Issue 26299: wsgiref.util FileWrapper raises ValueError: I/O operation on closed file. (original) (raw)

While developing, I am using wsgiref.simple_server. Using to serve static content isn't working. The attached program demonstrates the issue. Run it and connect to http://127.0.0.1:8000/. You will see three buttons. Clicking on 'wsgi.filewrapper' causes the FileWrapper class found in wsgiref.util to be used, while clicking on 'PEP 0333' uses code suggested in PEP 0333 (https://www.python.org/dev/peps/pep-0333/#id36). Both of these fail. Clicking on 'slurp' causes the entire file to loaded and returned in a list. This works.

When an application returns an instance of environ['wsgi.file_wrapper'], or creates it's own iterator, an error is raised during the initial read of the file. Reading the entire file and returning a single-element list (the 'slurp' technique) works, but is impractical for larger files.

I've tested this with both Python 2.7.9 and 3.4.3 under Windows 7 (my laptop) and 3.4.3 under Alpine Linux (a Docker instance).