Show status in trace empty-state; discard empty captures; polish capture-mode

Frontend:
- trace empty-state now shows connection status + capture mode (boxed,
  colored) in the center, updated live via checkConnection
- capture-mode uses amber warning style (gsmtap/disabled), green for direct
- stopCapture clears currentSessionId

Server:
- gsmtap read_packet catches OSError on socket close (no more EBADF
  traceback on stop)
- stop_session joins the loop and discards a session with zero messages;
  /api/capture/stop reports discarded
- startup prints server version

Tests: 122 (gsmtap close, empty/non-empty capture lifecycle).

frontend/index.html

@@ -24,6 +24,7 @@
     --warn-bg: #7f1d1d;
     --warn: #facc15;
     --warn-hover: #eab308;
+    --warning-bg: #78350f;
     --error: #f87171;
     --code-bg: #1e293b;
     --scrollbar-track: #0f172a;
@@ -49,6 +50,7 @@
     --warn-bg: #fee2e2;
     --warn: #f59e0b;
     --warn-hover: #d97706;
+    --warning-bg: #fef3c7;
     --error: #dc2626;
     --code-bg: #f3f4f6;
     --scrollbar-track: #fafafa;
@@ -168,12 +170,15 @@ body { font: 14px/1.5 system-ui, sans-serif; background: var(--bg); color: var(-
 .settings-url-row button { padding: 8px 16px; background: var(--accent); color: #fff; border: none; border-radius: 4px; cursor: pointer; font-weight: 600; white-space: nowrap; }
 .settings-url-row button:hover { background: var(--accent-hover); }
 .settings-url-row button.disconnected { background: var(--bg-input); }
-.settings-view .conn-status { padding: 12px; border-radius: 4px; margin-bottom: 12px; }
+.conn-status { padding: 12px; border-radius: 4px; margin-bottom: 12px; }
-.settings-view .conn-status.connected { background: var(--accent-bg); color: var(--green); }
+.conn-status.connected { background: var(--accent-bg); color: var(--green); }
-.settings-view .conn-status.disconnected { background: var(--warn-bg); color: var(--error); }
+.conn-status.disconnected { background: var(--warn-bg); color: var(--error); }
 .conn-hint { font-size: 12px; color: var(--text-muted); margin: 8px 0 0; line-height: 1.5; }
-.capture-mode { font-size: 12px; color: var(--text-muted); margin: 8px 0 0; line-height: 1.5; }
+.capture-mode { padding: 12px; border-radius: 4px; margin-bottom: 12px; font-size: 13px; line-height: 1.5; }
 .capture-mode:empty { display: none; }
+.capture-mode.gsmtap { background: var(--warning-bg); color: var(--warn); }
+.capture-mode.direct { background: var(--accent-bg); color: var(--green); }
+.capture-mode.disabled { background: var(--warning-bg); color: var(--warn); }
 .version-warn { font-size: 12px; color: var(--warn); margin: 8px 0 0; line-height: 1.5; }
 .version-warn:empty { display: none; }
 .conn-instructions { margin-top: 16px; font-size: 13px; color: var(--text-faint); line-height: 1.7; }
@@ -186,6 +191,7 @@ body { font: 14px/1.5 system-ui, sans-serif; background: var(--bg); color: var(-
 /* Empty state */
 .empty-state { display: flex; flex-direction: column; align-items: center; justify-content: center; height: 100%; color: var(--text-muted); gap: 16px; }
 .empty-state button { padding: 12px 24px; background: var(--accent); color: #fff; border: none; border-radius: 4px; cursor: pointer; font-size: 16px; }
+.empty-state .conn-status, .empty-state .capture-mode { width: 100%; max-width: 560px; text-align: left; }
 
 /* Modal */
 .modal-overlay { display: none; position: fixed; inset: 0; background: var(--modal-bg); z-index: 100; align-items: center; justify-content: center; }
@@ -321,6 +327,8 @@ const STATE = {
     typeCounts: [],
     pendingDeleteId: null,
     serverAvailable: false,
+    serverName: '',
+    serverVersion: '',
     captureMode: '',
 };
 
@@ -762,6 +770,27 @@ function matchesFilter(m, i, filterType) {
     return false;
 }
 
+function renderTraceEmptyState() {
+    if (STATE.captureActive || STATE.sessionViewId) return;
+    const list = el('apdu-list');
+    const connCls = STATE.serverAvailable ? 'connected' : 'disconnected';
+    const modeText = captureModeText();
+    const modeHtml = modeText
+        ? `<div class="capture-mode ${STATE.captureMode}">${modeText}</div>`
+        : '';
+    const action = STATE.captureMode === 'disabled'
+        ? `<p style="font-size:12px;">${t('Open a saved session from the Sessions tab.')}</p>`
+        : `<button id="trace-start-btn">${t('Start Capture')}</button>`;
+    list.innerHTML = `<div class="empty-state">
+        <div class="conn-status ${connCls}">${connectionStatusText()}</div>
+        ${modeHtml}
+        ${action}
+    </div>`;
+    const btn = $('#trace-start-btn', list);
+    if (btn) btn.addEventListener('click', startCapture);
+    updateStatus();
+}
+
 function renderMessages() {
     const list = el('apdu-list');
     const searchQ = el('search-input').value.toLowerCase();
@@ -780,15 +809,7 @@ function renderMessages() {
     populateFilterOptions();
 
     if (!STATE.captureActive && !STATE.sessionViewId) {
-        if (STATE.captureMode === 'disabled') {
+        renderTraceEmptyState();
-            list.innerHTML = `<div class="empty-state"><p>${t('Capture unavailable')}</p>
-                <p style="font-size:12px;">${t('Open a saved session from the Sessions tab.')}</p></div>`;
-        } else {
-            list.innerHTML = `<div class="empty-state"><p>${t('No capture active')}</p>
-                <button id="trace-start-btn">${t('Start Capture')}</button></div>`;
-            $('#trace-start-btn', list).addEventListener('click', startCapture);
-        }
-        updateStatus();
         return;
     }
 
@@ -882,6 +903,7 @@ async function stopCapture() {
     try {
         await API.stopCapture();
         STATE.captureActive = false;
+        STATE.currentSessionId = null;
         STATE.sessionViewId = null;
         updateCaptureButton();
         updateStatus();
@@ -1106,23 +1128,33 @@ function updateVersionWarn(serverVersion) {
     elv.textContent = '';
 }
 
-function updateCaptureModeLine() {
+function captureModeText() {
-    const elm = el('capture-mode');
     switch (STATE.captureMode) {
         case 'gsmtap':
-            elm.textContent = t('Capture mode: GSMTAP — the server is listening for incoming UDP/GSMTAP traffic. Ensure a GSMTAP source (e.g. simtrace2-pysniff or simtrace2-sniff) is feeding the server.');
+            return t('Capture mode: GSMTAP — the server is listening for incoming UDP/GSMTAP traffic. Ensure a GSMTAP source (e.g. simtrace2-pysniff or simtrace2-sniff) is feeding the server.');
-            break;
         case 'direct':
-            elm.textContent = t('Capture mode: direct — the server captures from SIMtrace2 hardware. Keep the device connected.');
+            return t('Capture mode: direct — the server captures from SIMtrace2 hardware. Keep the device connected.');
-            break;
         case 'disabled':
-            elm.textContent = t('Capture is disabled — only pre-captured traces (saved sessions / PCAP import) are available.');
+            return t('Capture is disabled — only pre-captured traces (saved sessions / PCAP import) are available.');
-            break;
         default:
-            elm.textContent = '';
+            return '';
     }
 }
 
+function connectionStatusText() {
+    if (STATE.serverAvailable) {
+        return '⬤ ' + t('Connected') + ' — ' + STATE.serverName + ' v' + STATE.serverVersion;
+    }
+    return '⬤ ' + t('Not connected — ensure the server is running on the URL above');
+}
+
+function updateCaptureModeLine() {
+    const elm = el('capture-mode');
+    const mode = STATE.captureMode;
+    elm.textContent = captureModeText();
+    elm.className = 'capture-mode' + (mode ? ' ' + mode : '');
+}
+
 function connectServer() {
     if (_connTimer) return;
     _connTimer = setInterval(checkConnection, 5000);
@@ -1135,9 +1167,13 @@ function disconnectServer() {
         _connTimer = null;
     }
     STATE.serverAvailable = false;
+    STATE.serverName = '';
+    STATE.serverVersion = '';
+    STATE.captureMode = '';
     el('conn-status').textContent = '⬤ ' + t('Disconnected — click Connect to resume');
     el('conn-status').className = 'conn-status disconnected';
     el('capture-mode').textContent = '';
+    el('capture-mode').className = 'capture-mode';
     el('version-warn').textContent = '';
     el('conn-hint').textContent = '';
     el('conn-instructions').innerHTML = '';
@@ -1152,6 +1188,7 @@ function disconnectServer() {
         STATE.captureActive = false;
         STATE.currentSessionId = null;
     }
+    renderTraceEmptyState();
 }
 
 async function checkConnection() {
@@ -1159,7 +1196,9 @@ async function checkConnection() {
         const data = await API.status();
         STATE.serverAvailable = true;
         STATE.captureMode = data.capture_mode || '';
-        el('conn-status').textContent = '⬤ ' + t('Connected') + ' — ' + data.server + ' v' + (data.version || '?');
+        STATE.serverName = data.server || 'simtrace-analyser-server';
+        STATE.serverVersion = data.version || '';
+        el('conn-status').textContent = connectionStatusText();
         el('conn-status').className = 'conn-status connected';
         updateVersionWarn(data.version);
         updateCaptureModeLine();
@@ -1174,12 +1213,15 @@ async function checkConnection() {
             STATE.currentSessionId = data.session_id;
         }
         updateCaptureButton();
+        renderTraceEmptyState();
     } catch (e) {
         STATE.serverAvailable = false;
         STATE.captureMode = '';
-        el('conn-status').textContent = '⬤ ' + t('Not connected — ensure the server is running on the URL above');
+        STATE.serverName = '';
+        STATE.serverVersion = '';
+        el('conn-status').textContent = connectionStatusText();
         el('conn-status').className = 'conn-status disconnected';
-        el('capture-mode').textContent = '';
+        updateCaptureModeLine();
         el('version-warn').textContent = '';
         const url = STATE.serverUrl || location.origin;
         el('conn-hint').textContent = t(isLikelyBlocked() ? HINT_BLOCKED : HINT_UNREACHABLE).replace('{url}', url);
@@ -1209,6 +1251,7 @@ async function checkConnection() {
         el('status-dot').className = 'status-dot off';
         el('status-text').textContent = t('Not connected');
         updateCaptureButton();
+        renderTraceEmptyState();
     }
 }
 
@@ -1433,6 +1476,7 @@ function init() {
 
     el('pwa-version').textContent = 'v' + PWA_VERSION;
     syncServerSourceUi();
+    renderTraceEmptyState();
 
     document.querySelectorAll('.header-tab').forEach(tab => {
         tab.addEventListener('click', () => switchTab(tab.dataset.tab));

simtrace2_pysniff/gsmtap.py

@@ -81,7 +81,7 @@ class GsmtapReceiver:
         """
         try:
             packet, addr = self._sock.recvfrom(65536)
-        except socket.timeout:
+        except (socket.timeout, OSError):
             return None, None
 
         if len(packet) < _GSMTAP_HDR_SIZE:

simtrace2_pysniff/server/__main__.py

@@ -13,6 +13,7 @@ from http.server import HTTPServer
 from .server import RequestHandler
 from .database import Database, DEFAULT_DB_PATH
 from .capture import CaptureManager, GsmtapListener, DirectSniffer
+from .. import __version__
 
 
 def _default_web_dir():
@@ -56,7 +57,7 @@ def main():
     server = HTTPServer((args.host, args.port), RequestHandler)
     server.web_dir = args.web_dir
 
-    print(f'simtrace2-pysniff-server — http://{args.host}:{args.port}', file=sys.stderr)
+    print(f'simtrace2-pysniff-server v{__version__} — http://{args.host}:{args.port}', file=sys.stderr)
     print(f'  capture mode: {args.capture}', file=sys.stderr)
     if args.capture == 'gsmtap':
         print(f'  GSMTAP port:  {args.gsmtap_port}', file=sys.stderr)

simtrace2_pysniff/server/capture.py

@@ -94,12 +94,17 @@ class CaptureManager:
 
     def stop_session(self):
         if self._session_id is None:
-            return
+            return None
         self._backend.stop()
-        self._db.close_session(self._session_id)
+        if self._thread is not None:
+            self._thread.join(timeout=2.0)
         sid = self._session_id
         self._session_id = None
         self._start_time = 0.0
+        if self._db.count_messages(sid) == 0:
+            self._db.delete_session(sid)
+            return None
+        self._db.close_session(sid)
         return sid
 
     def _capture_loop(self):

simtrace2_pysniff/server/server.py

@@ -293,6 +293,9 @@ class RequestHandler(BaseHTTPRequestHandler):
             self._send_error(400, 'No active capture')
             return
         session_id = self.capture.stop_session()
+        if session_id is None:
+            self._send_json({'session_id': None, 'messages_count': 0, 'discarded': True})
+            return
         session = self.db.get_session(session_id)
         self._send_json({
             'session_id': session_id,

tests/test_capture.py

@@ -0,0 +1,49 @@
+"""Tests for CaptureManager session lifecycle (empty-session discard)."""
+
+import os
+import tempfile
+import unittest
+
+from simtrace2_pysniff.server.capture import CaptureManager
+from simtrace2_pysniff.server.database import Database
+
+
+class _FakeBackend:
+    def __init__(self, messages=()):
+        self._messages = list(messages)
+
+    def start(self):
+        pass
+
+    def stop(self):
+        pass
+
+    def iter_messages(self):
+        yield from self._messages
+
+
+class TestCaptureManager(unittest.TestCase):
+    def _manager(self, backend):
+        tmp = tempfile.NamedTemporaryFile(suffix='.db', delete=False)
+        tmp.close()
+        db = Database(tmp.name)
+        self.addCleanup(lambda: (db._conn.close(), os.remove(tmp.name)))
+        return CaptureManager(backend, db), db
+
+    def test_empty_capture_discarded(self):
+        mgr, db = self._manager(_FakeBackend())
+        sid = mgr.start_session()
+        self.assertIsNotNone(sid)
+        self.assertIsNone(mgr.stop_session())
+        self.assertIsNone(db.get_session(sid))
+
+    def test_non_empty_capture_kept(self):
+        mgr, db = self._manager(_FakeBackend([('tpdu', b'\x80\xf2\x00\x00\x00', 0)]))
+        sid = mgr.start_session()
+        self.assertEqual(mgr.stop_session(), sid)
+        self.assertIsNotNone(db.get_session(sid))
+        self.assertEqual(db.count_messages(sid), 1)
+
+
+if __name__ == '__main__':
+    unittest.main()

tests/test_gsmtap.py

@@ -0,0 +1,16 @@
+"""Tests for GSMTAP receiver shutdown behavior."""
+
+import unittest
+
+from simtrace2_pysniff.gsmtap import GsmtapReceiver
+
+
+class TestGsmtapReceiver(unittest.TestCase):
+    def test_read_after_close_returns_none(self):
+        r = GsmtapReceiver(bind_port=0)
+        r.close()
+        self.assertEqual(r.read_packet(), (None, None))
+
+
+if __name__ == '__main__':
+    unittest.main()