[python,aiohttp] Don't create persistent aiohttp.ClientSession in __init__

aiohttp's `ClientSession` & `TCPConnector` used to obtain an event loop in
__init__ (via `asyncio.get_event_loop`). However, as of aio-libs/aiohttp#8512 both
classes now obtain the running event loop and won't potentially create one. This
makes it impossible to create `ClientSession` and `TCPConnector` objects outside
of coroutines, as `get_running_loop` must be called from a coroutine.

Thus we defer the creation of a `ClientSession` into the actual request and
cache it for later usage. Thereby we pay only a very small price on the first
request, but subsequent requests will not be any more expensive.

Author: dcermak

modules/openapi-generator/src/main/resources/python/asyncio/rest.mustache

@@ -44,51 +44,31 @@ class RESTClientObject:
     def __init__(self, configuration) -> None:
 
         # maxsize is number of requests to host that are allowed in parallel
-        maxsize = configuration.connection_pool_maxsize
+        self.maxsize = configuration.connection_pool_maxsize
 
-        ssl_context = ssl.create_default_context(
+        self.ssl_context = ssl.create_default_context(
             cafile=configuration.ssl_ca_cert
         )
         if configuration.cert_file:
-            ssl_context.load_cert_chain(
+            self.ssl_context.load_cert_chain(
                 configuration.cert_file, keyfile=configuration.key_file
             )
 
         if not configuration.verify_ssl:
-            ssl_context.check_hostname = False
-            ssl_context.verify_mode = ssl.CERT_NONE
-
-        connector = aiohttp.TCPConnector(
-            limit=maxsize,
-            ssl=ssl_context
-        )
+            self.ssl_context.check_hostname = False
+            self.ssl_context.verify_mode = ssl.CERT_NONE
 
         self.proxy = configuration.proxy
         self.proxy_headers = configuration.proxy_headers
 
-        # https pool manager
-        self.pool_manager = aiohttp.ClientSession(
-            connector=connector,
-            trust_env=True
-        )
+        self.retries = configuration.retries
 
-        retries = configuration.retries
-        self.retry_client: Optional[aiohttp_retry.RetryClient]
-        if retries is not None:
-            self.retry_client = aiohttp_retry.RetryClient(
-                client_session=self.pool_manager,
-                retry_options=aiohttp_retry.ExponentialRetry(
-                    attempts=retries,
-                    factor=2.0,
-                    start_timeout=0.1,
-                    max_timeout=120.0
-                )
-            )
-        else:
-            self.retry_client = None
+        self.pool_manager: Optional[aiohttp.ClientSession] = None
+        self.retry_client: Optional[aiohttp_retry.RetryClient] = None
 
-    async def close(self):
-        await self.pool_manager.close()
+    async def close(self) -> None:
+        if self.pool_manager:
+            await self.pool_manager.close()
         if self.retry_client is not None:
             await self.retry_client.close()
 
@@ -195,10 +175,27 @@ class RESTClientObject:
                 raise ApiException(status=0, reason=msg)
 
         pool_manager: Union[aiohttp.ClientSession, aiohttp_retry.RetryClient]
-        if self.retry_client is not None and method in ALLOW_RETRY_METHODS:
+
+        # https pool manager
+        if self.pool_manager is None:
+            self.pool_manager = aiohttp.ClientSession(
+                connector=aiohttp.TCPConnector(limit=self.maxsize, ssl=self.ssl_context),
+                trust_env=True,
+            )
+        pool_manager = self.pool_manager
+
+        if self.retries is not None and method in ALLOW_RETRY_METHODS:
+            if self.retry_client is None:
+                self.retry_client = aiohttp_retry.RetryClient(
+                    client_session=self.pool_manager,
+                    retry_options=aiohttp_retry.ExponentialRetry(
+                        attempts=self.retries,
+                        factor=2.0,
+                        start_timeout=0.1,
+                        max_timeout=120.0
+                    )
+                )
             pool_manager = self.retry_client
-        else:
-            pool_manager = self.pool_manager
 
         r = await pool_manager.request(**args)
 

samples/openapi3/client/petstore/python-aiohttp/petstore_api/rest.py

@@ -54,51 +54,31 @@ class RESTClientObject:
     def __init__(self, configuration) -> None:
 
         # maxsize is number of requests to host that are allowed in parallel
-        maxsize = configuration.connection_pool_maxsize
+        self.maxsize = configuration.connection_pool_maxsize
 
-        ssl_context = ssl.create_default_context(
+        self.ssl_context = ssl.create_default_context(
             cafile=configuration.ssl_ca_cert
         )
         if configuration.cert_file:
-            ssl_context.load_cert_chain(
+            self.ssl_context.load_cert_chain(
                 configuration.cert_file, keyfile=configuration.key_file
             )
 
         if not configuration.verify_ssl:
-            ssl_context.check_hostname = False
-            ssl_context.verify_mode = ssl.CERT_NONE
-
-        connector = aiohttp.TCPConnector(
-            limit=maxsize,
-            ssl=ssl_context
-        )
+            self.ssl_context.check_hostname = False
+            self.ssl_context.verify_mode = ssl.CERT_NONE
 
         self.proxy = configuration.proxy
         self.proxy_headers = configuration.proxy_headers
 
-        # https pool manager
-        self.pool_manager = aiohttp.ClientSession(
-            connector=connector,
-            trust_env=True
-        )
+        self.retries = configuration.retries
 
-        retries = configuration.retries
-        self.retry_client: Optional[aiohttp_retry.RetryClient]
-        if retries is not None:
-            self.retry_client = aiohttp_retry.RetryClient(
-                client_session=self.pool_manager,
-                retry_options=aiohttp_retry.ExponentialRetry(
-                    attempts=retries,
-                    factor=2.0,
-                    start_timeout=0.1,
-                    max_timeout=120.0
-                )
-            )
-        else:
-            self.retry_client = None
+        self.pool_manager: Optional[aiohttp.ClientSession] = None
+        self.retry_client: Optional[aiohttp_retry.RetryClient] = None
 
-    async def close(self):
-        await self.pool_manager.close()
+    async def close(self) -> None:
+        if self.pool_manager:
+            await self.pool_manager.close()
         if self.retry_client is not None:
             await self.retry_client.close()
 
@@ -205,10 +185,27 @@ async def request(
                 raise ApiException(status=0, reason=msg)
 
         pool_manager: Union[aiohttp.ClientSession, aiohttp_retry.RetryClient]
-        if self.retry_client is not None and method in ALLOW_RETRY_METHODS:
+
+        # https pool manager
+        if self.pool_manager is None:
+            self.pool_manager = aiohttp.ClientSession(
+                connector=aiohttp.TCPConnector(limit=self.maxsize, ssl=self.ssl_context),
+                trust_env=True,
+            )
+        pool_manager = self.pool_manager
+
+        if self.retries is not None and method in ALLOW_RETRY_METHODS:
+            if self.retry_client is None:
+                self.retry_client = aiohttp_retry.RetryClient(
+                    client_session=self.pool_manager,
+                    retry_options=aiohttp_retry.ExponentialRetry(
+                        attempts=self.retries,
+                        factor=2.0,
+                        start_timeout=0.1,
+                        max_timeout=120.0
+                    )
+                )
             pool_manager = self.retry_client
-        else:
-            pool_manager = self.pool_manager
 
         r = await pool_manager.request(**args)
 

samples/openapi3/client/petstore/python-aiohttp/tests/test_api_client.py

@@ -10,14 +10,6 @@
 HOST = 'http://localhost/v2'
 
 class TestApiClient(unittest.IsolatedAsyncioTestCase):
-    async def test_context_manager_closes_client(self):
-        async with petstore_api.ApiClient() as client:
-            # pool_manager
-            self.assertFalse(client.rest_client.pool_manager.closed)
-            rest_pool_ref = client.rest_client.pool_manager
-
-        self.assertTrue(rest_pool_ref.closed)
-
     async def test_ignore_operation_servers(self):
         config = petstore_api.Configuration(host=HOST)
         async with petstore_api.ApiClient(config) as client: