[VNG-Realisatie#210] add FileFieldExtension

Based on https://drf-spectacular.readthedocs.io/en/latest/blueprints.html#drf-extra-fields-base64filefield

vng_api_common/inspectors/__init__.py

@@ -4,6 +4,7 @@
     HyperlinkedRelatedFieldExtension,
     ReadOnlyFieldExtension,
 )
+from .files import FileFieldExtension
 from .geojson import GeometryFieldExtension
 from .polymorphic import PolymorphicSerializerExtension
 from .query import FilterExtension

vng_api_common/inspectors/files.py

@@ -0,0 +1,26 @@
+from django.utils.translation import gettext as _
+
+from drf_spectacular.extensions import OpenApiSerializerFieldExtension
+from drf_spectacular.plumbing import build_basic_type
+from drf_spectacular.types import OpenApiTypes
+
+
+class FileFieldExtension(OpenApiSerializerFieldExtension):
+    target_class = "drf_extra_fields.fields.Base64FileField"
+    match_subclasses = True
+
+    def map_serializer_field(self, auto_schema, direction):
+        base64_schema = {
+            **build_basic_type(OpenApiTypes.BYTE),
+            "description": _("Base64 encoded binary content."),
+        }
+
+        uri_schema = {
+            **build_basic_type(OpenApiTypes.URI),
+            "description": _("Download URL of the binary content."),
+        }
+
+        if direction == "request":
+            return base64_schema
+        elif direction == "response":
+            return uri_schema if not self.target.represent_in_base64 else base64_schema