Fixed some Android compatibility issues

sdk/build.gradle

@@ -47,6 +47,11 @@ dependencies {
     implementation 'javax.annotation:javax.annotation-api:1.3.2'
     implementation 'com.esaulpaugh:headlong:10.0.0'
 
+    // NOTE: This is to support Android API <= 30.
+    // https://github.com/stefan-zobel/streamsupport
+    // https://developer.android.com/about/dashboards/index.html
+    api "net.sourceforge.streamsupport:streamsupport-cfuture:1.7.4"
+
     testImplementation "org.assertj:assertj-core:3.24.2"
     testImplementation "io.github.json-snapshot:json-snapshot:1.0.17"
     testImplementation "org.junit.jupiter:junit-jupiter-engine:5.10.0"

sdk/src/main/java/com/hedera/hashgraph/sdk/AccountInfoFlow.java

@@ -19,7 +19,7 @@
  */
 package com.hedera.hashgraph.sdk;
 
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeoutException;
 
 /**

sdk/src/main/java/com/hedera/hashgraph/sdk/AccountInfoQuery.java

@@ -25,7 +25,7 @@
 import com.hedera.hashgraph.sdk.proto.Response;
 import com.hedera.hashgraph.sdk.proto.ResponseHeader;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Objects;

sdk/src/main/java/com/hedera/hashgraph/sdk/AddressBookQuery.java

@@ -32,7 +32,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Nonnegative;
 import javax.annotation.Nullable;

sdk/src/main/java/com/hedera/hashgraph/sdk/BaseNode.java

@@ -30,7 +30,7 @@
 import java.time.Duration;
 import java.time.Instant;
 import java.util.Objects;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Nullable;

sdk/src/main/java/com/hedera/hashgraph/sdk/ChunkedTransaction.java

@@ -26,11 +26,11 @@
 import com.hedera.hashgraph.sdk.proto.SignedTransaction;
 import com.hedera.hashgraph.sdk.proto.TransactionBody;
 import com.hedera.hashgraph.sdk.proto.TransactionID;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.CompletionStage;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
-import java.util.function.Function;
+import java8.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletionStage;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
+import java8.util.function.Function;
 import java.time.Duration;
 
 import javax.annotation.Nullable;

sdk/src/main/java/com/hedera/hashgraph/sdk/Client.java

@@ -37,11 +37,14 @@
 import java.nio.file.Files;
 import java.time.Duration;
 import java.time.Instant;
+import java8.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletionStage;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
+import java8.util.function.Function;
 import java.util.*;
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
 import java.util.function.Supplier;
 import java.util.function.UnaryOperator;
 
@@ -735,7 +738,7 @@ public synchronized Client setOperator(AccountId accountId, PrivateKey privateKe
      * @return {@code this}
      */
     public synchronized Client setOperatorWith(AccountId accountId, PublicKey publicKey,
-                                               UnaryOperator<byte[]> transactionSigner) {
+        Function<byte[], byte[]> transactionSigner) {
         if (getNetworkName() != null) {
             try {
                 accountId.validateChecksum(this);
@@ -1385,9 +1388,9 @@ public synchronized void close(Duration timeout) throws TimeoutException {
     static class Operator {
         final AccountId accountId;
         final PublicKey publicKey;
-        final UnaryOperator<byte[]> transactionSigner;
+        final Function<byte[], byte[]> transactionSigner;
 
-        Operator(AccountId accountId, PublicKey publicKey, UnaryOperator<byte[]> transactionSigner) {
+        Operator(AccountId accountId, PublicKey publicKey, Function<byte[], byte[]> transactionSigner) {
             this.accountId = accountId;
             this.publicKey = publicKey;
             this.transactionSigner = transactionSigner;

sdk/src/main/java/com/hedera/hashgraph/sdk/ConsumerHelper.java

@@ -1,9 +1,9 @@
 package com.hedera.hashgraph.sdk;
 
 
-import java.util.concurrent.CompletableFuture;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
+import java8.util.concurrent.CompletableFuture;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
 
 
 class ConsumerHelper {

sdk/src/main/java/com/hedera/hashgraph/sdk/ContractCallQuery.java

@@ -26,7 +26,7 @@
 import com.hedera.hashgraph.sdk.proto.ResponseHeader;
 import com.hedera.hashgraph.sdk.proto.SmartContractServiceGrpc;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Arrays;

sdk/src/main/java/com/hedera/hashgraph/sdk/ContractCreateFlow.java

@@ -27,11 +27,11 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeoutException;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
-import java.util.function.UnaryOperator;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
+import java8.util.function.Function;
 import javax.annotation.Nullable;
 import org.bouncycastle.util.encoders.Hex;
 
@@ -120,7 +120,7 @@ public class ContractCreateFlow {
     private PublicKey signPublicKey = null;
 
     @Nullable
-    private UnaryOperator<byte[]> transactionSigner = null;
+    private Function<byte[], byte[]> transactionSigner = null;
 
     /**
      * Constructor
@@ -544,7 +544,7 @@ public ContractCreateFlow sign(PrivateKey privateKey) {
      * @param transactionSigner the key list
      * @return {@code this}
      */
-    public ContractCreateFlow signWith(PublicKey publicKey, UnaryOperator<byte[]> transactionSigner) {
+    public ContractCreateFlow signWith(PublicKey publicKey, Function<byte[], byte[]> transactionSigner) {
         this.signPublicKey = publicKey;
         this.transactionSigner = transactionSigner;
         this.signPrivateKey = null;

sdk/src/main/java/com/hedera/hashgraph/sdk/ContractInfoQuery.java

@@ -25,7 +25,7 @@
 import com.hedera.hashgraph.sdk.proto.ResponseHeader;
 import com.hedera.hashgraph.sdk.proto.SmartContractServiceGrpc;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Objects;

sdk/src/main/java/com/hedera/hashgraph/sdk/Delayer.java

@@ -19,9 +19,7 @@
  */
 package com.hedera.hashgraph.sdk;
 
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.Executors;
-import java.util.concurrent.ScheduledExecutorService;
+import java8.util.concurrent.CompletableFuture;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import java.time.Duration;
@@ -35,12 +33,6 @@
 final class Delayer {
     private static final Logger logger = LoggerFactory.getLogger(Delayer.class);
 
-    private static final ScheduledExecutorService SCHEDULER = Executors.newSingleThreadScheduledExecutor(r -> {
-        Thread t = new Thread(r);
-        t.setDaemon(true);
-        return t;
-    });
-
     private static final Duration MIN_DELAY = Duration.ofMillis(500);
 
     /**
@@ -75,10 +67,6 @@ static CompletableFuture<Void> delayFor(long milliseconds, Executor executor) {
         return CompletableFuture.runAsync(
             () -> {
             },
-            delayedExecutor(milliseconds, TimeUnit.MILLISECONDS, executor));
-    }
-
-    private static Executor delayedExecutor(long delay, TimeUnit unit, Executor executor) {
-        return r -> SCHEDULER.schedule(() -> executor.execute(r), delay, unit);
+            CompletableFuture.delayedExecutor(milliseconds, TimeUnit.MILLISECONDS, executor));
     }
 }

sdk/src/main/java/com/hedera/hashgraph/sdk/EthereumFlow.java

@@ -3,10 +3,10 @@
 import javax.annotation.Nullable;
 import java.time.Duration;
 import java.util.Arrays;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeoutException;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
 
 /**
  * Execute an Ethereum transaction on Hedera

sdk/src/main/java/com/hedera/hashgraph/sdk/Executable.java

@@ -37,12 +37,12 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.Random;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.function.UnaryOperator;

sdk/src/main/java/com/hedera/hashgraph/sdk/FileContentsQuery.java

@@ -26,7 +26,7 @@
 import com.hedera.hashgraph.sdk.proto.Response;
 import com.hedera.hashgraph.sdk.proto.ResponseHeader;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Objects;

sdk/src/main/java/com/hedera/hashgraph/sdk/FileInfoQuery.java

@@ -25,7 +25,7 @@
 import com.hedera.hashgraph.sdk.proto.Response;
 import com.hedera.hashgraph.sdk.proto.ResponseHeader;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Objects;

sdk/src/main/java/com/hedera/hashgraph/sdk/Query.java

@@ -28,9 +28,9 @@
 import com.hedera.hashgraph.sdk.proto.Transaction;
 import com.hedera.hashgraph.sdk.proto.TransactionBody;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
+import java8.util.concurrent.CompletableFuture;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
 import java.time.Duration;
 import java.time.Instant;
 

sdk/src/main/java/com/hedera/hashgraph/sdk/ScheduleInfoQuery.java

@@ -26,7 +26,7 @@
 import com.hedera.hashgraph.sdk.proto.ScheduleGetInfoQuery;
 import com.hedera.hashgraph.sdk.proto.ScheduleServiceGrpc;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Objects;

sdk/src/main/java/com/hedera/hashgraph/sdk/SystemDeleteTransaction.java

@@ -28,7 +28,7 @@
 import com.hedera.hashgraph.sdk.proto.TransactionResponse;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.time.Instant;
 
 import javax.annotation.Nullable;

sdk/src/main/java/com/hedera/hashgraph/sdk/SystemUndeleteTransaction.java

@@ -27,7 +27,7 @@
 import com.hedera.hashgraph.sdk.proto.TransactionBody;
 import com.hedera.hashgraph.sdk.proto.TransactionResponse;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.LinkedHashMap;

sdk/src/main/java/com/hedera/hashgraph/sdk/TokenInfoQuery.java

@@ -26,7 +26,7 @@
 import com.hedera.hashgraph.sdk.proto.TokenGetInfoQuery;
 import com.hedera.hashgraph.sdk.proto.TokenServiceGrpc;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 import java.util.Objects;

sdk/src/main/java/com/hedera/hashgraph/sdk/TokenNftInfoQuery.java

@@ -26,7 +26,7 @@
 import com.hedera.hashgraph.sdk.proto.TokenGetNftInfoQuery;
 import com.hedera.hashgraph.sdk.proto.TokenServiceGrpc;
 import io.grpc.MethodDescriptor;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nonnegative;
 import javax.annotation.Nullable;

sdk/src/main/java/com/hedera/hashgraph/sdk/Transaction.java

@@ -40,8 +40,8 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.concurrent.CompletableFuture;
-import java.util.function.Function;
+import java8.util.concurrent.CompletableFuture;
+import java8.util.function.Function;
 import java.util.function.UnaryOperator;
 import javax.annotation.Nullable;
 import org.bouncycastle.crypto.digests.SHA384Digest;
@@ -834,7 +834,7 @@ public final T sign(PrivateKey privateKey) {
      * @param transactionSigner the key list
      * @return {@code this}
      */
-    public T signWith(PublicKey publicKey, UnaryOperator<byte[]> transactionSigner) {
+    public T signWith(PublicKey publicKey, Function<byte[], byte[]> transactionSigner) {
         if (!isFrozen()) {
             throw new IllegalStateException("Signing requires transaction to be frozen");
         }

sdk/src/main/java/com/hedera/hashgraph/sdk/TransactionId.java

@@ -19,20 +19,20 @@
  */
 package com.hedera.hashgraph.sdk;
 
-import static java.util.concurrent.CompletableFuture.completedFuture;
-import static java.util.concurrent.CompletableFuture.failedFuture;
+import static java8.util.concurrent.CompletableFuture.completedFuture;
+import static java8.util.concurrent.CompletableFuture.failedFuture;
 
 import com.google.errorprone.annotations.Var;
 import com.google.protobuf.InvalidProtocolBufferException;
 import com.hedera.hashgraph.sdk.proto.TransactionID;
 import java.time.Duration;
 import java.time.Instant;
 import java.util.Objects;
-import java.util.concurrent.CompletableFuture;
+import java8.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicLong;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
 import javax.annotation.Nullable;
 
 /**

sdk/src/main/java/com/hedera/hashgraph/sdk/TransactionResponse.java

@@ -20,9 +20,9 @@
 package com.hedera.hashgraph.sdk;
 
 import com.google.common.base.MoreObjects;
-import java.util.concurrent.CompletableFuture;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
+import java8.util.concurrent.CompletableFuture;
+import java8.util.function.BiConsumer;
+import java8.util.function.Consumer;
 import org.bouncycastle.util.encoders.Hex;
 import java.time.Duration;