add network test feature (PING/PONG with latency stats)

New frame types PING (0x0B) and PONG (0x0C), each carrying an 8-byte
nonce. Server echoes PING nonce verbatim in PONG. Client sends pings
at random 10-100ms intervals, correlates nonces to measure RTT.

Stats shown live: sent/recv counts, loss %, average latency, jitter
(mean absolute delta of consecutive RTTs). Test button toggles on/off.

Updated both Rust server (echo in main.rs) and C# client (PingTest.cs,
SessionManager routing, MainForm Test button + stats label).

PROTOCOL.md

@@ -46,6 +46,8 @@ emitted in v1.
 | 0x05 | OPEN_NAK    | S → C         | 0          | `upstream_id:1, reason:1`        |
 | 0x06 | DATA        | both          | session    | raw bytes (≤1480)                |
 | 0x07 | CLOSE       | both          | session    | optional `reason:1`              |
+| 0x0B | PING        | C → S         | 0          | `nonce:8`                        |
+| 0x0C | PONG        | S → C         | 0          | `nonce:8` (echoed)               |
 
 Reserved (unimplemented in v1; parse returns Err, encode unimplemented):
 
@@ -59,18 +61,27 @@ Reserved (unimplemented in v1; parse returns Err, encode unimplemented):
 
 ### MANIFEST payload
 
-Variable-length entries, parsed sequentially until the payload is consumed.
+A hostname prefix followed by variable-length entries, parsed sequentially
+until the payload is consumed.
 
 ```
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
-+---------------+---------------+-------------------------------+
++---------------+-----------------------------------------------+
+| hostname_len  | hostname (UTF-8, hostname_len bytes) ...       |
++---------------+-----------------------------------------------+
 | id            | proto         | port (big-endian)             |
 +---------------+---------------+-------------------------------+
 | label_len     | label (UTF-8, label_len bytes) ...           |
 +---------------+-----------------------------------------------+
+| ... repeated ...                                             |
++---------------------------------------------------------------+
 ```
 
+- **hostname_len** (u8): length in bytes of the server's hostname. `0` is valid
+  (unknown hostname).
+- **hostname** (`hostname_len` bytes, UTF-8): the server's hostname, read via
+  `gethostname(2)` at startup. Maximum 255 bytes.
 - **id** (u8): upstream identifier (1-based positional index from `gatunad`
   cmdline).
 - **proto** (u8): `1 = TCP`, `2 = UDP` (reserved; not emitted in v1).
@@ -80,7 +91,8 @@ Variable-length entries, parsed sequentially until the payload is consumed.
 - **label** (`label_len` bytes, UTF-8): human-readable name for the upstream,
   taken from the `PORT[:label]` cmdline argument. Maximum 255 bytes.
 
-To parse: read the 5-byte fixed prefix, then `label_len` bytes, and repeat until
+To parse: read `hostname_len`, then `hostname_len` bytes of hostname, then read
+5-byte fixed entry prefixes + `label_len` bytes of label each, repeating until
 the payload is exhausted. The number of entries is not carried explicitly.
 
 ### OPEN payload
@@ -130,6 +142,18 @@ field identifies which session the bytes belong to.
 
 - **reason** (u8, optional): present iff payload length ≥ 1. See reason codes.
 
+### PING / PONG payload
+
+```
++                                                               +
+| nonce (big-endian, 8 bytes)                                   |
++                                                               +
+```
+
+- **nonce** (u64, big-endian): arbitrary value chosen by the client. The
+  server echoes it verbatim in the PONG reply. Used to correlate RTT
+  measurements.
+
 ## Reason codes
 
 | Value | Meaning           |

gatunad/src/frame.rs

@@ -16,6 +16,8 @@ pub const TYPE_CLOSE: u8 = 0x07;
 pub const TYPE_UDP_OPEN: u8 = 0x08;
 pub const TYPE_UDP_DATA: u8 = 0x09;
 pub const TYPE_UDP_CLOSE: u8 = 0x0A;
+pub const TYPE_PING: u8 = 0x0B;
+pub const TYPE_PONG: u8 = 0x0C;
 
 pub const PROTO_TCP: u8 = 1;
 pub const PROTO_UDP: u8 = 2;
@@ -39,12 +41,14 @@ pub struct UpstreamEntry {
 #[derive(Clone, Debug)]
 pub enum Frame {
     Discover,
-    Manifest(Vec<UpstreamEntry>),
+    Manifest { hostname: String, entries: Vec<UpstreamEntry> },
     Open { upstream_id: u8 },
     OpenAck { session_id: u32, upstream_id: u8 },
     OpenNak { upstream_id: u8, reason: u8 },
     Data { session_id: u32, payload: Vec<u8> },
     Close { session_id: u32, reason: Option<u8> },
+    Ping { nonce: u64 },
+    Pong { nonce: u64 },
 }
 
 #[derive(Debug)]
@@ -94,8 +98,12 @@ impl Frame {
     pub fn encode(&self) -> Vec<u8> {
         match self {
             Frame::Discover => build(TYPE_DISCOVER, 0, Vec::new()),
-            Frame::Manifest(entries) => {
+            Frame::Manifest { hostname, entries } => {
                 let mut payload = Vec::new();
+                let hn_bytes = hostname.as_bytes();
+                let hn_len = hn_bytes.len().min(255) as u8;
+                payload.push(hn_len);
+                payload.extend_from_slice(&hn_bytes[..hn_len as usize]);
                 for e in entries {
                     encode_entry(&mut payload, e);
                 }
@@ -116,6 +124,8 @@ impl Frame {
                 };
                 build(TYPE_CLOSE, *session_id, p)
             }
+            Frame::Ping { nonce } => build(TYPE_PING, 0, nonce.to_be_bytes().to_vec()),
+            Frame::Pong { nonce } => build(TYPE_PONG, 0, nonce.to_be_bytes().to_vec()),
         }
     }
 
@@ -143,29 +153,38 @@ impl Frame {
                 Ok(Frame::Discover)
             }
             TYPE_MANIFEST => {
+                if payload.is_empty() {
+                    return Err(DecodeError::BadPayload("MANIFEST missing hostname prefix"));
+                }
+                let hn_len = payload[0] as usize;
+                if 1 + hn_len > payload.len() {
+                    return Err(DecodeError::BadPayload("MANIFEST hostname truncated"));
+                }
+                let hostname = String::from_utf8_lossy(&payload[1..1 + hn_len]).into_owned();
+                let rest = &payload[1 + hn_len..];
                 let mut entries = Vec::new();
                 let mut i = 0;
-                while i < payload.len() {
-                    if i + 5 > payload.len() {
+                while i < rest.len() {
+                    if i + 5 > rest.len() {
                         return Err(DecodeError::BadPayload("MANIFEST entry truncated"));
                     }
-                    let id = payload[i];
-                    let proto = payload[i + 1];
-                    let port = u16::from_be_bytes([payload[i + 2], payload[i + 3]]);
-                    let label_len = payload[i + 4] as usize;
+                    let id = rest[i];
+                    let proto = rest[i + 1];
+                    let port = u16::from_be_bytes([rest[i + 2], rest[i + 3]]);
+                    let label_len = rest[i + 4] as usize;
                     i += 5;
-                    if i + label_len > payload.len() {
+                    if i + label_len > rest.len() {
                         return Err(DecodeError::BadPayload("MANIFEST label truncated"));
                     }
                     let label = if label_len == 0 {
                         None
                     } else {
-                        Some(String::from_utf8_lossy(&payload[i..i + label_len]).into_owned())
+                        Some(String::from_utf8_lossy(&rest[i..i + label_len]).into_owned())
                     };
                     i += label_len;
                     entries.push(UpstreamEntry { id, proto, port, label });
                 }
-                Ok(Frame::Manifest(entries))
+                Ok(Frame::Manifest { hostname, entries })
             }
             TYPE_OPEN => {
                 if payload.len() != 1 {
@@ -199,6 +218,20 @@ impl Frame {
                 };
                 Ok(Frame::Close { session_id, reason })
             }
+            TYPE_PING => {
+                if payload.len() != 8 {
+                    return Err(DecodeError::BadPayload("PING payload must be 8 bytes"));
+                }
+                let nonce = u64::from_be_bytes(payload.try_into().unwrap());
+                Ok(Frame::Ping { nonce })
+            }
+            TYPE_PONG => {
+                if payload.len() != 8 {
+                    return Err(DecodeError::BadPayload("PONG payload must be 8 bytes"));
+                }
+                let nonce = u64::from_be_bytes(payload.try_into().unwrap());
+                Ok(Frame::Pong { nonce })
+            }
             TYPE_UDP_OPEN | TYPE_UDP_DATA | TYPE_UDP_CLOSE => {
                 Err(DecodeError::BadPayload("UDP frame types not implemented in v1"))
             }

gatunad/src/main.rs

@@ -52,6 +52,8 @@ async fn main() -> ExitCode {
         }
     };
 
+    let hostname = Arc::new(upstream::get_hostname());
+
     let link = match Link::open(&args.iface) {
         Ok(l) => Arc::new(l),
         Err(e) => {
@@ -112,7 +114,7 @@ async fn main() -> ExitCode {
                         continue;
                     }
                 };
-                handle_frame(frame, src, &tx, &store, &next_id, &table).await;
+                handle_frame(frame, src, &tx, &store, &next_id, &table, &hostname).await;
             }
             Ok(None) => {
                 // Ignorable frame (outgoing/short/mismatch) or transient; do not
@@ -135,10 +137,14 @@ async fn handle_frame(
     store: &SessionStore,
     next_id: &Arc<AtomicU32>,
     table: &Arc<crate::upstream::UpstreamTable>,
+    hostname: &Arc<String>,
 ) {
     match frame {
         Frame::Discover => {
-            let manifest = Frame::Manifest(table.entries());
+            let manifest = Frame::Manifest {
+                hostname: (**hostname).clone(),
+                entries: table.entries(),
+            };
             let _ = tx.send((src, manifest.encode())).await;
         }
         Frame::Open { upstream_id } => {
@@ -201,7 +207,12 @@ async fn handle_frame(
         Frame::Close { session_id, reason: _ } => {
             store.lock().expect("store poisoned").remove(&session_id);
         }
+        Frame::Ping { nonce } => {
+            let pong = Frame::Pong { nonce };
+            let _ = tx.send((src, pong.encode())).await;
+        }
         // Not expected from a client; ignore.
-        Frame::Manifest(_) | Frame::OpenAck { .. } | Frame::OpenNak { .. } => {}
+        Frame::Manifest { .. } | Frame::OpenAck { .. } | Frame::OpenNak { .. }
+        | Frame::Pong { .. } => {}
     }
 }

gatunad/src/upstream.rs

@@ -1,6 +1,20 @@
 //! Upstream table: cmdline parsing and MANIFEST entry construction.
 
-use crate::frame::{UpstreamEntry, PROTO_TCP, PROTO_UDP};
+use crate::frame::{Frame, UpstreamEntry, PROTO_TCP, PROTO_UDP};
+
+/// Read the system hostname via `gethostname(2)`.
+pub fn get_hostname() -> String {
+    let mut buf = [0u8; 256];
+    let ret = unsafe {
+        libc::gethostname(buf.as_mut_ptr() as *mut libc::c_char, buf.len())
+    };
+    if ret == 0 {
+        let len = buf.iter().position(|&b| b == 0).unwrap_or(buf.len());
+        String::from_utf8_lossy(&buf[..len]).into_owned()
+    } else {
+        String::new()
+    }
+}
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 #[allow(dead_code)]

win/gatuna-client/Frame.cs

@@ -17,6 +17,8 @@ static class Proto
     public const byte TypeOpenNak = 0x05;
     public const byte TypeData = 0x06;
     public const byte TypeClose = 0x07;
+    public const byte TypePing = 0x0B;
+    public const byte TypePong = 0x0C;
 
     public const byte ProtoTcp = 1;
     public const byte ProtoUdp = 2;
@@ -40,12 +42,14 @@ readonly record struct UpstreamEntry(
 abstract record Frame
 {
     internal record Discover : Frame;
-    internal record Manifest(UpstreamEntry[] Entries) : Frame;
+    internal record Manifest(string Hostname, UpstreamEntry[] Entries) : Frame;
     internal record Open(byte UpstreamId) : Frame;
     internal record OpenAck(uint SessionId, byte UpstreamId) : Frame;
     internal record OpenNak(byte UpstreamId, byte Reason) : Frame;
     internal record Data(uint SessionId, byte[] Payload) : Frame;
     internal record Close(uint SessionId, byte? Reason) : Frame;
+    internal record Ping(ulong Nonce) : Frame;
+    internal record Pong(ulong Nonce) : Frame;
 }
 
 static class FrameCodec
@@ -74,7 +78,7 @@ static class FrameCodec
             Frame.Discover =>
                 Build(Proto.TypeDiscover, 0, []),
             Frame.Manifest manifest =>
-                Build(Proto.TypeManifest, 0, BuildManifestPayload(manifest.Entries)),
+                Build(Proto.TypeManifest, 0, BuildManifestPayload(manifest.Hostname, manifest.Entries)),
             Frame.Open open =>
                 Build(Proto.TypeOpen, 0, [open.UpstreamId]),
             Frame.OpenAck ack =>
@@ -86,13 +90,22 @@ static class FrameCodec
             Frame.Close close =>
                 Build(Proto.TypeClose, close.SessionId,
                     close.Reason.HasValue ? [close.Reason.Value] : []),
+            Frame.Ping ping =>
+                Build(Proto.TypePing, 0, EncodeNonce(ping.Nonce)),
+            Frame.Pong pong =>
+                Build(Proto.TypePong, 0, EncodeNonce(pong.Nonce)),
             _ => throw new InvalidOperationException($"unknown frame type: {frame.GetType()}"),
         };
     }
 
-    static byte[] BuildManifestPayload(UpstreamEntry[] entries)
+    static byte[] BuildManifestPayload(string hostname, UpstreamEntry[] entries)
     {
         using var ms = new MemoryStream();
+        var hnBytes = Encoding.UTF8.GetBytes(hostname);
+        var hnLen = (byte)Math.Min(hnBytes.Length, 255);
+        ms.WriteByte(hnLen);
+        if (hnLen > 0)
+            ms.Write(hnBytes, 0, hnLen);
         foreach (var e in entries)
         {
             var labelBytes = Encoding.UTF8.GetBytes(e.Label ?? "");
@@ -133,33 +146,65 @@ static class FrameCodec
                 new Frame.Data(sessionId, payload.ToArray()),
             Proto.TypeClose when payload.Length is 0 or 1 =>
                 new Frame.Close(sessionId, payload.Length == 1 ? payload[0] : null),
+            Proto.TypePong when payload.Length == 8 =>
+                new Frame.Pong(ParseNonce(payload)),
+            Proto.TypePing when payload.Length == 8 =>
+                new Frame.Ping(ParseNonce(payload)),
             Proto.TypeDiscover when payload.Length == 0 =>
                 new Frame.Discover(),
             _ => null,
         };
     }
 
+    static ulong ParseNonce(ReadOnlySpan<byte> payload)
+    {
+        ulong nonce = 0;
+        for (int i = 0; i < 8; i++)
+            nonce = (nonce << 8) | payload[i];
+        return nonce;
+    }
+
+    static byte[] EncodeNonce(ulong nonce)
+    {
+        return [
+            (byte)(nonce >> 56), (byte)(nonce >> 48),
+            (byte)(nonce >> 40), (byte)(nonce >> 32),
+            (byte)(nonce >> 24), (byte)(nonce >> 16),
+            (byte)(nonce >> 8),  (byte)(nonce & 0xFF),
+        ];
+    }
+
     static Frame.Manifest? ParseManifest(ReadOnlySpan<byte> payload)
     {
+        if (payload.Length < 1)
+            return null;
+        var hnLen = payload[0];
+        if (1 + hnLen > payload.Length)
+            return null;
+        var hostname = hnLen == 0
+            ? ""
+            : Encoding.UTF8.GetString(payload[1..(1 + hnLen)]);
+        var rest = payload[(1 + hnLen)..];
+
         var entries = new List<UpstreamEntry>();
         int i = 0;
-        while (i < payload.Length)
+        while (i < rest.Length)
         {
-            if (i + 5 > payload.Length)
+            if (i + 5 > rest.Length)
                 return null;
-            var id = payload[i];
-            var proto = payload[i + 1];
-            var port = (ushort)(payload[i + 2] << 8 | payload[i + 3]);
-            var labelLen = payload[i + 4];
+            var id = rest[i];
+            var proto = rest[i + 1];
+            var port = (ushort)(rest[i + 2] << 8 | rest[i + 3]);
+            var labelLen = rest[i + 4];
             i += 5;
-            if (i + labelLen > payload.Length)
+            if (i + labelLen > rest.Length)
                 return null;
             string? label = labelLen == 0
                 ? null
-                : Encoding.UTF8.GetString(payload[i..(i + labelLen)]);
+                : Encoding.UTF8.GetString(rest[i..(i + labelLen)]);
             i += labelLen;
             entries.Add(new UpstreamEntry(id, proto, port, label));
         }
-        return new Frame.Manifest(entries.ToArray());
+        return new Frame.Manifest(hostname, entries.ToArray());
     }
 }

win/gatuna-client/MainForm.cs

@@ -7,23 +7,26 @@ public partial class MainForm : Form
     readonly SessionManager _sessions = new();
     readonly ComboBox _deviceBox = new();
     readonly Button _discoverBtn = new();
+    readonly Button _testBtn = new();
+    readonly Label _serverLabel = new();
+    readonly Label _pingStatsLabel = new();
     readonly ListView _listView = new();
     readonly Label _statusLabel = new();
     TunnelLink? _link;
+    PingTest? _pingTest;
 
     public MainForm()
     {
         Text = "gatuna";
         Width = 520;
-        Height = 380;
-        FormBorderStyle = FormBorderStyle.FixedSingle;
-        MaximizeBox = false;
-        MinimizeBox = false;
+        Height = 420;
         StartPosition = FormStartPosition.CenterScreen;
+        Icon = SystemIcons.GetStockIcon(StockIconId.NetworkConnect, 32);
         InitializeComponents();
 
         _sessions.Log += msg => this.Invoke(() => _statusLabel.Text = msg);
-        _sessions.ManifestReceived += entries => this.Invoke(() => PopulateList(entries));
+        _sessions.ManifestReceived += (hostname, mac, entries) =>
+            this.Invoke(() => PopulateList(hostname, mac, entries));
 
         foreach (var d in TunnelLink.ListDevices())
         {
@@ -54,9 +57,27 @@ public partial class MainForm : Form
         _discoverBtn.Click += OnDiscover;
         Controls.Add(_discoverBtn);
 
-        _listView.Left = pad; _listView.Top = _discoverBtn.Bottom + 8;
+        _testBtn.Text = "Test";
+        _testBtn.Left = _discoverBtn.Right + 8; _testBtn.Top = _discoverBtn.Top;
+        _testBtn.Width = 60;
+        _testBtn.Click += OnTest;
+        Controls.Add(_testBtn);
+
+        _serverLabel.Left = pad; _serverLabel.Top = _discoverBtn.Bottom + 8;
+        _serverLabel.Width = ClientSize.Width - pad * 2;
+        _serverLabel.AutoEllipsis = true;
+        _serverLabel.Text = "Server: not connected";
+        Controls.Add(_serverLabel);
+
+        _pingStatsLabel.Left = pad; _pingStatsLabel.Top = _serverLabel.Bottom + 4;
+        _pingStatsLabel.Width = ClientSize.Width - pad * 2;
+        _pingStatsLabel.AutoEllipsis = true;
+        _pingStatsLabel.Text = "";
+        Controls.Add(_pingStatsLabel);
+
+        _listView.Left = pad; _listView.Top = _pingStatsLabel.Bottom + 8;
         _listView.Width = ClientSize.Width - pad * 2;
-        _listView.Height = 220;
+        _listView.Height = 180;
         _listView.View = View.Details;
         _listView.FullRowSelect = true;
         _listView.CheckBoxes = true;
@@ -96,11 +117,43 @@ public partial class MainForm : Form
         _sessions.AttachLink(_link);
         _link.Open();
         _sessions.Discover();
+        _serverLabel.Text = "Server: discovering...";
         _statusLabel.Text = "discovering...";
     }
 
-    void PopulateList(UpstreamEntry[] entries)
+    void OnTest(object? s, EventArgs e)
     {
+        if (_pingTest != null && _pingTest.Running)
+        {
+            _sessions.StopPing();
+            _pingTest = null;
+            _testBtn.Text = "Test";
+            return;
+        }
+
+        _pingTest = _sessions.StartPing();
+        if (_pingTest == null)
+        {
+            MessageBox.Show("Discover a server first.");
+            return;
+        }
+        _pingTest.StatsUpdated += stats => this.Invoke(() =>
+        {
+            _pingStatsLabel.Text =
+                $"sent: {stats.Sent}  recv: {stats.Received}  " +
+                $"loss: {stats.LossPct:F1}%  " +
+                $"avg: {stats.AvgLatencyMs:F1}ms  " +
+                $"jitter: {stats.JitterMs:F1}ms";
+        });
+        _testBtn.Text = "Stop";
+        _pingStatsLabel.Text = "pinging...";
+    }
+
+    void PopulateList(string hostname, byte[] mac, UpstreamEntry[] entries)
+    {
+        var macStr = string.Join(":", mac.Select(b => b.ToString("X2")));
+        _serverLabel.Text = $"Server: {hostname} — {macStr}";
+
         _listView.BeginUpdate();
         _listView.Items.Clear();
         foreach (var up in entries)
@@ -134,14 +187,19 @@ public partial class MainForm : Form
         }
     }
 
+    protected override void OnResize(EventArgs e)
+    {
+        base.OnResize(e);
+        if (WindowState == FormWindowState.Minimized)
+        {
+            Hide();
+            WindowState = FormWindowState.Normal;
+        }
+    }
+
     protected override void OnFormClosing(FormClosingEventArgs e)
     {
-        if (e.CloseReason == CloseReason.UserClosing)
-        {
-            e.Cancel = true;
-            Hide();
-            return;
-        }
+        Shutdown();
         base.OnFormClosing(e);
     }
 

win/gatuna-client/PingTest.cs

@@ -0,0 +1,101 @@
+using System.Collections.Concurrent;
+
+namespace gatuna_client;
+
+sealed class PingTest
+{
+    readonly TunnelLink _link;
+    readonly byte[] _serverMac;
+    readonly CancellationTokenSource _cts = new();
+    readonly ConcurrentDictionary<ulong, long> _outstanding = new();
+    readonly ConcurrentQueue<double> _rtts = new();
+    long _sent;
+    long _received;
+    double _lastRttMs;
+    double _jitterSum;
+    long _jitterCount;
+
+    public event Action<PingStats>? StatsUpdated;
+    public event Action<string>? Log;
+
+    public bool Running { get; private set; }
+
+    public PingTest(TunnelLink link, byte[] serverMac)
+    {
+        _link = link;
+        _serverMac = serverMac;
+    }
+
+    public void Start()
+    {
+        Running = true;
+        _ = RunLoop();
+    }
+
+    public void Stop()
+    {
+        Running = false;
+        _cts.Cancel();
+    }
+
+    async Task RunLoop()
+    {
+        var rng = new Random();
+        var timer = new PeriodicTimer(TimeSpan.FromMilliseconds(10));
+        while (!_cts.IsCancellationRequested)
+        {
+            var nonce = (ulong)Interlocked.Increment(ref _sent);
+            var ticks = DateTime.UtcNow.Ticks;
+            _outstanding[nonce] = ticks;
+
+            _link.SendTo(_serverMac, new Frame.Ping(nonce));
+
+            var interval = rng.Next(10, 101);
+            try
+            {
+                await Task.Delay(interval, _cts.Token);
+            }
+            catch { break; }
+        }
+        Running = false;
+    }
+
+    public void HandlePong(ulong nonce)
+    {
+        if (_outstanding.TryRemove(nonce, out var sentTicks))
+        {
+            var rttMs = (DateTime.UtcNow.Ticks - sentTicks) / (double)TimeSpan.TicksPerMillisecond;
+            _rtts.Enqueue(rttMs);
+            Interlocked.Increment(ref _received);
+
+            if (_jitterCount > 0)
+            {
+                _jitterSum += Math.Abs(rttMs - _lastRttMs);
+            }
+            _lastRttMs = rttMs;
+            Interlocked.Increment(ref _jitterCount);
+
+            EmitStats();
+        }
+    }
+
+    void EmitStats()
+    {
+        var sent = Interlocked.Read(ref _sent);
+        var recv = Interlocked.Read(ref _received);
+        var loss = sent > 0 ? (1.0 - (double)recv / sent) * 100.0 : 0;
+
+        var rttList = _rtts.ToArray();
+        var avg = rttList.Length > 0 ? rttList.Average() : 0;
+        var jitter = _jitterCount > 1 ? _jitterSum / (_jitterCount - 1) : 0;
+
+        StatsUpdated?.Invoke(new PingStats(sent, recv, loss, avg, jitter));
+    }
+}
+
+readonly record struct PingStats(
+    long Sent,
+    long Received,
+    double LossPct,
+    double AvgLatencyMs,
+    double JitterMs);

win/gatuna-client/Program.cs

@@ -11,7 +11,7 @@ static class Program
 
         using var tray = new NotifyIcon
         {
-            Icon = SystemIcons.Application,
+            Icon = SystemIcons.GetStockIcon(StockIconId.NetworkConnect, 32),
             Text = "gatuna",
             Visible = true,
         };
@@ -20,18 +20,19 @@ static class Program
         tray.ContextMenuStrip.Items.Add("Show", null, (_, _) =>
         {
             form.Show();
+            form.WindowState = FormWindowState.Normal;
             form.Activate();
         });
         tray.ContextMenuStrip.Items.Add("-");
         tray.ContextMenuStrip.Items.Add("Exit", null, (_, _) =>
         {
-            form.Shutdown();
             tray.Visible = false;
-            Application.Exit();
+            form.Close();
         });
         tray.DoubleClick += (_, _) =>
         {
             form.Show();
+            form.WindowState = FormWindowState.Normal;
             form.Activate();
         };
 

win/gatuna-client/SessionManager.cs

@@ -12,7 +12,9 @@ sealed class SessionManager : IDisposable
     readonly ConcurrentDictionary<int, ListenerState> _listeners = new();
 
     byte[]? _serverMac;
+    string _serverHostname = "";
     UpstreamEntry[] _upstreams = [];
+    PingTest? _pingTest;
 
     // Serialized OPEN: only one outstanding at a time.
     readonly object _openLock = new();
@@ -20,10 +22,11 @@ sealed class SessionManager : IDisposable
     readonly Queue<PendingOpen> _openQueue = new();
 
     public event Action<string>? Log;
-    public event Action<UpstreamEntry[]>? ManifestReceived;
+    public event Action<string, byte[], UpstreamEntry[]>? ManifestReceived;
 
     public UpstreamEntry[] Upstreams => _upstreams;
     public byte[]? ServerMac => _serverMac;
+    public string ServerHostname => _serverHostname;
     public TunnelLink? Link => _link;
 
     public void AttachLink(TunnelLink link)
@@ -45,15 +48,32 @@ sealed class SessionManager : IDisposable
         _link.SendBroadcast(new Frame.Discover());
     }
 
+    public PingTest? StartPing()
+    {
+        if (_link == null || _serverMac == null)
+            return null;
+        _pingTest?.Stop();
+        _pingTest = new PingTest(_link, _serverMac);
+        _pingTest.Start();
+        return _pingTest;
+    }
+
+    public void StopPing()
+    {
+        _pingTest?.Stop();
+        _pingTest = null;
+    }
+
     public void HandleFrame(Frame frame, byte[] srcMac)
     {
         switch (frame)
         {
             case Frame.Manifest manifest:
                 _serverMac = srcMac;
+                _serverHostname = manifest.Hostname;
                 _upstreams = manifest.Entries;
-                Log?.Invoke($"manifest: {manifest.Entries.Length} upstreams from {BitConverter.ToString(srcMac)}");
-                ManifestReceived?.Invoke(manifest.Entries);
+                Log?.Invoke($"manifest: {manifest.Entries.Length} upstreams from {manifest.Hostname} ({BitConverter.ToString(srcMac)})");
+                ManifestReceived?.Invoke(manifest.Hostname, srcMac, manifest.Entries);
                 break;
 
             case Frame.OpenAck ack:
@@ -82,18 +102,58 @@ sealed class SessionManager : IDisposable
                 if (_sessions.TryRemove(close.SessionId, out var s))
                     s.Dispose();
                 break;
+
+            case Frame.Pong pong:
+                _pingTest?.HandlePong(pong.Nonce);
+                break;
+
+            case Frame.Ping _:
+                break;
         }
     }
 
+    /// <summary>
+    /// Compute a deterministic mirror port from the server MAC and the
+    /// upstream port. XOR the upstream port with (mac[0]<<8 | mac[5]),
+    /// then ensure the result is outside the privileged range.
+    /// </summary>
+    static ushort ComputeMirrorPort(byte[] serverMac, ushort upstreamPort)
+    {
+        var k = (ushort)((serverMac[0] << 8) | serverMac[5]);
+        var port = (ushort)(upstreamPort ^ k);
+        if (port < 1024)
+            port += 1024;
+        return port;
+    }
+
     /// <summary>
     /// Start a local TCP listener for the given upstream. Returns the mirror
     /// port, or 0 on failure.
     /// </summary>
     public int StartListener(UpstreamEntry upstream)
     {
-        var listener = new TcpListener(IPAddress.Loopback, 0);
-        listener.Start();
-        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+        if (_serverMac == null)
+            return 0;
+
+        var preferred = ComputeMirrorPort(_serverMac, upstream.Port);
+
+        // Try the deterministic port first; fall back to OS assignment.
+        TcpListener listener;
+        int port;
+        try
+        {
+            listener = new TcpListener(IPAddress.Loopback, preferred);
+            listener.Start();
+            port = ((IPEndPoint)listener.LocalEndpoint).Port;
+        }
+        catch
+        {
+            listener = new TcpListener(IPAddress.Loopback, 0);
+            listener.Start();
+            port = ((IPEndPoint)listener.LocalEndpoint).Port;
+            Log?.Invoke($"port {preferred} in use, fell back to {port}");
+        }
+
         var state = new ListenerState(listener, upstream);
         _listeners[port] = state;
         _ = AcceptLoop(state);
@@ -191,6 +251,7 @@ sealed class SessionManager : IDisposable
 
     public void StopAll()
     {
+        StopPing();
         foreach (var kv in _listeners)
             kv.Value.Listener.Stop();
         _listeners.Clear();

win/gatuna-client/TunnelLink.cs

@@ -50,6 +50,11 @@ sealed class TunnelLink : IDisposable
         var et = (ushort)(data[12] << 8 | data[13]);
         if (et != Proto.EtherType)
             return;
+        // Skip our own outgoing frames (Npcap loops them back in promiscuous mode).
+        if (data[6] == _ourMac[0] && data[7] == _ourMac[1]
+            && data[8] == _ourMac[2] && data[9] == _ourMac[3]
+            && data[10] == _ourMac[4] && data[11] == _ourMac[5])
+            return;
         var srcMac = new byte[6];
         Buffer.BlockCopy(data, 6, srcMac, 0, 6);
         var payload = data.AsSpan(Proto.EthHeaderLen);