And nullable/nonnullable annotation to improve Kotlin API

centrifuge/build.gradle

@@ -26,6 +26,7 @@ dependencies {
     implementation 'com.squareup.okhttp3:okhttp:4.10.0'
     implementation 'com.google.protobuf:protobuf-javalite:3.21.12'
     implementation 'net.sourceforge.streamsupport:streamsupport-cfuture:1.7.0'
+    compileOnly 'com.google.code.findbugs:jsr305:3.0.2'
 
     testImplementation 'junit:junit:4.13.2'
 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/Client.java

@@ -17,6 +17,8 @@
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 
+import javax.annotation.Nullable;
+
 import io.github.centrifugal.centrifuge.internal.backoff.Backoff;
 import io.github.centrifugal.centrifuge.internal.protocol.Protocol;
 
@@ -352,7 +354,7 @@ public void onClosed(WebSocket webSocket, int code, String reason) {
             }
 
             @Override
-            public void onFailure(WebSocket webSocket, Throwable t, Response response) {
+            public void onFailure(WebSocket webSocket, Throwable t, @Nullable Response response) {
                 super.onFailure(webSocket, t, response);
                 try {
                     Client.this.executor.submit(() -> {
@@ -770,7 +772,7 @@ private void sendRefresh() {
                     }
                     return;
                 }
-                if (result.getExpires()) {
+                if (result != null && result.getExpires()) {
                     int ttl = result.getTtl();
                     Client.this.refreshTask = Client.this.scheduler.schedule(Client.this::sendRefresh, ttl, TimeUnit.SECONDS);
                 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/CompletionCallback.java

@@ -1,8 +1,10 @@
 package io.github.centrifugal.centrifuge;
 
+import javax.annotation.Nullable;
+
 public interface CompletionCallback {
     /**
      * Called when operation done. Caller must check possible error (it's null in case of success).
      */
-    void onDone(Throwable e);
+    void onDone(@Nullable Throwable e);
 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/Dns.java

@@ -4,11 +4,14 @@
 import java.net.UnknownHostException;
 import java.util.List;
 
+import javax.annotation.Nonnull;
+
 /**
  * Represents DNS client used to resolve addresses of a host.
  */
 public interface Dns {
 
+    @Nonnull
     List<InetAddress> resolve(String host) throws UnknownHostException;
 
 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/RefreshError.java

@@ -1,5 +1,7 @@
 package io.github.centrifugal.centrifuge;
 
+import javax.annotation.Nullable;
+
 public class RefreshError extends Throwable {
     private final Throwable error;
 
@@ -8,7 +10,7 @@ public class RefreshError extends Throwable {
         this.error = error;
     }
 
-    public Throwable getError() {
+    public @Nullable Throwable getError() {
         return error;
     }
 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/ResultCallback.java

@@ -1,8 +1,10 @@
 package io.github.centrifugal.centrifuge;
 
+import javax.annotation.Nullable;
+
 public interface ResultCallback<T> {
     /**
      * onDone will be called when the operation completed. Either Throwable or T will be not null.
      */    
-    void onDone(Throwable e, T result);
+    void onDone(@Nullable Throwable e, @Nullable T result);
 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/ServerSubscribedEvent.java

@@ -1,7 +1,9 @@
 package io.github.centrifugal.centrifuge;
 
+import javax.annotation.Nullable;
+
 public class ServerSubscribedEvent {
-    ServerSubscribedEvent(String channel, Boolean wasRecovering, Boolean recovered, Boolean positioned, Boolean recoverable, StreamPosition streamPosition, byte[] data) {
+    ServerSubscribedEvent(String channel, Boolean wasRecovering, Boolean recovered, Boolean positioned, Boolean recoverable, @Nullable StreamPosition streamPosition, @Nullable byte[] data) {
         this.channel = channel;
         this.wasRecovering = wasRecovering;
         this.recovered = recovered;

centrifuge/src/main/java/io/github/centrifugal/centrifuge/SubscribedEvent.java

@@ -1,7 +1,9 @@
 package io.github.centrifugal.centrifuge;
 
+import javax.annotation.Nullable;
+
 public class SubscribedEvent {
-    SubscribedEvent(Boolean wasRecovering, Boolean recovered, Boolean positioned, Boolean recoverable, StreamPosition streamPosition, byte[] data) {
+    SubscribedEvent(Boolean wasRecovering, Boolean recovered, Boolean positioned, Boolean recoverable, @Nullable StreamPosition streamPosition, @Nullable byte[] data) {
         this.wasRecovering = wasRecovering;
         this.recovered = recovered;
         this.data = data;

centrifuge/src/main/java/io/github/centrifugal/centrifuge/TokenCallback.java

@@ -1,6 +1,8 @@
 package io.github.centrifugal.centrifuge;
 
+import javax.annotation.Nullable;
+
 public interface TokenCallback {
     /* Call this with exception or token. If called with null error and empty token then client considers access unauthorized */
-    void Done(Throwable e, String token);
+    void Done(@Nullable Throwable e, @Nullable String token);
 }

centrifuge/src/main/java/io/github/centrifugal/centrifuge/package-info.java

@@ -0,0 +1,8 @@
+/**
+ * File: package-info.java
+ * Make all method parameters @NonNull by default
+ */
+@ParametersAreNonnullByDefault
+package io.github.centrifugal.centrifuge;
+
+import javax.annotation.ParametersAreNonnullByDefault;

demo/build.gradle

@@ -34,6 +34,7 @@ dependencies {
     implementation project(':centrifuge')
     implementation 'com.android.support:appcompat-v7:27.1.1'
     implementation 'com.android.support.constraint:constraint-layout:1.1.3'
+    compileOnly 'com.google.code.findbugs:jsr305:3.0.2'
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'com.android.support.test:runner:1.0.2'
     androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

demo/src/main/java/io/github/centrifugal/centrifuge/demo/MainActivity.java

@@ -2,6 +2,7 @@
 
 import android.annotation.SuppressLint;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 import android.widget.TextView;
 import android.widget.Toast;
@@ -26,13 +27,16 @@
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 
+import javax.annotation.ParametersAreNonnullByDefault;
+
+@ParametersAreNonnullByDefault
 public class MainActivity extends AppCompatActivity {
 
     private Client client;
     private boolean activityPaused;
 
     @Override
-    protected void onCreate(Bundle savedInstanceState) {
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         TextView tv = findViewById(R.id.text);

example/build.gradle

@@ -6,4 +6,5 @@ dependencies {
     implementation project(':centrifuge')
     implementation 'ch.qos.logback:logback-classic:1.0.1'
     implementation 'ch.qos.logback:logback-core:1.0.1'
+    compileOnly 'com.google.code.findbugs:jsr305:3.0.2'
 }

example/src/main/java/io/github/centrifugal/centrifuge/example/Main.java

@@ -1,10 +1,7 @@
 package io.github.centrifugal.centrifuge.example;
 
 import io.github.centrifugal.centrifuge.Client;
-import io.github.centrifugal.centrifuge.ClientState;
 import io.github.centrifugal.centrifuge.ConnectingEvent;
-import io.github.centrifugal.centrifuge.ConnectionTokenEvent;
-import io.github.centrifugal.centrifuge.ConnectionTokenGetter;
 import io.github.centrifugal.centrifuge.DuplicateSubscriptionException;
 import io.github.centrifugal.centrifuge.HistoryOptions;
 import io.github.centrifugal.centrifuge.JoinEvent;
@@ -28,14 +25,16 @@
 import io.github.centrifugal.centrifuge.SubscriptionErrorEvent;
 import io.github.centrifugal.centrifuge.SubscribedEvent;
 import io.github.centrifugal.centrifuge.SubscriptionOptions;
-import io.github.centrifugal.centrifuge.TokenCallback;
 import io.github.centrifugal.centrifuge.UnsubscribedEvent;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 
+import javax.annotation.ParametersAreNonnullByDefault;
+
+@ParametersAreNonnullByDefault
 public class Main {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(Main.class);
@@ -182,15 +181,15 @@ public void onLeave(Subscription sub, LeaveEvent event) {
         });
 
         sub.presenceStats((err, res) -> {
-            if (err != null) {
+            if (res == null || err != null) {
                 System.out.println("error presence stats: " + err);
                 return;
             }
             System.out.println("Num clients connected: " + res.getNumClients());
         });
 
         sub.history(new HistoryOptions.Builder().withLimit(-1).build(), (err, res) -> {
-            if (err != null) {
+            if (res == null || err != null) {
                 System.out.println("error history: " + err);
                 return;
             }