[Backport] Issue 3468: Export project then import destroyed the attachments

taiga/export_import/serializers.py

@@ -66,7 +66,20 @@ class AttachedFileField(serializers.WritableField):
     def from_native(self, data):
         if not data:
             return None
-        return ContentFile(base64.b64decode(data['data']), name=data['name'])
+
+        # Each sequence of 3 octets is represented by 4 characters in base64.
+        # The file was encoded in chunks of 8190 (multiple of three) so the proper way of decoding it is:
+        # - split the encoded data in multiple of four chars blocks
+        # - decode each block
+        decoded_data = b''
+        pending_data = data['data']
+        chunk_size = 8192
+        while pending_data:
+            decoding_data = pending_data[0:chunk_size]
+            decoded_data += base64.b64decode(decoding_data)
+            pending_data = pending_data[chunk_size:]
+
+        return ContentFile(decoded_data, name=data['name'])
 
 
 class RelatedNoneSafeField(serializers.RelatedField):

taiga/export_import/service.py

@@ -56,7 +56,7 @@ def add_errors(section, errors):
         _errors_log[section] = [errors]
 
 
-def render_project(project, outfile, chunk_size = 8192):
+def render_project(project, outfile, chunk_size = 8190):
     serializer = serializers.ProjectExportSerializer(project)
     outfile.write('{\n')