Own printers, driverless only
The fourth panel this desktop handed to GNOME Settings, and the last one worth owning. Driverless only, deliberately. Adding a printer that describes its own capabilities over IPP is supported; choosing a PPD or fetching a vendor driver is not, and the page says so rather than pretending. That restraint is the whole design: a wrong driver produces a printer that accepts jobs, reports success, and prints nothing, which is the worst failure this page could ship because it looks like it worked. A printer old enough to need a PPD stays a job for the system printer tool. Printers and the queue are separate cards because they answer separate questions. Which printers exist is one; where a document went is the other, and it is the one that actually brings someone here -- so the queue is a single list across every printer. Device URIs are validated by scheme before reaching CUPS, whose backends run as root. file: and pipe: do not lead to a printer and are refused here rather than further down. This machine has no printer, so the page was built against a temporary CUPS queue that was created, exercised through the service, and removed; the service was confirmed to observe the removal rather than merely perform it. Discovery and the driverless add path are verified by their refusals rather than against hardware. Claude-Session: https://claude.ai/code/session_01BRvzt4H8XXLPVH5MyYdk9L
This commit is contained in:
Gabriel Brown
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#!/usr/bin/env python3
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"""Printers, through CUPS' own API rather than by parsing lpstat.
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Driverless only, on purpose. This adds printers that describe their own
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capabilities over IPP -- IPP Everywhere, which is every printer sold in roughly
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the last decade -- and does not choose PPDs or download vendor drivers. Driver
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selection is most of what the panel this replaces does, and getting it wrong
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produces a printer that accepts jobs and silently prints nothing. A printer old
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enough to need a PPD is better served by system-config-printer, and the page
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says so rather than pretending.
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panama-printers snapshot
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panama-printers discover
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panama-printers add URI NAME
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panama-printers remove NAME
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panama-printers set-default NAME
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panama-printers pause NAME | resume NAME
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panama-printers cancel JOB_ID
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panama-printers test-page NAME
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"""
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from __future__ import annotations
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import json
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import re
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import shutil
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import subprocess
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import sys
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# What may be printed to. Everything else -- file:, pipe:, a shell fragment --
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# is refused: this validates the URI rather than trusting a settings page,
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# because a device URI is handed to a backend that runs as root.
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SAFE_SCHEMES = ("ipp", "ipps", "socket", "dnssd", "http", "https")
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URI = re.compile(r"^(%s)://[A-Za-z0-9._~:/?#\[\]@!$&'()*+,;=%%-]+$" % "|".join(SAFE_SCHEMES))
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# CUPS queue names: no spaces, slashes, or '#'.
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QUEUE = re.compile(r"^[A-Za-z0-9_.-]{1,127}$")
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# The only model this adds. Naming it in one place means the driverless promise
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# is checkable rather than scattered.
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DRIVERLESS_MODEL = "everywhere"
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class BoundaryError(RuntimeError):
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"""A user-visible validation or CUPS failure."""
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def connect():
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try:
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import cups
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return cups, cups.Connection()
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except Exception as error: # noqa: BLE001 - no cups is a legitimate state
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raise BoundaryError("The printing service is not answering.") from error
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def run(command: list[str], timeout: float = 30.0) -> subprocess.CompletedProcess:
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try:
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return subprocess.run(command, capture_output=True, text=True,
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timeout=timeout, check=False)
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except (OSError, subprocess.TimeoutExpired) as error:
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raise BoundaryError(f"{command[0]} did not answer.") from error
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def service_state() -> dict:
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active = run(["systemctl", "is-active", "cups.service"]).stdout.strip()
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enabled = run(["systemctl", "is-enabled", "cups.service"]).stdout.strip()
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avahi = run(["systemctl", "is-active", "avahi-daemon.service"]).stdout.strip()
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return {
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"running": active == "active",
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# "on demand" is a real answer and a reasonable configuration, not a
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# problem to report: socket activation starts CUPS when something prints.
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"startsAtBoot": enabled == "enabled",
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"startMode": enabled or "unknown",
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"discoveryAvailable": avahi == "active",
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}
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def printer_state(attributes: dict) -> str:
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"""CUPS reports state as a number; people read words."""
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return {3: "idle", 4: "printing", 5: "stopped"}.get(
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int(attributes.get("printer-state", 0)), "unknown")
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def snapshot() -> dict:
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cups, connection = connect()
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try:
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raw = connection.getPrinters()
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default = connection.getDefault()
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jobs = connection.getJobs(which_jobs="not-completed", my_jobs=False,
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requested_attributes=[
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"job-id", "job-name", "job-printer-uri",
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"job-state", "job-originating-user-name",
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"job-impressions", "time-at-creation"])
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except Exception as error: # noqa: BLE001
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raise BoundaryError("The printing service could not be read.") from error
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printers = []
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for name, attributes in raw.items():
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printers.append({
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"name": name,
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"description": str(attributes.get("printer-info") or name),
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"location": str(attributes.get("printer-location") or ""),
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"makeAndModel": str(attributes.get("printer-make-and-model") or ""),
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"uri": str(attributes.get("device-uri") or ""),
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"state": printer_state(attributes),
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"stateMessage": str(attributes.get("printer-state-message") or ""),
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"accepting": bool(attributes.get("printer-is-accepting-jobs", True)),
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"shared": bool(attributes.get("printer-is-shared", False)),
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"isDefault": name == default,
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})
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printers.sort(key=lambda entry: (not entry["isDefault"], entry["name"].lower()))
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queue = []
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for job in jobs.values() if isinstance(jobs, dict) else []:
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printer_uri = str(job.get("job-printer-uri") or "")
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queue.append({
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"id": int(job.get("job-id") or 0),
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"name": str(job.get("job-name") or "Untitled"),
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"printer": printer_uri.rsplit("/", 1)[-1] if printer_uri else "",
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"state": {3: "pending", 4: "held", 5: "processing",
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6: "stopped", 7: "cancelled"}.get(int(job.get("job-state", 0)), "unknown"),
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"user": str(job.get("job-originating-user-name") or ""),
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"pages": int(job.get("job-impressions") or 0),
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"createdAt": int(job.get("time-at-creation") or 0),
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})
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queue.sort(key=lambda entry: entry["createdAt"])
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return {"printers": printers, "jobs": queue, "service": service_state(), "error": ""}
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def discover() -> dict:
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"""Printers announcing themselves on the network, driverless ones only.
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A printer that does not advertise IPP Everywhere is reported as found but
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not addable, rather than offered and then failing at the point of adding.
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"""
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if not shutil.which("avahi-browse"):
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return {"found": [], "error": "Network discovery is not available."}
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found: dict[str, dict] = {}
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for service in ("_ipps._tcp", "_ipp._tcp"):
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result = run(["avahi-browse", "-rtp", service], timeout=20)
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for line in result.stdout.splitlines():
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if not line.startswith("="):
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continue
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parts = line.split(";")
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if len(parts) < 10:
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continue
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name, host, port, text = parts[3], parts[6], parts[8], parts[9]
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scheme = "ipps" if service == "_ipps._tcp" else "ipp"
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resource = ""
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for field in re.findall(r"\"([^\"]*)\"", text):
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if field.startswith("rp="):
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resource = field[3:]
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# Only IPP Everywhere. The attribute a driverless printer publishes
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# is its PDF/JPEG support; without it, CUPS would need a driver.
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driverless = "application/pdf" in text or "URF=" in text or "urf=" in text
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uri = f"{scheme}://{host}:{port}/{resource}" if resource else f"{scheme}://{host}:{port}/"
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found[uri] = {
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"name": name.replace("\\032", " "),
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"uri": uri,
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"host": host,
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"driverless": driverless,
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}
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return {"found": sorted(found.values(), key=lambda entry: entry["name"]), "error": ""}
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def require_queue(name: str) -> str:
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if not QUEUE.fullmatch(name or ""):
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raise BoundaryError("That is not a printer name.")
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return name
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def add(uri: str, name: str) -> None:
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if not URI.fullmatch(uri or ""):
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raise BoundaryError("That address cannot be used to reach a printer.")
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require_queue(name)
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cups, connection = connect()
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try:
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# ppdname is the driverless model and nothing else. There is no branch
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# here that selects a PPD, which is what keeps the promise checkable.
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connection.addPrinter(name, device=uri, ppdname=DRIVERLESS_MODEL)
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connection.enablePrinter(name)
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connection.acceptJobs(name)
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except Exception as error: # noqa: BLE001
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message = str(error)
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if "device-error" in message or "1284" in message:
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raise BoundaryError(
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"The printer did not answer, or does not support driverless printing.") from error
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if "not-authorized" in message or "forbidden" in message.lower():
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raise BoundaryError("Adding a printer was not authorized.") from error
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raise BoundaryError("That printer could not be added.") from error
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def remove(name: str) -> None:
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require_queue(name)
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cups, connection = connect()
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try:
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connection.deletePrinter(name)
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except Exception as error: # noqa: BLE001
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raise BoundaryError("That printer could not be removed.") from error
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def set_default(name: str) -> None:
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require_queue(name)
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cups, connection = connect()
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try:
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connection.setDefault(name)
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except Exception as error: # noqa: BLE001
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raise BoundaryError("That printer could not be made the default.") from error
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def set_paused(name: str, paused: bool) -> None:
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require_queue(name)
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cups, connection = connect()
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try:
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if paused:
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connection.disablePrinter(name)
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else:
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connection.enablePrinter(name)
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except Exception as error: # noqa: BLE001
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raise BoundaryError("That printer could not be changed.") from error
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def cancel(job_id: str) -> None:
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if not job_id.isdigit():
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raise BoundaryError("That is not a job.")
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cups, connection = connect()
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try:
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connection.cancelJob(int(job_id))
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except Exception as error: # noqa: BLE001
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raise BoundaryError("That job could not be cancelled.") from error
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def test_page(name: str) -> None:
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require_queue(name)
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result = run(["lp", "-d", name, "/usr/share/cups/data/testprint"], timeout=30)
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if result.returncode != 0:
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raise BoundaryError((result.stderr.strip() or "The test page could not be sent.")[:200])
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def main(arguments: list[str]) -> int:
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try:
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if arguments == ["snapshot"]:
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print(json.dumps(snapshot(), separators=(",", ":")))
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return 0
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if arguments == ["discover"]:
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print(json.dumps(discover(), separators=(",", ":")))
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return 0
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if len(arguments) == 3 and arguments[0] == "add":
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add(arguments[1], arguments[2])
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elif len(arguments) == 2 and arguments[0] == "remove":
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remove(arguments[1])
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elif len(arguments) == 2 and arguments[0] == "set-default":
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set_default(arguments[1])
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elif len(arguments) == 2 and arguments[0] == "pause":
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set_paused(arguments[1], True)
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elif len(arguments) == 2 and arguments[0] == "resume":
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set_paused(arguments[1], False)
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elif len(arguments) == 2 and arguments[0] == "cancel":
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cancel(arguments[1])
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elif len(arguments) == 2 and arguments[0] == "test-page":
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test_page(arguments[1])
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else:
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raise BoundaryError(
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"Usage: panama-printers snapshot | discover | add URI NAME | remove NAME | "
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"set-default NAME | pause NAME | resume NAME | cancel JOB_ID | test-page NAME")
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except BoundaryError as error:
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try:
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state = snapshot()
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except BoundaryError:
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state = {"printers": [], "jobs": [], "service": service_state()}
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state["error"] = str(error)
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print(json.dumps(state, separators=(",", ":")))
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return 0
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print(json.dumps(snapshot(), separators=(",", ":")))
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return 0
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if __name__ == "__main__":
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raise SystemExit(main(sys.argv[1:]))
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