Fix Hanging Protocols json field raised exception

app/grandchallenge/hanging_protocols/forms.py

@@ -58,13 +58,21 @@ def __init__(self, *args, **kwargs):
         )
 
     def clean_json(self):
-        json = self.cleaned_data["json"]
-        viewport_names = [x["viewport_name"] for x in json]
+        hanging_protocol_json = self.cleaned_data["json"]
+
+        try:
+            viewport_names = [
+                viewport["viewport_name"] for viewport in hanging_protocol_json
+            ]
+        except (KeyError, TypeError):
+            raise ValidationError(
+                "Hanging protocol definition is invalid. Have a look at the example in the helptext."
+            )
 
         self._validate_viewport_uniqueness(viewport_names=viewport_names)
-        self._validate_dimensions(value=json)
+        self._validate_dimensions(value=hanging_protocol_json)
 
-        for viewport in json:
+        for viewport in hanging_protocol_json:
             if "parent_id" in viewport:
                 self._validate_parent_id(
                     viewport=viewport, viewport_names=viewport_names
@@ -74,7 +82,7 @@ def clean_json(self):
                     viewport=viewport, viewport_names=viewport_names
                 )
 
-        return json
+        return hanging_protocol_json
 
     def _validate_viewport_uniqueness(self, *, viewport_names):
         if len(set(viewport_names)) != len(viewport_names):

app/tests/hanging_protocols_tests/test_forms.py

@@ -316,6 +316,88 @@ def test_hanging_protocol_clientside():
     assert form.is_valid()
 
 
+@pytest.mark.django_db
+@pytest.mark.parametrize(
+    "hanging_protocol_json, form_is_valid, expected_json_error",
+    (
+        ("[]", False, "This field is required."),
+        ("{}", False, "This field is required."),
+        (
+            '[{"viewport_name": "main"}]',
+            True,
+            None,
+        ),
+        (
+            12345,
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        ("main", False, "Enter a valid JSON."),
+        (
+            "[1,2,3,4,5]",
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            '["test1", "test2", "test3"]',
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            "[[],[],[]]",
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            "[{},{},{}]",
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            "true",
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            "false",
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            '{"viewport_name": "main"}',
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            "[{}]",
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            '[{"test":1}]',
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+        (
+            '[{"test1":"main"},{"test2":"secondary"}]',
+            False,
+            "Hanging protocol definition is invalid. Have a look at the example in the helptext.",
+        ),
+    ),
+)
+def test_hanging_protocol_form_json_validation(
+    hanging_protocol_json, form_is_valid, expected_json_error
+):
+    form = HangingProtocolForm(
+        {
+            "title": "main",
+            "json": hanging_protocol_json,
+        }
+    )
+    assert form.is_valid() is form_is_valid
+    assert form.errors.get("json", [None])[0] == expected_json_error
+
+
 def make_ci_list(
     *,
     number_of_images,