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[3.6] bpo-31158: Fix nondeterministic read in test_pty (GH-3808) #3852

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Oct 2, 2017
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[3.6] bpo-31158: Fix nondeterministic read in test_pty (GH-3808) #3852

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21 changes: 19 additions & 2 deletions Lib/test/test_pty.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
import select
import signal
import socket
import io # readline
import unittest

TEST_STRING_1 = b"I wish to buy a fish license.\n"
Expand All @@ -23,6 +24,16 @@ def debug(msg):
pass


# Note that os.read() is nondeterministic so we need to be very careful
# to make the test suite deterministic. A normal call to os.read() may
# give us less than expected.
#
# Beware, on my Linux system, if I put 'foo\n' into a terminal fd, I get
# back 'foo\r\n' at the other end. The behavior depends on the termios
# setting. The newline translation may be OS-specific. To make the
# test suite deterministic and OS-independent, the functions _readline
# and normalize_output can be used.

def normalize_output(data):
# Some operating systems do conversions on newline. We could possibly
# fix that by doing the appropriate termios.tcsetattr()s. I couldn't
Expand All @@ -44,6 +55,12 @@ def normalize_output(data):

return data

def _readline(fd):
"""Read one line. May block forever if no newline is read."""
reader = io.FileIO(fd, mode='rb', closefd=False)
return reader.readline()



# Marginal testing of pty suite. Cannot do extensive 'do or fail' testing
# because pty code is not too portable.
Expand Down Expand Up @@ -98,14 +115,14 @@ def test_basic(self):

debug("Writing to slave_fd")
os.write(slave_fd, TEST_STRING_1)
s1 = os.read(master_fd, 1024)
s1 = _readline(master_fd)
self.assertEqual(b'I wish to buy a fish license.\n',
normalize_output(s1))

debug("Writing chunked output")
os.write(slave_fd, TEST_STRING_2[:5])
os.write(slave_fd, TEST_STRING_2[5:])
s2 = os.read(master_fd, 1024)
s2 = _readline(master_fd)
self.assertEqual(b'For my pet fish, Eric.\n', normalize_output(s2))

os.close(slave_fd)
Expand Down