feat: add configio module for comment-preserving YAML round-trip writes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hbd/server/configio.py

@@ -0,0 +1,91 @@
+"""YAML round-trip read/write for .hb.yaml, with backup and atomic writes."""
+
+import glob
+import os
+import threading
+from datetime import datetime
+
+from ruamel.yaml import YAML
+
+_write_lock = threading.Lock()
+_yaml = YAML()
+_yaml.preserve_quotes = True
+
+# Top-level keys managed by the 'server' logical section
+_SERVER_KEYS = [
+    "hbd_port", "hbd_host", "ws_port", "wss_port", "hb_port",
+    "interval", "grace", "base_url", "threshold_renotify_interval",
+    "logfile", "pidfile", "pickfile", "journal_enabled", "journal_dir",
+    "journal_max_size", "journal_max_backups", "default_owner",
+]
+
+# Top-level keys managed by the 'dns' logical section
+_DNS_KEYS = ["nsupdate_bin", "dyndomains", "dyndnshosts", "drophosts"]
+
+
+def read_roundtrip(path: str):
+    """Load .hb.yaml with ruamel.yaml, preserving comments and ordering."""
+    with open(path, "r", encoding="utf-8") as f:
+        return _yaml.load(f)
+
+
+def write_config(path: str, data) -> None:
+    """Backup current file then atomically write data.
+
+    Backup naming: {path}.bak.YYYYMMDD-HHMMSS
+    Rotation: keep the 10 most recent backups, delete older ones.
+    Atomic write: write to {path}.tmp then os.replace({path}.tmp, path).
+    Acquires _write_lock for the full backup+write sequence.
+    """
+    with _write_lock:
+        ts = datetime.now().strftime("%Y%m%d-%H%M%S")
+        backup_path = f"{path}.bak.{ts}"
+        if os.path.exists(path):
+            with open(path, "rb") as src, open(backup_path, "wb") as dst:
+                dst.write(src.read())
+        backups = sorted(glob.glob(f"{path}.bak.*"), reverse=True)
+        for old in backups[10:]:
+            os.unlink(old)
+        tmp = f"{path}.tmp"
+        with open(tmp, "w", encoding="utf-8") as f:
+            _yaml.dump(data, f)
+        os.replace(tmp, path)
+
+
+def list_backups(path: str) -> list:
+    """Return backup paths sorted newest-first."""
+    return sorted(glob.glob(f"{path}.bak.*"), reverse=True)
+
+
+def apply_structured_section(data, section: str, values: dict) -> None:
+    """Merge a dict of scalar/list values into data for the named logical section.
+
+    For 'server': updates each known key individually, preserving comments on
+    unchanged keys. For 'users': replaces the entire users dict.
+    """
+    if section == "server":
+        for key in _SERVER_KEYS:
+            if key in values:
+                data[key] = values[key]
+    elif section == "users":
+        data["users"] = values
+    else:
+        raise ValueError(f"Unknown structured section: {section!r}")
+
+
+def apply_yaml_section(data, section: str, yaml_text: str) -> None:
+    """Replace the named logical section by parsing yaml_text."""
+    parsed = _yaml.load(yaml_text)
+    if section == "notification_channels":
+        data["notification_channels"] = parsed
+    elif section == "thresholds":
+        data["threshold_configs"] = parsed
+    elif section == "hosts":
+        data["hosts"] = parsed
+    elif section == "dns":
+        if parsed:
+            for key in _DNS_KEYS:
+                if key in parsed:
+                    data[key] = parsed[key]
+    else:
+        raise ValueError(f"Unknown YAML section: {section!r}")