lx-d02/windows/print_server.py

"""LX-D02 as a regular Windows printer.

Windows prints to the "LX-D02" printer: the stock POS-58 driver for 58 mm receipt
printers, on a TCP port 127.0.0.1:9100 (see install.ps1). The driver turns the page into
ESC/POS raster; this server takes it from the port and prints it over Bluetooth.

Usage: python print_server.py [MAC]       (without MAC the printer is found by name)
       python print_server.py --test FILE  (saved job -> FILE.png, no printing)
       python print_server.py --selftest
"""
import asyncio
import logging
import queue
import socketserver
import sys
import threading
from pathlib import Path

from PIL import Image, ImageOps

sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
from lxd02 import WIDTH, send  # noqa: E402

PORT = 9100
MAX_GAP = 48  # dots: longer white gaps are cut down to this (6 mm)
LAST_JOB = Path(__file__).with_name("last_job.bin")
log = logging.getLogger("lx-d02")


def render(data):
    """ESC/POS from the POS-58 driver -> 1-bit image WIDTH wide, ready to print.

    The driver sends the page as GS v 0 raster bands. Its ESC J feeds between the bands
    only move the paper by the band height, so the bands are just stacked."""
    rows, pos = [], 0
    while True:
        pos = data.find(b"\x1dv0", pos)
        if pos < 0 or pos + 8 > len(data):
            break
        w = data[pos + 4] | data[pos + 5] << 8
        h = data[pos + 6] | data[pos + 7] << 8
        band = data[pos + 8:pos + 8 + w * h]
        rows += [band[r * w:(r + 1) * w].ljust(WIDTH // 8, b"\0")[:WIDTH // 8] for r in range(h)]
        pos += 8 + w * h
    if not rows:
        raise ValueError(f"no ESC/POS raster in the job: {data[:16]!r} (is the driver POS-58?)")
    img = ImageOps.invert(Image.frombytes("1", (WIDTH, len(rows)), b"".join(rows)).convert("L"))
    box = ImageOps.invert(img).getbbox()
    if not box:
        raise ValueError("blank page")
    # Apps keep their page margins: drop the left one and the white above and below
    shift = max(0, box[0] - 4)
    img = img.crop((shift, max(0, box[1] - 4), WIDTH + shift, min(img.height, box[3] + 4)))
    img.paste(255, (WIDTH - shift, 0, WIDTH, img.height))  # the crop past the right edge is black
    return squeeze(img).convert("1")


def squeeze(img, gap=MAX_GAP):
    """Shorten white gaps longer than `gap` rows: page layouts put the footer a whole
    page below the text, and the tape is not a page."""
    raw = img.tobytes()
    keep, blank = [], 0
    for y in range(img.height):
        row = raw[y * img.width:(y + 1) * img.width]
        blank = blank + 1 if min(row) == 255 else 0
        if blank <= gap:
            keep.append(row)
    return Image.frombytes("L", (img.width, len(keep)), b"".join(keep))


class Job(socketserver.BaseRequestHandler):
    jobs = queue.Queue()

    def handle(self):
        chunks = []
        while True:
            chunk = self.request.recv(65536)
            if not chunk:
                break
            chunks.append(chunk)
        if chunks:  # an empty connection is Windows checking the port
            self.jobs.put(b"".join(chunks))


def printer_loop(mac):
    """One job at a time: the printer takes a single Bluetooth connection."""
    while True:
        data = Job.jobs.get()
        LAST_JOB.write_bytes(data)  # for debugging a strange print: --test last_job.bin
        try:
            img = render(data)
            log.info("job: %d bytes, %d dots long", len(data), img.height)
            asyncio.run(send(img, mac))
            log.info("printed")
        except Exception:
            log.exception("job failed")


def main(mac):
    threading.Thread(target=printer_loop, args=(mac,), daemon=True).start()
    server = socketserver.ThreadingTCPServer(("127.0.0.1", PORT), Job)
    log.info("waiting for jobs on 127.0.0.1:%d", PORT)
    server.serve_forever()


if __name__ == "__main__":
    handlers = [logging.FileHandler(Path(__file__).with_name("print_server.log"), encoding="utf-8")]
    if sys.stderr:  # None under pythonw
        handlers.append(logging.StreamHandler())
    logging.basicConfig(level=logging.INFO, format="%(asctime)s %(message)s", handlers=handlers)
    if sys.argv[1:2] == ["--selftest"]:
        # one blank row, then one row with a single dot at x = 7: comes out shifted left
        job = b"\x1b@\x1dv0\x00" + bytes([48, 0, 2, 0]) + bytes(48) + b"\x01" + bytes(47) + b"\x1bJ\x15"
        img = render(job)
        assert img.width == WIDTH and img.getpixel((4, 1)) == 0 and img.getpixel((7, 1)) == 255
        assert squeeze(Image.new("L", (8, 100), 255), 10).height == 10
        print("ok")
    elif sys.argv[1:2] == ["--test"]:
        src = Path(sys.argv[2])
        render(src.read_bytes()).save(src.with_suffix(".png"))
        print("ok", src.with_suffix(".png"))
    else:
        main(sys.argv[1] if len(sys.argv) > 1 else None)