[Python-Dev] off-by-one on ftell on wine, but no regression test to catch it

[Luke Kenneth Casson Leighton]

folks, hi,
http://bugs.winehq.org/show_bug.cgi?id=16982 related to this:

from array import array

TESTFN = "testfile.txt"

def fail(x):
    print x

testlines = [
    "spam, spam and eggs\n",
    "eggs, spam, ham and spam\n",
    "saussages, spam, spam and eggs\n",
    "spam, ham, spam and eggs\n",
    "spam, spam, spam, spam, spam, ham, spam\n",
    "wonderful spaaaaaam.\n"
]

try:
    # Prepare the testfile
    bag = open(TESTFN, "w")
    bag.writelines(testlines)
    bag.close()

    f = open(TESTFN)
    testline = testlines.pop(0)
    line = f.readline()
    testline = testlines.pop(0)
    buf = array("c", "\x00" * len(testline))
    f.readinto(buf)
    testline = testlines.pop(0)
    print "length of testline:", len(testline)
    line = f.read(len(testline))

    if line != testline:
        fail("read() after next() with empty buffer "
                  "failed. Got %r, expected %r" % (line, testline))

    lines = f.readlines()

    if lines != testlines:
        fail("readlines() after next() with empty buffer "
                  "failed. Got %r, expected %r" % (line, testline))
    f.close()
finally:
    os.unlink(TESTFN)


which is a reduced version of Lib/test/test_file.py

running under wine, ftell() has an off-by-one bug, where the file
position accidentally doesn't include the fact that the CR of the CRLF
has been skipped.  but, now with the fgets() bug fixed, the regression
tests pass, but there's still the off-by-one bug which _isn't_ caught.

this really should be added as a windows test.  actually, it should be
added as a test for everything: it's not always reasonable to assume
that OSes get their file positions right :)

l.