make case attachments with S3 work

corehq/form_processor/models.py

@@ -408,15 +408,17 @@ class AbstractAttachment(DisabledDbMixin, models.Model, SaveStateMixin):
     properties = JSONField(default=dict)
 
     def write_content(self, content):
+        info = self._put_blob(content)
+        self.md5 = info.md5_hash
+        self.content_length = info.length
+        self.blob_id = info.identifier
+
+    def _put_blob(self, content):
         if not self.name:
             raise InvalidAttachment("cannot save attachment without name")
-
         db = get_blob_db()
         bucket = self._blobdb_bucket()
-        info = db.put(content, self.name, bucket)
-        self.md5 = info.md5_hash
-        self.content_length = info.length
-        self.blob_id = info.identifier
+        return db.put(content, self.name, bucket)
 
     def read_content(self, stream=False):
         db = get_blob_db()
@@ -900,7 +902,12 @@ def copy_content(self, attachment):
                     self._blobdb_bucket(), self.blob_id
                 )
         content = attachment.read_content(stream=True)
-        self.write_content(content)
+        with content:
+            info = self._put_blob(content)
+        self.blob_id = info.identifier
+        assert self.content_length == info.length
+        if self.md5 and info.md5_hash:
+            assert self.md5 == info.md5_hash
 
     @classmethod
     def from_case_update(cls, attachment):