Add protection against invalid image path declarations for add

This is a bit painful, because datalad-next parameter validation
is not available, but worth adding given the issue.

Closes datalad#150

datalad_container/containers_add.py

@@ -199,6 +199,16 @@ def __call__(name, url=None, dataset=None, call_fmt=None, image=None,
                              purpose='add container')
         runner = WitlessRunner()
 
+        if image is not None:
+            if op.isabs(image):
+                raise ValueError(
+                    f'image must be a relative path, got {image!r}')
+            if ds.pathobj.resolve() \
+                    not in (ds.pathobj / image).resolve().parents:
+                raise ValueError(
+                    'image must be a relative path pointing inside'
+                    f'the dataset, got {image!r}')
+
         # prevent madness in the config file
         if not re.match(r'^[0-9a-zA-Z-]+$', name):
             raise ValueError(

datalad_container/tests/test_add.py

@@ -15,8 +15,27 @@
 
 from datalad_container.containers_add import _ensure_datalad_remote
 
-# NOTE: At the moment, testing of the containers-add itself happens implicitly
-# via use in other tests.
+# NOTE: At the moment, most testing of the containers-add itself happens implicitly
+# this via use in other tests.
+
+common_kwargs = {'result_renderer': 'disabled'}
+
+
+def test_add_invalid_imgpath(tmp_path):
+    ds = Dataset(tmp_path).create(**common_kwargs)
+    # path spec must be relative
+    with pytest.raises(ValueError):
+        ds.containers_add(
+            'dummy',
+            image=tmp_path,
+            **common_kwargs
+        )
+    with pytest.raises(ValueError):
+        ds.containers_add(
+            'dummy',
+            image=Path('..', 'sneaky'),
+            **common_kwargs
+        )
 
 
 @with_tempfile
@@ -41,4 +60,4 @@ def test_ensure_datalad_remote_maybe_enable(path=None, *, autoenable):
     if not autoenable:
         assert_not_in("datalad", repo.get_remotes())
     _ensure_datalad_remote(repo)
-    assert_in("datalad", repo.get_remotes())
+    assert_in("datalad", repo.get_remotes())