feat: add promote member support.

jetcd-core/src/main/java/io/etcd/jetcd/Cluster.java

@@ -22,6 +22,7 @@
 
 import io.etcd.jetcd.cluster.MemberAddResponse;
 import io.etcd.jetcd.cluster.MemberListResponse;
+import io.etcd.jetcd.cluster.MemberPromoteResponse;
 import io.etcd.jetcd.cluster.MemberRemoveResponse;
 import io.etcd.jetcd.cluster.MemberUpdateResponse;
 import io.etcd.jetcd.support.CloseableClient;
@@ -72,4 +73,11 @@ public interface Cluster extends CloseableClient {
      */
     CompletableFuture<MemberUpdateResponse> updateMember(long memberID, List<URI> peerAddrs);
 
+    /**
+     * Promotes a member from raft learner (non-voting) to raft voting member.
+     *
+     * @param  memberID the raft learner to be promoted to a raft voting member.
+     * @return          the response
+     */
+    CompletableFuture<MemberPromoteResponse> promoteMember(long memberID);
 }

jetcd-core/src/main/java/io/etcd/jetcd/cluster/MemberPromoteResponse.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2025 The jetcd authors
+ *
+ * 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 io.etcd.jetcd.cluster;
+
+import java.util.List;
+
+import io.etcd.jetcd.Cluster;
+import io.etcd.jetcd.impl.AbstractResponse;
+
+/**
+ * MemberPromoteResponse returned by {@link Cluster#promoteMember(long)}
+ * contains a header and a list of members after the member update.
+ */
+public class MemberPromoteResponse extends AbstractResponse<io.etcd.jetcd.api.MemberPromoteResponse> {
+
+    private List<Member> members;
+
+    public MemberPromoteResponse(io.etcd.jetcd.api.MemberPromoteResponse response) {
+        super(response, response.getHeader());
+    }
+
+    /**
+     * Return a list of all members after promoting the member.
+     *
+     * @return the list of members.
+     */
+    public synchronized List<Member> getMembers() {
+        if (members == null) {
+            members = Util.toMembers(getResponse().getMembersList());
+        }
+
+        return members;
+    }
+}

jetcd-core/src/main/java/io/etcd/jetcd/impl/ClusterImpl.java

@@ -24,11 +24,13 @@
 import io.etcd.jetcd.Cluster;
 import io.etcd.jetcd.api.MemberAddRequest;
 import io.etcd.jetcd.api.MemberListRequest;
+import io.etcd.jetcd.api.MemberPromoteRequest;
 import io.etcd.jetcd.api.MemberRemoveRequest;
 import io.etcd.jetcd.api.MemberUpdateRequest;
 import io.etcd.jetcd.api.VertxClusterGrpc;
 import io.etcd.jetcd.cluster.MemberAddResponse;
 import io.etcd.jetcd.cluster.MemberListResponse;
+import io.etcd.jetcd.cluster.MemberPromoteResponse;
 import io.etcd.jetcd.cluster.MemberRemoveResponse;
 import io.etcd.jetcd.cluster.MemberUpdateResponse;
 
@@ -116,4 +118,22 @@ public CompletableFuture<MemberUpdateResponse> updateMember(long memberID, List<
             this.stub.memberUpdate(memberUpdateRequest),
             MemberUpdateResponse::new);
     }
+
+    /**
+     * Promotes a member from raft learner (non-voting) to raft voting member.
+     *
+     * @param  memberID the raft learner to be promoted to a raft voting member
+     * @return          the response
+     */
+    @Override
+    public CompletableFuture<MemberPromoteResponse> promoteMember(long memberID) {
+        MemberPromoteRequest memberPromoteRequest = MemberPromoteRequest.newBuilder()
+            .setID(memberID)
+            .build();
+
+        return completable(
+            this.stub.memberPromote(memberPromoteRequest),
+            MemberPromoteResponse::new);
+    }
+
 }

jetcd-core/src/main/proto/rpc.proto

@@ -99,6 +99,9 @@ service Cluster {
 
   // MemberList lists all the members in the cluster.
   rpc MemberList(MemberListRequest) returns (MemberListResponse) {}
+
+  // MemberPromote promotes a member from raft learner (non-voting) to raft voting member.
+  rpc MemberPromote(MemberPromoteRequest) returns (MemberPromoteResponse) {}
 }
 
 service Maintenance {
@@ -659,6 +662,17 @@ message MemberListResponse {
   repeated Member members = 2;
 }
 
+message MemberPromoteRequest {
+  // ID is the member ID of the member to promote.
+  uint64 ID = 1;
+}
+
+message MemberPromoteResponse {
+  ResponseHeader header = 1;
+  // members is a list of all members after promoting the member.
+  repeated Member members = 2;
+}
+
 message DefragmentRequest {
 }
 

jetcd-core/src/test/java/io/etcd/jetcd/impl/ClusterMembersTest.java

@@ -18,6 +18,7 @@
 
 import java.util.List;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 
@@ -29,9 +30,11 @@
 import io.etcd.jetcd.Client;
 import io.etcd.jetcd.Cluster;
 import io.etcd.jetcd.cluster.Member;
+import io.etcd.jetcd.cluster.MemberPromoteResponse;
 import io.etcd.jetcd.test.EtcdClusterExtension;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.AssertionsForClassTypes.assertThatExceptionOfType;
 
 @Timeout(value = 30, unit = TimeUnit.SECONDS)
 public class ClusterMembersTest {
@@ -112,4 +115,23 @@ public void testMemberManagementAddLearner() throws ExecutionException, Interrup
         assertThat(members).hasSize(2);
         assertThat(members.stream().filter(Member::isLearner).findAny()).isPresent();
     }
+
+    @Test
+    public void testMemberManagementAddLearnerAndPromote() throws ExecutionException, InterruptedException, TimeoutException {
+        final Client client = Client.builder().endpoints(n1.clientEndpoints()).build();
+        final Cluster clusterClient = client.getClusterClient();
+
+        Member m2 = clusterClient.addMember(n2.peerEndpoints(), true)
+            .get(5, TimeUnit.SECONDS)
+            .getMember();
+
+        assertThat(m2).isNotNull();
+        assertThat(m2.isLearner()).isTrue();
+
+        // Now attempt to promote a member; although it fails, it confirms that the API was executed.
+        Future<MemberPromoteResponse> promoteResponseFuture = clusterClient.promoteMember(m2.getId());
+        assertThatExceptionOfType(ExecutionException.class)
+            .isThrownBy(promoteResponseFuture::get).withMessageEndingWith(
+                "io.etcd.jetcd.common.exception.EtcdException: etcdserver: can only promote a learner member which is in sync with leader");
+    }
 }

jetcd-grpc/src/main/proto/rpc.proto

@@ -99,6 +99,9 @@ service Cluster {
 
   // MemberList lists all the members in the cluster.
   rpc MemberList(MemberListRequest) returns (MemberListResponse) {}
+
+  // MemberPromote promotes a member from raft learner (non-voting) to raft voting member.
+  rpc MemberPromote(MemberPromoteRequest) returns (MemberPromoteResponse) {}
 }
 
 service Maintenance {
@@ -659,6 +662,17 @@ message MemberListResponse {
   repeated Member members = 2;
 }
 
+message MemberPromoteRequest {
+  // ID is the member ID of the member to promote.
+  uint64 ID = 1;
+}
+
+message MemberPromoteResponse {
+  ResponseHeader header = 1;
+  // members is a list of all members after promoting the member.
+  repeated Member members = 2;
+}
+
 message DefragmentRequest {
 }