fix: replace WebSocket listener mechanism with a slower polling mechanism

src/main/java/com/iexec/core/chain/BlockchainListener.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2025-2026 IEXEC BLOCKCHAIN TECH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.iexec.core.chain;
+
+import com.iexec.core.chain.event.LatestBlockEvent;
+import io.micrometer.core.instrument.Metrics;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.scheduling.annotation.Scheduled;
+import org.springframework.stereotype.Service;
+import org.web3j.protocol.Web3j;
+import org.web3j.protocol.core.DefaultBlockParameterName;
+import org.web3j.protocol.core.methods.response.EthBlock;
+import org.web3j.protocol.exceptions.JsonRpcError;
+import org.web3j.protocol.http.HttpService;
+import org.web3j.utils.Async;
+
+import java.time.Instant;
+import java.util.concurrent.atomic.AtomicLong;
+
+@Slf4j
+@Service
+public class BlockchainListener {
+    static final String LATEST_BLOCK_METRIC_NAME = "iexec.chain.block.latest";
+
+    private final ApplicationEventPublisher applicationEventPublisher;
+    private final Web3j web3Client;
+    private final AtomicLong lastSeenBlock;
+
+    public BlockchainListener(final ApplicationEventPublisher applicationEventPublisher,
+                              final ChainConfig chainConfig) {
+        this.applicationEventPublisher = applicationEventPublisher;
+        this.web3Client = Web3j.build(new HttpService(chainConfig.getNodeAddress()),
+                chainConfig.getBlockTime().toMillis(), Async.defaultExecutorService());
+        lastSeenBlock = Metrics.gauge(LATEST_BLOCK_METRIC_NAME, new AtomicLong(0));
+    }
+
+    @Scheduled(fixedRate = 5000)
+    private void run() {
+        try {
+            final EthBlock ethBlock = web3Client.ethGetBlockByNumber(DefaultBlockParameterName.LATEST, false).send();
+            if (ethBlock.hasError()) {
+                throw new JsonRpcError(ethBlock.getError());
+            }
+            final long blockNumber = ethBlock.getBlock().getNumber().longValue();
+            final long lastSeenBlockNumber = lastSeenBlock.get();
+            if (blockNumber > lastSeenBlockNumber) {
+                final String blockHash = ethBlock.getBlock().getHash();
+                final long blockTimestamp = ethBlock.getBlock().getTimestamp().longValue();
+                final Instant blockTimestampInstant = Instant.ofEpochSecond(blockTimestamp);
+                log.info("Last seen block [number:{}, hash:{}, timestamp:{}, instant:{}]",
+                        blockNumber, blockHash, blockTimestamp, blockTimestampInstant);
+                lastSeenBlock.set(blockNumber);
+                applicationEventPublisher.publishEvent(new LatestBlockEvent(this, blockNumber, blockHash, blockTimestamp));
+            }
+        } catch (Exception e) {
+            log.error("An error happened while fetching data on-chain", e);
+        }
+    }
+}

src/main/resources/application.yml

@@ -52,7 +52,7 @@ wallet:
 
 chain:
   node-address: ${IEXEC_BLOCKCHAIN_NODE_ADDRESS:http://localhost:8545}
-  out-of-service-threshold: PT5S
+  out-of-service-threshold: PT15S
   pool-address: ${POOL_ADDRESS:0x365E7BABAa85eC61Dffe5b520763062e6C29dA27}
   start-block-number: ${IEXEC_START_BLOCK_NUMBER:0}
   gas-price-multiplier: ${IEXEC_GAS_PRICE_MULTIPLIER:1.0} # txs will be sent with networkGasPrice*gasPriceMultiplier, 4.0 means super fast

src/test/java/com/iexec/core/chain/WebSocketBlockchainListenerTests.java → src/test/java/com/iexec/core/chain/BlockchainListenerTests.java

@@ -33,13 +33,13 @@
 import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
-import static com.iexec.core.chain.WebSocketBlockchainListener.LATEST_BLOCK_METRIC_NAME;
+import static com.iexec.core.chain.BlockchainListener.LATEST_BLOCK_METRIC_NAME;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.awaitility.Awaitility.await;
 
 @Testcontainers
 @SpringBootTest(properties = "chain.out-of-service-threshold=PT30S")
-class WebSocketBlockchainListenerTests {
+class BlockchainListenerTests {
     private static final String CHAIN_SVC_NAME = "chain";
     private static final int CHAIN_SVC_PORT = 8545;
     private static final String CONFIG_SVC_NAME = "config-server";