stages/ostree.commit: port from assembler

Port the `org.osbuild.ostree.commit` assembler to a new assembler
like stage. The notable differences are: the fs tree preparation
now happens in the `ostree.preptree` stage and there is no option
to create a tarball, since that should be handled by a tar stage.

stages/org.osbuild.ostree.commit

@@ -0,0 +1,118 @@
+#!/usr/bin/python3
+"""
+Assemble a file system tree into a ostree commit
+
+Needs a file system tree that is already conforming to the ostree
+system layout[1], specified via the `tree` input and commits it
+to a repository. The repository must have been created at `/repo`.
+
+Additional metadata is stored in `/compose.json` which contains
+the commit compose information. This is also returned via the
+metadata API to osbuild.
+
+[1] https://ostree.readthedocs.io/en/stable/manual/adapting-existing/
+"""
+
+
+import json
+import os
+import subprocess
+import sys
+import tempfile
+
+from osbuild import api
+from osbuild.util import ostree
+
+
+SCHEMA_2 = """
+"options": {
+  "additionalProperties": false,
+  "required": ["ref"],
+  "properties": {
+    "ref": {
+      "description": "OStree ref to create for the commit",
+      "type": "string",
+      "default": ""
+    },
+    "os_version": {
+      "description": "Set the version of the OS as commit metadata",
+      "type": "string"
+    },
+    "parent": {
+      "description": "commit id of the parent commit",
+      "type": "string"
+    }
+  }
+},
+"inputs": {
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["tree"],
+  "properties": {
+    "tree": {
+      "type": "object",
+      "additionalProperties": true
+    }
+  }
+}
+"""
+
+
+def main(inputs, output_dir, options, meta):
+    tree = inputs["tree"]["path"]
+
+    ref = options["ref"]
+    os_version = options.get("os_version", None)
+    parent = options.get("parent", None)
+
+    # rpm-ostree compose commit wants to consume the commit
+    # so for now, we copy the whole tree and let it have its
+    # way
+    with tempfile.TemporaryDirectory(dir=output_dir) as root:
+        subprocess.run(["cp", "--reflink=auto", "-a",
+                        f"{tree}/.", root],
+                       check=True)
+
+        repo = os.path.join(output_dir, "repo")
+
+        treefile = ostree.Treefile()
+        treefile["ref"] = ref
+
+        argv = ["rpm-ostree", "compose", "commit"]
+        argv += [f"--repo={repo}"]
+
+        if parent:
+            argv += [f"--parent={parent}"]
+
+        if os_version:
+            argv += [
+                f"--add-metadata-string=version={os_version}",
+            ]
+
+        argv += [
+            f"--add-metadata-string=rpmostree.inputhash={meta['id']}",
+            f"--write-composejson-to={output_dir}/compose.json"
+        ]
+
+        with treefile.as_tmp_file() as path:
+            argv += [path, root]
+
+            subprocess.run(argv,
+                           stdout=sys.stderr,
+                           check=True)
+
+        with open(os.path.join(output_dir, "compose.json"), "r") as f:
+            compose = json.load(f)
+
+        api.metadata({"compose": compose})
+
+
+if __name__ == '__main__':
+    args = api.arguments()
+
+    r = main(args["inputs"],
+             args["tree"],
+             args["options"],
+             args["meta"])
+
+    sys.exit(r)