Fix OpenAPI multipart file fields to use binary format

Fixes #11246

src/backend/InvenTree/InvenTree/schema.py

@@ -16,6 +16,7 @@ from drf_spectacular.utils import (
     extend_schema,
     extend_schema_view,
 )
+from rest_framework import serializers
 from rest_framework.pagination import LimitOffsetPagination
 
 from InvenTree.permissions import OASTokenMixin
@@ -46,6 +47,20 @@ class ExtendedOAuth2Scheme(DjangoOAuthToolkitScheme):
 class ExtendedAutoSchema(AutoSchema):
     """Extend drf-spectacular to allow customizing the schema to match the actual API behavior."""
 
+    def _map_serializer_field(self, field, direction, *args, **kwargs):
+        """Custom field mapping overrides, falling back to default behavior."""
+        schema = super()._map_serializer_field(field, direction, *args, **kwargs)
+
+        direction_value = getattr(direction, 'value', direction)
+
+        # File and image fields in request schemas must be represented as binary
+        # payloads. In response schemas they are still rendered as URLs.
+        if direction_value == 'request' and isinstance(field, serializers.FileField):
+            schema['type'] = 'string'
+            schema['format'] = 'binary'
+
+        return schema
+
     def is_bulk_action(self, ref: str) -> bool:
         """Check the class of the current view for the bulk mixins."""
         return ref in [c.__name__ for c in type(self.view).__mro__]

src/backend/InvenTree/InvenTree/tests.py

@@ -22,6 +22,7 @@ from djmoney.contrib.exchange.exceptions import MissingRate
 from djmoney.contrib.exchange.models import Rate, convert_money
 from djmoney.money import Money
 from maintenance_mode.core import get_maintenance_mode, set_maintenance_mode
+from rest_framework import serializers
 from sesame.utils import get_user
 from stdimage.models import StdImageFieldFile
 
@@ -1817,6 +1818,35 @@ class SchemaPostprocessingTest(TestCase):
         # required key removed when empty
         self.assertNotIn('required', schemas_out.get('SalesOrderShipment'))
 
+    def test_file_field_request_schema_binary(self):
+        """Verify only request file fields are exposed as binary."""
+        auto_schema = object.__new__(schema.ExtendedAutoSchema)
+
+        mapped_schemas = [
+            {'type': 'string', 'format': 'uri', 'nullable': True},
+            {'type': 'string', 'format': 'uri'},
+            {'type': 'string', 'format': 'uri', 'nullable': True},
+        ]
+
+        with mock.patch(
+            'drf_spectacular.openapi.AutoSchema._map_serializer_field',
+            side_effect=mapped_schemas,
+        ):
+            file_request = auto_schema._map_serializer_field(
+                serializers.FileField(allow_null=True), 'request'
+            )
+            url_request = auto_schema._map_serializer_field(
+                serializers.URLField(), 'request'
+            )
+            file_response = auto_schema._map_serializer_field(
+                serializers.FileField(allow_null=True), 'response'
+            )
+
+        self.assertEqual(file_request['format'], 'binary')
+        self.assertTrue(file_request['nullable'])
+        self.assertEqual(url_request['format'], 'uri')
+        self.assertEqual(file_response['format'], 'uri')
+
 
 class URLCompatibilityTest(InvenTreeTestCase):
     """Unit test for legacy URL compatibility."""