Refactor Sniffer and make it testable

client/rest/src/main/java/org/elasticsearch/client/RestClient.java

@@ -61,6 +61,7 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -132,7 +133,7 @@ public synchronized void setHosts(HttpHost... hosts) {
         if (hosts == null || hosts.length == 0) {
             throw new IllegalArgumentException("hosts must not be null nor empty");
         }
-        Set<HttpHost> httpHosts = new HashSet<>();
+        Set<HttpHost> httpHosts = new LinkedHashSet<>();
         AuthCache authCache = new BasicAuthCache();
         for (HttpHost host : hosts) {
             Objects.requireNonNull(host, "host cannot be null");
@@ -143,6 +144,13 @@ public synchronized void setHosts(HttpHost... hosts) {
         this.blacklist.clear();
     }
 
+    /**
+     * Returns the configured hosts
+     */
+    public List<HttpHost> getHosts() {
+        return new ArrayList<>(hostTuple.hosts);
+    }
+
     /**
      * Sends a request to the Elasticsearch cluster that the client points to.
      * Blocks until the request is completed and returns its response or fails

client/rest/src/test/java/org/elasticsearch/client/RestClientTests.java

@@ -25,6 +25,7 @@
 
 import java.io.IOException;
 import java.net.URI;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
@@ -251,6 +252,37 @@ public void testSetHostsWrongArguments() throws IOException {
         }
     }
 
+    public void testSetHostsPreservesOrdering() throws Exception {
+        try (RestClient restClient = createRestClient()) {
+            HttpHost[] hosts = randomHosts();
+            restClient.setHosts(hosts);
+            assertEquals(Arrays.asList(hosts), restClient.getHosts());
+        }
+    }
+
+    private static HttpHost[] randomHosts() {
+        int numHosts = randomIntBetween(1, 10);
+        HttpHost[] hosts = new HttpHost[numHosts];
+        for (int i = 0; i < hosts.length; i++) {
+            hosts[i] = new HttpHost("host-" + i, 9200);
+        }
+        return hosts;
+    }
+
+    public void testSetHostsDuplicatedHosts() throws Exception {
+        try (RestClient restClient = createRestClient()) {
+            int numHosts = randomIntBetween(1, 10);
+            HttpHost[] hosts = new HttpHost[numHosts];
+            HttpHost host = new HttpHost("host", 9200);
+            for (int i = 0; i < hosts.length; i++) {
+                hosts[i] = host;
+            }
+            restClient.setHosts(hosts);
+            assertEquals(1, restClient.getHosts().size());
+            assertEquals(host, restClient.getHosts().get(0));
+        }
+    }
+
     /**
      * @deprecated will remove method in 7.0 but needs tests until then. Replaced by {@link RequestTests#testConstructor()}.
      */

client/sniffer/src/main/java/org/elasticsearch/client/sniff/SniffOnFailureListener.java

@@ -58,7 +58,6 @@ public void onFailure(HttpHost host) {
         if (sniffer == null) {
             throw new IllegalStateException("sniffer was not set, unable to sniff on failure");
         }
-        //re-sniff immediately but take out the node that failed
-        sniffer.sniffOnFailure(host);
+        sniffer.sniffOnFailure();
     }
 }