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using System;
using System.Buffers;
using System.Buffers.Binary;
using System.Runtime.CompilerServices;
using System.Text;
using Impostor.Api;
using Impostor.Api.Net.Messages;
using Microsoft.Extensions.ObjectPool;
namespace Impostor.Hazel
{
public class MessageReader : IMessageReader
{
private static readonly ArrayPool<byte> ArrayPool = ArrayPool<byte>.Shared;
private readonly ObjectPool<MessageReader> _pool;
private bool _inUse;
internal MessageReader(ObjectPool<MessageReader> pool)
{
_pool = pool;
}
public byte[] Buffer { get; private set; }
public int Offset { get; internal set; }
public int Position { get; internal set; }
public int Length { get; internal set; }
public byte Tag { get; private set; }
public MessageReader Parent { get; private set; }
private int ReadPosition => Offset + Position;
public void Update(byte[] buffer, int offset = 0, int position = 0, int? length = null, byte tag = byte.MaxValue, MessageReader parent = null)
{
_inUse = true;
Buffer = buffer;
Offset = offset;
Position = position;
Length = length ?? buffer.Length;
Tag = tag;
Parent = parent;
}
internal void Reset()
{
_inUse = false;
Tag = byte.MaxValue;
Buffer = null;
Offset = 0;
Position = 0;
Length = 0;
Parent = null;
}
public IMessageReader ReadMessage()
{
var length = ReadUInt16();
var tag = FastByte();
var pos = ReadPosition;
Position += length;
var reader = _pool.Get();
reader.Update(Buffer, pos, 0, length, tag, this);
return reader;
}
public bool ReadBoolean()
{
byte val = FastByte();
return val != 0;
}
public sbyte ReadSByte()
{
return (sbyte)FastByte();
}
public byte ReadByte()
{
return FastByte();
}
public ushort ReadUInt16()
{
var output = BinaryPrimitives.ReadUInt16LittleEndian(Buffer.AsSpan(ReadPosition));
Position += sizeof(ushort);
return output;
}
public short ReadInt16()
{
var output = BinaryPrimitives.ReadInt16LittleEndian(Buffer.AsSpan(ReadPosition));
Position += sizeof(short);
return output;
}
public uint ReadUInt32()
{
var output = BinaryPrimitives.ReadUInt32LittleEndian(Buffer.AsSpan(ReadPosition));
Position += sizeof(uint);
return output;
}
public int ReadInt32()
{
var output = BinaryPrimitives.ReadInt32LittleEndian(Buffer.AsSpan(ReadPosition));
Position += sizeof(int);
return output;
}
public unsafe float ReadSingle()
{
var output = BinaryPrimitives.ReadSingleLittleEndian(Buffer.AsSpan(ReadPosition));
Position += sizeof(float);
return output;
}
public string ReadString()
{
var len = ReadPackedInt32();
var output = Encoding.UTF8.GetString(Buffer.AsSpan(ReadPosition, len));
Position += len;
return output;
}
public ReadOnlyMemory<byte> ReadBytesAndSize()
{
var len = ReadPackedInt32();
return ReadBytes(len);
}
public ReadOnlyMemory<byte> ReadBytes(int length)
{
var output = Buffer.AsMemory(ReadPosition, length);
Position += length;
return output;
}
public int ReadPackedInt32()
{
return (int)ReadPackedUInt32();
}
public uint ReadPackedUInt32()
{
bool readMore = true;
int shift = 0;
uint output = 0;
while (readMore)
{
byte b = FastByte();
if (b >= 0x80)
{
readMore = true;
b ^= 0x80;
}
else
{
readMore = false;
}
output |= (uint)(b << shift);
shift += 7;
}
return output;
}
public void CopyTo(IMessageWriter writer)
{
writer.Write((ushort) Length);
writer.Write((byte) Tag);
writer.Write(Buffer.AsMemory(Offset, Length));
}
public void Seek(int position)
{
Position = position;
}
public void RemoveMessage(IMessageReader message)
{
if (message.Buffer != Buffer)
{
throw new ImpostorProtocolException("Tried to remove message from a message that does not have the same buffer.");
}
// Offset of where to start removing.
var offsetStart = message.Offset - 3;
// Offset of where to end removing.
var offsetEnd = message.Offset + message.Length;
// The amount of bytes to copy over ourselves.
var lengthToCopy = message.Buffer.Length - offsetEnd;
System.Buffer.BlockCopy(Buffer, offsetEnd, Buffer, offsetStart, lengthToCopy);
((MessageReader) message).Parent.AdjustLength(message.Offset, message.Length + 3);
}
private void AdjustLength(int offset, int amount)
{
this.Length -= amount;
if (this.ReadPosition > offset)
{
this.Position -= amount;
}
if (Parent != null)
{
var lengthOffset = this.Offset - 3;
var curLen = this.Buffer[lengthOffset] |
(this.Buffer[lengthOffset + 1] << 8);
curLen -= amount;
this.Buffer[lengthOffset] = (byte)curLen;
this.Buffer[lengthOffset + 1] = (byte)(this.Buffer[lengthOffset + 1] >> 8);
Parent.AdjustLength(offset, amount);
}
}
public IMessageReader Copy(int offset = 0)
{
var reader = _pool.Get();
reader.Update(Buffer, Offset + offset, Position, Length - offset, Tag, Parent);
return reader;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private byte FastByte()
{
return Buffer[Offset + Position++];
}
public void Dispose()
{
if (_inUse)
{
_pool.Return(this);
}
}
}
}
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