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using System;
using VNLib.Net.Http;
using VNLib.Net.Messaging.FBM.Client;
using VNLib.Plugins.Sessions.Cache.Client;
namespace VNLib.Plugins.Essentials.Sessions.VNCache
{
/// <summary>
/// The implementation of a VNCache web based session
/// </summary>
internal sealed class WebSessionProvider : SessionCacheClient, ISessionProvider
{
static readonly TimeSpan BackgroundUpdateTimeout = TimeSpan.FromSeconds(10);
private readonly IWebSessionIdFactory factory;
private readonly uint MaxConnections;
/// <summary>
/// Initializes a new <see cref="WebSessionProvider"/>
/// </summary>
/// <param name="client">The cache client to make cache operations against</param>
/// <param name="maxCacheItems">The max number of items to store in cache</param>
/// <param name="maxWaiting">The maxium number of waiting session events before 503s are sent</param>
/// <param name="factory">The session-id factory</param>
public WebSessionProvider(FBMClient client, int maxCacheItems, uint maxWaiting, IWebSessionIdFactory factory) : base(client, maxCacheItems)
{
this.factory = factory;
MaxConnections = maxWaiting;
}
private string UpdateSessionId(IHttpEvent entity, string oldId)
{
//Generate and set a new sessionid
string newid = factory.GenerateSessionId(entity);
//Aquire lock on cache
lock (CacheLock)
{
//Change the cache lookup id
if (CacheTable.Remove(oldId, out RemoteSession? session))
{
CacheTable.Add(newid, session);
}
}
return newid;
}
protected override RemoteSession SessionCtor(string sessionId) => new WebSession(sessionId, Client, BackgroundUpdateTimeout, UpdateSessionId);
private uint _waitingCount;
public async ValueTask<SessionHandle> GetSessionAsync(IHttpEvent entity, CancellationToken cancellationToken)
{
//Callback to close the session when the handle is closeed
static ValueTask HandleClosedAsync(ISession session, IHttpEvent entity)
{
return (session as SessionBase)!.UpdateAndRelease(true, entity);
}
try
{
//Get session id
if (!factory.TryGetSessionId(entity, out string? sessionId))
{
//Id not allowed/found, so do not attach a session
return SessionHandle.Empty;
}
//Limit max number of waiting clients
if (_waitingCount > MaxConnections)
{
//Set 503 for temporary unavail
entity.CloseResponse(System.Net.HttpStatusCode.ServiceUnavailable);
return new SessionHandle(null, FileProcessArgs.VirtualSkip, null);
}
RemoteSession session;
//Inc waiting count
Interlocked.Increment(ref _waitingCount);
try
{
//Recover the session
session = await GetSessionAsync(entity, sessionId, cancellationToken);
}
finally
{
//Dec on exit
Interlocked.Decrement(ref _waitingCount);
}
//If the session is new (not in cache), then overwrite the session id with a new one as user may have specified their own
if (session.IsNew)
{
session.RegenID();
}
//Make sure the session has not expired yet
if (session.Created.Add(factory.ValidFor) < DateTimeOffset.UtcNow)
{
//Invalidate the session, so its technically valid for this request, but will be cleared on this handle close cycle
session.Invalidate();
//Clear basic login status
session.Token = null;
session.UserID = null;
session.Privilages = 0;
session.SetLoginToken(null);
}
return new SessionHandle(session, HandleClosedAsync);
}
catch (OperationCanceledException)
{
throw;
}
catch (SessionException)
{
throw;
}
catch (Exception ex)
{
throw new SessionException("Exception raised while retreiving or loading Web session", ex);
}
}
}
}
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