fix(tak): resolve frequent TAK client disconnections (#5015)

core/takserver/src/commonMain/kotlin/org/meshtastic/core/takserver/TAKClientConnection.kt

@@ -52,6 +52,9 @@ class TAKClientConnection(
     private val writeChannel: ByteWriteChannel = socket.openWriteChannel(autoFlush = true)
     private val writeMutex = Mutex()
 
+    /** Tracks the last time data was received from the client, used for idle timeout detection. */
+    @Volatile private var lastDataReceived: Instant = Clock.System.now()
+
     /** Guards against emitting [TAKConnectionEvent.Disconnected] more than once. */
     @Volatile private var disconnectedEmitted = false
 
@@ -86,6 +89,7 @@ class TAKClientConnection(
                 readChannel.awaitContent()
                 val bytesRead = readChannel.readAvailable(buffer)
                 if (bytesRead > 0) {
+                    lastDataReceived = Clock.System.now()
                     processReceivedData(buffer.copyOfRange(0, bytesRead))
                 } else if (bytesRead == -1) {
                     break // EOF
@@ -102,16 +106,34 @@ class TAKClientConnection(
     }
 
     private suspend fun keepaliveLoop() {
+        val idleTimeoutMs = TAK_KEEPALIVE_INTERVAL_MS * TAK_READ_IDLE_TIMEOUT_MULTIPLIER
         while (scope.coroutineIsActive && !socket.isClosed) {
             kotlinx.coroutines.delay(TAK_KEEPALIVE_INTERVAL_MS)
+
+            val idleMs = (Clock.System.now() - lastDataReceived).inWholeMilliseconds
+            if (idleMs > idleTimeoutMs) {
+                Logger.w {
+                    "TAK client ${currentClientInfo.id} idle for ${idleMs}ms " +
+                        "(threshold ${idleTimeoutMs}ms), closing connection"
+                }
+                close()
+                return
+            }
+
             sendKeepalive()
         }
     }
 
     private fun sendKeepalive() {
         val now = Clock.System.now()
-        val stale = now + TAK_KEEPALIVE_INTERVAL_MS.milliseconds
-        sendXml(buildEventXml(uid = "takPong", type = "t-x-d-d", now = now, stale = stale, detail = ""))
+        val stale = now + (TAK_KEEPALIVE_INTERVAL_MS * TAK_KEEPALIVE_STALE_MULTIPLIER).milliseconds
+        sendXml(buildEventXml(uid = "takPong", type = "t-x-c-t", now = now, stale = stale, detail = ""))
+    }
+
+    private fun sendPong() {
+        val now = Clock.System.now()
+        val stale = now + (TAK_KEEPALIVE_INTERVAL_MS * TAK_KEEPALIVE_STALE_MULTIPLIER).milliseconds
+        sendXml(buildEventXml(uid = "takPong", type = "t-x-c-t-r", now = now, stale = stale, detail = ""))
     }
 
     private fun processReceivedData(newData: ByteArray) {
@@ -131,7 +153,7 @@ class TAKClientConnection(
                     return
                 }
                 cotMessage.type == "t-x-c-t" || cotMessage.uid == "ping" -> {
-                    // Keepalive / ping — discard silently
+                    sendPong()
                     return
                 }
                 else -> {
@@ -201,6 +223,7 @@ class TAKClientConnection(
                 throw e
             } catch (e: Exception) {
                 Logger.w(e) { "TAK client send error: ${currentClientInfo.id}" }
+                close()
             }
         }
     }

core/takserver/src/commonMain/kotlin/org/meshtastic/core/takserver/TAKDefaults.kt

@@ -29,6 +29,8 @@ internal const val DEFAULT_TAK_STALE_MINUTES = 10
 internal const val TAK_HEX_RADIX = 16
 internal const val TAK_XML_READ_BUFFER_SIZE = 4_096
 internal const val TAK_KEEPALIVE_INTERVAL_MS = 30_000L
+internal const val TAK_KEEPALIVE_STALE_MULTIPLIER = 3
+internal const val TAK_READ_IDLE_TIMEOUT_MULTIPLIER = 5
 internal const val TAK_ACCEPT_LOOP_DELAY_MS = 100L
 internal const val TAK_COORDINATE_SCALE = 1e7
 internal const val TAK_UNKNOWN_POINT_VALUE = 9_999_999.0

core/takserver/src/commonTest/kotlin/org/meshtastic/core/takserver/TAKDefaultsTest.kt

@@ -21,6 +21,7 @@ import org.meshtastic.proto.Team
 import org.meshtastic.proto.User
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertTrue
 
 class TAKDefaultsTest {
 
@@ -104,4 +105,22 @@ class TAKDefaultsTest {
         val user = User(id = "!1234", long_name = "", short_name = "")
         assertEquals("!1234", user.toTakCallsign())
     }
+
+    // ── keepalive / idle timeout constants ─────────────────────────────────────
+
+    @Test
+    fun `keepalive stale window is wider than keepalive interval`() {
+        val staleMs = TAK_KEEPALIVE_INTERVAL_MS * TAK_KEEPALIVE_STALE_MULTIPLIER
+        assertTrue(
+            staleMs > TAK_KEEPALIVE_INTERVAL_MS,
+            "Stale window ($staleMs ms) must exceed keepalive interval ($TAK_KEEPALIVE_INTERVAL_MS ms)",
+        )
+    }
+
+    @Test
+    fun `idle timeout exceeds keepalive stale window`() {
+        val idleTimeoutMs = TAK_KEEPALIVE_INTERVAL_MS * TAK_READ_IDLE_TIMEOUT_MULTIPLIER
+        val staleMs = TAK_KEEPALIVE_INTERVAL_MS * TAK_KEEPALIVE_STALE_MULTIPLIER
+        assertTrue(idleTimeoutMs > staleMs, "Idle timeout ($idleTimeoutMs ms) must exceed stale window ($staleMs ms)")
+    }
 }