Add ClientConnectorDNSError for differentiating DNS errors from others

CHANGES/8455.feature.rst

@@ -0,0 +1 @@
+Added :exc:`aiohttp.ClientConnectorDNSError` for differentiating DNS resolution errors from other connector errors -- by :user:`mstojcevich`.

CONTRIBUTORS.txt

@@ -230,6 +230,7 @@ Manuel Miranda
 Marat Sharafutdinov
 Marc Mueller
 Marco Paolini
+Marcus Stojcevich
 Mariano Anaya
 Mariusz Masztalerczuk
 Marko Kohtala

aiohttp/__init__.py

@@ -8,6 +8,7 @@
     ClientConnectionError,
     ClientConnectionResetError,
     ClientConnectorCertificateError,
+    ClientConnectorDNSError,
     ClientConnectorError,
     ClientConnectorSSLError,
     ClientError,
@@ -120,6 +121,7 @@
     "ClientConnectionError",
     "ClientConnectionResetError",
     "ClientConnectorCertificateError",
+    "ClientConnectorDNSError",
     "ClientConnectorError",
     "ClientConnectorSSLError",
     "ClientError",

aiohttp/client.py

@@ -44,6 +44,7 @@
     ClientConnectionError,
     ClientConnectionResetError,
     ClientConnectorCertificateError,
+    ClientConnectorDNSError,
     ClientConnectorError,
     ClientConnectorSSLError,
     ClientError,
@@ -110,6 +111,7 @@
     "ClientConnectionError",
     "ClientConnectionResetError",
     "ClientConnectorCertificateError",
+    "ClientConnectorDNSError",
     "ClientConnectorError",
     "ClientConnectorSSLError",
     "ClientError",

aiohttp/client_exceptions.py

@@ -29,6 +29,7 @@
     "ClientConnectorError",
     "ClientProxyConnectionError",
     "ClientSSLError",
+    "ClientConnectorDNSError",
     "ClientConnectorSSLError",
     "ClientConnectorCertificateError",
     "ConnectionTimeoutError",
@@ -173,6 +174,14 @@ def __str__(self) -> str:
     __reduce__ = BaseException.__reduce__
 
 
+class ClientConnectorDNSError(ClientConnectorError):
+    """DNS resolution failed during client connection.
+
+    Raised in :class:`aiohttp.connector.TCPConnector` if
+        DNS resolution fails.
+    """
+
+
 class ClientProxyConnectionError(ClientConnectorError):
     """Proxy connection error.
 

aiohttp/connector.py

@@ -39,6 +39,7 @@
 from .client_exceptions import (
     ClientConnectionError,
     ClientConnectorCertificateError,
+    ClientConnectorDNSError,
     ClientConnectorError,
     ClientConnectorSSLError,
     ClientHttpProxyError,
@@ -1222,7 +1223,7 @@ async def _create_direct_connection(
                 raise
             # in case of proxy it is not ClientProxyConnectionError
             # it is problem of resolving proxy ip itself
-            raise ClientConnectorError(req.connection_key, exc) from exc
+            raise ClientConnectorDNSError(req.connection_key, exc) from exc
 
         last_exc: Optional[Exception] = None
         addr_infos = self._convert_hosts_to_addr_infos(hosts)

docs/client_reference.rst

@@ -2254,6 +2254,12 @@ Connection errors
 
    Derived from :exc:`ClientOSError`
 
+.. class:: ClientConnectorDNSError
+
+   DNS resolution error.
+
+   Derived from :exc:`ClientConnectorError`
+
 .. class:: ClientProxyConnectionError
 
    Derived from :exc:`ClientConnectorError`
@@ -2335,6 +2341,8 @@ Hierarchy of exceptions
 
         * :exc:`ClientProxyConnectionError`
 
+        * :exc:`ClientConnectorDNSError`
+
         * :exc:`ClientSSLError`
 
           * :exc:`ClientConnectorCertificateError`

tests/test_client_functional.py

@@ -3315,6 +3315,17 @@ async def test_aiohttp_request_ctx_manager_not_found() -> None:
             assert False, "never executed"  # pragma: no cover
 
 
+async def test_raising_client_connector_dns_error_on_dns_failure() -> None:
+    """Verify that the exception raised when a DNS lookup fails is specific to DNS."""
+    with mock.patch(
+        "aiohttp.connector.TCPConnector._resolve_host", autospec=True, spec_set=True
+    ) as mock_resolve_host:
+        mock_resolve_host.side_effect = OSError(None, "DNS lookup failed")
+        with pytest.raises(aiohttp.ClientConnectorDNSError, match="DNS lookup failed"):
+            async with aiohttp.request("GET", "http://wrong-dns-name.com"):
+                assert False, "never executed"
+
+
 async def test_aiohttp_request_coroutine(aiohttp_server: AiohttpServer) -> None:
     async def handler(request: web.Request) -> web.Response:
         return web.Response()