stages(tar): expose new transforms option to tar stage

This commit adds a new `transforms` option to the tar stages that
maps directly to the `--transform=` comamndline argument of tar(1).

This allows to transform the names while files/dirs are added to
a tarfile. This is useful for the `gcp` pipeline for
bootc-image-builder where we want to create a gcp tar file that
expects the disk image filename in the tar to be exactly `disk.raw`.

stages/org.osbuild.tar

@@ -12,6 +12,7 @@ def main(inputs, output_dir, options):
     tarfmt = options.get("format", "gnu")
     root_node = options.get("root-node", "include")
     paths = options.get("paths", [])
+    transform = options.get("transforms", [])
 
     extra_args = []
     # Set environment variables for the tar operation.
@@ -33,6 +34,10 @@ def main(inputs, output_dir, options):
     if options.get("sparse", False):
         extra_args += ["--sparse"]
 
+    transforms = options.get("transforms")
+    if transforms:
+        extra_args += [f"--transform={t}" for t in transforms]
+
     # Set up the tar command.
     tar_cmd = [
         "tar",

stages/org.osbuild.tar.meta.json

@@ -98,7 +98,14 @@
           "description": "Make archive files sparse",
           "type": "boolean",
           "default": false
-        }
+        },
+        "transforms": {
+          "type": "array",
+          "items": {
+            "type": "string",
+	    "description": "Transformation of names during tar(1)"
+          }
+	}
       }
     },
     "inputs": {

stages/test/test_tar.py

@@ -19,11 +19,16 @@
         "root-node": "include",
         "paths": ["file1"]
     }, "{'filename': 'out.tar', 'root-node': 'include', 'paths': ['file1']} is not valid under any of the given schemas"),
+    ({
+        "filename": "foo",
+        "transforms": "not-an-array",
+    }, "'not-an-array' is not of type 'array'"),
     # good
     ({"filename": "out.tar", "root-node": "include"}, ""),
     ({"filename": "out.tar", "paths": ["file1"]}, ""),
     ({"filename": "out.tar", "sparse": True}, ""),
     ({"filename": "out.tar"}, ""),
+    ({"filename": "out.tar", "transforms": ["s/foo/bar"]}, ""),
 ])
 def test_schema_validation_tar(stage_schema, test_data, expected_err):
     test_input = {
@@ -99,3 +104,23 @@ def test_tar_paths(tmp_path, stage_module, fake_inputs):
     assert os.path.exists(tar_path)
     output = subprocess.check_output(["tar", "-tf", tar_path], encoding="utf-8").split("\n")
     assert ["file2", "file1", "file1", "file2", ""] == output
+
+
+@pytest.mark.skipif(not has_executable("tar"), reason="no tar executable")
+def test_tar_transforms(tmp_path, stage_module, fake_inputs):
+    options = {
+        "filename": "out.tar",
+        "paths": [
+            "file1",
+            "file2",
+        ],
+        "transforms": [
+            "s/file1/foo99/",
+        ],
+    }
+    stage_module.main(fake_inputs, tmp_path, options)
+
+    tar_path = os.path.join(tmp_path, "out.tar")
+    assert os.path.exists(tar_path)
+    output = subprocess.check_output(["tar", "-tf", tar_path], encoding="utf-8").split("\n")
+    assert ["foo99", "file2"] == output