avoid reading in whole blob during NamedBlobFile validation (slows TUS uploads)

plone/namedfile/field.py

@@ -20,7 +20,7 @@
 from zope.interface import Interface
 from zope.schema import Object
 from zope.schema import ValidationError
-
+from zope.schema._bootstrapinterfaces import SchemaNotProvided
 
 _ = MessageFactory("plone")
 
@@ -106,7 +106,12 @@ def __init__(self, **kw):
         super().__init__(schema=self.schema, **kw)
 
     def _validate(self, value):
-        super()._validate(value)
+        # we don't want default validation of super()._validate(value)
+        # as that will read the whole file into memory
+        # schema has to be provided by value
+        if not self.schema.providedBy(value):
+            raise SchemaNotProvided(self.schema, value).with_field_and_value(
+                self, value)
         validate_file_field(self, value)
 
 
@@ -123,5 +128,10 @@ def __init__(self, **kw):
         super().__init__(schema=self.schema, **kw)
 
     def _validate(self, value):
-        super()._validate(value)
+        # we don't want default validation of super()._validate(value)
+        # as that will read the whole file into memory
+        # schema has to be provided by value
+        if not self.schema.providedBy(value):
+            raise SchemaNotProvided(self.schema, value).with_field_and_value(
+                self, value)
         validate_image_field(self, value)

plone/namedfile/tests/test_storable.py

@@ -18,6 +18,8 @@
 from OFS.Image import Pdata
 from plone.namedfile.file import FileChunk
 from plone.namedfile.file import NamedBlobImage
+from plone.namedfile.file import NamedBlobFile
+from plone.namedfile import field
 from plone.namedfile.testing import PLONE_NAMEDFILE_FUNCTIONAL_TESTING
 from plone.namedfile.tests import getFile
 
@@ -56,3 +58,47 @@ def test_opened_file_storable(self):
             if os.path.exists(path):
                 os.remove(path)
         self.assertEqual(303, fi.getSize())
+
+    def test_upload_no_read(self):
+        # ensure we don't read the whole file into memory
+
+        import ZODB.blob
+
+        old_open = ZODB.blob.Blob.open
+        blob_read = 0
+        blob_write = 0
+
+        def count_open(self, mode="r"):
+            nonlocal blob_read, blob_write
+            blob_read += 1 if "r" in mode else 0
+            blob_write += 1 if "w" in mode else 0
+            return old_open(self, mode)
+
+        ZODB.blob.Blob.open = count_open
+
+        data = getFile("image.gif")
+        f = tempfile.NamedTemporaryFile(delete=False)
+        try:
+            path = f.name
+            f.write(data)
+            f.close()
+            with open(path, "rb") as f:
+                fi = NamedBlobFile(f, filename="image.gif")
+        finally:
+            if os.path.exists(path):
+                os.remove(path)
+        self.assertEqual(303, fi.getSize())
+        self.assertEqual(blob_read, 1, "blob should have only been opened to get size")
+        self.assertEqual(
+            blob_write,
+            1,
+            "Slow write to blob instead of os rename. Should be only 1 on init",
+        )
+        blob_read = 0
+
+        blob_field = field.NamedBlobFile()
+        blob_field.validate(fi)
+
+        self.assertEqual(blob_read, 0, "Validation is reading the whole blob in memory")
+
+        ZODB.blob.Blob.open = old_open