I have small FastCGI application on Python+Flask. Server 2012 R2, IIS 8.5.
When I return from handler redirect( url_for(...), 302) in Python code, Flask returns response with some html about "You will be redirected" and properly set Content-Length in response object.
IIS see response status code 302 and add another html to response content before already added by Flask:
<head><title>Document Moved</title></head><body><h1>Object Moved</h1>This document may be found <a HREF="...">here</a></body>
But IIS don't set right value of Content-Length after code insertion.
As result my customers see in browser source code of page where redirection was targeted.
What can I do to resolve this problem?