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/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Plugins.Sessions.Cache.Client
* File: SessionDataSerialzer.cs
*
* SessionDataSerialzer.cs is part of VNLib.Plugins.Sessions.Cache.Client which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Sessions.Cache.Client is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* VNLib.Plugins.Sessions.Cache.Client is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.Text;
using System.Buffers;
using System.Diagnostics;
using System.Collections.Generic;
using VNLib.Utils.Memory;
using VNLib.Utils.Logging;
using VNLib.Utils.Extensions;
using VNLib.Data.Caching;
namespace VNLib.Plugins.Sessions.Cache.Client
{
/// <summary>
/// Very basic session data serializer memory optimized for key-value
/// string pairs
/// </summary>
internal sealed class SessionDataSerialzer : ICacheObjectSerializer, ICacheObjectDeserializer
{
const string KV_DELIMITER = "\0\0";
readonly int CharBufferSize;
readonly ILogProvider? _debugLog;
public SessionDataSerialzer(int charBufferSize, ILogProvider? debugLog)
{
CharBufferSize = charBufferSize;
_debugLog = debugLog;
debugLog?.Warn("Sensitive session logging is enabled. This will leak session data!");
}
[Conditional("DEBUG")]
private void DebugSessionItems(IDictionary<string, string> sessionData, bool serializing)
{
if (_debugLog is null)
{
return;
}
StringBuilder sdBuilder = new();
foreach (KeyValuePair<string, string> item in sessionData)
{
sdBuilder.Append(item.Key);
sdBuilder.Append('=');
sdBuilder.Append(item.Value);
sdBuilder.Append(", ");
}
if (serializing)
{
_debugLog.Debug("Serialzing session data: {sd} ", sdBuilder);
}
else
{
_debugLog.Debug("Deserialzing session data: {sd} ", sdBuilder);
}
}
T? ICacheObjectDeserializer.Deserialize<T>(ReadOnlySpan<byte> objectData) where T : default
{
if (!typeof(T).IsAssignableTo(typeof(IDictionary<string, string>)))
{
throw new NotSupportedException("This deserialzer only supports IDictionary<string,string>");
}
//Get char count from bin buffer
int charCount = Encoding.UTF8.GetCharCount(objectData);
//Alloc decode buffer
using UnsafeMemoryHandle<char> charBuffer = MemoryUtil.UnsafeAllocNearestPage<char>(charCount, true);
//decode chars
Encoding.UTF8.GetChars(objectData, charBuffer.Span);
//Alloc new dict to write strings to
Dictionary<string, string> output = new(StringComparer.OrdinalIgnoreCase);
//Reader to track position of char buffer
ForwardOnlyReader<char> reader = new(charBuffer.Span[0..charCount]);
//Read data from the object data buffer
while (reader.WindowSize > 0)
{
//get index of next separator
int sep = GetNextToken(ref reader);
//No more separators are found, skip
if (sep == -1)
{
break;
}
//Get pointer to key before reading value
ReadOnlySpan<char> key = reader.Window[0..sep];
//Advance reader to next sequence
reader.Advance(sep + KV_DELIMITER.Length);
//Find next sepearator to recover the value
sep = GetNextToken(ref reader);
if (sep == -1)
{
break;
}
//Store value
ReadOnlySpan<char> value = reader.Window[0..sep];
//Set the kvp in the dict
output[key.ToString()] = value.ToString();
//Advance reader again
reader.Advance(sep + 2);
}
DebugSessionItems(output, false);
return (T?)(output as object);
}
private static int GetNextToken(ref ForwardOnlyReader<char> reader) => reader.Window.IndexOf(KV_DELIMITER);
void ICacheObjectSerializer.Serialize<T>(T obj, IBufferWriter<byte> finiteWriter)
{
if(obj is not Dictionary<string, string> dict)
{
throw new NotSupportedException("Data type is not supported by this serializer");
}
//Write debug info
DebugSessionItems(dict, true);
//Alloc char buffer, sessions should be under 16k
using UnsafeMemoryHandle<char> charBuffer = MemoryUtil.UnsafeAllocNearestPage<char>(CharBufferSize);
using Dictionary<string, string>.Enumerator e = dict.GetEnumerator();
ForwardOnlyWriter<char> writer = new(charBuffer.Span);
while (e.MoveNext())
{
KeyValuePair<string, string> element = e.Current;
/*
* confim there is enough room in the writer, if there is not
* flush to the buffer writer
*/
if(element.Key.Length + element.Value.Length + 4 > writer.RemainingSize)
{
//Flush to the output
Encoding.UTF8.GetBytes(writer.AsSpan(), finiteWriter);
//Reset the writer
writer.Reset();
}
//Add key/value elements
writer.Append(element.Key);
writer.Append(KV_DELIMITER);
writer.Append(element.Value);
writer.Append(KV_DELIMITER);
}
//encode remaining data
Encoding.UTF8.GetBytes(writer.AsSpan(), finiteWriter);
}
}
}
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