using System.Buffers.Binary;
using System.Runtime.InteropServices;
namespace System.Net.Sockets.Kcp
{
///
/// 调整了没存布局，直接拷贝块提升性能。
/// 结构体保存内容只有一个指针，不用担心参数传递过程中的性能
/// https://github.com/skywind3000/kcp/issues/118#issuecomment-338133930
/// 不要对没有初始化的KcpSegment(内部指针为0，所有属性都将指向位置区域) 进行任何赋值操作，可能导致内存损坏。
/// 出于性能考虑，没有对此项进行安全检查。
///
public struct KcpSegment : IKcpSegment
{
internal readonly unsafe byte* ptr;
public unsafe KcpSegment(byte* intPtr, uint appendDateSize)
{
this.ptr = intPtr;
len = appendDateSize;
}
///
/// 使用完必须显示释放，否则内存泄漏
///
///
///
public static KcpSegment AllocHGlobal(int appendDateSize)
{
var total = LocalOffset + HeadOffset + appendDateSize;
IntPtr intPtr = Marshal.AllocHGlobal(total);
unsafe
{
///清零 不知道是不是有更快的清0方法？
Span span = new Span(intPtr.ToPointer(), total);
span.Clear();
return new KcpSegment((byte*)intPtr.ToPointer(), (uint)appendDateSize);
}
}
///
/// 释放非托管内存
///
///
public static void FreeHGlobal(KcpSegment seg)
{
unsafe
{
Marshal.FreeHGlobal((IntPtr)seg.ptr);
}
}
/// 以下为本机使用的参数
///
/// offset = 0
///
public uint resendts
{
get
{
unsafe
{
return *(uint*)(ptr + 0);
}
}
set
{
unsafe
{
*(uint*)(ptr + 0) = value;
}
}
}
///
/// offset = 4
///
public uint rto
{
get
{
unsafe
{
return *(uint*)(ptr + 4);
}
}
set
{
unsafe
{
*(uint*)(ptr + 4) = value;
}
}
}
///
/// offset = 8
///
public uint fastack
{
get
{
unsafe
{
return *(uint*)(ptr + 8);
}
}
set
{
unsafe
{
*(uint*)(ptr + 8) = value;
}
}
}
///
/// offset = 12
///
public uint xmit
{
get
{
unsafe
{
return *(uint*)(ptr + 12);
}
}
set
{
unsafe
{
*(uint*)(ptr + 12) = value;
}
}
}
///以下为需要网络传输的参数
public const int LocalOffset = 4 * 4;
public const int HeadOffset = KcpConst.IKCP_OVERHEAD;
///
/// offset =
///
/// https://github.com/skywind3000/kcp/issues/134
public uint conv
{
get
{
unsafe
{
return *(uint*)(LocalOffset + 0 + ptr);
}
}
set
{
unsafe
{
*(uint*)(LocalOffset + 0 + ptr) = value;
}
}
}
///
/// offset = + 4
///
public byte cmd
{
get
{
unsafe
{
return *(LocalOffset + 4 + ptr);
}
}
set
{
unsafe
{
*(LocalOffset + 4 + ptr) = value;
}
}
}
///
/// offset = + 5
///
public byte frg
{
get
{
unsafe
{
return *(LocalOffset + 5 + ptr);
}
}
set
{
unsafe
{
*(LocalOffset + 5 + ptr) = value;
}
}
}
///
/// offset = + 6
///
public ushort wnd
{
get
{
unsafe
{
return *(ushort*)(LocalOffset + 6 + ptr);
}
}
set
{
unsafe
{
*(ushort*)(LocalOffset + 6 + ptr) = value;
}
}
}
///
/// offset = + 8
///
public uint ts
{
get
{
unsafe
{
return *(uint*)(LocalOffset + 8 + ptr);
}
}
set
{
unsafe
{
*(uint*)(LocalOffset + 8 + ptr) = value;
}
}
}
///
/// SendNumber?
/// offset = + 12
///
public uint sn
{
get
{
unsafe
{
return *(uint*)(LocalOffset + 12 + ptr);
}
}
set
{
unsafe
{
*(uint*)(LocalOffset + 12 + ptr) = value;
}
}
}
///
/// offset = + 16
///
public uint una
{
get
{
unsafe
{
return *(uint*)(LocalOffset + 16 + ptr);
}
}
set
{
unsafe
{
*(uint*)(LocalOffset + 16 + ptr) = value;
}
}
}
///
/// AppendDateSize
/// offset = + 20
///
public uint len
{
get
{
unsafe
{
return *(uint*)(LocalOffset + 20 + ptr);
}
}
private set
{
unsafe
{
*(uint*)(LocalOffset + 20 + ptr) = value;
}
}
}
///
///
///
/// https://github.com/skywind3000/kcp/issues/35#issuecomment-263770736
public Span data
{
get
{
unsafe
{
return new Span(LocalOffset + HeadOffset + ptr, (int)len);
}
}
}
///
/// 将片段中的要发送的数据拷贝到指定缓冲区
///
///
///
public int Encode(Span buffer)
{
var datelen = (int)(HeadOffset + len);
///备用偏移值 现阶段没有使用
const int offset = 0;
if (KcpConst.IsLittleEndian)
{
if (BitConverter.IsLittleEndian)
{
///小端可以一次拷贝
unsafe
{
///要发送的数据从LocalOffset开始。
///本结构体调整了要发送字段和单机使用字段的位置，让报头数据和数据连续，节约一次拷贝。
Span sendDate = new Span(ptr + LocalOffset, datelen);
sendDate.CopyTo(buffer);
}
}
else
{
BinaryPrimitives.WriteUInt32LittleEndian(buffer.Slice(offset), conv);
buffer[offset + 4] = cmd;
buffer[offset + 5] = frg;
BinaryPrimitives.WriteUInt16LittleEndian(buffer.Slice(offset + 6), wnd);
BinaryPrimitives.WriteUInt32LittleEndian(buffer.Slice(offset + 8), ts);
BinaryPrimitives.WriteUInt32LittleEndian(buffer.Slice(offset + 12), sn);
BinaryPrimitives.WriteUInt32LittleEndian(buffer.Slice(offset + 16), una);
BinaryPrimitives.WriteUInt32LittleEndian(buffer.Slice(offset + 20), len);
data.CopyTo(buffer.Slice(HeadOffset));
}
}
else
{
if (BitConverter.IsLittleEndian)
{
BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(offset), conv);
buffer[offset + 4] = cmd;
buffer[offset + 5] = frg;
BinaryPrimitives.WriteUInt16BigEndian(buffer.Slice(offset + 6), wnd);
BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(offset + 8), ts);
BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(offset + 12), sn);
BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(offset + 16), una);
BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(offset + 20), len);
data.CopyTo(buffer.Slice(HeadOffset));
}
else
{
///大端可以一次拷贝
unsafe
{
///要发送的数据从LocalOffset开始。
///本结构体调整了要发送字段和单机使用字段的位置，让报头数据和数据连续，节约一次拷贝。
Span sendDate = new Span(ptr + LocalOffset, datelen);
sendDate.CopyTo(buffer);
}
}
}
return datelen;
}
}
}