implement adaptor for ethereum gas price

Author: Puneethkumarck

ethereum-app/src/main/java/com/blockchain/api/application/exception/GasPriceRetrievalException.java

@@ -0,0 +1,11 @@
+package com.blockchain.api.application.exception;
+
+public class GasPriceRetrievalException extends RuntimeException {
+  public GasPriceRetrievalException(String message, Throwable cause) {
+    super(message, cause);
+  }
+
+  public static GasPriceRetrievalException build(Throwable e) {
+    return new GasPriceRetrievalException("error while retrieving gas price", e);
+  }
+}

ethereum-app/src/main/java/com/blockchain/api/domain/service/transfer/TransferClient.java

@@ -7,4 +7,6 @@ public interface TransferClient {
   void transfer(TransferRequest transferRequest);
 
   CompletableFuture<BigInteger> getNonce(String address);
+
+  CompletableFuture<BigInteger> getGasPrice();
 }

ethereum-app/src/main/java/com/blockchain/api/infrastructure/client/transfer/TransferAdaptor.java

@@ -1,5 +1,6 @@
 package com.blockchain.api.infrastructure.client.transfer;
 
+import com.blockchain.api.application.exception.GasPriceRetrievalException;
 import com.blockchain.api.application.exception.NonceRetrievalException;
 import com.blockchain.api.domain.service.transfer.TransferClient;
 import com.blockchain.api.domain.service.transfer.TransferRequest;
@@ -39,4 +40,21 @@ public CompletableFuture<BigInteger> getNonce(String address) {
               throw NonceRetrievalException.withAddress(address);
             });
   }
+
+  @Override
+  public CompletableFuture<BigInteger> getGasPrice() {
+    return rpcClient
+        .ethGasPrice()
+        .sendAsync()
+        .thenApply(
+            gasPrice -> {
+              log.info("Gas price request completed successfully");
+              return gasPrice.getGasPrice();
+            })
+        .exceptionally(
+            throwable -> {
+              log.error("Error occurred while fetching gas price", throwable);
+              throw GasPriceRetrievalException.build(throwable);
+            });
+  }
 }

ethereum-app/src/test/java/com/blockchain/api/application/EthereumITest.java

@@ -3,6 +3,7 @@
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 import com.blockchain.api.domain.service.balance.BalanceClient;
+import com.blockchain.api.domain.service.transfer.TransferClient;
 import java.math.BigDecimal;
 import lombok.extern.slf4j.Slf4j;
 import org.junit.jupiter.api.Test;
@@ -17,6 +18,8 @@
 public class EthereumITest {
   @Autowired private BalanceClient balanceClient;
 
+  @Autowired private TransferClient transferClient;
+
   @Test
   void shouldReturnBalance() {
     // given
@@ -29,4 +32,14 @@ void shouldReturnBalance() {
     assertNotNull(result);
     log.info("Balance BigInteger: {}", Convert.fromWei(new BigDecimal(result), Convert.Unit.ETHER));
   }
+
+  @Test
+  void shouldGetGasPrice() {
+    // when
+    var result = transferClient.getGasPrice().join();
+
+    // then
+    assertNotNull(result);
+    log.info("original value {} Gas price: {}", result,Convert.fromWei(new BigDecimal(result), Convert.Unit.ETHER));
+  }
 }

ethereum-app/src/test/java/com/blockchain/api/infrastructure/client/transfer/TransferAdaptorTest.java

@@ -1,5 +1,6 @@
 package com.blockchain.api.infrastructure.client.transfer;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.*;
 import static org.mockito.ArgumentMatchers.eq;
@@ -18,6 +19,7 @@
 import org.web3j.protocol.Web3j;
 import org.web3j.protocol.core.DefaultBlockParameterName;
 import org.web3j.protocol.core.Request;
+import org.web3j.protocol.core.methods.response.EthGasPrice;
 import org.web3j.protocol.core.methods.response.EthGetTransactionCount;
 
 @ExtendWith(MockitoExtension.class)
@@ -72,4 +74,21 @@ void shouldThrowNonceRetrievalException_whenNonceRequestFails() {
 
     verify(rpcClient).ethGetTransactionCount(eq(address), eq(DefaultBlockParameterName.LATEST));
   }
+
+  @Test
+  void shouldRetrieveGasPrice() {
+    // given
+    when(rpcClient.ethGasPrice()).thenReturn(mock(Request.class));
+    var ethGasPrice = mock(EthGasPrice.class);
+    var gasPrice = BigInteger.valueOf(42);
+    when(ethGasPrice.getGasPrice()).thenReturn(gasPrice);
+    when(rpcClient.ethGasPrice().sendAsync())
+        .thenReturn(CompletableFuture.completedFuture(ethGasPrice));
+
+    // when
+    var result = transferAdaptor.getGasPrice();
+
+    // then
+    assertThat(result.join()).isEqualTo(gasPrice);
+  }
 }