Bugfix: readinto/readline/readlines SubFile methods EOF behavior

[pressler-vsc]

Description

While trying to work with an image segment as a SubFile, I found that certain methods did not behave as I expected (e.g. they were going beyond the SubFile's length). To demonstrate this, I split out the readinto, readline, and readlines checks into their own tests and then run in main:

run new tests in main

$ pytest test/test_core.py
=================================================================================================================================================================== test session starts ====================================================================================================================================================================
platform linux -- Python 3.14.0, pytest-8.4.2, pluggy-1.6.0
rootdir: /home/vscuser/git/glweb/software/third-party/jbpy
configfile: pyproject.toml
collected 38 items                                                                                                                                                                                                                                                                                                                                         

test/test_core.py ...................................FFF                                                                                                                                                                                                                                                                                             [100%]

========================================================================================================================================================================= FAILURES =========================================================================================================================================================================
__________________________________________________________________________________________________________________________________________________________________ test_subfile_readinto ___________________________________________________________________________________________________________________________________________________________________

    def test_subfile_readinto():
        all_data = bytearray(
            "".join(random.choices(string.ascii_letters + string.digits, k=1000)).encode()
        )
        start = 400
        length = 400
        f_all = io.BytesIO(all_data)
        f_io = io.BytesIO(all_data[start : start + length])
        f_jb = jbpy.core.SubFile(f_all, start, length)
    
        # read small piece
        b_io = bytearray(50)
        b_jb = bytearray(50)
        assert f_jb.readinto(b_jb) == f_io.readinto(b_io)
        assert b_jb == b_io
    
        # read rest of subfile into too large of a buffer
        b_io.resize(length * 2)
        b_jb.resize(length * 2)
>       assert f_jb.readinto(b_jb) == f_io.readinto(b_io)
E       AssertionError: assert 550 == 350
E        +  where 550 = readinto(bytearray(b'savX7XNsqHGVo46G9DgtyA95ICwdVB7fYsd3eXDyj0UQ6Lhgyz3qyAclZpG8STajKvmyLjAFKm2PVB5RRw13a8ElNmna1Rh2Xcz6qVhHWE...0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'))
E        +    where readinto = <jbpy.core.SubFile object at 0x7f492a333b10>.readinto
E        +  and   350 = <built-in method readinto of _io.BytesIO object at 0x7f4929c23d80>(bytearray(b'savX7XNsqHGVo46G9DgtyA95ICwdVB7fYsd3eXDyj0UQ6Lhgyz3qyAclZpG8STajKvmyLjAFKm2PVB5RRw13a8ElNmna1Rh2Xcz6qVhHWE...0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'))
E        +    where <built-in method readinto of _io.BytesIO object at 0x7f4929c23d80> = <_io.BytesIO object at 0x7f4929c23d80>.readinto

test/test_core.py:809: AssertionError
__________________________________________________________________________________________________________________________________________________________________ test_subfile_readline ___________________________________________________________________________________________________________________________________________________________________

    def test_subfile_readline():
        all_data = bytearray(
            "".join(random.choices(string.ascii_letters + string.digits, k=1000)).encode()
        )
        newline_positions = (500, 550, 600, 650, 700)
        for pos in newline_positions:
            all_data[pos] = ord("\n")
    
        start = 400
        length = 400
        f_all = io.BytesIO(all_data)
        f_io = io.BytesIO(all_data[start : start + length])
        f_jb = jbpy.core.SubFile(f_all, start, length)
    
        # Hit size limit, don't read full line
        assert f_jb.readline(3) == f_io.readline(3) == all_data[start : start + 3]
        # Set limit way too high, hit first newline
        assert (
            f_jb.readline(3 * length)
            == f_io.readline(3 * length)
            == all_data[start + 3 : 501]
        )
        # Read the rest of the lines
        for _ in range(len(newline_positions)):
>           assert f_jb.readline() == (b := f_io.readline())
E           AssertionError: assert b'f9Yb2BS58hi...fXgTsYfZLfFJh' == b''
E             
E             Use -v to get more diff

test/test_core.py:844: AssertionError
__________________________________________________________________________________________________________________________________________________________________ test_subfile_readlines __________________________________________________________________________________________________________________________________________________________________

    def test_subfile_readlines():
        all_data = bytearray(
            "".join(random.choices(string.ascii_letters + string.digits, k=1000)).encode()
        )
        newline_positions = (500, 550, 600, 650, 700)
        for pos in newline_positions:
            all_data[pos] = ord("\n")
    
        start = 400
        length = 400
        f_all = io.BytesIO(all_data)
        f_io = io.BytesIO(all_data[start : start + length])
        f_jb = jbpy.core.SubFile(f_all, start, length)
    
        # Hit size limit, only read first line
        assert (
            f_jb.readlines(1)
            == f_io.readlines(1)
            == [all_data[start : newline_positions[0] + 1]]
        )
        # Hit size limit, read next two lines
        assert f_jb.readlines(70) == (l_io := f_io.readlines(70))
        assert len(l_io) == 2
        # Read the rest
>       assert f_jb.readlines() == (l_io := f_io.readlines())
E       AssertionError: assert [b'goyJSeNhK2...LkPpp9juFT8k'] == []
E         
E         Left contains 3 more items, first extra item: b'goyJSeNhK21TkFog8R9vcIzSXjkeOCtnht7NAHB8rM2XkpsY3\n'
E         Use -v to get more diff

test/test_core.py:875: AssertionError
================================================================================================================================================================= short test summary info ==================================================================================================================================================================
FAILED test/test_core.py::test_subfile_readinto - AssertionError: assert 550 == 350
FAILED test/test_core.py::test_subfile_readline - AssertionError: assert b'f9Yb2BS58hi...fXgTsYfZLfFJh' == b''
FAILED test/test_core.py::test_subfile_readlines - AssertionError: assert [b'goyJSeNhK2...LkPpp9juFT8k'] == []
=============================================================================================================================================================== 3 failed, 35 passed in 0.76s ===============================================================================================================================================================