fix: handle incoming invalid dynamic metadata

Not currently validated by `packaging` library.
Provides the user a better error message than a 500 response.

Fixes: pypi#17389

Signed-off-by: Mike Fiedler <[email protected]>

tests/unit/forklift/test_metadata.py

@@ -274,6 +274,20 @@ def test_invalid_dists(self, field_name):
             metadata.parse(None, form_data=data)
         _assert_invalid_metadata(excinfo.value, field_name.replace("_", "-"))
 
+    def test_valid_dynamic(self):
+        data = MultiDict(metadata_version="2.2", name="spam", version="2.0")
+        data.add("dynamic", "keywords")
+        data.add("dynamic", "author")
+        meta = metadata.parse(None, form_data=data)
+        assert meta.dynamic == ["keywords", "author"]
+
+    def test_invalid_dynamic(self):
+        data = MultiDict(metadata_version="2.2", name="spam", version="2.0")
+        data.add("dynamic", "requires")
+        with pytest.raises(ExceptionGroup) as excinfo:
+            metadata.parse(None, form_data=data)
+        _assert_invalid_metadata(excinfo.value, "dynamic")
+
 
 class TestFromFormData:
     def test_valid(self):

warehouse/forklift/metadata.py

@@ -30,6 +30,7 @@
 from trove_classifiers import all_classifiers, deprecated_classifiers
 from webob.multidict import MultiDict
 
+from warehouse.packaging.models import DynamicFieldsEnum
 from warehouse.utils import http
 
 SUPPORTED_METADATA_VERSIONS = {"1.0", "1.1", "1.2", "2.1", "2.2", "2.3", "2.4"}
@@ -141,7 +142,7 @@ def _validate_metadata(metadata: Metadata, *, backfill: bool = False):
             InvalidMetadata("classifier", f"{classifier!r} is not a valid classifier.")
         )
 
-    # Validate that no deprecated classifers are being used.
+    # Validate that no deprecated classifiers are being used.
     # NOTE: We only check this is we're not doing a backfill, because backfill
     #       operations may legitimately use deprecated classifiers.
     if not backfill:
@@ -235,6 +236,19 @@ def _validate_metadata(metadata: Metadata, *, backfill: bool = False):
                         )
                     )
 
+    # Validate that any `dynamic` fields passed are in the allowed list
+    # TODO: This probably should be lifted up to packaging.metadata
+    for field in {"dynamic"}:
+        if (value := getattr(metadata, field)) is not None:
+            for key in value:
+                if key not in map(str.lower, DynamicFieldsEnum.enums):
+                    errors.append(
+                        InvalidMetadata(
+                            _RAW_TO_EMAIL_MAPPING.get(field, field),
+                            f"Dynamic field {key!r} is not a valid dynamic field.",
+                        )
+                    )
+
     # Ensure that License and License-Expression are mutually exclusive
     # See https://peps.python.org/pep-0639/#deprecate-license-field
     if metadata.license and metadata.license_expression:
@@ -263,12 +277,12 @@ def _validate_metadata(metadata: Metadata, *, backfill: bool = False):
 
 
 def parse_form_metadata(data: MultiDict) -> Metadata:
-    # We construct a RawMetdata using the form data, which we will later pass
+    # We construct a RawMetadata using the form data, which we will later pass
     # to Metadata to get a validated metadata.
     #
-    # NOTE: Form data is very similiar to the email format where the only difference
+    # NOTE: Form data is very similar to the email format where the only difference
     #       between a list and a single value is whether or not the same key is used
-    #       multiple times. Thus we will handle things in a similiar way, always
+    #       multiple times. Thus, we will handle things in a similar way, always
     #       fetching things as a list and then determining what to do based on the
     #       field type and how many values we found.
     #