.read() doesn't advance offset

[lopisan]

Hi,
I've find a possible bug in AsyncPath lib:
f.read(count) doesn't advacne offset, so two consecutive reads read just the beggining of the file.
I've created tests showing the bug:

from pathlib import Path

import pytest
from tempfile import TemporaryDirectory
from aiopath import AsyncPath


@pytest.mark.asyncio
async def test_async_path():
    with TemporaryDirectory(prefix='read_test') as temp_dir:
        file = AsyncPath(temp_dir) / 'test.bin'
        await file.write_bytes(b'0123456789abcdefghijklmnopqrstuvwxyz')
        async with file.open('rb') as f:
            chunk = await f.read(10)
            assert chunk == b'0123456789'
            chunk = await f.read(10)
            assert chunk == b'abcdefghij' # THIS LINE FAILS - eventhough it shouldn't (in pathlib this works)


def test_path():
    with TemporaryDirectory(prefix='read_test') as temp_dir:
        file = Path(temp_dir) / 'test.bin'
        file.write_bytes(b'0123456789abcdefghijklmnopqrstuvwxyz')
        with file.open('rb') as f:
            chunk = f.read(10)
            assert chunk == b'0123456789'
            chunk = f.read(10)
            assert chunk == b'abcdefghij'

[alexdelorenzo]

Hi @lopisan, thanks for opening an issue and including test cases.

When you use the AsyncPath.open() context manager, it yields an AIOFile object from the aiofile project. From what I can tell, this behavior of the AIOFile.read() method is deliberate, as the README for aiofile indicates that it wants you to use the seek() method between reads if you want to advance the offset. If you want a quick fix for your own project, check out the documentation for aiofile.

However, aiopath subclasses AIOFile as IterableAIOFIle in order to mimic the behavior of the file-like object pathlib.Path.open() yields.

I agree that the behavior of read() should increment the offset between calls, so I'll modify the read() method so that it behaves the same way it does with pathlib.

[alexdelorenzo]

v0.5.6 fixes this issue on Python 3.7 - 3.9. For 3.10, it's available as v0.6.5 on PyPI.

Thanks again for the test cases, @lopisan.

[lopisan]

Thanks for a quick fix! It works like a charm now.

[alexdelorenzo]

Glad to hear it!