False
+
     _workers: List[FunctionServer] = []
     _cache: Dict[str, Dict[str, Any]] = {
         "api": {},
@@ -61,13 +63,26 @@ def _create_resource(cls, resource: Type[BT], name: str, *args: Any, **kwargs: A
                 "The nitric server may not be running or the host/port is inaccessible"
             ) from cre
 
+    @classmethod
+    def has_run(cls) -> bool:
+        """
+        Check if the Nitric application has been started.
+
+        Returns:
+            bool: True if the Nitric application has been started, False otherwise.
+        """
+        return cls._has_run
+
     @classmethod
     def run(cls) -> None:
         """
         Start the nitric application.
 
         This will execute in an existing event loop if there is one, otherwise it will attempt to create its own.
         """
+        if cls._has_run:
+            print("The Nitric application has already been started, Nitric.run() should only be called once.")
+        cls._has_run = True
         try:
             try:
                 loop = asyncio.get_running_loop()

nitric/channel.py

@@ -0,0 +1,52 @@
+import atexit
+import re
+from urllib.parse import urlparse
+from grpclib.client import Channel
+
+from nitric.application import Nitric
+from nitric.config import settings
+from nitric.exception import NitricNotRunningException
+
+
+def format_url(url: str):
+    """Add the default http scheme prefix to urls without one."""
+    if not re.match("^((?:http|ftp|https):)?//", url.lower()):
+        return "http://{0}".format(url)
+    return url
+
+
+class ChannelManager:
+    """A singleton class to manage the gRPC channel."""
+
+    channel = None
+
+    @classmethod
+    def get_channel(cls) -> Channel:
+        """Return the channel instance."""
+
+        if cls.channel is None:
+            cls._create_channel()
+        return cls.channel  # type: ignore
+
+    @classmethod
+    def _create_channel(cls):
+        """Create a new channel instance."""
+
+        channel_url = urlparse(format_url(settings.SERVICE_ADDRESS))
+        cls.channel = Channel(host=channel_url.hostname, port=channel_url.port)
+        atexit.register(cls._close_channel)
+
+    @classmethod
+    def _close_channel(cls):
+        """Close the channel instance."""
+
+        if cls.channel is not None:
+            cls.channel.close()
+            cls.channel = None
+
+            # If the program exits without calling Nitric.run(), it may have been a mistake.
+            if not Nitric.has_run():
+                print(
+                    "WARNING: The Nitric application was not started. "
+                    "If you intended to start the application, call Nitric.run() before exiting."
+                )

nitric/exception.py

@@ -157,6 +157,13 @@ def __init__(self, message: str):
         super().__init__("Unable to connect to nitric server." + (" " + message if message else ""))
 
 
+class NitricNotRunningException(Exception):
+    """The Nitric application wasn't started before the program exited."""
+
+    def __init__(self):
+        super().__init__("The Nitric application was not started, call Nitric.run() to start the application.")
+
+
 def exception_from_grpc_error(error: GRPCError):
     """Translate a gRPC error to a nitric api exception."""
     return exception_from_grpc_code(error.status.value, error.message or "")

nitric/resources/apis.py

@@ -60,7 +60,7 @@
     ResourceType,
 )
 from nitric.resources.resource import Resource as BaseResource
-from nitric.utils import new_default_channel
+from nitric.channel import ChannelManager
 
 
 @dataclass
@@ -479,7 +479,7 @@ async def _route_request_iterator(self):
 
     async def start(self) -> None:
         """Register this API route handler and handle http requests."""
-        channel = new_default_channel()
+        channel = ChannelManager.get_channel()
         server = ApiStub(channel=channel)
 
         # Attach security rules for this route

nitric/resources/buckets.py

@@ -52,7 +52,7 @@
     StorageWriteRequest,
 )
 from nitric.resources.resource import SecureResource
-from nitric.utils import new_default_channel
+from nitric.channel import ChannelManager
 
 
 class BucketNotifyRequest:
@@ -142,7 +142,7 @@ class BucketRef(object):
 
     def __init__(self, name: str):
         """Construct a Nitric Storage Client."""
-        self._channel: Union[Channel, None] = new_default_channel()
+        self._channel: Union[Channel, None] = ChannelManager.get_channel()
         self._storage_stub = StorageStub(channel=self._channel)
         self.name = name
 
@@ -428,7 +428,7 @@ async def _listener_request_iterator(self):
 
     async def start(self) -> None:
         """Register this bucket listener and listen for events."""
-        channel = new_default_channel()
+        channel = ChannelManager.get_channel()
         server = StorageListenerStub(channel=channel)
 
         try:

nitric/resources/kv.py

@@ -42,7 +42,8 @@
     ResourceType,
 )
 from nitric.resources.resource import SecureResource
-from nitric.utils import dict_from_struct, new_default_channel, struct_from_dict
+from nitric.utils import dict_from_struct, struct_from_dict
+from nitric.channel import ChannelManager
 
 
 class KeyValueStoreRef:
@@ -54,7 +55,7 @@ class KeyValueStoreRef:
 
     def __init__(self, name: str):
         """Construct a reference to a deployed key value store."""
-        self._channel: Channel = new_default_channel()
+        self._channel: Channel = ChannelManager.get_channel()
         self._kv_stub = KvStoreStub(channel=self._channel)
         self.name = name
 

nitric/resources/queues.py

@@ -31,7 +31,8 @@
 from nitric.proto.queues.v1 import QueuesStub as QueueServiceStub
 from nitric.proto.resources.v1 import Action, ResourceDeclareRequest, ResourceIdentifier, ResourceType
 from nitric.resources.resource import SecureResource
-from nitric.utils import dict_from_struct, new_default_channel, struct_from_dict
+from nitric.utils import dict_from_struct, struct_from_dict
+from nitric.channel import ChannelManager
 
 
 @dataclass(frozen=True, order=True)
@@ -91,7 +92,7 @@ class QueueRef(object):
 
     def __init__(self, name: str) -> None:
         """Construct a Nitric Queue Client."""
-        self._channel: Channel = new_default_channel()
+        self._channel: Channel = ChannelManager.get_channel()
         self._queue_stub = QueueServiceStub(channel=self._channel)
         self.name = name
 

nitric/resources/resource.py

@@ -34,7 +34,7 @@
     ResourcesStub,
     ResourceType,
 )
-from nitric.utils import new_default_channel
+from nitric.channel import ChannelManager
 
 T = TypeVar("T", bound="Resource")
 
@@ -48,7 +48,7 @@ def __init__(self, name: str):
         """Construct a new resource."""
         self.name = name
         self._reg: Optional[Task[Any]] = None  # type: ignore
-        self._channel = new_default_channel()
+        self._channel = ChannelManager.get_channel()
         self._resources_stub = ResourcesStub(channel=self._channel)
 
     @abstractmethod
@@ -85,9 +85,6 @@ def _perms_to_actions(self, *args: Any) -> List[Action]:
         pass
 
     async def _register_policy_async(self, *args: str) -> None:
-        # if self._reg is not None:
-        #     await asyncio.wait({self._reg})
-
         policy = PolicyResource(
             principals=[ResourceIdentifier(type=ResourceType.Service)],
             actions=self._perms_to_actions(*args),

nitric/resources/schedules.py

@@ -37,7 +37,7 @@
     ScheduleEvery,
     SchedulesStub,
 )
-from nitric.utils import new_default_channel
+from nitric.channel import ChannelManager
 
 
 class ScheduleServer(FunctionServer):
@@ -93,7 +93,7 @@ async def _schedule_request_iterator(self):
 
     async def start(self) -> None:
         """Register this schedule and start listening for requests."""
-        channel = new_default_channel()
+        channel = ChannelManager.get_channel()
         schedules_stub = SchedulesStub(channel=channel)
 
         try: