Extract shared resolve_snap helper from duplicate plugin implementations

imagecraft/plugins/_utils.py

@@ -0,0 +1,32 @@
+# This file is part of imagecraft.
+#
+# Copyright 2026 Canonical Ltd.
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU General Public License version 3, as published
+# by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranties of MERCHANTABILITY,
+# SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Shared plugin utilities."""
+
+
+def resolve_snap(snap: str) -> str:
+    """Resolve a snap reference to the format expected by snap prepare-image.
+
+    If the snap reference contains a channel (e.g. ``name/track/risk``), it is
+    converted to the ``name=track/risk`` form that ``snap prepare-image``
+    expects.  Plain snap names and local ``.snap`` file paths are returned
+    unchanged.
+    """
+    snap = snap.strip()
+    if "/" in snap and not snap.endswith(".snap"):
+        name, channel = snap.split("/", 1)
+        snap = f"{name}={channel}"
+    return snap

imagecraft/plugins/snap_preseed_plugin.py

@@ -21,6 +21,8 @@
 from craft_parts.plugins import Plugin, PluginProperties
 from typing_extensions import override
 
+from ._utils import resolve_snap
+
 
 class SnapPreseedPluginProperties(PluginProperties, frozen=True):
     """Properties for the 'snap-preseed' plugin."""
@@ -77,17 +79,10 @@ def get_build_commands(self) -> list[str]:
         )
 
         cmd.extend(
-            f"--snap={self._resolve_snap(snap)}" for snap in options.snap_preseed_snaps
+            f"--snap={resolve_snap(snap)}" for snap in options.snap_preseed_snaps
         )
 
         cmd.append(
             f'"{options.snap_preseed_model_assert}" {self._part_info.part_install_dir}'
         )
         return [" ".join(cmd)]
-
-    def _resolve_snap(self, snap: str) -> str:
-        snap = snap.strip()
-        if "/" in snap and not snap.endswith(".snap"):
-            name, channel = snap.split("/", 1)
-            snap = f"{name}={channel}"
-        return snap

imagecraft/plugins/uc_prepare_plugin.py

@@ -22,6 +22,8 @@
 from pydantic import model_validator
 from typing_extensions import Self, override
 
+from ._utils import resolve_snap
+
 
 class UcPreparePluginProperties(PluginProperties, frozen=True):
     """Properties for the uc-prepare plugin."""
@@ -118,18 +120,11 @@ def get_build_commands(self) -> list[str]:
         )
 
         cmd.extend(
-            f"--snap={self._resolve_snap(snap)}" for snap in options.uc_prepare_snaps
+            f"--snap={resolve_snap(snap)}" for snap in options.uc_prepare_snaps
         )
 
         cmd.append(
             f"{options.uc_prepare_model_assert} {self._part_info.part_install_dir}"
         )
 
         return [" ".join(cmd)]
-
-    def _resolve_snap(self, snap: str) -> str:
-        snap = snap.strip()
-        if "/" in snap and not snap.endswith(".snap"):
-            name, channel = snap.split("/", 1)
-            snap = f"{name}={channel}"
-        return snap

tests/unit/plugins/test_utils.py

@@ -0,0 +1,38 @@
+# This file is part of imagecraft.
+#
+# Copyright 2026 Canonical Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import pytest
+from imagecraft.plugins._utils import resolve_snap
+
+
+@pytest.mark.parametrize(
+    ("snap", "expected"),
+    [
+        # Plain snap name – unchanged
+        ("core24", "core24"),
+        # Leading/trailing whitespace is stripped
+        ("  core24  ", "core24"),
+        # Local .snap file path with a slash – unchanged (not a channel)
+        ("./my-snap_1.0_amd64.snap", "./my-snap_1.0_amd64.snap"),
+        # snap name with channel – converted to name=channel
+        ("hello-world/latest/stable", "hello-world=latest/stable"),
+        ("core24/stable", "core24=stable"),
+        # snap name with channel and leading whitespace
+        ("  hello-world/latest/stable  ", "hello-world=latest/stable"),
+    ],
+)
+def test_resolve_snap(snap, expected):
+    assert resolve_snap(snap) == expected