119 lines
4.4 KiB
C#
119 lines
4.4 KiB
C#
using System.Buffers.Binary;
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using System.Net.Sockets;
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using Monitor.Protocol;
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namespace Monitor.Measurement;
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/// <summary>内核对一条 TCP 连接的采样（Linux <c>TCP_INFO</c>）。</summary>
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public readonly record struct TcpInfoSample(long SrttUs, long RttVarUs, long Cwnd, long TotalRetrans, long SegsOut, long BytesAcked);
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/// <summary>
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/// 读 Linux 的 <c>TCP_INFO</c>：通过 <see cref="Socket.GetRawSocketOption(int, int, Span{byte})"/>，不需要 P/Invoke（NativeAOT、glibc 和 musl 都一样）。
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/// 缓冲区先清零，并且只读内核实际返回的长度之内的字段：老内核返回的结构更短，缺的字段是 0，而不是垃圾值。
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/// 其他平台返回 false（没有这一类采样，指标在对应窗口里就是没有数据）。
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/// </summary>
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public static class TcpInfo
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{
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private const int SolTcp = 6;
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private const int TcpInfoOption = 11;
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// struct tcp_info 的偏移（include/uapi/linux/tcp.h）：8 字节的状态位之后是 u32 字段；total_retrans 之后是对齐到 8 字节的 u64 字段
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private const int RttOffset = 68;
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private const int RttVarOffset = 72;
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private const int SndCwndOffset = 80;
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private const int TotalRetransOffset = 100;
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private const int BytesAckedOffset = 120;
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private const int SegsOutOffset = 136;
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/// <summary>读到 <c>segs_out</c> 为止（内核 ≥ 4.2）。</summary>
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public const int Length = SegsOutOffset + 4;
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public static bool Supported => OperatingSystem.IsLinux();
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public static bool TrySample(Socket socket, out TcpInfoSample sample)
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{
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sample = default;
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if (!Supported)
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{
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return false;
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}
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try
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{
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Span<byte> buffer = stackalloc byte[Length];
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buffer.Clear();
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int returned = socket.GetRawSocketOption(SolTcp, TcpInfoOption, buffer);
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if (returned < RttVarOffset + 4)
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{
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return false;
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}
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ReadOnlySpan<byte> info = buffer[..Math.Min(returned, Length)];
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sample = new TcpInfoSample(
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U32(info, RttOffset),
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U32(info, RttVarOffset),
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U32(info, SndCwndOffset),
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U32(info, TotalRetransOffset),
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U32(info, SegsOutOffset),
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U64(info, BytesAckedOffset));
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return true;
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}
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catch (Exception ex) when (ex is SocketException or ObjectDisposedException or PlatformNotSupportedException)
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{
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return false;
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}
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}
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private static long U32(ReadOnlySpan<byte> info, int offset) => offset + 4 <= info.Length ? BinaryPrimitives.ReadUInt32LittleEndian(info[offset..]) : 0;
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private static long U64(ReadOnlySpan<byte> info, int offset) => offset + 8 <= info.Length ? (long)BinaryPrimitives.ReadUInt64LittleEndian(info[offset..]) : 0;
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}
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/// <summary>
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/// 一条连接上周期性的内核采样（<c>tcp_info</c> 流）：每个采样一行 (ts, side, srtt, rttvar, cwnd, retrans_total, segs_out, bytes_acked)。
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/// 两端各采样自己的套接字：Probe 的重传反映上行方向，Agent 的重传反映下行方向（代理场景里大流量走这个方向）。
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/// 累计计数器在 Backend 按 side 分别求差。
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/// </summary>
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public sealed class TcpInfoRecorder
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{
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private readonly MonoClock _clock;
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private readonly long _side;
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public TcpInfoRecorder(StreamSpec spec, Side side, MonoClock clock)
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{
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Rows = new RowStore(spec, side, 4096);
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_clock = clock;
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_side = side == Side.Probe ? 0 : 1;
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}
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public RowStore Rows { get; }
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/// <summary>每隔 <paramref name="interval"/> 采样一次，直到取消或套接字不可用（连接断开）。</summary>
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public async Task RunAsync(Socket socket, TimeSpan interval, CancellationToken ct)
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{
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if (!TcpInfo.Supported)
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{
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return;
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}
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try
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{
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using var timer = new PeriodicTimer(interval, _clock.Time);
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while (await timer.WaitForNextTickAsync(ct))
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{
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if (!TcpInfo.TrySample(socket, out TcpInfoSample s))
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{
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return;
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}
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long key = Rows.Append();
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Rows.SetRow(key, [_clock.NowUs(), _side, s.SrttUs, s.RttVarUs, s.Cwnd, s.TotalRetrans, s.SegsOut, s.BytesAcked]);
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}
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}
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catch (OperationCanceledException)
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{
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// 连接结束
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}
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}
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}
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