Cannot use datetimes before UNIX epoch on Windows

py-pgproto's codecs/datetime.pyx のリンク先の行から始め、参照されている CPython Windows issue とその挙動を比較します。Windows 上で executemany() を使って datetime.datetime(1969, 12, 31) の bind を再現します。エンコード中に UNIX エポックより前の datetimes が OSError を発生させなくなれば完了です。

• asyncpg version: 0.29.0
• PostgreSQL version: 15.5
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: Local PostgreSQL install
• Python version: 3.10.1
• Platform: Windows
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: N/A
• Can the issue be reproduced under both asyncio and
  uvloop?: N/A

If I have this query:

INSERT INTO process.start_and_end (user_id, process_id, start_dt, end_dt) VALUES  ($1, $2, $3, $4);

and in Python I do:

await conn.executemany(query, [(1325, 1001, datetime.datetime(1969, 12, 31, 0, 0), None)])

this line throws the following exception:

Traceback (most recent call last):
  File "asyncpg\protocol\prepared_stmt.pyx", line 175, in asyncpg.protocol.protocol.PreparedStatementState._encode_bind_msg
  File "asyncpg\protocol\codecs/base.pyx", line 227, in asyncpg.protocol.protocol.Codec.encode
  File "asyncpg\protocol\codecs/base.pyx", line 129, in asyncpg.protocol.protocol.Codec.encode_scalar
  File "asyncpg\pgproto\./codecs/datetime.pyx", line 222, in asyncpg.pgproto.pgproto.timestamptz_encode
OSError: [Errno 22] Invalid argument

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "main.py", line 919, in <module>
    loop.run_until_complete(async_main())
  File "C:\Scoop\apps\python\current\lib\asyncio\base_events.py", line 641, in run_until_complete
    return future.result()
  [...]
  File "main.py", line 401, in __insert_tape
    await conn.executemany(query, [(1325, 1001, datetime.datetime(1969, 12, 31, 0, 0), None)])
  File ".venv\lib\site-packages\asyncpg\connection.py", line 391, in executemany
    return await self._executemany(command, args, timeout)
  File ".venv\lib\site-packages\asyncpg\connection.py", line 1911, in _executemany
    result, _ = await self._do_execute(query, executor, timeout)
  File ".venv\lib\site-packages\asyncpg\connection.py", line 1945, in _do_execute
    result = await executor(stmt, None)
  File "asyncpg\protocol\protocol.pyx", line 267, in bind_execute_many
  File "asyncpg\protocol\coreproto.pyx", line 974, in asyncpg.protocol.protocol.CoreProtocol._bind_execute_many_more
  File "asyncpg\protocol\protocol.pyx", line 230, in genexpr
  File "asyncpg\protocol\prepared_stmt.pyx", line 204, in asyncpg.protocol.protocol.PreparedStatementState._encode_bind_msg
asyncpg.exceptions.DataError: invalid input for query argument $3 in element #0 of executemany() sequence: datetime.datetime(1969, 12, 31, 0, 0) ([Errno 22] Invalid argument)

Digging into it a bit more, I found that the culprit is this line in the codec for datetime objects, which is related to this old CPython issue on Windows: https://github.com/python/cpython/issues/80940.

The fix looks quite simple, but unfortunately I do not have the time to work on that, so I'm opening an issue instead of a PR.