❗ raise an exception for relative paths

dash/_utils.py

@@ -10,6 +10,7 @@
 from io import open  # pylint: disable=redefined-builtin
 from functools import wraps
 import future.utils as utils
+from . import exceptions
 
 logger = logging.getLogger()
 
@@ -57,10 +58,13 @@ def get_asset_path(requests_pathname, asset_path, asset_url_path):
 def get_relative_path(requests_pathname, path):
     if requests_pathname == '/' and path == '':
         return '/'
-    if requests_pathname == '/' and not path.startswith('/'):
-        return path
+    elif requests_pathname != '/' and path == '':
+        return requests_pathname
     elif not path.startswith('/'):
-        return requests_pathname + path
+        raise exceptions.UnsupportedRelativePath(
+            "Paths that aren't prefixed with a leading / are not supported.\n" +
+            "You supplied: {}".format(path)
+        )
     return "/".join(
         [
             requests_pathname.rstrip("/"),

dash/exceptions.py

@@ -98,3 +98,7 @@ class SameInputOutputException(CallbackException):
 
 class MissingCallbackContextException(CallbackException):
     pass
+
+
+class UnsupportedRelativePath(CallbackException):
+    pass

tests/unit/test_configs.py

@@ -177,13 +177,20 @@ def test_app_name_server(empty_environ, name, server, expected):
         ("/my-dash-app/", "/page-1/", "/my-dash-app/page-1/"),
 
         ("/", "/page-1/sub-page-1", "/page-1/sub-page-1"),
-
-        ("/", "relative-page-1", "relative-page-1"),
-        ("/my-dash-app", "relative-page-1", "/my-dash-apprelative-page-1"),
         ("/my-dash-app/", "/page-1/sub-page-1", "/my-dash-app/page-1/sub-page-1"),
     ]
 )
-
 def test_pathname_prefix_relative_url(prefix, partial_path, expected):
     path = get_relative_path(prefix, partial_path)
     assert path == expected
+
+@pytest.mark.parametrize(
+    "prefix, partial_path",
+    [
+        ("/", "relative-page-1"),
+        ("/my-dash-app/", "relative-page-1"),
+    ]
+)
+def test_invalid_get_relative_path(prefix, partial_path):
+    with pytest.raises(_exc.UnsupportedRelativePath):
+        get_relative_path(prefix, partial_path)