Add Nacos Support (#5409)

Motivation:

Nacos is a service discovery application extensively used. By providing
native support for Nacos, it will be beneficial to Armeria users.

#5360 #5365


Modification:

- Add a `nacos` module.
- Add `NacosClient`. 
Its internal implementation includes `LoginClient` for obtaining an
accessToken through basic Nacos authentication, `QueryInstancesClient`
for querying service instances, and `RegisterInstanceClient` for
handling the registration and deregistration of instances.
- Implement `NacosEndpointGroup` and `NacosUpdatingListener`.
- Configure unit tests using Testcontainers and the Nacos image to
facilitate actual call testing.


Result:

Closes #5365

Nacos discovery and instance registration functionalities are now
integrated into Armeria.

---

In writing this code, I was strongly influenced by the implementation on
the consul and eureka modules.
I appreciate your review and feedback. Thank you.

---------

Co-authored-by: jrhee17 <guins_j@guins.org>
Co-authored-by: Ikhun Um <ikhun.um@linecorp.com>
Co-authored-by: minwoox <songmw725@gmail.com>

nacos/build.gradle.kts

@@ -0,0 +1,4 @@
+dependencies {
+    implementation(libs.caffeine)
+    testImplementation(libs.testcontainers.junit.jupiter)
+}

nacos/src/main/java/com/linecorp/armeria/client/nacos/NacosEndpointGroup.java

@@ -0,0 +1,133 @@
+/*
+ * Copyright 2024 LY Corporation
+ *
+ * LY Corporation licenses this file to you 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:
+ *
+ *   https://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.linecorp.armeria.client.nacos;
+
+import static java.util.Objects.requireNonNull;
+
+import java.net.URI;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.common.base.MoreObjects;
+
+import com.linecorp.armeria.client.Endpoint;
+import com.linecorp.armeria.client.endpoint.DynamicEndpointGroup;
+import com.linecorp.armeria.client.endpoint.EndpointGroup;
+import com.linecorp.armeria.client.endpoint.EndpointSelectionStrategy;
+import com.linecorp.armeria.common.CommonPools;
+import com.linecorp.armeria.common.annotation.Nullable;
+import com.linecorp.armeria.common.annotation.UnstableApi;
+import com.linecorp.armeria.internal.nacos.NacosClient;
+
+import io.netty.util.concurrent.EventExecutor;
+
+/**
+ * A Nacos-based {@link EndpointGroup} implementation that retrieves the list of {@link Endpoint} from Nacos
+ * using <a href="https://nacos.io/en-us/docs/v2/guide/user/open-api.html">Nacos's HTTP Open API</a>
+ * and updates the {@link Endpoint}s periodically.
+ */
+@UnstableApi
+public final class NacosEndpointGroup extends DynamicEndpointGroup {
+
+    private static final Logger logger = LoggerFactory.getLogger(NacosEndpointGroup.class);
+
+    /**
+     * Returns a {@link NacosEndpointGroup} with the specified {@code serviceName}.
+     */
+    public static NacosEndpointGroup of(URI nacosUri, String serviceName) {
+        return builder(nacosUri, serviceName).build();
+    }
+
+    /**
+     * Returns a newly-created {@link NacosEndpointGroupBuilder} with the specified {@code nacosUri}
+     * and {@code serviceName} to build {@link NacosEndpointGroupBuilder}.
+     *
+     * @param nacosUri the URI of Nacos API service, including the path up to but not including API version.
+     *                 (example: http://localhost:8848/nacos)
+     */
+    public static NacosEndpointGroupBuilder builder(URI nacosUri, String serviceName) {
+        return new NacosEndpointGroupBuilder(nacosUri, serviceName);
+    }
+
+    private final NacosClient nacosClient;
+
+    private final long registryFetchIntervalMillis;
+
+    private final EventExecutor eventLoop;
+
+    @Nullable
+    private ScheduledFuture<?> scheduledFuture;
+
+    NacosEndpointGroup(EndpointSelectionStrategy selectionStrategy, boolean allowEmptyEndpoints,
+                       long selectionTimeoutMillis, NacosClient nacosClient,
+                       long registryFetchIntervalMillis) {
+        super(selectionStrategy, allowEmptyEndpoints, selectionTimeoutMillis);
+        this.nacosClient = requireNonNull(nacosClient, "nacosClient");
+        this.registryFetchIntervalMillis = registryFetchIntervalMillis;
+        eventLoop = CommonPools.workerGroup().next();
+
+        update();
+    }
+
+    private void update() {
+        if (isClosing()) {
+            return;
+        }
+
+        nacosClient.endpoints()
+                   .handleAsync((endpoints, cause) -> {
+                       if (isClosing()) {
+                           return null;
+                       }
+
+                       if (cause != null) {
+                           logger.warn("Unexpected exception while fetching the registry from: {}",
+                                       nacosClient.uri(), cause);
+                       } else {
+                           setEndpoints(endpoints);
+                       }
+
+                       scheduledFuture = eventLoop.schedule(this::update, registryFetchIntervalMillis,
+                                                            TimeUnit.MILLISECONDS);
+                       return null;
+                   }, eventLoop);
+    }
+
+    @Override
+    protected void doCloseAsync(CompletableFuture<?> future) {
+        if (!eventLoop.inEventLoop()) {
+            eventLoop.execute(() -> doCloseAsync(future));
+            return;
+        }
+
+        if (scheduledFuture != null) {
+            scheduledFuture.cancel(true);
+        }
+
+        future.complete(null);
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(this)
+                          .add("registryFetchIntervalMillis", registryFetchIntervalMillis)
+                          .toString();
+    }
+}

nacos/src/main/java/com/linecorp/armeria/client/nacos/NacosEndpointGroupBuilder.java

@@ -0,0 +1,138 @@
+/*
+ * Copyright 2024 LY Corporation
+
+ * LY Corporation licenses this file to you 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:
+ *
+ *   https://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.linecorp.armeria.client.nacos;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.Objects.requireNonNull;
+
+import java.net.URI;
+import java.time.Duration;
+
+import com.linecorp.armeria.client.endpoint.AbstractDynamicEndpointGroupBuilder;
+import com.linecorp.armeria.client.endpoint.EndpointSelectionStrategy;
+import com.linecorp.armeria.common.Flags;
+import com.linecorp.armeria.common.annotation.UnstableApi;
+import com.linecorp.armeria.common.nacos.NacosConfigSetters;
+import com.linecorp.armeria.internal.nacos.NacosClient;
+import com.linecorp.armeria.internal.nacos.NacosClientBuilder;
+
+/**
+ * A builder class for {@link NacosEndpointGroup}.
+ * <h2>Examples</h2>
+ * <pre>{@code
+ * NacosEndpointGroup endpointGroup = NacosEndpointGroup.builder(nacosUri, "myService")
+ *                                                      .build();
+ * WebClient client = WebClient.of(SessionProtocol.HTTPS, endpointGroup);
+ * }</pre>
+ */
+@UnstableApi
+public final class NacosEndpointGroupBuilder
+        extends AbstractDynamicEndpointGroupBuilder<NacosEndpointGroupBuilder>
+        implements NacosConfigSetters<NacosEndpointGroupBuilder> {
+
+    private static final long DEFAULT_CHECK_INTERVAL_MILLIS = 10_000;
+
+    private final NacosClientBuilder nacosClientBuilder;
+    private EndpointSelectionStrategy selectionStrategy = EndpointSelectionStrategy.weightedRoundRobin();
+    private long registryFetchIntervalMillis = DEFAULT_CHECK_INTERVAL_MILLIS;
+
+    NacosEndpointGroupBuilder(URI nacosUri, String serviceName) {
+        super(Flags.defaultResponseTimeoutMillis());
+        nacosClientBuilder = NacosClient.builder(nacosUri, requireNonNull(serviceName, "serviceName"));
+    }
+
+    /**
+     * Sets the {@link EndpointSelectionStrategy} of the {@link NacosEndpointGroup}.
+     */
+    public NacosEndpointGroupBuilder selectionStrategy(EndpointSelectionStrategy selectionStrategy) {
+        this.selectionStrategy = requireNonNull(selectionStrategy, "selectionStrategy");
+        return this;
+    }
+
+    @Override
+    public NacosEndpointGroupBuilder namespaceId(String namespaceId) {
+        nacosClientBuilder.namespaceId(namespaceId);
+        return this;
+    }
+
+    @Override
+    public NacosEndpointGroupBuilder groupName(String groupName) {
+        nacosClientBuilder.groupName(groupName);
+        return this;
+    }
+
+    @Override
+    public NacosEndpointGroupBuilder clusterName(String clusterName) {
+        nacosClientBuilder.clusterName(clusterName);
+        return this;
+    }
+
+    @Override
+    public NacosEndpointGroupBuilder app(String app) {
+        nacosClientBuilder.app(app);
+        return this;
+    }
+
+    @Override
+    public NacosEndpointGroupBuilder nacosApiVersion(String nacosApiVersion) {
+        nacosClientBuilder.nacosApiVersion(nacosApiVersion);
+        return this;
+    }
+
+    @Override
+    public NacosEndpointGroupBuilder authorization(String username, String password) {
+        nacosClientBuilder.authorization(username, password);
+        return this;
+    }
+
+    /**
+     * Sets the healthy to retrieve only healthy instances from Nacos.
+     * Make sure that your target endpoints are health-checked by Nacos before enabling this feature.
+     * If not set, false is used by default.
+     */
+    public NacosEndpointGroupBuilder useHealthyEndpoints(boolean useHealthyEndpoints) {
+        nacosClientBuilder.healthyOnly(useHealthyEndpoints);
+        return this;
+    }
+
+    /**
+     * Sets the interval between fetching registry requests.
+     * If not set, {@value #DEFAULT_CHECK_INTERVAL_MILLIS} milliseconds is used by default.
+     */
+    public NacosEndpointGroupBuilder registryFetchInterval(Duration registryFetchInterval) {
+        requireNonNull(registryFetchInterval, "registryFetchInterval");
+        return registryFetchIntervalMillis(registryFetchInterval.toMillis());
+    }
+
+    /**
+     * Sets the interval between fetching registry requests.
+     * If not set, {@value #DEFAULT_CHECK_INTERVAL_MILLIS} milliseconds is used by default.
+     */
+    public NacosEndpointGroupBuilder registryFetchIntervalMillis(long registryFetchIntervalMillis) {
+        checkArgument(registryFetchIntervalMillis > 0, "registryFetchIntervalMillis: %s (expected: > 0)",
+                      registryFetchIntervalMillis);
+        this.registryFetchIntervalMillis = registryFetchIntervalMillis;
+        return this;
+    }
+
+    /**
+     * Returns a newly-created {@link NacosEndpointGroup}.
+     */
+    public NacosEndpointGroup build() {
+        return new NacosEndpointGroup(selectionStrategy, shouldAllowEmptyEndpoints(), selectionTimeoutMillis(),
+                                      nacosClientBuilder.build(), registryFetchIntervalMillis);
+    }
+}

nacos/src/main/java/com/linecorp/armeria/client/nacos/package-info.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2024 LY Corporation
+
+ * LY Corporation licenses this file to you 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:
+ *
+ *   https://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.
+ */
+
+/**
+ * Nacos-based {@link com.linecorp.armeria.client.endpoint.EndpointGroup} implementation.
+ */
+@NonNullByDefault
+@UnstableApi
+package com.linecorp.armeria.client.nacos;
+
+import com.linecorp.armeria.common.annotation.NonNullByDefault;
+import com.linecorp.armeria.common.annotation.UnstableApi;

nacos/src/main/java/com/linecorp/armeria/common/nacos/NacosConfigSetters.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2024 LY Corporation
+ *
+ * LY Corporation licenses this file to you 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:
+ *
+ *   https://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.linecorp.armeria.common.nacos;
+
+import com.linecorp.armeria.common.annotation.UnstableApi;
+import com.linecorp.armeria.internal.nacos.NacosClientBuilder;
+
+/**
+ * Sets properties for building a Nacos client.
+ */
+@UnstableApi
+public interface NacosConfigSetters<SELF extends NacosConfigSetters<SELF>> {
+
+    /**
+     * Sets the namespace ID to query or register instances.
+     */
+    SELF namespaceId(String namespaceId);
+
+    /**
+     * Sets the group name to query or register instances.
+     */
+    SELF groupName(String groupName);
+
+    /**
+     * Sets the cluster name to query or register instances.
+     */
+    SELF clusterName(String clusterName);
+
+    /**
+     * Sets the app name to query or register instances.
+     */
+    SELF app(String app);
+
+    /**
+     * Sets the specified Nacos's API version.
+     * @param nacosApiVersion the version of Nacos API service, default: {@value
+     *                         NacosClientBuilder#DEFAULT_NACOS_API_VERSION}
+     */
+    SELF nacosApiVersion(String nacosApiVersion);
+
+    /**
+     * Sets the username and password pair for Nacos's API.
+     * Please refer to the
+     * <a href=https://nacos.io/en-us/docs/v2/guide/user/auth.html>Nacos Authentication Document</a>
+     * for more details.
+     *
+     * @param username the username for access Nacos API, default: {@code null}
+     * @param password the password for access Nacos API, default: {@code null}
+     */
+    SELF authorization(String username, String password);
+}

nacos/src/main/java/com/linecorp/armeria/common/nacos/package-info.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2024 LY Corporation
+
+ * LY Corporation licenses this file to you 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:
+ *
+ *   https://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.
+ */
+
+/**
+ * Various classes used internally. Anything in this package can be changed or removed at any time.
+ */
+@NonNullByDefault
+@UnstableApi
+package com.linecorp.armeria.common.nacos;
+
+import com.linecorp.armeria.common.annotation.NonNullByDefault;
+import com.linecorp.armeria.common.annotation.UnstableApi;