Set a file field through its field manager, not the raw mutator

docs/changelog.rst

@@ -15,6 +15,7 @@ Changelog
    applied. Uninstalling from the same panel removes the PAS plugin
    and the per-user JWT signing secrets.
 
+- #118 Set a file field through its field manager, not the raw mutator
 - #109 Add a partition operation endpoint
 - #106 Fix single-valued UID reference fields not settable through the JSON API
 - #112 Allow updating the Laboratory through the API

src/senaite/jsonapi/datamanagers.py

@@ -32,13 +32,23 @@
 from senaite.jsonapi.interfaces import IDataManager
 from senaite.jsonapi.interfaces import IFieldManager
 from senaite.jsonapi.fieldmanagers import DurationFieldManager
+from senaite.jsonapi.fieldmanagers import NamedFileFieldManager
 from senaite.jsonapi.fieldmanagers import UIDReferenceFieldMixin
 
 # Field managers that normalize the incoming value (resolve UIDs, coerce
 # a duration mapping to a timedelta, ...). For these the raw set<Name>
 # mutator would store the value unconverted, so the data manager must go
 # through the field manager instead of the setter.
-NORMALIZING_FIELD_MANAGERS = (UIDReferenceFieldMixin, DurationFieldManager)
+NORMALIZING_FIELD_MANAGERS = (
+    UIDReferenceFieldMixin,
+    DurationFieldManager,
+    # A file arrives as base64 text and the manager decodes it and
+    # builds the NamedFile or NamedImage the field holds. The raw
+    # mutator would store the text itself, which the field then fails
+    # to validate as the wrong type. NamedImageFieldManager is a
+    # subclass, so it is covered here too.
+    NamedFileFieldManager,
+)
 
 
 class BaseDataManager(object):