Add Metrics to instance API

Patch by Alex Petrov; reviewed by Benedict Elliott Smith for CASSANDRA-16136
diff --git a/CHANGES.txt b/CHANGES.txt
index 849c787..0e40234 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,8 @@
+# 0.0.7
+
+CASSANDRA-16136: Add Metrics to instance API
+CASSANDRA-16272: Nodetool assert apis do not include the new stdout and stderr in the failure message
+
 # 0.0.6
 
 CASSANDRA-16148: Add IInstance#getReleaseVersionString
diff --git a/src/main/java/org/apache/cassandra/distributed/api/IInstance.java b/src/main/java/org/apache/cassandra/distributed/api/IInstance.java
index 045ea00..8ac6235 100644
--- a/src/main/java/org/apache/cassandra/distributed/api/IInstance.java
+++ b/src/main/java/org/apache/cassandra/distributed/api/IInstance.java
@@ -23,6 +23,8 @@
 import java.util.UUID;
 import java.util.concurrent.Future;
 
+import org.apache.cassandra.distributed.shared.Metrics;
+
 // The cross-version API requires that an Instance has a constructor signature of (IInstanceConfig, ClassLoader)
 public interface IInstance extends IIsolatedExecutor
 {
@@ -55,6 +57,8 @@
 
     int liveMemberCount();
 
+    Metrics metrics();
+
     NodeToolResult nodetoolResult(boolean withNotifications, String... commandAndArgs);
 
     default NodeToolResult nodetoolResult(String... commandAndArgs)
diff --git a/src/main/java/org/apache/cassandra/distributed/shared/Metrics.java b/src/main/java/org/apache/cassandra/distributed/shared/Metrics.java
new file mode 100644
index 0000000..6a702ad
--- /dev/null
+++ b/src/main/java/org/apache/cassandra/distributed/shared/Metrics.java
@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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
+ *
+ *     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 org.apache.cassandra.distributed.shared;
+
+import java.util.List;
+import java.util.Map;
+import java.util.function.Predicate;
+
+public interface Metrics
+{
+    List<String> getNames();
+
+    long getCounter(String name);
+    Map<String, Long> getCounters(Predicate<String> filter);
+
+    double getHistogram(String name, MetricValue value);
+    Map<String, Double> getHistograms(Predicate<String> filter, MetricValue value);
+
+    Object getGauge(String name);
+    Map<String, Object> getGauges(Predicate<String> filter);
+
+    double getMeter(String name, Rate value);
+    Map<String, Double> getMeters(Predicate<String> filter, Rate value);
+
+    double getTimer(String name, MetricValue value);
+    Map<String, Double> getTimers(Predicate<String> filter, MetricValue value);
+
+    enum MetricValue
+    {
+        COUNT,
+        MEDIAN, P75, P95, P98, P99, P999,
+        MAX, MEAN, MIN, STDDEV
+    }
+
+    enum Rate
+    {
+        RATE15_MIN,
+        RATE5_MIN,
+        RATE1_MIN,
+        RATE_MEAN
+    }
+}