Add checking whether a device supports the button press

src/demetriek/local_auth.py

@@ -154,6 +154,50 @@ def _parse_challenge(self, data: Any) -> AuthChallenge:
             )
             raise LaMetricError(msg) from exception
 
+    async def supported(self) -> bool:
+        """Tell whether the device can hand out its API key with a button press.
+
+        This only checks for the web interface of the device, so unlike
+        `request_challenge()`, nothing shows on the screen of the device.
+
+        Returns
+        -------
+            True when the device has the web interface, like devices from 2022
+            onward. An LM 37X8 TIME asks for credentials instead.
+
+        Raises
+        ------
+            LaMetricConnectionError: An error occurred while communicating with
+                the LaMetric device.
+            LaMetricConnectionTimeoutError: A timeout occurred while communicating
+                with the LaMetric device.
+
+        """
+        url = URL.build(scheme="https", host=self.host, path="/")
+
+        if self.session is None:
+            self.session = aiohttp.ClientSession()
+            self._close_session = True
+
+        try:
+            async with (
+                asyncio.timeout(self.request_timeout),
+                self.session.get(url, ssl=False) as response,
+            ):
+                return response.status == HTTPStatus.OK
+        except TimeoutError as exception:
+            msg = (
+                "Timeout occurred while connecting to the LaMetric device"
+                f" at {self.host}"
+            )
+            raise LaMetricConnectionTimeoutError(msg) from exception
+        except (aiohttp.ClientError, socket.gaierror) as exception:
+            msg = (
+                "Error occurred while communicating with the LaMetric device"
+                f" at {self.host}"
+            )
+            raise LaMetricConnectionError(msg) from exception
+
     async def request_challenge(self) -> AuthChallenge:
         """Ask the device to have its button pressed.
 

tests/test_local_auth.py

@@ -253,3 +253,57 @@ async def test_internal_session(responses: aioresponses) -> None:
     assert challenge.resolved is True
     assert session is not None
     assert session.closed
+
+
+@pytest.mark.parametrize(
+    ("status", "supported"),
+    [
+        # A device from 2022 onward serves its web interface.
+        (200, True),
+        # An LM 37X8 TIME asks for credentials instead.
+        (401, False),
+    ],
+)
+async def test_supported(
+    responses: aioresponses,
+    auth: LaMetricLocalAuth,
+    status: int,
+    supported: bool,  # noqa: FBT001
+) -> None:
+    """Test checking support, without asking the device for a button press."""
+    responses.get(f"{WEB_URL}/", status=status, body="")
+
+    assert await auth.supported() is supported
+    assert ("POST", URL(REQUEST_URL)) not in responses.requests
+
+
+@pytest.mark.parametrize(
+    ("exception", "expected"),
+    [
+        (TimeoutError(), LaMetricConnectionTimeoutError),
+        (aiohttp.ClientError(), LaMetricConnectionError),
+    ],
+)
+async def test_supported_connection_errors(
+    responses: aioresponses,
+    auth: LaMetricLocalAuth,
+    exception: Exception,
+    expected: type[Exception],
+) -> None:
+    """Test connection problems while checking support raise connection errors."""
+    responses.get(f"{WEB_URL}/", exception=exception)
+
+    with pytest.raises(expected):
+        await auth.supported()
+
+
+async def test_supported_internal_session(responses: aioresponses) -> None:
+    """Test checking support creates and closes its own session."""
+    responses.get(f"{WEB_URL}/", status=200, body="")
+
+    async with LaMetricLocalAuth(host="127.0.0.2") as auth:
+        assert await auth.supported() is True
+        session = auth.session
+
+    assert session is not None
+    assert session.closed