[DPE-5588] Create architecture helpers lib (#560)

lib/charms/mysql/v0/architecture.py

@@ -0,0 +1,86 @@
+# Copyright 2024 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Library to provide hardware architecture checks for VMs and K8s charms.
+
+The WrongArchitectureWarningCharm class is designed to be used alongside
+the is-wrong-architecture helper function, as follows:
+
+```python
+import sys
+
+from ops import main
+from charms.mysql.v0.architecture import WrongArchitectureWarningCharm, is_wrong_architecture
+
+if __name__ == "__main__":
+    if is_wrong_architecture():
+        main(WrongArchitectureWarningCharm)
+```
+"""
+
+import logging
+import os
+import pathlib
+import platform
+import sys
+
+import yaml
+from ops import BlockedStatus, CharmBase
+
+# The unique Charmhub library identifier, never change it
+LIBID = "827e04542dba4c2a93bdc70ae40afdb1"
+LIBAPI = 0
+LIBPATCH = 1
+
+PYDEPS = ["ops>=2.0.0", "pyyaml>=5.0"]
+
+
+logger = logging.getLogger(__name__)
+
+
+class WrongArchitectureWarningCharm(CharmBase):
+    """A fake charm class that only signals a wrong architecture deploy."""
+
+    def __init__(self, *args):
+        super().__init__(*args)
+
+        hw_arch = platform.machine()
+        self.unit.status = BlockedStatus(f"Error: Charm incompatible with {hw_arch} architecture")
+        sys.exit(0)
+
+
+def is_wrong_architecture() -> bool:
+    """Checks if charm was deployed on wrong architecture."""
+    manifest_path = pathlib.Path(os.environ["CHARM_DIR"], "manifest.yaml")
+
+    if not manifest_path.exists():
+        logger.error("Cannot check architecture: manifest file not found in %s", manifest_path)
+        return False
+
+    manifest = yaml.safe_load(manifest_path.read_text())
+
+    manifest_archs = []
+    for base in manifest["bases"]:
+        base_archs = base.get("architectures", [])
+        manifest_archs.extend(base_archs)
+
+    hardware_arch = platform.machine()
+    if ("amd64" in manifest_archs and hardware_arch == "x86_64") or (
+        "arm64" in manifest_archs and hardware_arch == "aarch64"
+    ):
+        logger.debug("Charm architecture matches")
+        return False
+
+    logger.error("Charm architecture does not match")
+    return True

tests/unit/test_architecture.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python3
+# Copyright 2024 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+from unittest.mock import patch
+
+from charms.mysql.v0.architecture import is_wrong_architecture
+
+TEST_MANIFEST = """
+    bases:
+        - architectures:
+            - {arch}
+          channel: '22.04'
+          name: ubuntu
+"""
+
+
+def test_wrong_architecture_file_not_found():
+    """Tests if the function returns False when the charm file doesn't exist."""
+    with (
+        patch("os.environ", return_value={"CHARM_DIR": "/tmp"}),
+        patch("pathlib.Path.exists", return_value=False),
+    ):
+        assert not is_wrong_architecture()
+
+
+def test_wrong_architecture_amd64():
+    """Tests if the function correctly identifies arch when charm is AMD."""
+    with (
+        patch("os.environ", return_value={"CHARM_DIR": "/tmp"}),
+        patch("pathlib.Path.exists", return_value=True),
+        patch("pathlib.Path.read_text", return_value=TEST_MANIFEST.format(arch="amd64")),
+        patch("platform.machine") as machine,
+    ):
+        machine.return_value = "x86_64"
+        assert not is_wrong_architecture()
+        machine.return_value = "aarch64"
+        assert is_wrong_architecture()
+
+
+def test_wrong_architecture_arm64():
+    """Tests if the function correctly identifies arch when charm is ARM."""
+    with (
+        patch("os.environ", return_value={"CHARM_DIR": "/tmp"}),
+        patch("pathlib.Path.exists", return_value=True),
+        patch("pathlib.Path.read_text", return_value=TEST_MANIFEST.format(arch="arm64")),
+        patch("platform.machine") as machine,
+    ):
+        machine.return_value = "x86_64"
+        assert is_wrong_architecture()
+        machine.return_value = "aarch64"
+        assert not is_wrong_architecture()