Add a special serializer class for FileField which has a custom to_representation function

- This was solving a very subtle bug which will probably only ever apply to a single installation instance
- Future me will most likely not remember what this was for or how it works
- In any case, there we go
- Ref: http://www.cdrf.co/3.9/rest_framework.fields/Field.html

(cherry picked from commit 7305094854)

InvenTree/InvenTree/serializers.py

@@ -8,6 +8,9 @@ from __future__ import unicode_literals
 
 from rest_framework import serializers
 
+import os
+
+from django.conf import settings
 from django.contrib.auth.models import User
 
 
@@ -50,3 +53,32 @@ class InvenTreeModelSerializer(serializers.ModelSerializer):
         instance.clean()
 
         return data
+
+
+class InvenTreeAttachmentSerializerField(serializers.FileField):
+    """
+    Override the DRF native FileField serializer,
+    to remove the leading server path.
+
+    For example, the FileField might supply something like:
+
+    http://127.0.0.1:8000/media/foo/bar.jpg
+
+    Whereas we wish to return:
+
+    /media/foo/bar.jpg
+
+    Why? You can't handle the why!
+
+    Actually, if the server process is serving the data at 127.0.0.1,
+    but a proxy service (e.g. nginx) is then providing DNS lookup to the outside world,
+    then an attachment which prefixes the "address" of the internal server
+    will not be accessible from the outside world.
+    """
+
+    def to_representation(self, value):
+
+        if not value:
+            return None
+
+        return os.path.join(str(settings.MEDIA_URL), str(value))

InvenTree/stock/serializers.py

@@ -15,6 +15,7 @@ from django.db.models.functions import Coalesce
 from company.serializers import SupplierPartSerializer
 from part.serializers import PartBriefSerializer
 from InvenTree.serializers import UserSerializerBrief, InvenTreeModelSerializer
+from InvenTree.serializers import InvenTreeAttachmentSerializerField
 
 
 class LocationBriefSerializer(InvenTreeModelSerializer):
@@ -232,6 +233,8 @@ class StockItemTestResultSerializer(InvenTreeModelSerializer):
 
     key = serializers.CharField(read_only=True)
 
+    attachment = InvenTreeAttachmentSerializerField()
+
     def __init__(self, *args, **kwargs):
         user_detail = kwargs.pop('user_detail', False)