_artifactelement.py: New ArtifactElement object (derived from Element)

This object should be used when we want to handle artifact refs directly
from the command line.
An ArtifactElementError has also been added to _exceptions.py

2 files changed, 97 insertions, 0 deletions

diff --git a/buildstream/_artifactelement.py b/buildstream/_artifactelement.py
new file mode 100644
index 000000000..a88e83aab
--- /dev/null
+++ b/buildstream/_artifactelement.py
@@ -0,0 +1,88 @@
+#
+#  Copyright (C) 2019 Bloomberg Finance LP
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library 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
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+#  Authors:
+#        James Ennis <james.ennis@codethink.co.uk>
+from . import Element
+from . import _cachekey
+from ._exceptions import ArtifactElementError
+from ._loader.metaelement import MetaElement
+
+
+# ArtifactElement()
+#
+# Object to be used for directly processing an artifact
+#
+# Args:
+#    context (Context): The Context object
+#    ref (str): The artifact ref
+#
+class ArtifactElement(Element):
+    def __init__(self, context, ref):
+        _, element, key = verify_artifact_ref(ref)
+
+        self._ref = ref
+        self._key = key
+
+        project = context.get_toplevel_project()
+        meta = MetaElement(project, element)  # NOTE element has no .bst suffix
+        plugin_conf = None
+
+        super().__init__(context, project, meta, plugin_conf)
+
+    # Override Element.get_artifact_name()
+    def get_artifact_name(self, key=None):
+        return self._ref
+
+    # Dummy configure method
+    def configure(self, node):
+        pass
+
+    # Dummy preflight method
+    def preflight(self):
+        pass
+
+    # Override Element._calculate_cache_key
+    def _calculate_cache_key(self, dependencies=None):
+        return self._key
+
+
+# verify_artifact_ref()
+#
+# Verify that a ref string matches the format of an artifact
+#
+# Args:
+#    ref (str): The artifact ref
+#
+# Returns:
+#    project (str): The project's name
+#    element (str): The element's name
+#    key (str): The cache key
+#
+# Raises:
+#    ArtifactElementError if the ref string does not match
+#    the expected format
+#
+def verify_artifact_ref(ref):
+    try:
+        project, element, key = ref.split('/', 2)  # This will raise a Value error if unable to split
+        # Explicitly raise a ValueError if the key lenght is not as expected
+        if len(key) != len(_cachekey.generate_key({})):
+            raise ValueError
+    except ValueError:
+        raise ArtifactElementError("Artifact: {} is not of the expected format".format(ref))
+
+    return project, element, key
diff --git a/buildstream/_exceptions.py b/buildstream/_exceptions.py
index 6d8ea6d38..0797e7207 100644
--- a/buildstream/_exceptions.py
+++ b/buildstream/_exceptions.py
@@ -344,3 +344,12 @@ class AppError(BstError):
 #
 class SkipJob(Exception):
     pass
+
+
+# ArtifactElementError
+#
+# Raised when errors are encountered by artifact elements
+#
+class ArtifactElementError(BstError):
+    def __init__(self, message, *, detail=None, reason=None):
+        super().__init__(message, detail=detail, domain=ErrorDomain.ELEMENT, reason=reason)