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using System.Diagnostics.CodeAnalysis;
using VNLib.Hashing;
using VNLib.Net.Http;
using VNLib.Utils.Memory;
using VNLib.Utils.Extensions;
using VNLib.Plugins.Essentials.Extensions;
namespace VNLib.Plugins.Essentials.Sessions.VNCache
{
/// <summary>
/// <see cref="IWebSessionIdFactory"/> implementation, using
/// http cookies as session id storage
/// </summary>
internal sealed class WebSessionIdFactoryImpl : IWebSessionIdFactory
{
public TimeSpan ValidFor { get; }
public string GenerateSessionId(IHttpEvent entity)
{
//Random hex hash
string cookie = RandomHash.GetRandomBase32(_tokenSize);
//Set the session id cookie
entity.Server.SetCookie(SessionCookieName, cookie, ValidFor, secure: true, httpOnly: true);
//return session-id value from cookie value
return ComputeSessionIdFromCookie(cookie);
}
bool ISessionIdFactory.TryGetSessionId(IHttpEvent entity, [NotNullWhen(true)] out string? sessionId)
{
//Get authorization token and make sure its not too large to cause a buffer overflow
if (entity.Server.GetCookie(SessionCookieName, out string? cookie) && (cookie.Length + SessionIdPrefix.Length) <= _bufferSize)
{
//Compute session id from token
sessionId = ComputeSessionIdFromCookie(cookie);
return true;
}
//Only add sessions for user-agents
else if(entity.Server.IsBrowser())
{
//Get a new session id
sessionId = GenerateSessionId(entity);
return true;
}
else
{
sessionId = null;
return false;
}
}
private readonly string SessionCookieName;
private readonly string SessionIdPrefix;
private readonly int _bufferSize;
private readonly int _tokenSize;
/// <summary>
/// Initialzies a new web session Id factory
/// </summary>
/// <param name="cookieSize">The size of the cookie in bytes</param>
/// <param name="sessionCookieName">The name of the session cookie</param>
/// <param name="sessionIdPrefix">The session-id internal prefix</param>
/// <param name="validFor">The time the session cookie is valid for</param>
public WebSessionIdFactoryImpl(uint cookieSize, string sessionCookieName, string sessionIdPrefix, TimeSpan validFor)
{
ValidFor = validFor;
SessionCookieName = sessionCookieName;
SessionIdPrefix = sessionIdPrefix;
_tokenSize = (int)cookieSize;
//Calc buffer size
_bufferSize = Math.Max(32, ((int)cookieSize * 3) + sessionIdPrefix.Length);
}
private string ComputeSessionIdFromCookie(string sessionId)
{
//Buffer to copy data to
using UnsafeMemoryHandle<char> buffer = Memory.UnsafeAlloc<char>(_bufferSize, true);
//Writer to accumulate data
ForwardOnlyWriter<char> writer = new(buffer.Span);
//Append prefix and session id
writer.Append(SessionIdPrefix);
writer.Append(sessionId);
//Compute base64 hash of token and
return ManagedHash.ComputeBase64Hash(writer.AsSpan(), HashAlg.SHA256);
}
}
}
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