Fix silent stalls in native_subscribe WS subscriptions (Solana, eth pending tx) (#827)

src/main/kotlin/io/emeraldpay/dshackle/upstream/ethereum/subscribe/WebsocketPendingTxes.kt

@@ -27,6 +27,7 @@ import org.slf4j.LoggerFactory
 import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
 import java.time.Duration
+import java.util.concurrent.TimeoutException
 
 class WebsocketPendingTxes(
     private val chain: Chain,
@@ -35,6 +36,7 @@ class WebsocketPendingTxes(
 
     companion object {
         private val log = LoggerFactory.getLogger(WebsocketPendingTxes::class.java)
+        private val IDLE_TIMEOUT: Duration = Duration.ofSeconds(85)
     }
 
     override fun createConnection(): Flux<TransactionId> {
@@ -42,7 +44,15 @@ class WebsocketPendingTxes(
         return sub
             .data
             .flatMapMany { it.t2 }
-            .timeout(Duration.ofSeconds(85), Mono.empty())
+            // Surface stalls as TimeoutException so the surrounding DurableFlux re-invokes
+            // createConnection() and issues a fresh eth_subscribe. Without this, a silent
+            // upstream pubsub leaves the shared Flux completed and clients stop receiving events.
+            .timeout(
+                IDLE_TIMEOUT,
+                Mono.error(
+                    TimeoutException("No events from eth_subscribe newPendingTransactions in $IDLE_TIMEOUT, forcing resubscribe"),
+                ),
+            )
             .map {
                 // comes as a JS string, i.e., within quotes
                 val value = ByteArray(it.size - 2)
@@ -60,7 +70,6 @@ class WebsocketPendingTxes(
                         log.info("unsubscribed from ${sub.subId.get()}")
                     }
             }
-            .doOnError { t -> log.warn("Invalid pending transaction", t) }
+            .doOnError { t -> log.warn("Error during pending tx subscription: {}", t.message) }
-            .onErrorResume { Mono.empty() }
     }
 }

src/main/kotlin/io/emeraldpay/dshackle/upstream/generic/GenericIngressSubscription.kt

@@ -13,6 +13,7 @@ import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
 import java.time.Duration
 import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.TimeoutException
 
 class GenericIngressSubscription(
     val chain: Chain,
@@ -49,6 +50,7 @@ class GenericSubscriptionConnect(
 
     companion object {
         private val log = LoggerFactory.getLogger(GenericSubscriptionConnect::class.java)
+        private val IDLE_TIMEOUT: Duration = Duration.ofSeconds(85)
     }
 
     @Suppress("UNCHECKED_CAST")
@@ -56,16 +58,16 @@ class GenericSubscriptionConnect(
         val sub = conn.subscribe(ChainRequest(topic, ListParams(getParams(params) as List<Any>)))
         return sub.data
             .flatMapMany { it.t2 }
+            // Some upstreams (notably Solana RPCs) silently stop delivering events on a subscription
+            // while keeping the WebSocket connection alive. Emit a TimeoutException so the surrounding
+            // DurableFlux re-invokes createConnection() and re-issues `subscribe` with a fresh subId.
             .timeout(
-                Duration.ofSeconds(85),
+                IDLE_TIMEOUT,
-                Mono.empty<ByteArray>().doOnEach {
+                Mono.error(
-                    log.warn("Timeout during subscription to $topic after 85 seconds")
+                    TimeoutException("No events from subscription to $topic in $IDLE_TIMEOUT, forcing resubscribe"),
-                },
+                ),
             )
-            .onErrorResume {
+            .doOnError { log.warn("Error during subscription to $topic: {}", it.message) }
-                log.error("Error during subscription to $topic", it)
-                Mono.empty()
-            }
             .doFinally {
                 if (unsubscribeMethod != "") {
                     conn.unsubscribe(

src/test/groovy/io/emeraldpay/dshackle/upstream/ethereum/subscribe/WebsocketPendingTxesSpec.groovy

@@ -22,10 +22,12 @@ import io.emeraldpay.dshackle.upstream.ethereum.WsSubscriptions
 import io.emeraldpay.dshackle.upstream.rpcclient.ListParams
 import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
+import reactor.test.StepVerifier
 import reactor.util.function.Tuples
 import spock.lang.Specification
 
 import java.time.Duration
+import java.util.concurrent.TimeoutException
 import java.util.concurrent.atomic.AtomicReference
 
 class WebsocketPendingTxesSpec extends Specification {
@@ -55,4 +57,26 @@ class WebsocketPendingTxesSpec extends Specification {
                 "0x67f22a3b441ea312306f97694ca8159f8d6faaccf0f5ce6442c84b13991f1d23",
         ]
     }
+
+    def "Emits TimeoutException when upstream goes silent past idle timeout"() {
+        // Pins the fix for the silent-stall bug: a healthy WS that simply stops delivering
+        // newPendingTransactions events must surface a TimeoutException so DurableFlux
+        // re-issues eth_subscribe.
+        setup:
+        def ws = Stub(WsSubscriptions) {
+            subscribe(new ChainRequest("eth_subscribe", new ListParams(["newPendingTransactions"]))) >> new WsSubscriptions.SubscribeData(
+                    Mono.just(Tuples.of("sub-1", Flux.never())), "conn-1", new AtomicReference<String>("sub-1")
+            )
+            unsubscribe(_) >> Mono.empty()
+        }
+        def pending = new WebsocketPendingTxes(Chain.ETHEREUM__MAINNET, ws)
+
+        expect:
+        StepVerifier.withVirtualTime { pending.createConnection() }
+                .expectSubscription()
+                .expectNoEvent(Duration.ofSeconds(84))
+                .thenAwait(Duration.ofSeconds(2))
+                .expectError(TimeoutException)
+                .verify(Duration.ofSeconds(5))
+    }
 }

src/test/kotlin/io/emeraldpay/dshackle/upstream/generic/GenericSubscriptionConnectTest.kt

@@ -6,13 +6,16 @@ import io.emeraldpay.dshackle.upstream.ethereum.WsSubscriptions
 import io.emeraldpay.dshackle.upstream.rpcclient.ListParams
 import org.junit.jupiter.api.Test
 import org.mockito.Mockito.verify
+import org.mockito.kotlin.any
 import org.mockito.kotlin.doReturn
 import org.mockito.kotlin.mock
+import org.mockito.kotlin.times
 import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
 import reactor.test.StepVerifier
 import reactor.util.function.Tuples
 import java.time.Duration
+import java.util.concurrent.TimeoutException
 import java.util.concurrent.atomic.AtomicReference
 
 class GenericSubscriptionConnectTest {
@@ -36,4 +39,70 @@ class GenericSubscriptionConnectTest {
 
         verify(ws).subscribe(ChainRequest(topic, ListParams(param)))
     }
+
+    @Test
+    fun `emits TimeoutException when upstream goes silent past idle timeout`() {
+        // Simulates the Solana-like failure: WS subscription is established, but upstream stops
+        // delivering events without closing the connection. The Flux must surface a TimeoutException
+        // so the surrounding DurableFlux re-subscribes.
+        val param: List<Any> = listOf("all")
+        val topic = "slotSubscribe"
+        val ws = mock<WsSubscriptions> {
+            on { subscribe(ChainRequest(topic, ListParams(param))) } doReturn
+                WsSubscriptions.SubscribeData(
+                    Mono.just(Tuples.of("sub-id-1", Flux.never<ByteArray>())),
+                    "conn-1",
+                    AtomicReference("sub-id-1"),
+                )
+        }
+
+        val genericSubscriptionConnect = GenericSubscriptionConnect(Chain.SOLANA__MAINNET, ws, topic, param, "")
+
+        StepVerifier.withVirtualTime { genericSubscriptionConnect.createConnection() }
+            .expectSubscription()
+            .expectNoEvent(Duration.ofSeconds(84))
+            .thenAwait(Duration.ofSeconds(2))
+            .expectError(TimeoutException::class.java)
+            .verify(Duration.ofSeconds(5))
+    }
+
+    @Test
+    fun `idle timeout triggers resubscribe via DurableFlux retry`() {
+        // End-to-end on the GenericSubscriptionConnect: when the first subscription stalls,
+        // DurableFlux must call createConnection() again, which issues a fresh `subscribe` RPC.
+        val param: List<Any> = listOf("all")
+        val topic = "slotSubscribe"
+
+        val secondAttempt = WsSubscriptions.SubscribeData(
+            Mono.just(Tuples.of("sub-id-2", Flux.just("recovered".toByteArray()))),
+            "conn-1",
+            AtomicReference("sub-id-2"),
+        )
+        val firstAttempt = WsSubscriptions.SubscribeData(
+            Mono.just(Tuples.of("sub-id-1", Flux.never<ByteArray>())),
+            "conn-1",
+            AtomicReference("sub-id-1"),
+        )
+
+        val ws = mock<WsSubscriptions> {
+            on { subscribe(ChainRequest(topic, ListParams(param))) }
+                .doReturn(firstAttempt, secondAttempt)
+            on { unsubscribe(any()) } doReturn Mono.empty()
+        }
+
+        val genericSubscriptionConnect = GenericSubscriptionConnect(Chain.SOLANA__MAINNET, ws, topic, param, "slotUnsubscribe")
+
+        // GenericPersistentConnect wraps createConnection() with DurableFlux + SharedFluxHolder.
+        // The first subscription stalls (Flux.never) → timeout (85s) → TimeoutException →
+        // DurableFlux schedules retry → second subscription delivers "recovered".
+        StepVerifier.withVirtualTime { genericSubscriptionConnect.connect(io.emeraldpay.dshackle.upstream.Selector.empty) }
+            .expectSubscription()
+            .thenAwait(Duration.ofSeconds(90))
+            .expectNextMatches { it is ByteArray && String(it) == "recovered" }
+            .thenCancel()
+            .verify(Duration.ofSeconds(5))
+
+        // Verifies we re-subscribed (= sent slotSubscribe again on the same WS).
+        verify(ws, times(2)).subscribe(ChainRequest(topic, ListParams(param)))
+    }
 }