wsgiref.util FileWrapper raises ValueError: I/O operation on closed file.

[samwyse]

BPO	26299
Nosy	@pjeby
Files	wsgitest.py: demonstrates the issue

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-02-05.18:40:05.816>
labels = ['library']
title = 'wsgiref.util FileWrapper raises ValueError: I/O operation on closed file.'
updated_at = <Date 2016-02-07.11:21:48.517>
user = 'https://bugs.python.org/samwyse'

bugs.python.org fields:

activity = <Date 2016-02-07.11:21:48.517>
actor = 'SilentGhost'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2016-02-05.18:40:05.816>
creator = 'samwyse'
dependencies = []
files = ['41828']
hgrepos = []
issue_num = 26299
keywords = []
message_count = 1.0
messages = ['259685']
nosy_count = 2.0
nosy_names = ['pje', 'samwyse']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue26299'
versions = ['Python 2.7', 'Python 3.6']

[samwyse]

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).

[devdanzin]

This issue repros in main (3.15) with the provided script.