1 files changed, 96 insertions, 0 deletions
diff --git a/Libs/VNLib.Plugins.Essentials.Sessions.VNCache/WebSessionIdFactoryImpl.cs b/Libs/VNLib.Plugins.Essentials.Sessions.VNCache/WebSessionIdFactoryImpl.cs
new file mode 100644
index 0000000..001723a
--- /dev/null
+++ b/Libs/VNLib.Plugins.Essentials.Sessions.VNCache/WebSessionIdFactoryImpl.cs
@@ -0,0 +1,96 @@
+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);
+        }
+    }
+}
+\ No newline at end of file