Find portable installs when enforcing cache limits

[HebaruSan]

Problem

A user mentioned this exception with a "portable" install:

System.InvalidOperationException: Sequence contains no elements
   at System.Linq.Enumerable.Aggregate[TSource](IEnumerable`1 source, Func`3 func)
   at CKAN.NetFileCache.EnforceSizeLimit(Int64 bytes, Registry registry)
   at CKAN.ModuleInstaller.EnforceCacheSizeLimit()
   at CKAN.ModuleInstaller.InstallList(ICollection`1 modules, RelationshipResolverOptions options, IDownloader downloader, Boolean ConfirmPrompt)
   at CKAN.Main.InstallMods(Object sender, DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)

https://forum.kerbalspaceprogram.com/index.php?/topic/154922-ckan-the-comprehensive-kerbal-archive-network-v1264-orion/&do=findComment&comment=3660841

Cause

NetFileCache.EnforceSizeLimit assumes that the current instance will be in manager.Instances.

CKAN/Core/Net/NetFileCache.cs

Lines 294 to 298 in a162c8b

	// This object will let us determine whether a module is compatible with any of our instances
	KspVersionCriteria aggregateCriteria = manager?.Instances.Values
	.Where(ksp => ksp.Valid)
	.Select(ksp => ksp.VersionCriteria())
	.Aggregate((a, b) => a.Union(b));

"Portable" instances are an exception to this:

CKAN/Core/KSPManager.cs

Line 66 in a162c8b

/// This *will not* touch the registry if we find a portable install.

If all you have is a portable install, manager.Instances will be empty, and Aggregate will throw that exception.

Changes

Now we use Aggregate's optional first parameter to set a default element based on the current instance's version criteria, which should cover portables, falling back to an empty range if not found.

[DasSkelett]

Sooo...
What are portable installs? 🤔

[HebaruSan]

A portable install is when you put ckan.exe in your KSP folder and run it from there. We check to see whether the current folder is a KSP folder, and if so, then we make an ad hoc instance that doesn't get saved to the registry (or the new JSON config file). I think the idea was that you could set this up on a USB drive and then be able to use CKAN on multiple computers conveniently.

CKAN/Core/KSP.cs

Lines 175 to 190 in 9da096b

	public static string PortableDir()
	{
	// Find the directory our executable is stored in.
	// In Perl, this is just `use FindBin qw($Bin);` Verbose enough, C#?
	string exe_dir = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
	log.DebugFormat("Checking if KSP is in my exe dir: {0}", exe_dir);
	if (IsKspDir(exe_dir))
	{
	log.InfoFormat("KSP found at {0}", exe_dir);
	return exe_dir;
	}
	return null;
	}

CKAN/Core/KSPManager.cs

Lines 83 to 94 in 9da096b

	// First check if we're part of a portable install
	// Note that this *does not* register in the registry.
	string path = KSP.PortableDir();
	if (path != null)
	{
	KSP portableInst = new KSP(path, "portable", User);
	if (portableInst.Valid)
	{
	return portableInst;
	}
	}

[DasSkelett]

Thanks!