Harden backup integrity, implement verified restore and safe upgrades
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#!/usr/bin/env python3
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"""Strict backup-set metadata and tar validation; never execute backup metadata.
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GNU tar performs extraction to preserve ACLs/xattrs. This helper first validates
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all member names and link relationships, independent of archive member order.
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"""
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import configparser
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import datetime as dt
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import hashlib
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import json
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import os
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from pathlib import Path, PurePosixPath
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import re
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import subprocess
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import sys
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import tarfile
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FORMAT = 2
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LABEL = re.compile(r"(?:meta|wordpress|nextcloud(?:-data)?|gitea(?:-etc|-repos|-custom)?|mail|postfix|dovecot|mail-home-\d+|extra-\d+|db-(?:wordpress|nextcloud|gitea))\Z")
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RUN = re.compile(r"[A-Za-z0-9][A-Za-z0-9_-]*_(\d{4}-\d{2}-\d{2}_\d{2}-\d{2}-\d{2})_[0-9a-f]{8}\Z")
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def digest(path):
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h = hashlib.sha256()
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with open(path, "rb") as stream:
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for chunk in iter(lambda: stream.read(1024 * 1024), b""):
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h.update(chunk)
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return h.hexdigest()
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def regular(path):
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if path.is_symlink() or not path.is_file():
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raise ValueError(f"Not a regular file: {path}")
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def expected_root(label):
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if label == "meta":
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return "meta"
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if label.startswith("db-"):
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return f"db/{label[3:]}.sql"
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return f"files/{label}"
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def load_set(folder, metadata_only=False):
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regular(folder / "manifest.json")
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regular(folder / "COMPLETE")
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raw = (folder / "manifest.json").read_bytes()
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if len(raw) > 1024 * 1024:
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raise ValueError("Manifest too large")
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if (folder / "COMPLETE").read_text() != f"APP_BACKUP_V2 {hashlib.sha256(raw).hexdigest()}\n":
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raise ValueError("Missing or mismatched completion marker")
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data = json.loads(raw)
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if data["format"] != FORMAT or not RUN.fullmatch(data["run_id"]):
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raise ValueError("Unsupported backup format/run ID")
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if not isinstance(data["created_epoch"], int) or data["created_epoch"] <= 0:
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raise ValueError("Invalid creation time")
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seen = set()
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if not isinstance(data["archives"], list) or not data["archives"]:
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raise ValueError("Empty backup set")
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for item in data["archives"]:
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label = item["label"]
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if not LABEL.fullmatch(label) or label in seen:
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raise ValueError(f"Invalid/duplicate component: {label}")
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seen.add(label)
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if item["root"] != expected_root(label):
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raise ValueError("Unexpected archive root")
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if item["file"] not in (f"{label}.tar.gz", f"{label}.tar.zst"):
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raise ValueError("Unsafe archive filename")
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if not re.fullmatch(r"[0-9a-f]{64}", item["sha256"]):
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raise ValueError("Invalid SHA256")
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if not isinstance(item["size"], int) or item["size"] <= 0:
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raise ValueError("Invalid archive size")
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if not metadata_only:
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archive = folder / item["file"]
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regular(archive)
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if archive.stat().st_size != item["size"] or digest(archive) != item["sha256"]:
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raise ValueError(f"Archive checksum/size mismatch: {archive.name}")
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if "meta" not in seen:
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raise ValueError("Missing metadata component")
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if not metadata_only:
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allowed = {a["file"] for a in data["archives"]} | {"manifest.json", "COMPLETE", "UPLOADED"}
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if {p.name for p in folder.iterdir()} - allowed:
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raise ValueError("Unexpected files in backup set")
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return data
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def member_name(value):
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path = PurePosixPath(value)
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if path.is_absolute() or ".." in path.parts or not path.parts:
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raise ValueError(f"Unsafe tar path: {value!r}")
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if any(ord(c) < 32 for c in value):
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raise ValueError("Control character in tar path")
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return str(path)
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def check_tar(path, roots):
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command = ["zstd", "-dc", "--", str(path)] if str(path).endswith(".zst") else ["gzip", "-dc", "--", str(path)]
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proc = subprocess.Popen(command, stdout=subprocess.PIPE)
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entries = {}
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hardlinks = []
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try:
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with tarfile.open(fileobj=proc.stdout, mode="r|") as archive:
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for item in archive:
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name = member_name(item.name)
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if not any(name == root or name.startswith(root + "/") for root in roots):
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raise ValueError(f"Member outside component root: {name}")
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if name in entries:
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raise ValueError(f"Duplicate tar member: {name}")
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if not (item.isdir() or item.isfile() or item.issym() or item.islnk()):
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raise ValueError(f"Special device/FIFO/socket not supported: {name}")
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entries[name] = "dir" if item.isdir() else "file" if item.isfile() else "link"
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if item.islnk():
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hardlinks.append((name, member_name(item.linkname)))
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# Symlinks may point outside the archive (e.g. /etc/alternatives),
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# but no member may be extracted THROUGH a symlink or hardlink.
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for name in entries:
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for parent in PurePosixPath(name).parents:
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if str(parent) in entries and entries[str(parent)] != "dir":
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raise ValueError(f"Tar member descends through a non-directory: {name}")
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for name, target in hardlinks:
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if entries.get(target) != "file":
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raise ValueError(f"Hardlink target is not an archived regular file: {name}")
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if any(entries.get(root) != ("file" if root.endswith(".sql") else "dir") for root in roots):
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raise ValueError("Required archive root missing")
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# Consume the compression trailer, including errors after the tar EOF.
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while proc.stdout.read(1024 * 1024):
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pass
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if proc.wait() != 0:
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raise ValueError(f"Decompression failed: {path}")
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finally:
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proc.stdout.close()
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if proc.poll() is None:
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proc.terminate()
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proc.wait()
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def create(folder, run_id, plan):
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entries = []
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for line in Path(plan).read_text().splitlines():
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label, source = line.split("\t")
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matches = list(folder.glob(f"{label}.tar.*"))
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if len(matches) != 1:
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raise ValueError(f"Missing/ambiguous archive: {label}")
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path = matches[0]
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check_tar(path, [expected_root(label)])
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entries.append(dict(label=label, source=source, root=expected_root(label), file=path.name,
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size=path.stat().st_size, sha256=digest(path)))
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manifest = dict(format=FORMAT, run_id=run_id, created_epoch=int(dt.datetime.now(dt.timezone.utc).timestamp()),
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hostname=os.uname().nodename, archives=entries)
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(folder / "manifest.json").write_text(json.dumps(manifest, indent=2, ensure_ascii=True) + "\n")
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(folder / "COMPLETE").write_text(f"APP_BACKUP_V2 {digest(folder / 'manifest.json')}\n")
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def crypt(name):
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cfg = configparser.ConfigParser(interpolation=None)
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try:
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cfg.read_string(sys.stdin.read())
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except configparser.Error:
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raise ValueError("Invalid rclone configuration (details suppressed)") from None
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remote = cfg[name]
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if remote.get("type") != "crypt":
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raise ValueError("Remote must have type=crypt")
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if remote.get("filename_encryption", "standard") != "standard":
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raise ValueError("Require filename_encryption=standard")
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if not remote.getboolean("directory_name_encryption", True):
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raise ValueError("Directory encryption is disabled")
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if remote.getboolean("no_data_encryption", False):
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raise ValueError("Content encryption is disabled")
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print("Crypt configuration accepted (contents, filenames, directories)")
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def candidates(prefix, days, keep):
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# Only v2 names supplied AFTER completion-marker validation are eligible.
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names = set(sys.stdin.read().splitlines())
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valid = []
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for name in names:
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match = RUN.fullmatch(name)
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if match and name.startswith(prefix + "_"):
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date = dt.datetime.strptime(match[1], "%Y-%m-%d_%H-%M-%S").replace(tzinfo=dt.timezone.utc)
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valid.append((date, name))
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valid.sort(reverse=True)
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cutoff = dt.datetime.now(dt.timezone.utc) - dt.timedelta(days=int(days))
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for date, name in valid[int(keep):]:
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if date < cutoff:
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print(name)
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def write_status(folder, operation, run_id, code):
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data = dict(operation=operation, run=run_id, exit_code=int(code),
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time=int(dt.datetime.now(dt.timezone.utc).timestamp()))
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names = [f"last-{operation}.json"]
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if operation == "backup" and int(code) == 0:
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names.append("last-successful-backup.json")
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for name in names:
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path = Path(folder) / name
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with open(str(path) + ".tmp", "w") as stream:
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json.dump(data, stream)
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stream.write("\n")
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stream.flush()
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os.fsync(stream.fileno())
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os.replace(str(path) + ".tmp", path)
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def main():
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op, *args = sys.argv[1:]
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if op == "status":
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write_status(*args)
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elif op == "crypt":
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crypt(*args)
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elif op == "create":
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create(Path(args[0]), *args[1:])
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elif op in ("verify", "metadata", "list"):
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data = load_set(Path(args[0]), metadata_only=op == "metadata")
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if op == "verify":
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for item in data["archives"]:
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check_tar(Path(args[0]) / item["file"], [item["root"]])
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print(f"Verified: {data['run_id']} ({len(data['archives'])} archives)")
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elif op == "list":
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for item in data["archives"]:
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print("\t".join([item["label"], item["file"], item["root"]]))
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elif op == "candidates":
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candidates(*args)
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elif op == "tar":
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check_tar(Path(args[0]), args[1:])
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else:
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raise ValueError("Unknown operation")
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if __name__ == "__main__":
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try:
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main()
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except (ValueError, KeyError, OSError, tarfile.TarError, configparser.Error) as exc:
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print(f"ERROR: {exc}", file=sys.stderr)
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sys.exit(1)
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