feat: add HStreamClient.describeCluster for getting uptime (#146)

Author: s12f

client/src/main/java/io/hstream/Cluster.java

@@ -0,0 +1,31 @@
+package io.hstream;
+
+public class Cluster {
+  /** unit: Seconds. */
+  long uptime;
+
+  public long getUptime() {
+    return uptime;
+  }
+
+  public static class Builder {
+    long uptime;
+
+    public Builder uptime(long uptime) {
+      this.uptime = uptime;
+      return this;
+    }
+
+    public Cluster build() {
+      return new Cluster(uptime);
+    }
+  }
+
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  Cluster(long uptime) {
+    this.uptime = uptime;
+  }
+}

client/src/main/java/io/hstream/HStreamClient.java

@@ -117,4 +117,6 @@ static HStreamClientBuilder builder() {
    * @param force the flag whether to enable force deletion
    */
   void deleteSubscription(String subscriptionId, boolean force);
+
+  Cluster describeCluster();
 }

client/src/main/kotlin/io/hstream/impl/HStreamClientKtImpl.kt

@@ -3,6 +3,7 @@ package io.hstream.impl
 import com.google.protobuf.Empty
 import io.grpc.ChannelCredentials
 import io.hstream.BufferedProducerBuilder
+import io.hstream.Cluster
 import io.hstream.ConsumerBuilder
 import io.hstream.HStreamClient
 import io.hstream.ProducerBuilder
@@ -176,6 +177,13 @@ class HStreamClientKtImpl(bootstrapServerUrls: List<String>, credentials: Channe
         }
     }
 
+    override fun describeCluster(): Cluster {
+        return unaryCallBlocked {
+            val result = it.describeCluster(Empty.getDefaultInstance())
+            return@unaryCallBlocked Cluster.newBuilder().uptime(result.clusterUpTime).build()
+        }
+    }
+
     private final suspend fun lookupSubscriptionServerUrl(subscriptionId: String?): String {
         return unaryCallCoroutine {
             val req: LookupSubscriptionRequest =