Aborting a ckan scan halfway through leaves a corrupt registry.json file

[lamont-granquist]

Think this is related to or possibly a spiritual-duplicate of #1114

I don't really want to recreate the issue at this point and I've since repaired my installation, but the use case was simple, which was to do ckan scan on the commandline and then ctrl-c it halfway through it. I actually had typed something like ckan scan Proc when I meant ckan search Proc so I just quickly ctrl-c'd it to fix the typo.

What resulted was a registry.json which was clearly half-written and truncated, and any subsequent ckan command was throwing JSON parsing errors. Doing a ckan repair registry didn't help any.

It's probably a simple case of where the routines that write out JSON files need to write to a tempfile first, then close the filehandle, then move/rename the file into place.

[HebaruSan]

We've already got a file system transaction library, maybe we can use that?

EDIT: We already do!

CKAN/Core/Registry/RegistryManager.cs

Lines 413 to 455 in f2209e2

	public void Save(bool enforce_consistency = true)
	{
	TxFileManager file_transaction = new TxFileManager();
	log.InfoFormat("Saving CKAN registry at {0}", path);
	if (enforce_consistency)
	{
	// No saving the registry unless it's in a sane state.
	registry.CheckSanity();
	}
	string directoryPath = Path.GetDirectoryName(path);
	if (directoryPath == null)
	{
	log.ErrorFormat("Failed to save registry, invalid path: {0}", path);
	throw new DirectoryNotFoundKraken(path, "Can't find a directory in " + path);
	}
	if (!Directory.Exists(directoryPath))
	{
	Directory.CreateDirectory(directoryPath);
	}
	file_transaction.WriteAllText(path, Serialize());
	ExportInstalled(
	Path.Combine(directoryPath, $"installed-{ksp.Name}.ckan"),
	false, true
	);
	if (!Directory.Exists(ksp.InstallHistoryDir()))
	{
	Directory.CreateDirectory(ksp.InstallHistoryDir());
	}
	ExportInstalled(
	Path.Combine(
	ksp.InstallHistoryDir(),
	$"installed-{ksp.Name}-{DateTime.Now.ToString("yyyy-MM-dd_HH-mm-ss")}.ckan"
	),
	false, true
	);
	}

That raises some questions. Does the transaction not work? Are we using it wrong?

EDIT II: The scan operation has a transaction, but the Save call takes place outside of (after) it. That looks like a bad idea.

CKAN/Core/KSP.cs

Lines 409 to 445 in f2209e2

	public void ScanGameData()
	{
	var manager = RegistryManager.Instance(this);
	using (TransactionScope tx = CkanTransaction.CreateTransactionScope())
	{
	manager.registry.ClearDlls();
	// TODO: It would be great to optimise this to skip .git directories and the like.
	// Yes, I keep my GameData in git.
	// Alas, EnumerateFiles is *case-sensitive* in its pattern, which causes
	// DLL files to be missed under Linux; we have to pick .dll, .DLL, or scanning
	// GameData *twice*.
	//
	// The least evil is to walk it once, and filter it ourselves.
	IEnumerable<string> files = Directory.EnumerateFiles(
	GameData(),
	"*",
	SearchOption.AllDirectories
	);
	files = files.Where(file => Regex.IsMatch(file, @"\.dll$", RegexOptions.IgnoreCase));
	foreach (string dll in files.Select(KSPPathUtils.NormalizePath))
	{
	var relativePath = ToRelativeGameDir(dll);
	if (!DllIgnoreList.Contains(relativePath))
	manager.registry.RegisterDll(this, dll);
	}
	manager.ScanDlc();
	tx.Complete();
	}
	manager.Save(enforce_consistency: false);
	}