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https://github.com/kuhyx/testsAndMisc.git
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Krzysztof kuhy Rudnicki
ad3d70f197
usb_query.py 267 -> 180. The non-blocking fd handling - _drain_buffer, _write_with_deadline, _read_nonblocking, _wait_for_pjl_response and pjl_query - moves to _pjl_io.py. usb_query imports the three names test_usb_query.py patches back, which is safe here only because all three still have real call sites in the code that stayed; an import-only name would be stripped by ruff's F401 sweep and break the patch. os and time also stay: they are patched on usb_query as well as on _pjl_io. test_usb_query.py needs no edit. Pass count is 402 before and after. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011w2Pj4Ek3ZNMQVYcFHgXDY
109 lines
3.9 KiB
Python
109 lines
3.9 KiB
Python
"""Non-blocking PJL transport over the raw /dev/usb/lp* file descriptor.
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Split out of :mod:`python_pkg.brother_printer.usb_query` to keep it under the
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250-line cap. ``tests/test_usb_query_part2.py`` patches ``os``, ``select`` and
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``time`` on this module, so those imports are load-bearing; the query callers
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that stay in ``usb_query`` import these functions back, which is what keeps
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``tests/test_usb_query.py`` patching them there.
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"""
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from __future__ import annotations
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import contextlib
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import os
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import select
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import time
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# ── PJL over USB ─────────────────────────────────────────────────────
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# The printer's fd is opened and kept non-blocking. usblp blocks indefinitely
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# on a plain open() and on writes whenever the printer is not ready to talk -
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# stuck mid-job, wedged, or simply asleep - so a blocking fd turns "the printer
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# is unwell" into "this tool hangs forever", which is the worst possible answer
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# when a status report is exactly what you wanted.
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def _drain_buffer(fd: int) -> None:
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"""Read and discard any stale data from the USB buffer."""
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with contextlib.suppress(OSError):
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while os.read(fd, 4096):
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pass
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def _write_with_deadline(fd: int, data: bytes, deadline: float) -> bool:
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"""Write all of data to a non-blocking fd. Returns False if the deadline passes.
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Args:
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fd: Non-blocking file descriptor for the printer.
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data: Bytes to send.
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deadline: Absolute monotonic-ish time (time.time()) to give up at.
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Returns:
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True when everything was written, False on timeout or write error.
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"""
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sent = 0
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while sent < len(data):
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remaining = deadline - time.time()
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if remaining <= 0:
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return False
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try:
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sent += os.write(fd, data[sent:])
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except BlockingIOError:
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# Printer's buffer is full or it is not accepting data: wait for it
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# to become writable rather than spinning or blocking forever.
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_, writable, _ = select.select([], [fd], [], min(remaining, 0.5))
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if not writable:
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continue
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except OSError:
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return False
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return True
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def _read_nonblocking(fd: int) -> bytes:
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"""Read all currently available data from a non-blocking fd."""
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data = b""
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with contextlib.suppress(OSError):
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while True:
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chunk = os.read(fd, 4096)
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if not chunk:
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break
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data += chunk
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return data
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def _wait_for_pjl_response(fd: int, deadline: float) -> bytes:
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"""Poll fd until PJL data arrives or deadline expires."""
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response = b""
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while time.time() < deadline:
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remaining = deadline - time.time()
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if remaining <= 0:
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break
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readable, _, _ = select.select([fd], [], [], min(remaining, 1.0))
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if readable:
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response += _read_nonblocking(fd)
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if response and (b"=" in response or b"@PJL" in response):
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break
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return response
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def pjl_query(fd: int, cmd: str, timeout_sec: float = 5.0) -> str:
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"""Send a PJL command via raw fd and read the response.
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Args:
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fd: Non-blocking file descriptor for the printer.
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cmd: PJL command, e.g. "@PJL INFO STATUS".
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timeout_sec: Total budget for sending the command and reading the reply.
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Returns:
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The printer's reply, or "" if it did not answer in time. A silent
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printer is a normal outcome here, not an error: it happens whenever the
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printer is busy digesting a job.
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"""
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deadline = time.time() + timeout_sec
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pjl_cmd = f"\x1b%-12345X@PJL\r\n{cmd}\r\n\x1b%-12345X"
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if not _write_with_deadline(fd, pjl_cmd.encode(), deadline):
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return ""
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response = _wait_for_pjl_response(fd, deadline)
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return response.decode("ascii", errors="replace")
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