diff --git a/src/Elasticsearch/Client.php b/src/Elasticsearch/Client.php
index 9f6ed9b5c..f49aff5fa 100644
--- a/src/Elasticsearch/Client.php
+++ b/src/Elasticsearch/Client.php
@@ -34,6 +34,8 @@
  */
 class Client
 {
+    const VERSION = '6.5.1';
+
     /**
      * @var Transport
      */
@@ -155,6 +157,39 @@ public function ping($params = [])
         return true;
     }
 
+    /**
+     * $params['body']  = (string) The ranking evaluation search definition, including
+     *        search requests, document ratings and ranking metric definition (Required)
+     *        ['index'] = (list) A comma-separated list of index names to search; use `_all` or
+     *        empty string to perform the operation on all indices
+     *        ['ignore_unavailable'] = (boolean) Whether specified concrete indices should be
+     *        ignored when unavailable (missing or closed)
+     *        ['allow_no_indices'] = (boolean) Whether to ignore if a wildcard indices expression
+     *        resolves into no concrete indices. (This includes `_all` string or when no indices have been specified)
+     *        ['expand_wildcards'] = (enum) Whether to expand wildcard expression to concrete indices that are open,
+     *        closed or both.
+     *
+     * @return callable|array
+     */
+    public function rankEval(array $params)
+    {
+        $body = $this->extractArgument($params, 'body');
+        $index = $this->extractArgument($params, 'index');
+        /**
+ * @var callable $endpointBuilder
+*/
+        $endpointBuilder = $this->endpoints;
+        /**
+ * @var \Elasticsearch\Endpoints\RankEval $endpoint
+*/
+        $endpoint = $endpointBuilder('RankEval');
+        $endpoint->setBody($body)
+            ->setIndex($index);
+        $endpoint->setParams($params);
+
+        return $this->performRequest($endpoint);
+    }
+
     /**
      * $params['id']              = (string) The document ID (Required)
      *        ['index']           = (string) The name of the index (Required)
@@ -1011,6 +1046,27 @@ public function scroll($params = array())
         return $this->performRequest($endpoint);
     }
 
+    /**
+     * $params['body'] = (string) The script to execute
+     *
+     * @return callable|array
+     */
+    public function scriptsPainlessExecute(array $params = [])
+    {
+        $body = $this->extractArgument($params, 'body');
+        /**
+ * @var callable $endpointBuilder
+*/
+        $endpointBuilder = $this->endpoints;
+        /**
+ * @var \Elasticsearch\Endpoints\ScriptsPainlessExecute $endpoint
+*/
+        $endpoint = $endpointBuilder('ScriptsPainlessExecute');
+        $endpoint->setBody($body);
+        $endpoint->setParams($params);
+        return $this->performRequest($endpoint);
+    }
+
     /**
      * $params['scroll_id'] = (string) The scroll ID for scrolled search
      *        ['scroll']    = (duration) Specify how long a consistent view of the index should be maintained for scrolled search
diff --git a/src/Elasticsearch/Connections/Connection.php b/src/Elasticsearch/Connections/Connection.php
index b31de569f..928cefe05 100644
--- a/src/Elasticsearch/Connections/Connection.php
+++ b/src/Elasticsearch/Connections/Connection.php
@@ -4,6 +4,7 @@
 
 namespace Elasticsearch\Connections;
 
+use Elasticsearch\Client;
 use Elasticsearch\Common\Exceptions\AlreadyExpiredException;
 use Elasticsearch\Common\Exceptions\BadRequest400Exception;
 use Elasticsearch\Common\Exceptions\Conflict409Exception;
@@ -126,6 +127,15 @@ public function __construct(
             unset($connectionParams['client']['headers']);
         }
 
+        // Add the User-Agent using the format: <client-repo-name>/<client-version> (metadata-values)
+        $this->headers['User-Agent'] = [sprintf(
+            "elasticsearch-php/%s (%s %s, PHP %s)",
+            Client::VERSION,
+            php_uname("s"),
+            php_uname("r"),
+            phpversion()
+        )];
+
         $host = $hostDetails['host'].':'.$hostDetails['port'];
         $path = null;
         if (isset($hostDetails['path']) === true) {
@@ -179,6 +189,12 @@ public function performRequest($method, $uri, $params = null, $body = null, $opt
         return $future;
     }
 
+    /** @return array */
+    public function getHeaders()
+    {
+        return $this->headers;
+    }
+
     /** @return string */
     public function getTransportSchema()
     {
diff --git a/src/Elasticsearch/Endpoints/Cluster/AllocationExplain.php b/src/Elasticsearch/Endpoints/Cluster/AllocationExplain.php
index 429b5d0f4..51e78c8f8 100644
--- a/src/Elasticsearch/Endpoints/Cluster/AllocationExplain.php
+++ b/src/Elasticsearch/Endpoints/Cluster/AllocationExplain.php
@@ -59,6 +59,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Count.php b/src/Elasticsearch/Endpoints/Count.php
index e35e9938b..62f4ffec2 100644
--- a/src/Elasticsearch/Endpoints/Count.php
+++ b/src/Elasticsearch/Endpoints/Count.php
@@ -84,6 +84,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Explain.php b/src/Elasticsearch/Endpoints/Explain.php
index 1c668e8a6..4888db657 100644
--- a/src/Elasticsearch/Endpoints/Explain.php
+++ b/src/Elasticsearch/Endpoints/Explain.php
@@ -97,6 +97,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/FieldCaps.php b/src/Elasticsearch/Endpoints/FieldCaps.php
index f9ae24d9e..0c8f55c8b 100644
--- a/src/Elasticsearch/Endpoints/FieldCaps.php
+++ b/src/Elasticsearch/Endpoints/FieldCaps.php
@@ -66,6 +66,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Indices/Analyze.php b/src/Elasticsearch/Endpoints/Indices/Analyze.php
index ddcac13cd..4e918c35d 100644
--- a/src/Elasticsearch/Endpoints/Indices/Analyze.php
+++ b/src/Elasticsearch/Endpoints/Indices/Analyze.php
@@ -76,6 +76,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Indices/ClearCache.php b/src/Elasticsearch/Endpoints/Indices/ClearCache.php
index 1d7bce8cc..0e3a7987d 100644
--- a/src/Elasticsearch/Endpoints/Indices/ClearCache.php
+++ b/src/Elasticsearch/Endpoints/Indices/ClearCache.php
@@ -59,6 +59,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Indices/Flush.php b/src/Elasticsearch/Endpoints/Indices/Flush.php
index 90626ab58..97912e87b 100644
--- a/src/Elasticsearch/Endpoints/Indices/Flush.php
+++ b/src/Elasticsearch/Endpoints/Indices/Flush.php
@@ -63,6 +63,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Indices/ValidateQuery.php b/src/Elasticsearch/Endpoints/Indices/ValidateQuery.php
index 6a7cd57cc..1a9acde37 100644
--- a/src/Elasticsearch/Endpoints/Indices/ValidateQuery.php
+++ b/src/Elasticsearch/Endpoints/Indices/ValidateQuery.php
@@ -74,6 +74,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Ingest/Simulate.php b/src/Elasticsearch/Endpoints/Ingest/Simulate.php
index 16889ab5f..962713b55 100644
--- a/src/Elasticsearch/Endpoints/Ingest/Simulate.php
+++ b/src/Elasticsearch/Endpoints/Ingest/Simulate.php
@@ -62,6 +62,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/MTermVectors.php b/src/Elasticsearch/Endpoints/MTermVectors.php
index 00b69c259..93cd432b9 100644
--- a/src/Elasticsearch/Endpoints/MTermVectors.php
+++ b/src/Elasticsearch/Endpoints/MTermVectors.php
@@ -67,6 +67,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'POST';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Msearch.php b/src/Elasticsearch/Endpoints/Msearch.php
index 2fba78aec..45f4e73e2 100644
--- a/src/Elasticsearch/Endpoints/Msearch.php
+++ b/src/Elasticsearch/Endpoints/Msearch.php
@@ -103,6 +103,6 @@ public function getBody()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/MsearchTemplate.php b/src/Elasticsearch/Endpoints/MsearchTemplate.php
index efe440064..4c233921d 100644
--- a/src/Elasticsearch/Endpoints/MsearchTemplate.php
+++ b/src/Elasticsearch/Endpoints/MsearchTemplate.php
@@ -102,6 +102,6 @@ public function getBody()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/RankEval.php b/src/Elasticsearch/Endpoints/RankEval.php
new file mode 100644
index 000000000..6452cdaa3
--- /dev/null
+++ b/src/Elasticsearch/Endpoints/RankEval.php
@@ -0,0 +1,61 @@
+<?php
+declare(strict_types = 1);
+
+namespace Elasticsearch\Endpoints;
+
+/**
+ * Class RankEval
+ *
+ * @category Elasticsearch
+ * @package  Elasticsearch\Endpoints
+ * @author   Enrico Zimuel <enrico.zimuel@elastic.co>
+ * @license  http://www.apache.org/licenses/LICENSE-2.0 Apache2
+ * @link     http://elastic.co
+ */
+class RankEval extends AbstractEndpoint
+{
+    /**
+     * @return array
+     */
+    public function getParamWhitelist()
+    {
+        return [
+            'ignore_unavailable',
+            'allow_no_indices',
+            'expand_wildcards'
+        ];
+    }
+
+    /**
+     * @return string
+     */
+    public function getURI()
+    {
+        $index = $this->index ?? null;
+        if (isset($index)) {
+            return "/$index/_rank_eval";
+        }
+        return '/_rank_eval';
+    }
+
+    /**
+     * @return string
+     */
+    public function getMethod()
+    {
+        return 'POST';
+    }
+
+    /**
+     * @param array $body
+     * @return $this
+     */
+    public function setBody($body)
+    {
+        if (isset($body) !== true) {
+            return $this;
+        }
+        $this->body = $body;
+        return $this;
+    }
+}
diff --git a/src/Elasticsearch/Endpoints/RenderSearchTemplate.php b/src/Elasticsearch/Endpoints/RenderSearchTemplate.php
index 559226189..87d7ebef7 100644
--- a/src/Elasticsearch/Endpoints/RenderSearchTemplate.php
+++ b/src/Elasticsearch/Endpoints/RenderSearchTemplate.php
@@ -74,6 +74,6 @@ public function getBody()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/ScriptsPainlessExecute.php b/src/Elasticsearch/Endpoints/ScriptsPainlessExecute.php
new file mode 100644
index 000000000..f690636f2
--- /dev/null
+++ b/src/Elasticsearch/Endpoints/ScriptsPainlessExecute.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Elasticsearch\Endpoints;
+
+use Elasticsearch\Common\Exceptions\RuntimeException;
+
+/**
+ * Class Reindex
+ *
+ * @category Elasticsearch
+ * @package  Elasticsearch\Endpoints
+ * @author   Enrico Zimuel <enrico.zimuel@elastic.co>
+ * @license  http://www.apache.org/licenses/LICENSE-2.0 Apache2
+ * @link     http://elastic.co
+ */
+class ScriptsPainlessExecute extends AbstractEndpoint
+{
+    /**
+     * @return array
+     */
+    public function getParamWhitelist()
+    {
+        return [];
+    }
+
+    /**
+     * @return string
+     */
+    public function getURI()
+    {
+        return "/_scripts/painless/_execute";
+    }
+
+    /**
+     * @return string
+     */
+    public function getMethod()
+    {
+        return isset($this->body) ? 'POST' : 'GET';
+    }
+
+    /**
+     * @param array $body
+     * @return $this
+     */
+    public function setBody($body)
+    {
+        if (isset($body) !== true) {
+            return $this;
+        }
+
+        $this->body = $body;
+
+        return $this;
+    }
+}
diff --git a/src/Elasticsearch/Endpoints/Scroll.php b/src/Elasticsearch/Endpoints/Scroll.php
index 0bb31ac9c..d68c7324b 100644
--- a/src/Elasticsearch/Endpoints/Scroll.php
+++ b/src/Elasticsearch/Endpoints/Scroll.php
@@ -99,6 +99,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/Search.php b/src/Elasticsearch/Endpoints/Search.php
index b223e129f..598aad103 100644
--- a/src/Elasticsearch/Endpoints/Search.php
+++ b/src/Elasticsearch/Endpoints/Search.php
@@ -110,6 +110,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/SearchTemplate.php b/src/Elasticsearch/Endpoints/SearchTemplate.php
index f5298f3a1..776aadb7a 100644
--- a/src/Elasticsearch/Endpoints/SearchTemplate.php
+++ b/src/Elasticsearch/Endpoints/SearchTemplate.php
@@ -76,6 +76,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'GET';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/TermVectors.php b/src/Elasticsearch/Endpoints/TermVectors.php
index 26058107f..a461105be 100644
--- a/src/Elasticsearch/Endpoints/TermVectors.php
+++ b/src/Elasticsearch/Endpoints/TermVectors.php
@@ -92,6 +92,6 @@ public function getParamWhitelist()
      */
     public function getMethod()
     {
-        return 'POST';
+        return isset($this->body) ? 'POST' : 'GET';
     }
 }
diff --git a/src/Elasticsearch/Endpoints/UpdateByQuery.php b/src/Elasticsearch/Endpoints/UpdateByQuery.php
index bd2e5a8ee..24411752c 100644
--- a/src/Elasticsearch/Endpoints/UpdateByQuery.php
+++ b/src/Elasticsearch/Endpoints/UpdateByQuery.php
@@ -103,11 +103,14 @@ public function getParamWhitelist()
             'version',
             'version_type',
             'request_cache',
+            'request_per_second',
+            'slices',
             'refresh',
             'consistency',
             'scroll_size',
             'wait_for_completion',
-            'pipeline',
+            'wait_for_active_shards',
+            'pipeline'
         ];
     }
 
diff --git a/tests/Elasticsearch/Tests/Connections/ConnectionTest.php b/tests/Elasticsearch/Tests/Connections/ConnectionTest.php
new file mode 100644
index 000000000..8906e34df
--- /dev/null
+++ b/tests/Elasticsearch/Tests/Connections/ConnectionTest.php
@@ -0,0 +1,78 @@
+<?php
+namespace Elasticsearch\Tests\Connections;
+
+use Elasticsearch\Client;
+use Elasticsearch\ClientBuilder;
+use Elasticsearch\Connections\Connection;
+use Elasticsearch\Serializers\SerializerInterface;
+use Psr\Log\LoggerInterface;
+
+class ConnectionTest extends \PHPUnit\Framework\TestCase
+{
+    private $logger;
+    private $trace;
+    private $serializer;
+
+    protected function setUp()
+    {
+        $this->logger = $this->createMock(LoggerInterface::class);
+        $this->trace = $this->createMock(LoggerInterface::class);
+        $this->serializer = $this->createMock(SerializerInterface::class);
+    }
+
+    public function testConstructor()
+    {
+        $params = [];
+        $host = [
+            'host' => 'localhost'
+        ];
+        $connection = new Connection(
+            function(){},
+            $host,
+            $params,
+            $this->serializer,
+            $this->logger,
+            $this->trace
+        );
+        $this->assertInstanceOf(Connection::class, $connection);
+    }
+
+    public function testGetHeadersContainUserAgent()
+    {
+        $params = [];
+        $host = [
+            'host' => 'localhost'
+        ];
+        $connection = new Connection(
+            function(){},
+            $host,
+            $params,
+            $this->serializer,
+            $this->logger,
+            $this->trace
+        );
+        $headers =  $connection->getHeaders();
+        $this->assertArrayHasKey('User-Agent', $headers);
+        $this->assertContains('elasticsearch-php/'. Client::VERSION, $headers['User-Agent'][0]);
+    }
+
+    public function testUserAgentHeaderIsSent()
+    {
+        $params = [];
+        $host = [
+            'host' => 'localhost'
+        ];
+        $connection = new Connection(
+            ClientBuilder::defaultHandler(),
+            $host,
+            $params,
+            $this->serializer,
+            $this->logger,
+            $this->trace
+        );
+        $result = $connection->performRequest('GET', '/');
+        $request = $connection->getLastRequestInfo()['request'];
+        $this->assertArrayHasKey('User-Agent', $request['headers']);
+        $this->assertContains('elasticsearch-php/'. Client::VERSION, $request['headers']['User-Agent'][0]);
+    }
+}