bambuddy/backend/app/services/bambu_ftp.py

import asyncio
import ftplib  # nosec B402
import logging
import os
import socket
import ssl
import threading
import time
import weakref
from collections.abc import Awaitable, Callable
from concurrent.futures import ThreadPoolExecutor
from enum import Enum
from ftplib import FTP, FTP_TLS  # nosec B402
from io import BytesIO
from pathlib import Path
from typing import TypeVar

logger = logging.getLogger(__name__)

T = TypeVar("T")

# Every FTP call below is blocking ftplib work handed to a thread. They used to
# run on asyncio's *default* executor, which is sized min(32, cpu_count + 4) —
# six threads on a 2-core NAS — and is shared with every other ``to_thread`` /
# ``run_in_executor`` caller in the app. That was survivable only because the
# scheduler uploaded to exactly one printer at a time. Dispatching to several
# printers at once (#2555) would park one thread per in-flight upload for
# minutes at a stretch (a 41 MB 3MF at the ~150 KB/s a Bambu printer sustains
# takes ~4 min), starving the default pool and stalling unrelated work.
#
# A dedicated pool keeps that blast radius inside the FTP layer: the scheduler's
# own concurrency cap is what limits parallel uploads, and it can never exhaust
# the executor everything else depends on. Threads are created lazily, so an
# idle pool costs nothing.
#
# Sized well above `queue_max_concurrent_uploads` (max 16), because uploads are
# not the only traffic here: SD browsing, timelapse/recording listing, cover
# downloads, deletes and storage checks all run through this pool too, and on a
# farm they fan out across every printer at once. The pool's work queue is
# unbounded, so exceeding it does not fail — it queues. But `asyncio.wait_for`
# starts its clock at submission, not at thread start, so a task that sits in the
# queue can burn its whole timeout without ever running, and `list_files_async`
# reports a timeout as an empty listing — a silent "this printer has no files".
# Keep the headroom.
_FTP_MAX_WORKERS = 48
_ftp_executor = ThreadPoolExecutor(max_workers=_FTP_MAX_WORKERS, thread_name_prefix="bambu-ftp")

# Overall upload deadline (#2529). A flat wall-clock cap punishes big files on
# slow links rather than catching broken ones: a 96 MB 3MF at the ~75 KB/s an A1
# sustains over WiFi legitimately needs ~20 minutes, and the old flat 600 s
# declared it dead at ~70 MB. The deadline is therefore derived from the file
# size against a deliberately pessimistic floor rate. This is a backstop, not the
# failure detector — a link that has actually died is caught within
# ``socket_timeout`` by the blocking ``sendall``, long before this fires.
_UPLOAD_FLOOR_BYTES_PER_SEC = 25 * 1024
_UPLOAD_MIN_TIMEOUT = 600.0

# How long to give the worker thread to notice the cancel flag, unwind, and
# delete its partial file. It checks the flag once per CHUNK_SIZE, so on a link
# slow enough to have hit the deadline this is one chunk plus the delete.
_UPLOAD_CANCEL_GRACE = 60.0


class UploadCancelled(Exception):
    """Raised inside the upload worker to abort an in-flight transfer.

    ``upload_file`` treats any exception from its progress callback as "stop
    now": it breaks out of the send loop, deletes the partial file from the
    printer, and re-raises. That is the only way to stop a transfer — an
    executor thread cannot be cancelled from the event loop, so a bare
    ``asyncio.wait_for`` leaves it streaming (see ``upload_file_async``).
    """


class DeleteResult(Enum):
    """Outcome of an FTP delete attempt.

    Distinguishes "file isn't on the printer" (550, recovery impossible by
    retrying) from "delete failed for some other reason" (network, auth,
    transient FTP error — worth retrying). The post-print SD-card cleanup in
    main.py used to flatten both into ``False`` and log a "may linger" WARNING
    on every successful print where the printer self-cleaned its SD card
    before our cleanup ran (#1721 reporter's A1).
    """

    DELETED = "deleted"
    NOT_FOUND = "not_found"
    FAILED = "failed"


class FileNotOnPrinterError(Exception):
    """Raised when a remote FTP path returns 550 (file not found).

    550 means the file does not exist at that path — retrying the same path
    will never succeed. Callers use this sentinel with with_ftp_retry's
    non_retry_exceptions to immediately move on to the next candidate path
    instead of burning the full retry budget (up to 11 × 30s per path) on
    a lookup that cannot recover.
    """


class ImplicitFTP_TLS(FTP_TLS):
    """FTP_TLS subclass for implicit FTPS (port 990) with model-specific SSL handling.

    X1C/P1S printers (vsFTPd) require SSL with session reuse on the data channel.
    A1/A1 Mini printers have issues with SSL on the data channel entirely and
    timeout waiting for transfer completion. Set skip_session_reuse=True for A1
    printers to skip SSL on the data channel (control channel remains encrypted).

    Optionally caps the SSL context's maximum TLS version to v1.2 (P2S firmware
    01.02.00.00 needs this — see :mod:`ftp_profiles` and #1401).
    """

    def __init__(self, *args, skip_session_reuse: bool = False, cap_tls_v1_2: bool = False, **kwargs):
        super().__init__(*args, **kwargs)
        self._sock = None
        self.skip_session_reuse = skip_session_reuse
        self.ssl_context = ssl.create_default_context()
        self.ssl_context.check_hostname = False
        self.ssl_context.verify_mode = ssl.CERT_NONE
        # ``create_default_context()`` does NOT guarantee a protocol floor: it
        # leaves ``minimum_version`` at ``MINIMUM_SUPPORTED``, and what that
        # resolves to is a property of the OpenSSL build, not of this code.
        # Measured on identical OpenSSL 3.5.6: python:3.13-slim-trixie (our
        # Docker base) reports TLSv1_2, a bare-metal venv reports
        # MINIMUM_SUPPORTED. Docker users have therefore always been floored at
        # 1.2 — every Bambu model is reachable under that floor — while
        # bare-metal and appliance installs could silently negotiate TLS 1.0.
        # State the floor rather than inheriting it.
        self.ssl_context.minimum_version = ssl.TLSVersion.TLSv1_2
        if cap_tls_v1_2:
            # With the floor above this pins the connection to exactly TLS 1.2.
            self.ssl_context.maximum_version = ssl.TLSVersion.TLSv1_2

    def connect(self, host="", port=990, timeout=-999, source_address=None):
        """Connect to host, wrapping socket in TLS immediately (implicit FTPS)."""
        if host:
            self.host = host
        if port > 0:
            self.port = port
        if timeout != -999:
            self.timeout = timeout
        if source_address:
            self.source_address = source_address

        # Create and wrap socket immediately (implicit TLS)
        self.sock = socket.create_connection((self.host, self.port), self.timeout, source_address=self.source_address)
        self.sock = self.ssl_context.wrap_socket(self.sock, server_hostname=self.host)
        self.af = self.sock.family
        self.file = self.sock.makefile("r", encoding=self.encoding)
        self.welcome = self.getresp()
        return self.welcome

    def ntransfercmd(self, cmd, rest=None):
        """Override to wrap data connection in SSL for X1C/P1S only.

        X1C/P1S printers (vsFTPd) require SSL session reuse on the data channel.
        A1/A1 Mini printers have issues with SSL on the data channel entirely -
        they timeout waiting for the transfer completion response. For A1, we
        skip SSL wrapping on the data channel (control channel remains encrypted).
        """
        conn, size = FTP.ntransfercmd(self, cmd, rest)
        if self._prot_p and not self.skip_session_reuse:
            # X1C/P1S: Wrap data channel with SSL session reuse (required by vsFTPd)
            conn = self.ssl_context.wrap_socket(
                conn,
                server_hostname=self.host,
                session=self.sock.session,
            )
        # A1/A1 Mini (skip_session_reuse=True): Don't wrap data channel in SSL
        # The control channel remains encrypted via implicit FTPS
        return conn, size


class BambuFTPClient:
    """FTP client for retrieving files from Bambu Lab printers."""

    FTP_PORT = 990
    # Default timeout in seconds (increased for A1 printers)
    DEFAULT_TIMEOUT = 30
    # Models that may need SSL mode fallback (try prot_p first, fall back to prot_c)
    # These models have varying FTP SSL behavior depending on firmware version
    A1_MODELS = ("A1", "A1 Mini")
    # Chunk size for manual upload transfer (64KB)
    # Smaller chunks provide smoother progress reporting — at typical printer FTP
    # speeds (~50-100KB/s) this gives a progress update roughly every second.
    CHUNK_SIZE = 64 * 1024

    # Cache for working FTP modes per printer IP
    # Maps IP -> "prot_p" or "prot_c"
    _mode_cache: dict[str, str] = {}

    def __init__(
        self,
        ip_address: str,
        access_code: str,
        timeout: float | None = None,
        printer_model: str | None = None,
        force_prot_c: bool = False,
    ):
        self.ip_address = ip_address
        self.access_code = access_code
        self.timeout = timeout if timeout is not None else self.DEFAULT_TIMEOUT
        self.printer_model = printer_model
        self.force_prot_c = force_prot_c
        self._ftp: ImplicitFTP_TLS | None = None

    def _is_a1_model(self) -> bool:
        """Check if this is an A1 series printer."""
        if not self.printer_model:
            return False
        return self.printer_model in self.A1_MODELS

    def _get_cached_mode(self) -> str | None:
        """Get cached FTP mode for this printer."""
        return self._mode_cache.get(self.ip_address)

    @classmethod
    def cache_mode(cls, ip_address: str, mode: str):
        """Cache the working FTP mode for a printer."""
        cls._mode_cache[ip_address] = mode
        logger.info("FTP mode cached for %s: %s", ip_address, mode)

    def _should_use_prot_c(self) -> bool:
        """Determine if we should use prot_c (clear) mode."""
        # If explicitly forced, use prot_c
        if self.force_prot_c:
            return True
        # Check cache first
        cached = self._get_cached_mode()
        if cached:
            return cached == "prot_c"
        # Default: try prot_p first (will fall back if needed)
        return False

    def connect(self) -> bool:
        """Connect to the printer FTP server (implicit FTPS on port 990)."""
        try:
            use_prot_c = self._should_use_prot_c()
            from backend.app.services.ftp_profiles import get_ftp_profile

            profile = get_ftp_profile(self.printer_model)
            logger.debug(
                f"FTP connecting to {self.ip_address}:{self.FTP_PORT} "
                f"(timeout={self.timeout}s, model={self.printer_model}, prot_c={use_prot_c}, "
                f"cap_tls_v1_2={profile.cap_tls_v1_2})"
            )
            self._ftp = ImplicitFTP_TLS(
                skip_session_reuse=use_prot_c,
                cap_tls_v1_2=profile.cap_tls_v1_2,
            )
            self._ftp.connect(self.ip_address, self.FTP_PORT, timeout=self.timeout)
            logger.debug("FTP connected, logging in as bblp")
            self._ftp.login("bblp", self.access_code)
            if use_prot_c:
                # Use clear (unencrypted) data channel
                logger.debug("FTP logged in, setting prot_c (clear) and passive mode")
                self._ftp.prot_c()
            else:
                # Use protected (encrypted) data channel with session reuse
                logger.debug("FTP logged in, setting prot_p (protected) and passive mode")
                self._ftp.prot_p()
            self._ftp.set_pasv(True)
            # Log welcome message for debugging
            if hasattr(self._ftp, "welcome") and self._ftp.welcome:
                logger.debug("FTP server welcome: %s", self._ftp.welcome)
            logger.info(
                f"FTP connected successfully to {self.ip_address} (model={self.printer_model}, prot_c={use_prot_c})"
            )
            return True
        except ftplib.error_perm as e:
            logger.warning("FTP connection permission error to %s: %s", self.ip_address, e)
            self._ftp = None
            return False
        except TimeoutError as e:
            logger.warning("FTP connection timed out to %s: %s", self.ip_address, e)
            self._ftp = None
            return False
        except ssl.SSLError as e:
            logger.warning("FTP SSL error connecting to %s: %s", self.ip_address, e)
            self._ftp = None
            return False
        except (OSError, ftplib.Error) as e:
            logger.warning("FTP connection failed to %s: %s (type: %s)", self.ip_address, e, type(e).__name__)
            self._ftp = None
            return False

    def disconnect(self):
        """Disconnect from the FTP server."""
        if self._ftp:
            try:
                self._ftp.quit()
            except (OSError, ftplib.Error, EOFError):
                pass  # Best-effort FTP cleanup; connection may already be closed
            self._ftp = None

    def list_files(self, path: str = "/") -> list[dict]:
        """List files in a directory."""
        if not self._ftp:
            return []

        files = []
        try:
            self._ftp.cwd(path)
            items = []
            self._ftp.retrlines("LIST", items.append)

            for item in items:
                parts = item.split()
                if len(parts) >= 9:
                    name = " ".join(parts[8:])
                    is_dir = item.startswith("d")
                    size = int(parts[4]) if not is_dir else 0

                    # Parse modification time from FTP listing
                    # Format: "Nov 30 10:15" or "Nov 30  2024"
                    mtime = None
                    try:
                        from datetime import datetime

                        month = parts[5]
                        day = parts[6]
                        time_or_year = parts[7]

                        # Determine if it's time (HH:MM) or year
                        if ":" in time_or_year:
                            # Recent file: "Nov 30 10:15" - assume current year
                            year = datetime.now().year
                            time_str = f"{month} {day} {year} {time_or_year}"
                            mtime = datetime.strptime(time_str, "%b %d %Y %H:%M")
                            # If parsed date is in the future, use last year
                            if mtime > datetime.now():
                                mtime = mtime.replace(year=year - 1)
                        else:
                            # Older file: "Nov 30 2024" - no time, just date
                            time_str = f"{month} {day} {time_or_year}"
                            mtime = datetime.strptime(time_str, "%b %d %Y")
                    except (ValueError, IndexError):
                        pass  # Non-critical: mtime parsing is best-effort; file entry works without it

                    file_entry = {
                        "name": name,
                        "is_directory": is_dir,
                        "size": size,
                        "path": f"{path.rstrip('/')}/{name}",
                    }
                    if mtime:
                        file_entry["mtime"] = mtime
                    files.append(file_entry)
            logger.debug("Listed %s files in %s", len(files), path)
        except (OSError, ftplib.Error) as e:
            logger.info("FTP list_files failed for %s: %s", path, e)

        return files

    def download_file(self, remote_path: str) -> bytes | None:
        """Download a file from the printer."""
        if not self._ftp:
            return None

        try:
            buffer = BytesIO()
            self._ftp.retrbinary(f"RETR {remote_path}", buffer.write)
            return buffer.getvalue()
        except (OSError, ftplib.Error):
            return None

    def download_to_file(self, remote_path: str, local_path: Path) -> bool:
        """Download a file from the printer to local filesystem."""
        if not self._ftp:
            logger.warning("download_to_file called but FTP not connected")
            return False

        try:
            local_path.parent.mkdir(parents=True, exist_ok=True)
            with open(local_path, "wb") as f:
                self._ftp.retrbinary(f"RETR {remote_path}", f.write)
                f.flush()
                os.fsync(f.fileno())
            file_size = local_path.stat().st_size if local_path.exists() else 0
            if file_size == 0:
                logger.warning("FTP download returned 0 bytes for %s", remote_path)
                if local_path.exists():
                    local_path.unlink()
                return False
            logger.info("Successfully downloaded %s to %s (%s bytes)", remote_path, local_path, file_size)
            return True
        except (OSError, ftplib.Error) as e:
            # Clean up partial file if it exists
            if local_path.exists():
                try:
                    local_path.unlink()
                except OSError:
                    pass  # Best-effort partial file cleanup; not critical if removal fails
            # 550 means the file is not at this path. Surface as a sentinel so
            # with_ftp_retry can abandon this path immediately and the caller
            # can advance to the next candidate instead of retrying 11× at
            # 30s intervals (the pattern that cost #972's reporter ~48min).
            if isinstance(e, ftplib.error_perm) and str(e).startswith("550"):
                logger.info("FTP download failed for %s: %s (not on printer)", remote_path, e)
                raise FileNotOnPrinterError(f"{remote_path}: {e}") from e
            # Log at INFO level so we can see failures in normal logs
            logger.info("FTP download failed for %s: %s", remote_path, e)
            return False

    def diagnose_storage(self) -> dict:
        """Run storage diagnostics and return results. For debugging upload issues."""
        results = {
            "connected": self._ftp is not None,
            "can_list_root": False,
            "root_files": [],
            "can_list_cache": False,
            "storage_info": None,
            "pwd": None,
            "errors": [],
        }

        if not self._ftp:
            results["errors"].append("FTP not connected")
            return results

        # Try to get current directory
        try:
            results["pwd"] = self._ftp.pwd()
            logger.debug("FTP current directory: %s", results["pwd"])
        except (OSError, ftplib.Error) as e:
            results["errors"].append(f"PWD failed: {e}")
            logger.debug("FTP PWD failed: %s", e)

        # Try to list root directory
        try:
            self._ftp.cwd("/")
            items = []
            self._ftp.retrlines("LIST", items.append)
            results["can_list_root"] = True
            results["root_files"] = items[:10]  # First 10 entries
            logger.debug("FTP root listing (%s items): %s", len(items), items[:5])
        except (OSError, ftplib.Error) as e:
            results["errors"].append(f"LIST / failed: {e}")
            logger.debug("FTP LIST / failed: %s", e)

        # Try to list /cache (should exist on all printers)
        try:
            self._ftp.cwd("/cache")
            items = []
            self._ftp.retrlines("LIST", items.append)
            results["can_list_cache"] = True
            logger.debug("FTP /cache listing: %s items", len(items))
        except (OSError, ftplib.Error) as e:
            results["errors"].append(f"LIST /cache failed: {e}")
            logger.debug("FTP LIST /cache failed: %s", e)

        # Try to get storage info
        try:
            results["storage_info"] = self.get_storage_info()
            logger.debug("FTP storage info: %s", results["storage_info"])
        except (OSError, ftplib.Error) as e:
            results["errors"].append(f"Storage info failed: {e}")

        return results

    def upload_file(
        self,
        local_path: Path,
        remote_path: str,
        progress_callback: Callable[[int, int], None] | None = None,
    ) -> bool:
        """Upload a file to the printer with optional progress callback."""
        if not self._ftp:
            logger.warning("upload_file: FTP not connected")
            return False

        try:
            file_size = local_path.stat().st_size if local_path.exists() else 0
            logger.info("FTP uploading %s (%s bytes) to %s", local_path, file_size, remote_path)

            uploaded = 0
            callback_exception: Exception | None = None

            # Use manual transfer instead of storbinary() for A1 compatibility
            # A1 printers have issues with storbinary's voidresp() hanging after transfer
            with open(local_path, "rb") as f:
                logger.debug("FTP STOR command starting for %s", remote_path)
                t0 = time.monotonic()
                conn = self._ftp.transfercmd(f"STOR {remote_path}")
                logger.info(
                    "FTP data channel ready in %.1fs (PASV + TLS handshake)",
                    time.monotonic() - t0,
                )

                # Set explicit socket options for reliable transfer
                conn.setblocking(True)
                conn.settimeout(self.timeout)

                try:
                    while True:
                        chunk = f.read(self.CHUNK_SIZE)
                        if not chunk:
                            logger.debug("FTP upload: final chunk reached")
                            break

                        conn.sendall(chunk)
                        uploaded += len(chunk)
                        logger.debug("FTP upload progress: %s/%s bytes", uploaded, file_size)

                        if progress_callback:
                            try:
                                progress_callback(uploaded, file_size)
                            except Exception as e:
                                callback_exception = e
                                logger.info(
                                    "FTP upload callback requested stop for %s at %s/%s bytes: %s",
                                    remote_path,
                                    uploaded,
                                    file_size,
                                    e,
                                )
                                break

                except OSError as e:
                    logger.error("FTP connection lost during upload: %s", e)
                    raise
                finally:
                    try:
                        conn.close()
                    except OSError:
                        pass

            # Wait for the server's 226 "Transfer complete" response to confirm
            # the file has been flushed to the SD card. Without this, the printer
            # may try to read an incomplete file when the print command is sent,
            # causing 0500-C010 "MicroSD Card read/write exception" errors.
            # See: https://bugs.python.org/issue25458 (ftplib response desync)
            try:
                old_timeout = self._ftp.sock.gettimeout()
                # Use a generous timeout — H2D printers can take 30+ seconds
                # to send the 226 after the data channel closes.
                self._ftp.sock.settimeout(max(self.timeout, 60))
                try:
                    resp = self._ftp.voidresp()
                    logger.info("FTP STOR confirmed for %s: %s", remote_path, resp.strip())
                finally:
                    self._ftp.sock.settimeout(old_timeout)
            except ftplib.Error as e:
                # Some P2S firmware revisions return ftplib.Error (e.g. 426
                # "Failure reading network stream") on voidresp() even when
                # the file landed fully on the SD card — the TLS data
                # channel close races the 226 confirmation (#1417 follow-up).
                # Verify via SIZE: if the server-side file size matches what
                # we just uploaded, the file is intact and we proceed with
                # a warning. If not — or SIZE itself fails — the transfer
                # was genuinely truncated and we must fail so the print
                # command doesn't go out for a partial 3MF (the original
                # reason this catch was tightened in the previous round).
                try:
                    server_size = self._ftp.size(remote_path)
                except (OSError, ftplib.Error) as size_err:
                    logger.debug("Post-error SIZE check failed: %s", size_err)
                    server_size = None
                if server_size is not None and server_size == file_size:
                    logger.warning(
                        "FTP STOR returned %s for %s but file is intact on the "
                        "printer (%s bytes match) — proceeding: %s",
                        type(e).__name__,
                        remote_path,
                        file_size,
                        e,
                    )
                else:
                    logger.error(
                        "FTP STOR rejected by printer for %s: %s (%s); server size=%s expected=%s",
                        remote_path,
                        e,
                        type(e).__name__,
                        server_size,
                        file_size,
                    )
                    raise
            except Exception as e:
                # Timeout or socket-level error reading 226 — the data was sent
                # on our side and the printer may still have written the file.
                # H2D can take 30+ seconds to send 226 after the data channel
                # closes, so we proceed with a warning rather than failing here.
                logger.warning(
                    "FTP STOR confirmation not received for %s (proceeding): %s (%s)",
                    remote_path,
                    e,
                    type(e).__name__,
                )

            if callback_exception is not None:
                cleanup_result: DeleteResult = DeleteResult.FAILED
                try:
                    cleanup_result = self.delete_file(remote_path)
                except Exception as cleanup_error:
                    logger.warning("FTP cancel cleanup failed for %s: %s", remote_path, cleanup_error)

                # NOT_FOUND is success here — the partial file is gone (printer
                # may have already swept on cancel), which is the goal.
                if cleanup_result in (DeleteResult.DELETED, DeleteResult.NOT_FOUND):
                    logger.info("FTP cancel cleanup succeeded for %s (%s)", remote_path, cleanup_result.value)
                    raise callback_exception

                raise RuntimeError(
                    f"Upload cancelled but failed to remove partial file {remote_path} from printer"
                ) from callback_exception

            elapsed = time.monotonic() - t0
            speed_kbs = (file_size / 1024) / elapsed if elapsed > 0 else 0
            logger.info(
                "FTP upload complete: %s (%s bytes in %.1fs, %.0f KB/s)",
                remote_path,
                file_size,
                elapsed,
                speed_kbs,
            )
            return True
        except ftplib.error_perm as e:
            # Permanent FTP error (4xx/5xx response)
            error_code = str(e)[:3] if str(e) else "unknown"
            logger.error("FTP upload failed for %s: %s (error code: %s)", remote_path, e, error_code)
            if error_code == "553":
                logger.error(
                    "FTP 553 error - Could not create file. Possible causes: "
                    "1) No SD card inserted, 2) SD card full, 3) SD card not formatted correctly (needs FAT32/exFAT), "
                    "4) Printer busy/not ready, 5) File path issue"
                )
            elif error_code == "550":
                logger.error("FTP 550 error - File/directory not found or permission denied")
            elif error_code == "552":
                logger.error("FTP 552 error - Storage quota exceeded (SD card full?)")
            return False
        except (OSError, ftplib.Error) as e:
            logger.error("FTP upload failed for %s: %s (type: %s)", remote_path, e, type(e).__name__)
            return False

    def upload_bytes(self, data: bytes, remote_path: str) -> bool:
        """Upload bytes to the printer."""
        if not self._ftp:
            return False

        try:
            # Use manual transfer instead of storbinary() for A1 compatibility
            conn = self._ftp.transfercmd(f"STOR {remote_path}")
            conn.setblocking(True)
            conn.settimeout(self.timeout)

            try:
                # Send data in chunks
                offset = 0
                while offset < len(data):
                    chunk = data[offset : offset + self.CHUNK_SIZE]
                    conn.sendall(chunk)
                    offset += len(chunk)
            except OSError as e:
                logger.error("FTP connection lost during upload_bytes: %s", e)
                raise
            finally:
                try:
                    conn.close()
                except OSError:
                    pass
            # Wait for 226 confirmation (see upload_file for rationale).
            # ftplib.Error subclasses (e.g. 426 error_temp) mean the server
            # rejected the transfer and the file is partial — fail. Other
            # exceptions (timeout, socket-level) are tolerated as in upload_file.
            try:
                old_timeout = self._ftp.sock.gettimeout()
                self._ftp.sock.settimeout(max(self.timeout, 60))
                try:
                    self._ftp.voidresp()
                finally:
                    self._ftp.sock.settimeout(old_timeout)
            except ftplib.Error as e:
                # Same SIZE-verify path as upload_file (#1417 follow-up):
                # tolerate a transient 426 if the bytes are actually on the
                # printer, fail loudly if they aren't.
                try:
                    server_size = self._ftp.size(remote_path)
                except (OSError, ftplib.Error) as size_err:
                    logger.debug("Post-error SIZE check failed: %s", size_err)
                    server_size = None
                if server_size is not None and server_size == len(data):
                    logger.warning(
                        "FTP STOR returned %s for %s but file is intact on the "
                        "printer (%s bytes match) — proceeding: %s",
                        type(e).__name__,
                        remote_path,
                        len(data),
                        e,
                    )
                else:
                    logger.error(
                        "FTP STOR rejected by printer for %s: %s (%s); server size=%s expected=%s",
                        remote_path,
                        e,
                        type(e).__name__,
                        server_size,
                        len(data),
                    )
                    return False
            except Exception:
                pass  # Timeout / socket-level — proceed, data was sent.
            return True
        except (OSError, ftplib.Error):
            return False

    def delete_file(self, remote_path: str) -> DeleteResult:
        """Delete a file from the printer.

        Returns :class:`DeleteResult` distinguishing the file-not-found case
        (550) from network / auth / transient FTP failure. Callers that just
        want "did it work" should check ``result == DeleteResult.DELETED``.
        """
        if not self._ftp:
            return DeleteResult.FAILED

        try:
            self._ftp.delete(remote_path)
            return DeleteResult.DELETED
        except ftplib.error_perm as e:
            if str(e).startswith("550"):
                logger.debug("FTP delete: %s not on printer (550)", remote_path)
                return DeleteResult.NOT_FOUND
            logger.warning("Failed to delete %s: %s", remote_path, e)
            return DeleteResult.FAILED
        except (OSError, ftplib.Error) as e:
            logger.warning("Failed to delete %s: %s", remote_path, e)
            return DeleteResult.FAILED

    def get_file_size(self, remote_path: str) -> int | None:
        """Get the size of a file."""
        if not self._ftp:
            return None

        try:
            return self._ftp.size(remote_path)
        except (OSError, ftplib.Error):
            return None

    def get_storage_info(self) -> dict | None:
        """Get storage information from the printer."""
        if not self._ftp:
            return None

        result = {}

        # Try AVBL command (available space) - some FTP servers support this
        try:
            response = self._ftp.sendcmd("AVBL")
            logger.debug("AVBL response: %s", response)
            # Response format: "213 <bytes available>"
            if response.startswith("213"):
                parts = response.split()
                if len(parts) >= 2:
                    result["free_bytes"] = int(parts[1])
        except (OSError, ftplib.Error) as e:
            logger.debug("AVBL command not supported: %s", e)
            # Try STAT command as fallback
            try:
                response = self._ftp.sendcmd("STAT")
                logger.debug("STAT response: %s", response)
            except (OSError, ftplib.Error):
                pass  # Both AVBL and STAT unsupported; storage info will rely on directory scan

        # Calculate used space by listing root directories
        try:
            total_used = 0
            dirs_to_scan = ["/cache", "/timelapse", "/model", "/data", "/data/Metadata", "/"]

            for dir_path in dirs_to_scan:
                try:
                    self._ftp.cwd(dir_path)
                    items = []
                    self._ftp.retrlines("LIST", items.append)

                    for item in items:
                        parts = item.split()
                        if len(parts) >= 5 and not item.startswith("d"):
                            try:
                                total_used += int(parts[4])
                            except ValueError:
                                pass  # Skip entries with non-numeric size fields
                except (OSError, ftplib.Error):
                    pass  # Directory may not exist on this printer model; skip it

            result["used_bytes"] = total_used
        except (OSError, ftplib.Error):
            pass  # Storage scan failed; return whatever info was collected above

        return result if result else None


# Shared 3MF download cache (#972).
#
# Both the cover thumbnail endpoint (api/routes/printers.py) and the archive
# metadata flow (main.py) fetch the same 3MF file over FTP during a print.
# On slow / contended links (A1 Wi-Fi, large files) the duplicate transfers
# compete for the printer's single FTP socket and trigger 425 "can't open
# data channel" errors, feeding back into cause-2's retry storm.
#
# This cache stores the local path of a successfully-downloaded 3MF keyed
# by (printer_id, normalized_name). Whichever flow downloads first populates
# the cache; the other flow reuses the file read-only. Evicted on print
# completion so a later print with the same name re-downloads fresh bytes.
_threemf_path_cache: dict[tuple[int, str], Path] = {}


def normalize_3mf_name(name: str) -> str:
    """Collapse various 3MF filename variants to a cache key.

    Bambu tooling produces names as bare subtask ("Part"), with .3mf, with
    .gcode.3mf, or (Studio-normalized) with spaces → underscores. All of
    these refer to the same print job on the same printer, so they must
    hash to the same cache key.
    """
    # Lowercase first so .3MF / .GCODE.3MF variants strip cleanly — a
    # real-world case since Windows-side tooling sometimes uppercases
    # extensions.
    cleaned = name.strip().lower().replace(".gcode.3mf", "").replace(".gcode", "").replace(".3mf", "")
    return cleaned.replace(" ", "_")


def cache_3mf_download(printer_id: int, name: str, local_path: Path) -> None:
    """Record a successfully-downloaded 3MF so a sibling flow can reuse it."""
    _threemf_path_cache[(printer_id, normalize_3mf_name(name))] = local_path


def get_cached_3mf(printer_id: int, name: str) -> Path | None:
    """Return a cached 3MF path for this printer/name if the file still exists."""
    key = (printer_id, normalize_3mf_name(name))
    cached = _threemf_path_cache.get(key)
    if cached and cached.exists() and cached.stat().st_size > 0:
        return cached
    # Evict dead entry — the file was cleaned up (temp dir clean, manual
    # deletion, restart) so the cache value is no longer usable.
    if cached:
        _threemf_path_cache.pop(key, None)
    return None


def clear_3mf_cache(printer_id: int | None = None, delete_files: bool = True) -> None:
    """Drop cache entries for one printer (or all with None).

    When ``delete_files`` is True (default) the on-disk 3MF is removed as well
    — called from on_print_complete so temp files don't accumulate across
    prints. Tests that want to inspect the cache contents disable this.

    Only paths inside ``archive_dir/temp`` are unlinked. The dispatch sites
    added in #1166 also cache the live archive copy and library file bytes
    so /cover can skip FTP — those are *user data*, never the cache's to
    delete. Pre-fix this branch silently removed archive 3mfs on every print
    completion (#1212 + private reports of "file disappeared overnight").
    """
    from backend.app.core.config import settings as _config_settings

    temp_root = _config_settings.archive_dir / "temp"

    def _is_temp_path(path: Path) -> bool:
        try:
            return path.is_relative_to(temp_root)
        except (OSError, ValueError):
            return False

    def _maybe_unlink(path: Path) -> None:
        if not delete_files or not path.exists():
            return
        if not _is_temp_path(path):
            return
        try:
            path.unlink()
        except OSError as exc:
            logger.debug("3MF cache cleanup skipped %s: %s", path, exc)

    if printer_id is None:
        for path in list(_threemf_path_cache.values()):
            _maybe_unlink(path)
        _threemf_path_cache.clear()
        return
    for key in [k for k in _threemf_path_cache if k[0] == printer_id]:
        _maybe_unlink(_threemf_path_cache[key])
        _threemf_path_cache.pop(key, None)


async def download_file_async(
    ip_address: str,
    access_code: str,
    remote_path: str,
    local_path: Path,
    timeout: float = 60.0,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
) -> bool:
    """Async wrapper for downloading a file with timeout.

    For A1/A1 Mini printers, automatically tries prot_p first, then falls back
    to prot_c if the download fails. The working mode is cached for future operations.

    Args:
        ip_address: Printer IP address
        access_code: Printer access code
        remote_path: Remote file path on printer
        local_path: Local path to save file
        timeout: Overall operation timeout (asyncio)
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
    """
    loop = asyncio.get_event_loop()
    is_a1 = printer_model in BambuFTPClient.A1_MODELS if printer_model else False

    # Per-attempt completion state: asyncio.wait_for cannot cancel
    # run_in_executor threads, so on timeout the executor may still complete
    # the download after we stop waiting. The thread flips `success` to True
    # ONLY after the file is fully written — a post-timeout check lets us
    # salvage the download without mistaking an in-progress partial write
    # for a completed one. Each attempt gets its own dict and event so a
    # zombie from an earlier attempt can't flip the flag for a later one.
    # The event is set in `_download`'s finally block so the post-timeout
    # path can wait for genuine thread completion instead of a fixed sleep.

    def _download(force_prot_c: bool, completion: dict, done: threading.Event) -> bool:
        mode_str = "prot_c" if force_prot_c else "prot_p"
        try:
            client = BambuFTPClient(
                ip_address,
                access_code,
                timeout=socket_timeout,
                printer_model=printer_model,
                force_prot_c=force_prot_c,
            )
            if client.connect():
                try:
                    result = client.download_to_file(remote_path, local_path)
                    if result:
                        BambuFTPClient.cache_mode(ip_address, mode_str)
                        completion["success"] = True
                    return result
                finally:
                    client.disconnect()
            return False
        finally:
            done.set()

    async def _run(force_prot_c: bool) -> bool:
        completion = {"success": False}
        done = threading.Event()
        try:
            return await asyncio.wait_for(
                loop.run_in_executor(_ftp_executor, _download, force_prot_c, completion, done), timeout=timeout
            )
        except TimeoutError:
            # Slow WiFi links commonly overshoot ftp_timeout by 10–30 s without
            # actually being stuck, so starting attempt 2 now would just contend
            # with the still-progressing RETR on attempt 1 and produce the
            # zombie-write race reported in #1014 (file landed on disk minutes
            # after the retry loop had already given up). Wait for the worker
            # thread to genuinely finish — capped at 30 s so a truly stuck
            # connection can't stall a whole attempt indefinitely, with a 0.5 s
            # floor so artificially small test timeouts still give zombies a
            # realistic window to finish.
            grace = max(min(timeout, 30.0), 0.5)
            # Deliberately the DEFAULT executor, not `_ftp_executor`: this thread
            # blocks waiting on `_download`, which is itself an `_ftp_executor`
            # worker. Parking waiters in the same bounded pool as the workers they
            # wait for is how you build a deadlock — with enough concurrent
            # timeouts the waiters would occupy every slot and the downloads they
            # are waiting for could never be scheduled.
            await loop.run_in_executor(None, done.wait, grace)
            if completion["success"] and local_path.exists() and local_path.stat().st_size > 0:
                logger.info(
                    "FTP download wait_for timed out after %ss for %s, but thread completed within %ss grace (%s bytes) — salvaging",
                    timeout,
                    remote_path,
                    grace,
                    local_path.stat().st_size,
                )
                return True
            logger.warning(
                "FTP download timed out after %ss (plus %ss grace) for %s",
                timeout,
                grace,
                remote_path,
            )
            return False

    # Check if we have a cached mode for this printer
    cached_mode = BambuFTPClient._mode_cache.get(ip_address)

    if cached_mode:
        force_prot_c = cached_mode == "prot_c"
        return await _run(force_prot_c)

    # No cached mode - try prot_p first
    if await _run(False):
        return True

    # Download failed - for A1 models, try prot_c fallback
    if is_a1:
        logger.info("FTP download failed with prot_p for A1 model, trying prot_c fallback...")
        return await _run(True)

    return False


async def download_file_try_paths_async(
    ip_address: str,
    access_code: str,
    remote_paths: list[str],
    local_path: Path,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
    timeout: float = 90.0,
) -> bool:
    """Try downloading a file from multiple paths using a single connection.

    Args:
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
        timeout: overall async cap. The per-socket timeout only bounds an
            in-flight worker; it does NOT bound how long this coroutine waits
            for a free slot in the fixed-size ``_ftp_executor``. On a large
            farm where offline printers keep every worker busy on dead
            connects, that queue wait is otherwise unbounded — and any caller
            holding a DB connection while awaiting this would pin it until the
            pool is exhausted (#2572). The cap converts that into a bounded
            wait; the orphaned worker finishes and its result is discarded.
    """
    loop = asyncio.get_event_loop()

    def _download():
        client = BambuFTPClient(ip_address, access_code, timeout=socket_timeout, printer_model=printer_model)
        if not client.connect():
            return False

        try:
            # FileNotOnPrinterError signals "try the next path", not "give up" —
            # this function's whole purpose is to walk a list of candidates
            # over one connection. Only a real transport error should bubble.
            for remote_path in remote_paths:
                try:
                    if client.download_to_file(remote_path, local_path):
                        return True
                except FileNotOnPrinterError:
                    continue
            return False
        finally:
            client.disconnect()

    try:
        return await asyncio.wait_for(loop.run_in_executor(_ftp_executor, _download), timeout=timeout)
    except TimeoutError:
        logger.warning("FTP download_try_paths exceeded its %ss cap for %s (#2572)", timeout, ip_address)
        return False


def _upload_deadline(local_path: Path) -> float:
    """Derive an upload deadline from the file size (#2529).

    See ``_UPLOAD_FLOOR_BYTES_PER_SEC``. An unstat-able file falls back to the
    floor timeout — ``upload_file`` will fail on the open() anyway.
    """
    try:
        size = local_path.stat().st_size
    except OSError:
        return _UPLOAD_MIN_TIMEOUT
    return max(_UPLOAD_MIN_TIMEOUT, size / _UPLOAD_FLOOR_BYTES_PER_SEC)


# One upload at a time per printer. Two concurrent STOR commands for the same
# remote path leave a corrupt file on the SD card, and the printer reads as
# flaky rather than busy (#2529). Held for the duration of a transfer, so a
# second dispatch to the same printer queues behind the first instead of racing
# it. Keyed per event loop: an asyncio.Lock binds to the loop that first awaits
# it, and the test suite runs each case on a fresh loop.
_upload_locks: weakref.WeakKeyDictionary[asyncio.AbstractEventLoop, dict[str, asyncio.Lock]] = (
    weakref.WeakKeyDictionary()
)


def _upload_lock(loop: asyncio.AbstractEventLoop, ip_address: str) -> asyncio.Lock:
    per_loop = _upload_locks.setdefault(loop, {})
    lock = per_loop.get(ip_address)
    if lock is None:
        lock = asyncio.Lock()
        per_loop[ip_address] = lock
    return lock


async def upload_file_async(
    ip_address: str,
    access_code: str,
    local_path: Path,
    remote_path: str,
    timeout: float | None = None,
    progress_callback: Callable[[int, int], None] | None = None,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
) -> bool:
    """Async wrapper for uploading a file with timeout and progress callback.

    For A1/A1 Mini printers, automatically tries prot_p first, then falls back
    to prot_c if the upload fails. The working mode is cached for future uploads.

    Args:
        ip_address: Printer IP address
        access_code: Printer access code
        local_path: Local file path to upload
        remote_path: Remote path on printer
        timeout: Overall deadline. ``None`` (the default) derives it from the
            file size — see ``_upload_deadline``. A caller that passes a number
            gets exactly that, which is what the tests rely on.
        progress_callback: Optional callback for progress updates
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
    """
    loop = asyncio.get_event_loop()
    is_a1 = printer_model in BambuFTPClient.A1_MODELS if printer_model else False
    deadline = _upload_deadline(local_path) if timeout is None else timeout

    # Set when the deadline expires. The worker checks it once per chunk.
    cancel = threading.Event()

    def _guarded_progress(uploaded: int, total: int) -> None:
        if cancel.is_set():
            raise UploadCancelled(f"upload of {remote_path} exceeded its {deadline:.0f}s deadline")
        if progress_callback:
            progress_callback(uploaded, total)

    def _upload(force_prot_c: bool = False) -> bool:
        mode_str = "prot_c" if force_prot_c else "prot_p"
        logger.info(
            f"FTP connecting to {ip_address} for upload (model={printer_model}, "
            f"mode={mode_str}, socket_timeout={socket_timeout}s, deadline={deadline:.0f}s)..."
        )
        client = BambuFTPClient(
            ip_address, access_code, timeout=socket_timeout, printer_model=printer_model, force_prot_c=force_prot_c
        )
        if client.connect():
            logger.info("FTP connected to %s", ip_address)
            try:
                result = client.upload_file(local_path, remote_path, _guarded_progress)
                if result:
                    # Cache the working mode
                    BambuFTPClient.cache_mode(ip_address, mode_str)
                return result
            finally:
                client.disconnect()
        logger.warning("FTP connection failed to %s", ip_address)
        return False

    async def _attempt(force_prot_c: bool) -> bool:
        """Run one upload attempt, and make a timeout actually stop the transfer.

        ``asyncio.wait_for`` cancels the *future*, never the executor thread
        behind it. Before #2529 a slow-but-healthy upload that overran the
        deadline left that thread streaming: it kept pushing bytes, kept firing
        the progress callback, and the retry above put a *second* STOR of the
        same file onto the same printer. The reporter's 96 MB job ran four
        concurrent transfers and never landed. So on timeout we signal the
        worker (it raises ``UploadCancelled`` from the progress callback, which
        breaks the send loop and deletes the partial file) and wait for it to
        actually go.
        """
        fut = loop.run_in_executor(_ftp_executor, lambda: _upload(force_prot_c))
        try:
            return await asyncio.wait_for(asyncio.shield(fut), timeout=deadline)
        except TimeoutError:
            cancel.set()
            logger.warning(
                "FTP upload of %s exceeded its %.0fs deadline — cancelling the transfer",
                remote_path,
                deadline,
            )
            try:
                await asyncio.wait_for(asyncio.shield(fut), timeout=_UPLOAD_CANCEL_GRACE)
            except UploadCancelled:
                logger.info("FTP upload of %s cancelled; partial file removed from the printer", remote_path)
            except TimeoutError:
                # The thread is wedged somewhere that never reaches the callback
                # (a blocked sendall, say). Nothing more we can do from here —
                # but consume the eventual result so asyncio doesn't log the
                # future's exception as unretrieved when it is garbage-collected.
                logger.error(
                    "FTP upload thread for %s did not stop within %.0fs of the cancel signal",
                    remote_path,
                    _UPLOAD_CANCEL_GRACE,
                )
                fut.add_done_callback(_swallow_future_result)
            except Exception as e:
                logger.warning("FTP upload of %s errored while cancelling: %s", remote_path, e)
            # Raise rather than return False: a deadline expiry means the link
            # sustained less than the floor rate for the whole transfer, and a
            # retry would only spend another full deadline finding that out
            # again — with check_queue serialized, four of those block the
            # entire print queue for hours. ``with_ftp_retry`` never retries it.
            raise UploadCancelled(
                f"Upload of {remote_path} to {ip_address} exceeded its {deadline:.0f}s deadline "
                f"(link sustained less than {_UPLOAD_FLOOR_BYTES_PER_SEC // 1024} KB/s)"
            ) from None

    async with _upload_lock(loop, ip_address):
        # Check if we have a cached mode for this printer
        cached_mode = BambuFTPClient._mode_cache.get(ip_address)

        if cached_mode:
            # Use cached mode
            return await _attempt(cached_mode == "prot_c")

        # No cached mode - try prot_p first
        if await _attempt(False):
            return True

        # Upload failed - for A1 models, try prot_c fallback
        if is_a1:
            logger.info("FTP upload failed with prot_p for A1 model, trying prot_c fallback...")
            return await _attempt(True)

        return False


def _swallow_future_result(fut: asyncio.Future) -> None:
    """Retrieve a future's exception so asyncio doesn't log it as unhandled."""
    if not fut.cancelled():
        fut.exception()


async def list_files_async(
    ip_address: str,
    access_code: str,
    path: str = "/",
    timeout: float = 30.0,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
) -> list[dict]:
    """Async wrapper for listing files with timeout.

    Args:
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
    """
    loop = asyncio.get_event_loop()

    def _list():
        client = BambuFTPClient(ip_address, access_code, timeout=socket_timeout, printer_model=printer_model)
        if client.connect():
            try:
                return client.list_files(path)
            finally:
                client.disconnect()
        return []

    try:
        return await asyncio.wait_for(loop.run_in_executor(_ftp_executor, _list), timeout=timeout)
    except TimeoutError:
        logger.warning("FTP list_files timed out after %ss for %s", timeout, path)
        return []


async def delete_file_async(
    ip_address: str,
    access_code: str,
    remote_path: str,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
    timeout: float = 60.0,
) -> DeleteResult:
    """Async wrapper for deleting a file.

    Returns :class:`DeleteResult` so callers can distinguish ``NOT_FOUND``
    (550 — file isn't on the printer, no retry value) from ``FAILED``
    (network / auth / transient — worth retrying or surfacing).

    Args:
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
        timeout: overall async cap so a saturated ``_ftp_executor`` can't pin
            the caller (and any DB connection it holds) indefinitely (#2572).
    """
    loop = asyncio.get_event_loop()

    def _delete() -> DeleteResult:
        client = BambuFTPClient(ip_address, access_code, timeout=socket_timeout, printer_model=printer_model)
        if client.connect():
            try:
                return client.delete_file(remote_path)
            finally:
                client.disconnect()
        return DeleteResult.FAILED

    try:
        return await asyncio.wait_for(loop.run_in_executor(_ftp_executor, _delete), timeout=timeout)
    except TimeoutError:
        logger.warning("FTP delete_file exceeded its %ss cap for %s (#2572)", timeout, ip_address)
        return DeleteResult.FAILED


async def download_file_bytes_async(
    ip_address: str,
    access_code: str,
    remote_path: str,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
    timeout: float = 300.0,
) -> bytes | None:
    """Async wrapper for downloading file as bytes.

    Args:
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
        timeout: overall async cap so a saturated ``_ftp_executor`` can't pin
            the caller (and any DB connection it holds) indefinitely (#2572).
            Generous by default because this pulls whole files (timelapse
            video, gcode) which can legitimately take minutes over slow Wi-Fi —
            the cap only guards against a permanently-starved pool, not a
            slow-but-progressing transfer.
    """
    loop = asyncio.get_event_loop()

    def _download():
        client = BambuFTPClient(ip_address, access_code, timeout=socket_timeout, printer_model=printer_model)
        if client.connect():
            try:
                return client.download_file(remote_path)
            finally:
                client.disconnect()
        return None

    try:
        return await asyncio.wait_for(loop.run_in_executor(_ftp_executor, _download), timeout=timeout)
    except TimeoutError:
        logger.warning("FTP download_bytes exceeded its %ss cap for %s (#2572)", timeout, ip_address)
        return None


async def get_storage_info_async(
    ip_address: str,
    access_code: str,
    socket_timeout: float | None = None,
    printer_model: str | None = None,
    timeout: float = 60.0,
) -> dict | None:
    """Async wrapper for getting storage info.

    Args:
        socket_timeout: FTP socket timeout for slow connections (e.g., A1 printers)
        printer_model: Printer model for A1-specific workarounds
        timeout: overall async cap so a saturated ``_ftp_executor`` can't pin
            the caller (and any DB connection it holds) indefinitely (#2572).
    """
    loop = asyncio.get_event_loop()

    def _get_storage():
        client = BambuFTPClient(ip_address, access_code, timeout=socket_timeout, printer_model=printer_model)
        if client.connect():
            try:
                return client.get_storage_info()
            finally:
                client.disconnect()
        return None

    try:
        return await asyncio.wait_for(loop.run_in_executor(_ftp_executor, _get_storage), timeout=timeout)
    except TimeoutError:
        logger.warning("FTP get_storage_info exceeded its %ss cap for %s (#2572)", timeout, ip_address)
        return None


async def get_ftp_retry_settings() -> tuple[bool, int, float, float]:
    """Get FTP retry settings from database.

    Returns:
        Tuple of (retry_enabled, retry_count, retry_delay, timeout)
    """
    from backend.app.api.routes.settings import get_setting
    from backend.app.core.database import async_session

    async with async_session() as db:
        enabled = (await get_setting(db, "ftp_retry_enabled") or "true") == "true"
        count = int(await get_setting(db, "ftp_retry_count") or "3")
        delay = float(await get_setting(db, "ftp_retry_delay") or "2")
        timeout = float(await get_setting(db, "ftp_timeout") or "30")
    return enabled, count, delay, timeout


async def with_ftp_retry(
    operation: Callable[..., Awaitable[T]],
    *args,
    max_retries: int = 3,
    retry_delay: float = 2.0,
    operation_name: str = "FTP operation",
    non_retry_exceptions: tuple[type[BaseException], ...] = (),
    **kwargs,
) -> T | None:
    """Execute FTP operation with retry logic.

    Args:
        operation: Async function to execute
        *args: Positional arguments for the operation
        max_retries: Number of retry attempts (default: 3)
        retry_delay: Seconds to wait between retries (default: 2.0)
        operation_name: Name for logging purposes
        non_retry_exceptions: Exception types that should immediately abort retries
        **kwargs: Keyword arguments for the operation

    Returns:
        Result of the operation, or None if all attempts fail

    ``UploadCancelled`` is never retried, whatever the caller passes: it means
    the transfer overran its size-derived deadline, so a retry would spend
    another full deadline reaching the same conclusion (#2529).
    """
    last_error = None

    for attempt in range(max_retries + 1):
        try:
            result = await operation(*args, **kwargs)
            # Check for "falsy" success indicators
            if result not in (False, None, []):
                if attempt > 0:
                    logger.info("%s succeeded on attempt %s/%s", operation_name, attempt + 1, max_retries + 1)
                return result
            # Operation returned failure indicator
            if attempt > 0:
                logger.info("%s attempt %s/%s returned failure", operation_name, attempt + 1, max_retries + 1)
        except UploadCancelled:
            raise
        except Exception as e:
            if non_retry_exceptions and isinstance(e, non_retry_exceptions):
                raise
            last_error = e
            logger.warning("%s attempt %s/%s failed: %s", operation_name, attempt + 1, max_retries + 1, e)

        # Don't wait after the last attempt
        if attempt < max_retries:
            logger.info("%s will retry in %ss...", operation_name, retry_delay)
            await asyncio.sleep(retry_delay)

    logger.error("%s failed after %s attempts", operation_name, max_retries + 1)
    if last_error:
        logger.debug("Last error: %s", last_error)
    return None