[issue26848] asyncio.subprocess's communicate() method mishandles empty input bytes

[Berker Peksag]

Changes by Berker Peksag :


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resolution:  -> fixed
stage:  -> resolved
status: open -> closed

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[issue26848] asyncio.subprocess's communicate() method mishandles empty input bytes

[Roundup Robot]

Roundup Robot added the comment:

New changeset 148757a88f19 by Yury Selivanov in branch '3.5':
Issue #26848: Fix asyncio/subprocess.communicate() to handle empty input.
https://hg.python.org/cpython/rev/148757a88f19

New changeset f5e69e2f50d7 by Yury Selivanov in branch 'default':
Merge 3.5 (issue #26848)
https://hg.python.org/cpython/rev/f5e69e2f50d7

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[issue26848] asyncio.subprocess's communicate() method mishandles empty input bytes

[Jack O'Connor]

Jack O'Connor added the comment:

Related: The asyncio communicate() method differs from standard subprocess in 
how it treats input bytes when stdin is (probably mistakenly) not set to PIPE. 
Like this:

proc = await create_subprocess_shell("sleep 5")
await proc.communicate(b"foo")  # Oops, I forgot stdin=PIPE above!

The standard, non-async version of this example, communicate would ignore the 
input bytes entirely. But here in the asyncio version, communicate will try to 
write those bytes to stdin, which is None, and the result is an AttributeError.

Since the user probably only hits this case by mistake, I think raising an 
exception is preferable. But it would be nice to raise an exception that 
explicitly said "you've forgotten stdin=PIPE" instead of the unhelpful 
"'NoneType' object has no attribute 'write'". Maybe it would be worth cleaning 
this up while we're here?

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[issue26848] asyncio.subprocess's communicate() method mishandles empty input bytes

[Jack O'Connor]

Jack O'Connor added the comment:

Thanks for the heads up, Berker, I've re-submitted the PR as 
https://github.com/python/asyncio/pull/335.

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[issue26848] asyncio.subprocess's communicate() method mishandles empty input bytes

[Berker Peksag]

Berker Peksag added the comment:

python/cpython is a semi-official read-only mirror of hg.python.org/cpython. We 
haven't switched to GitHub yet. You may want to open a pull request to 
https://github.com/python/asyncio See 
https://github.com/python/asyncio/wiki/Contributing for details.

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[issue26848] asyncio.subprocess's communicate() method mishandles empty input bytes

[Jack O'Connor]

New submission from Jack O'Connor:

Setting stdin=PIPE and then calling communicate(b"") should close the child's 
stdin immediately, similar to stdin=DEVNULL. Instead, communicate() treats b"" 
like None and leaves the child's stdin open, which makes the child hang forever 
if it tries to read anything.

I have a PR open with a fix and a test: 
https://github.com/python/cpython/pull/33

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components: asyncio
messages: 264212
nosy: gvanrossum, haypo, oconnor663, yselivanov
priority: normal
severity: normal
status: open
title: asyncio.subprocess's communicate() method mishandles empty input bytes
type: behavior
versions: Python 3.5, Python 3.6

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