SftpContextAccessor.cs

using PrimalZed.CloudSync.Interop;
using PrimalZed.CloudSync.Remote.Abstractions;

namespace PrimalZed.CloudSync.Remote.Sftp;
public interface ISftpContextAccessor {
	SftpContext Context { get; }
}

public class SftpContextAccessor : IRemoteContextSetter, ISftpContextAccessor {
	private static readonly AsyncLocal<ContextHolder> _sftpContextCurrent = new();

	public string RemoteKind => SftpConstants.KIND;

	/// <inheritdoc/>
	public SftpContext Context {
		get => _sftpContextCurrent.Value?.Context! ?? throw new NullReferenceException();
		set {
			var holder = _sftpContextCurrent.Value;
			if (holder != null) {
				// Clear current SftpContext trapped in the AsyncLocals, as its done.
				holder.Context = null;
			}

			// Use an object indirection to hold the SftpContext in the AsyncLocal,
			// so it can be cleared in all ExecutionContexts when its cleared.
			_sftpContextCurrent.Value = new ContextHolder { Context = value };
		}
	}

	public void SetRemoteContext(byte[] contextBytes) {
		Context = StructBytes.FromBytes<SftpContext>(contextBytes);
	}

	private sealed class ContextHolder {
		public SftpContext? Context;
	}
}