codec.StreamReaderWriter: issues with interlaced read-write

[vstinner]

BPO	12513
Nosy	@malemburg, @doerwalter, @vstinner

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-06-28.01:39:55.708>
created_at = <Date 2011-07-07.13:12:46.746>
labels = ['type-bug', 'library', 'expert-unicode']
title = 'codec.StreamReaderWriter: issues with interlaced read-write'
updated_at = <Date 2017-06-28.01:39:55.707>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2017-06-28.01:39:55.707>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-06-28.01:39:55.708>
closer = 'vstinner'
components = ['Library (Lib)', 'Unicode']
creation = <Date 2011-07-07.13:12:46.746>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 12513
keywords = []
message_count = 3.0
messages = ['139975', '222225', '297128']
nosy_count = 4.0
nosy_names = ['lemburg', 'doerwalter', 'vstinner', 'BreamoreBoy']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue12513'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']

[vstinner]

The following test fails with an AssertionError('a' != 'b') on the first read.

import codecs

FILENAME = 'test'

with open(FILENAME, 'wb') as f:
    f.write('abcd'.encode('utf-8'))
with codecs.open(FILENAME, 'r+', encoding='utf-8') as f:
    f.write("1")

    pos = f.writer.tell()
    assert pos == 1, "writer pos: %s != 1" % pos
    pos = f.reader.tell()
    assert pos == 1, "reader pos: %s != 1" % pos
    pos = f.stream.tell()
    assert pos == 1, "stream pos: %s != 1" % pos

    # read() must call writer.flush()
    char = f.read(1)
    assert char == 'b', "%r != 'b'" % (char,)
    # write() must rewind the raw stream
    f.write('3')
    tail = f.read()
    assert tail == 'd', "%r != 'd'" % (tail,)
    f.flush()
    with open(FILENAME, 'rb') as f:
        assert f.read() == b'1b3d'

I suppose that readline(), readlines() and __next__() have also issues.

See also issue bpo-12215: similar issue with io.TextIOWrapper.

[BreamoreBoy]

Codecs gurus FYI.

[vstinner]

Sorry, I just lost track of this issue and so will just close it. Moreover, I also closed bpo-12215.