diff --git a/src/php/lib/Grpc/BaseStub.php b/src/php/lib/Grpc/BaseStub.php
index 5f3a96feaa3..7860233ca2c 100644
--- a/src/php/lib/Grpc/BaseStub.php
+++ b/src/php/lib/Grpc/BaseStub.php
@@ -38,12 +38,13 @@ class BaseStub
      *  - 'update_metadata': (optional) a callback function which takes in a
      * metadata array, and returns an updated metadata array
      *  - 'grpc.primary_user_agent': (optional) a user-agent string
-     * @param Channel $channel An already created Channel object (optional)
+     * @param Channel|InterceptorChannel $channel An already created Channel or InterceptorChannel object (optional)
      */
-    public function __construct($hostname, $opts, Channel $channel = null)
+    public function __construct($hostname, $opts, $channel = null)
     {
         $ssl_roots = file_get_contents(
-            dirname(__FILE__).'/../../../../etc/roots.pem');
+            dirname(__FILE__).'/../../../../etc/roots.pem'
+        );
         ChannelCredentials::setDefaultRootsPem($ssl_roots);
 
         $this->hostname = $hostname;
@@ -58,16 +59,20 @@ class BaseStub
             $this->hostname_override = $opts['grpc.ssl_target_name_override'];
         }
         if ($channel) {
-            if (!is_a($channel, 'Grpc\Channel')) {
-                throw new \Exception('The channel argument is not a'.
-                                     'Channel object');
+            if (!is_a($channel, 'Grpc\Channel') &&
+                !is_a($channel, 'Grpc\InterceptorChannel')) {
+                throw new \Exception('The channel argument is not a Channel object '.
+                    'or an InterceptorChannel object created by '.
+                    'Interceptor::intercept($channel, Interceptor|Interceptor[] $interceptors)');
             }
             $this->channel = $channel;
             return;
         }
 
         $package_config = json_decode(
-            file_get_contents(dirname(__FILE__).'/../../composer.json'), true);
+            file_get_contents(dirname(__FILE__).'/../../composer.json'),
+            true
+        );
         if (!empty($opts['grpc.primary_user_agent'])) {
             $opts['grpc.primary_user_agent'] .= ' ';
         } else {
@@ -77,8 +82,8 @@ class BaseStub
             'grpc-php/'.$package_config['version'];
         if (!array_key_exists('credentials', $opts)) {
             throw new \Exception("The opts['credentials'] key is now ".
-                                 'required. Please see one of the '.
-                                 'ChannelCredentials::create methods');
+                'required. Please see one of the '.
+                'ChannelCredentials::create methods');
         }
         $this->channel = new Channel($hostname, $opts);
     }
@@ -169,7 +174,8 @@ class BaseStub
         $last_slash_idx = strrpos($method, '/');
         if ($last_slash_idx === false) {
             throw new \InvalidArgumentException(
-                'service name must have a slash');
+                'service name must have a slash'
+            );
         }
         $service_name = substr($method, 0, $last_slash_idx);
 
@@ -197,7 +203,8 @@ class BaseStub
             if (!preg_match('/^[A-Za-z\d_-]+$/', $key)) {
                 throw new \InvalidArgumentException(
                     'Metadata keys must be nonempty strings containing only '.
-                    'alphanumeric characters, hyphens and underscores');
+                    'alphanumeric characters, hyphens and underscores'
+                );
             }
             $metadata_copy[strtolower($key)] = $value;
         }
@@ -205,9 +212,255 @@ class BaseStub
         return $metadata_copy;
     }
 
+    /**
+     * Create a function which can be used to create UnaryCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _GrpcUnaryUnary($channel, $deserialize)
+    {
+        return function ($method,
+                         $argument,
+                         array $metadata = [],
+                         array $options = []) use ($channel, $deserialize) {
+            $call = new UnaryCall(
+                $channel,
+                $method,
+                $deserialize,
+                $options
+            );
+            $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
+            if (is_callable($this->update_metadata)) {
+                $metadata = call_user_func(
+                    $this->update_metadata,
+                    $metadata,
+                    $jwt_aud_uri
+                );
+            }
+            $metadata = $this->_validate_and_normalize_metadata(
+                $metadata
+            );
+            $call->start($argument, $metadata, $options);
+            return $call;
+        };
+    }
+
+    /**
+     * Create a function which can be used to create ServerStreamingCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _GrpcStreamUnary($channel, $deserialize)
+    {
+        return function ($method,
+                         array $metadata = [],
+                         array $options = []) use ($channel, $deserialize) {
+            $call = new ClientStreamingCall(
+                $channel,
+                $method,
+                $deserialize,
+                $options
+            );
+            $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
+            if (is_callable($this->update_metadata)) {
+                $metadata = call_user_func(
+                    $this->update_metadata,
+                    $metadata,
+                    $jwt_aud_uri
+                );
+            }
+            $metadata = $this->_validate_and_normalize_metadata(
+                $metadata
+            );
+            $call->start($metadata);
+            return $call;
+        };
+    }
+
+    /**
+     * Create a function which can be used to create ClientStreamingCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _GrpcUnaryStream($channel, $deserialize)
+    {
+        return function ($method,
+                         $argument,
+                         array $metadata = [],
+                         array $options = []) use ($channel, $deserialize) {
+            $call = new ServerStreamingCall(
+                $channel,
+                $method,
+                $deserialize,
+                $options
+            );
+            $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
+            if (is_callable($this->update_metadata)) {
+                $metadata = call_user_func(
+                    $this->update_metadata,
+                    $metadata,
+                    $jwt_aud_uri
+                );
+            }
+            $metadata = $this->_validate_and_normalize_metadata(
+                $metadata
+            );
+            $call->start($argument, $metadata, $options);
+            return $call;
+        };
+    }
+
+    /**
+     * Create a function which can be used to create BidiStreamingCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _GrpcStreamStream($channel, $deserialize)
+    {
+        return function ($method,
+                         array $metadata = [],
+                         array $options = []) use ($channel ,$deserialize) {
+            $call = new BidiStreamingCall(
+                $channel,
+                $method,
+                $deserialize,
+                $options
+            );
+            $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
+            if (is_callable($this->update_metadata)) {
+                $metadata = call_user_func(
+                    $this->update_metadata,
+                    $metadata,
+                    $jwt_aud_uri
+                );
+            }
+            $metadata = $this->_validate_and_normalize_metadata(
+                $metadata
+            );
+            $call->start($metadata);
+
+            return $call;
+        };
+    }
+
+    /**
+     * Create a function which can be used to create UnaryCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _UnaryUnaryCallFactory($channel, $deserialize)
+    {
+        if (is_a($channel, 'Grpc\InterceptorChannel')) {
+            return function ($method,
+                             $argument,
+                             array $metadata = [],
+                             array $options = []) use ($channel, $deserialize) {
+                return $channel->getInterceptor()->interceptUnaryUnary(
+                    $method,
+                    $argument,
+                    $metadata,
+                    $options,
+                    $this->_UnaryUnaryCallFactory($channel->getNext(), $deserialize)
+                );
+            };
+        }
+        return $this->_GrpcUnaryUnary($channel, $deserialize);
+    }
+
+    /**
+     * Create a function which can be used to create ServerStreamingCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _UnaryStreamCallFactory($channel, $deserialize)
+    {
+        if (is_a($channel, 'Grpc\InterceptorChannel')) {
+            return function ($method,
+                             $argument,
+                             array $metadata = [],
+                             array $options = []) use ($channel, $deserialize) {
+                return $channel->getInterceptor()->interceptUnaryStream(
+                    $method,
+                    $argument,
+                    $metadata,
+                    $options,
+                    $this->_UnaryStreamCallFactory($channel->getNext(), $deserialize)
+                );
+            };
+        }
+        return $this->_GrpcUnaryStream($channel, $deserialize);
+    }
+
+    /**
+     * Create a function which can be used to create ClientStreamingCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _StreamUnaryCallFactory($channel, $deserialize)
+    {
+        if (is_a($channel, 'Grpc\InterceptorChannel')) {
+            return function ($method,
+                             array $metadata = [],
+                             array $options = []) use ($channel, $deserialize) {
+                return $channel->getInterceptor()->interceptStreamUnary(
+                    $method,
+                    $metadata,
+                    $options,
+                    $this->_StreamUnaryCallFactory($channel->getNext(), $deserialize)
+                );
+            };
+        }
+        return $this->_GrpcStreamUnary($channel, $deserialize);
+    }
+
+    /**
+     * Create a function which can be used to create BidiStreamingCall
+     *
+     * @param Channel|InterceptorChannel   $channel
+     * @param callable $deserialize A function that deserializes the response
+     *
+     * @return \Closure
+     */
+    private function _StreamStreamCallFactory($channel, $deserialize)
+    {
+        if (is_a($channel, 'Grpc\InterceptorChannel')) {
+            return function ($method,
+                             array $metadata = [],
+                             array $options = []) use ($channel, $deserialize) {
+                return $channel->getInterceptor()->interceptStreamStream(
+                    $method,
+                    $metadata,
+                    $options,
+                    $this->_StreamStreamCallFactory($channel->getNext(), $deserialize)
+                );
+            };
+        }
+        return $this->_GrpcStreamStream($channel, $deserialize);
+    }
+
     /* This class is intended to be subclassed by generated code, so
      * all functions begin with "_" to avoid name collisions. */
-
     /**
      * Call a remote method that takes a single argument and has a
      * single output.
@@ -221,26 +474,15 @@ class BaseStub
      *
      * @return UnaryCall The active call object
      */
-    protected function _simpleRequest($method,
-                                   $argument,
-                                   $deserialize,
-                                   array $metadata = [],
-                                   array $options = [])
-    {
-        $call = new UnaryCall($this->channel,
-                              $method,
-                              $deserialize,
-                              $options);
-        $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
-        if (is_callable($this->update_metadata)) {
-            $metadata = call_user_func($this->update_metadata,
-                                        $metadata,
-                                        $jwt_aud_uri);
-        }
-        $metadata = $this->_validate_and_normalize_metadata(
-            $metadata);
-        $call->start($argument, $metadata, $options);
-
+    protected function _simpleRequest(
+        $method,
+        $argument,
+        $deserialize,
+        array $metadata = [],
+        array $options = []
+    ) {
+        $call_factory = $this->_UnaryUnaryCallFactory($this->channel, $deserialize);
+        $call = $call_factory($method, $argument, $metadata, $options);
         return $call;
     }
 
@@ -256,25 +498,14 @@ class BaseStub
      *
      * @return ClientStreamingCall The active call object
      */
-    protected function _clientStreamRequest($method,
-                                         $deserialize,
-                                         array $metadata = [],
-                                         array $options = [])
-    {
-        $call = new ClientStreamingCall($this->channel,
-                                        $method,
-                                        $deserialize,
-                                        $options);
-        $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
-        if (is_callable($this->update_metadata)) {
-            $metadata = call_user_func($this->update_metadata,
-                                        $metadata,
-                                        $jwt_aud_uri);
-        }
-        $metadata = $this->_validate_and_normalize_metadata(
-            $metadata);
-        $call->start($metadata);
-
+    protected function _clientStreamRequest(
+        $method,
+        $deserialize,
+        array $metadata = [],
+        array $options = []
+    ) {
+        $call_factory = $this->_StreamUnaryCallFactory($this->channel, $deserialize);
+        $call = $call_factory($method, $metadata, $options);
         return $call;
     }
 
@@ -291,26 +522,15 @@ class BaseStub
      *
      * @return ServerStreamingCall The active call object
      */
-    protected function _serverStreamRequest($method,
-                                         $argument,
-                                         $deserialize,
-                                         array $metadata = [],
-                                         array $options = [])
-    {
-        $call = new ServerStreamingCall($this->channel,
-                                        $method,
-                                        $deserialize,
-                                        $options);
-        $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
-        if (is_callable($this->update_metadata)) {
-            $metadata = call_user_func($this->update_metadata,
-                                        $metadata,
-                                        $jwt_aud_uri);
-        }
-        $metadata = $this->_validate_and_normalize_metadata(
-            $metadata);
-        $call->start($argument, $metadata, $options);
-
+    protected function _serverStreamRequest(
+        $method,
+        $argument,
+        $deserialize,
+        array $metadata = [],
+        array $options = []
+    ) {
+        $call_factory = $this->_UnaryStreamCallFactory($this->channel, $deserialize);
+        $call = $call_factory($method, $argument, $metadata, $options);
         return $call;
     }
 
@@ -325,25 +545,14 @@ class BaseStub
      *
      * @return BidiStreamingCall The active call object
      */
-    protected function _bidiRequest($method,
-                                 $deserialize,
-                                 array $metadata = [],
-                                 array $options = [])
-    {
-        $call = new BidiStreamingCall($this->channel,
-                                      $method,
-                                      $deserialize,
-                                      $options);
-        $jwt_aud_uri = $this->_get_jwt_aud_uri($method);
-        if (is_callable($this->update_metadata)) {
-            $metadata = call_user_func($this->update_metadata,
-                                        $metadata,
-                                        $jwt_aud_uri);
-        }
-        $metadata = $this->_validate_and_normalize_metadata(
-            $metadata);
-        $call->start($metadata);
-
+    protected function _bidiRequest(
+        $method,
+        $deserialize,
+        array $metadata = [],
+        array $options = []
+    ) {
+        $call_factory = $this->_StreamStreamCallFactory($this->channel, $deserialize);
+        $call = $call_factory($method, $metadata, $options);
         return $call;
     }
 }
diff --git a/src/php/lib/Grpc/Interceptor.php b/src/php/lib/Grpc/Interceptor.php
new file mode 100644
index 00000000000..9c1b5616f25
--- /dev/null
+++ b/src/php/lib/Grpc/Interceptor.php
@@ -0,0 +1,86 @@
+<?php
+/*
+ *
+ * Copyright 2018 gRPC 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.
+ *
+ */
+
+namespace Grpc;
+
+/**
+ * Represents an interceptor that intercept RPC invocations before call starts.
+ * This is an EXPERIMENTAL API.
+ */
+class Interceptor
+{
+    public function interceptUnaryUnary(
+        $method,
+        $argument,
+        array $metadata = [],
+        array $options = [],
+        $continuation
+    ) {
+        return $continuation($method, $argument, $metadata, $options);
+    }
+
+    public function interceptStreamUnary(
+        $method,
+        array $metadata = [],
+        array $options = [],
+        $continuation
+    ) {
+        return $continuation($method, $metadata, $options);
+    }
+
+    public function interceptUnaryStream(
+        $method,
+        $argument,
+        array $metadata = [],
+        array $options = [],
+        $continuation
+    ) {
+        return $continuation($method, $argument, $metadata, $options);
+    }
+
+    public function interceptStreamStream(
+        $method,
+        array $metadata = [],
+        array $options = [],
+        $continuation
+    ) {
+        return $continuation($method, $metadata, $options);
+    }
+
+    /**
+     * Intercept the methods with Channel
+     *
+     * @param Channel|InterceptorChannel $channel An already created Channel or InterceptorChannel object (optional)
+     * @param Interceptor|Interceptor[] $interceptors interceptors to be added
+     *
+     * @return InterceptorChannel
+     */
+    public static function intercept($channel, $interceptors)
+    {
+        if (is_array($interceptors)) {
+            for ($i = count($interceptors) - 1; $i >= 0; $i--) {
+                $channel = new InterceptorChannel($channel, $interceptors[$i]);
+            }
+        } else {
+            $channel =  new InterceptorChannel($channel, $interceptors);
+        }
+        return $channel;
+    }
+}
+
diff --git a/src/php/lib/Grpc/Internal/InterceptorChannel.php b/src/php/lib/Grpc/Internal/InterceptorChannel.php
new file mode 100644
index 00000000000..9ac05748f34
--- /dev/null
+++ b/src/php/lib/Grpc/Internal/InterceptorChannel.php
@@ -0,0 +1,76 @@
+<?php
+/*
+ *
+ * Copyright 2018 gRPC 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.
+ *
+ */
+
+namespace Grpc;
+
+/**
+ * This is a PRIVATE API and can change without notice.
+ */
+class InterceptorChannel
+{
+    private $next = null;
+    private $interceptor;
+
+    /**
+     * @param Channel|InterceptorChannel $channel An already created Channel
+     * or InterceptorChannel object (optional)
+     * @param Interceptor  $interceptor
+     */
+    public function __construct($channel, $interceptor)
+    {
+        if (!is_a($channel, 'Grpc\Channel') &&
+            !is_a($channel, 'Grpc\InterceptorChannel')) {
+            throw new \Exception('The channel argument is not a Channel object '.
+                'or an InterceptorChannel object created by '.
+                'Interceptor::intercept($channel, Interceptor|Interceptor[] $interceptors)');
+        }
+        $this->interceptor = $interceptor;
+        $this->next = $channel;
+    }
+
+    public function getNext()
+    {
+        return $this->next;
+    }
+
+    public function getInterceptor()
+    {
+        return $this->interceptor;
+    }
+
+    public function getTarget()
+    {
+        return $this->getNext()->getTarget();
+    }
+
+    public function watchConnectivityState($new_state, $deadline)
+    {
+        return $this->getNext()->watchConnectivityState($new_state, $deadline);
+    }
+
+    public function getConnectivityState($try_to_connect = false)
+    {
+        return $this->getNext()->getConnectivityState($try_to_connect);
+    }
+
+    public function close()
+    {
+        return $this->getNext()->close();
+    }
+}
diff --git a/src/php/tests/unit_tests/InterceptorTest.php b/src/php/tests/unit_tests/InterceptorTest.php
new file mode 100644
index 00000000000..08f5abbb211
--- /dev/null
+++ b/src/php/tests/unit_tests/InterceptorTest.php
@@ -0,0 +1,427 @@
+<?php
+/*
+ *
+ * Copyright 2018 gRPC 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.
+ *
+ */
+/**
+ * Interface exported by the server.
+ */
+require_once(dirname(__FILE__).'/../../lib/Grpc/BaseStub.php');
+require_once(dirname(__FILE__).'/../../lib/Grpc/AbstractCall.php');
+require_once(dirname(__FILE__).'/../../lib/Grpc/UnaryCall.php');
+require_once(dirname(__FILE__).'/../../lib/Grpc/ClientStreamingCall.php');
+require_once(dirname(__FILE__).'/../../lib/Grpc/Interceptor.php');
+require_once(dirname(__FILE__).'/../../lib/Grpc/Internal/InterceptorChannel.php');
+
+class SimpleRequest
+{
+    private $data;
+    public function __construct($data)
+    {
+        $this->data = $data;
+    }
+    public function setData($data)
+    {
+        $this->data = $data;
+    }
+    public function serializeToString()
+    {
+        return $this->data;
+    }
+}
+
+class InterceptorClient extends Grpc\BaseStub
+{
+
+    /**
+     * @param string $hostname hostname
+     * @param array $opts channel options
+     * @param Channel|InterceptorChannel $channel (optional) re-use channel object
+     */
+    public function __construct($hostname, $opts, $channel = null)
+    {
+        parent::__construct($hostname, $opts, $channel);
+    }
+
+    /**
+     * A simple RPC.
+     * @param \Routeguide\Point $argument input argument
+     * @param array $metadata metadata
+     * @param array $options call options
+     */
+    public function UnaryCall(
+        SimpleRequest $argument,
+        $metadata = [],
+        $options = []
+    ) {
+        return $this->_simpleRequest(
+            '/dummy_method',
+            $argument,
+            [],
+            $metadata,
+            $options
+        );
+    }
+
+    /**
+     * A client-to-server streaming RPC.
+     * @param array $metadata metadata
+     * @param array $options call options
+     */
+    public function StreamCall(
+        $metadata = [],
+        $options = []
+    ) {
+        return $this->_clientStreamRequest('/dummy_method', [], $metadata, $options);
+    }
+}
+
+
+class ChangeMetadataInterceptor extends Grpc\Interceptor
+{
+    public function interceptUnaryUnary($method,
+                                        $argument,
+                                        array $metadata = [],
+                                        array $options = [],
+                                        $continuation)
+    {
+        $metadata["foo"] = array('interceptor_from_unary_request');
+        return $continuation($method, $argument, $metadata, $options);
+    }
+    public function interceptStreamUnary($method, array $metadata = [], array $options = [], $continuation)
+    {
+        $metadata["foo"] = array('interceptor_from_stream_request');
+        return $continuation($method, $metadata, $options);
+    }
+}
+
+class ChangeMetadataInterceptor2 extends Grpc\Interceptor
+{
+    public function interceptUnaryUnary($method,
+                                        $argument,
+                                        array $metadata = [],
+                                        array $options = [],
+                                        $continuation)
+    {
+        if (array_key_exists('foo', $metadata)) {
+            $metadata['bar'] = array('ChangeMetadataInterceptor should be executed first');
+        } else {
+            $metadata["bar"] = array('interceptor_from_unary_request');
+        }
+        return $continuation($method, $argument, $metadata, $options);
+    }
+    public function interceptStreamUnary($method,
+                                         array $metadata = [],
+                                         array $options = [],
+                                         $continuation)
+    {
+        if (array_key_exists('foo', $metadata)) {
+            $metadata['bar'] = array('ChangeMetadataInterceptor should be executed first');
+        } else {
+            $metadata["bar"] = array('interceptor_from_stream_request');
+        }
+        return $continuation($method, $metadata, $options);
+    }
+}
+
+class ChangeRequestCall
+{
+    private $call;
+
+    public function __construct($call)
+    {
+        $this->call = $call;
+    }
+    public function getCall()
+    {
+        return $this->call;
+    }
+
+    public function write($request)
+    {
+        $request->setData('intercepted_stream_request');
+        $this->getCall()->write($request);
+    }
+
+    public function wait()
+    {
+        return $this->getCall()->wait();
+    }
+}
+
+class ChangeRequestInterceptor extends Grpc\Interceptor
+{
+    public function interceptUnaryUnary($method,
+                                        $argument,
+                                        array $metadata = [],
+                                        array $options = [],
+                                        $continuation)
+    {
+        $argument->setData('intercepted_unary_request');
+        return $continuation($method, $argument, $metadata, $options);
+    }
+    public function interceptStreamUnary($method, array $metadata = [], array $options = [], $continuation)
+    {
+        return new ChangeRequestCall(
+            $continuation($method, $metadata, $options)
+        );
+    }
+}
+
+class StopCallInterceptor extends Grpc\Interceptor
+{
+    public function interceptUnaryUnary($method,
+                                        $argument,
+                                        array $metadata = [],
+                                        array $options = [],
+                                        $continuation)
+    {
+        $metadata["foo"] = array('interceptor_from_request_response');
+    }
+    public function interceptStreamUnary($method,
+                                         array $metadata = [],
+                                         array $options = [],
+                                         $continuation)
+    {
+        $metadata["foo"] = array('interceptor_from_request_response');
+    }
+}
+
+class InterceptorTest extends PHPUnit_Framework_TestCase
+{
+    public function setUp()
+    {
+        $this->server = new Grpc\Server([]);
+        $this->port = $this->server->addHttp2Port('0.0.0.0:0');
+        $this->channel = new Grpc\Channel('localhost:'.$this->port, ['credentials' => Grpc\ChannelCredentials::createInsecure()]);
+        $this->server->start();
+    }
+
+    public function tearDown()
+    {
+        $this->channel->close();
+    }
+
+
+    public function testClientChangeMetadataOneInterceptor()
+    {
+        $req_text = 'client_request';
+        $channel_matadata_interceptor = new ChangeMetadataInterceptor();
+        $intercept_channel = Grpc\Interceptor::intercept($this->channel, $channel_matadata_interceptor);
+        echo "create Client\n";
+        $client = new InterceptorClient('localhost:'.$this->port, [
+            'credentials' => Grpc\ChannelCredentials::createInsecure(),
+        ], $intercept_channel);
+        echo "create Call\n";
+        $req = new SimpleRequest($req_text);
+        echo "Call created\n";
+        $unary_call = $client->UnaryCall($req);
+        echo "start call\n";
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $this->assertSame(['interceptor_from_unary_request'], $event->metadata['foo']);
+
+        $stream_call = $client->StreamCall();
+        $stream_call->write($req);
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $this->assertSame(['interceptor_from_stream_request'], $event->metadata['foo']);
+
+        unset($unary_call);
+        unset($stream_call);
+        unset($server_call);
+    }
+
+    public function testClientChangeMetadataTwoInterceptor()
+    {
+        $req_text = 'client_request';
+        $channel_matadata_interceptor = new ChangeMetadataInterceptor();
+        $channel_matadata_intercepto2 = new ChangeMetadataInterceptor2();
+        // test intercept separately.
+        $intercept_channel1 = Grpc\Interceptor::intercept($this->channel, $channel_matadata_interceptor);
+        $intercept_channel2 = Grpc\Interceptor::intercept($intercept_channel1, $channel_matadata_intercepto2);
+        $client = new InterceptorClient('localhost:'.$this->port, [
+            'credentials' => Grpc\ChannelCredentials::createInsecure(),
+        ], $intercept_channel2);
+
+        $req = new SimpleRequest($req_text);
+        $unary_call = $client->UnaryCall($req);
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $this->assertSame(['interceptor_from_unary_request'], $event->metadata['foo']);
+        $this->assertSame(['interceptor_from_unary_request'], $event->metadata['bar']);
+
+        $stream_call = $client->StreamCall();
+        $stream_call->write($req);
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $this->assertSame(['interceptor_from_stream_request'], $event->metadata['foo']);
+        $this->assertSame(['interceptor_from_stream_request'], $event->metadata['bar']);
+
+        unset($unary_call);
+        unset($stream_call);
+        unset($server_call);
+
+        // test intercept by array.
+        $intercept_channel3 = Grpc\Interceptor::intercept($this->channel,
+            [$channel_matadata_intercepto2, $channel_matadata_interceptor]);
+        $client = new InterceptorClient('localhost:'.$this->port, [
+            'credentials' => Grpc\ChannelCredentials::createInsecure(),
+        ], $intercept_channel3);
+
+        $req = new SimpleRequest($req_text);
+        $unary_call = $client->UnaryCall($req);
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $this->assertSame(['interceptor_from_unary_request'], $event->metadata['foo']);
+        $this->assertSame(['interceptor_from_unary_request'], $event->metadata['bar']);
+
+        $stream_call = $client->StreamCall();
+        $stream_call->write($req);
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $this->assertSame(['interceptor_from_stream_request'], $event->metadata['foo']);
+        $this->assertSame(['interceptor_from_stream_request'], $event->metadata['bar']);
+
+        unset($unary_call);
+        unset($stream_call);
+        unset($server_call);
+    }
+
+    public function testClientChangeRequestInterceptor()
+    {
+        $req_text = 'client_request';
+        $change_request_interceptor = new ChangeRequestInterceptor();
+        $intercept_channel = Grpc\Interceptor::intercept($this->channel,
+            $change_request_interceptor);
+        $client = new InterceptorClient('localhost:'.$this->port, [
+            'credentials' => Grpc\ChannelCredentials::createInsecure(),
+        ], $intercept_channel);
+
+        $req = new SimpleRequest($req_text);
+        $unary_call = $client->UnaryCall($req);
+
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $server_call = $event->call;
+        $event = $server_call->startBatch([
+            Grpc\OP_SEND_INITIAL_METADATA => [],
+            Grpc\OP_SEND_STATUS_FROM_SERVER => [
+                'metadata' => [],
+                'code' => Grpc\STATUS_OK,
+                'details' => '',
+            ],
+            Grpc\OP_RECV_MESSAGE => true,
+            Grpc\OP_RECV_CLOSE_ON_SERVER => true,
+        ]);
+        $this->assertSame('intercepted_unary_request', $event->message);
+
+        $stream_call = $client->StreamCall();
+        $stream_call->write($req);
+        $event = $this->server->requestCall();
+        $this->assertSame('/dummy_method', $event->method);
+        $server_call = $event->call;
+        $event = $server_call->startBatch([
+            Grpc\OP_SEND_INITIAL_METADATA => [],
+            Grpc\OP_SEND_STATUS_FROM_SERVER => [
+                'metadata' => [],
+                'code' => Grpc\STATUS_OK,
+                'details' => '',
+            ],
+            Grpc\OP_RECV_MESSAGE => true,
+            Grpc\OP_RECV_CLOSE_ON_SERVER => true,
+        ]);
+        $this->assertSame('intercepted_stream_request', $event->message);
+
+        unset($unary_call);
+        unset($stream_call);
+        unset($server_call);
+    }
+
+    public function testClientChangeStopCallInterceptor()
+    {
+        $req_text = 'client_request';
+        $channel_request_interceptor = new StopCallInterceptor();
+        $intercept_channel = Grpc\Interceptor::intercept($this->channel,
+            $channel_request_interceptor);
+        $client = new InterceptorClient('localhost:'.$this->port, [
+            'credentials' => Grpc\ChannelCredentials::createInsecure(),
+        ], $intercept_channel);
+
+        $req = new SimpleRequest($req_text);
+        $unary_call = $client->UnaryCall($req);
+        $this->assertNull($unary_call);
+
+
+        $stream_call = $client->StreamCall();
+        $this->assertNull($stream_call);
+
+        unset($unary_call);
+        unset($stream_call);
+        unset($server_call);
+    }
+
+    public function testGetInterceptorChannelConnectivityState()
+    {
+        $channel = new Grpc\Channel(
+            'localhost:0',
+            ['credentials' => Grpc\ChannelCredentials::createInsecure()]
+        );
+        $interceptor_channel = Grpc\Interceptor::intercept($channel, new Grpc\Interceptor());
+        $state = $interceptor_channel->getConnectivityState();
+        $this->assertEquals(0, $state);
+        $channel->close();
+    }
+
+    public function testInterceptorChannelWatchConnectivityState()
+    {
+        $channel = new Grpc\Channel(
+            'localhost:0',
+            ['credentials' => Grpc\ChannelCredentials::createInsecure()]
+        );
+        $interceptor_channel = Grpc\Interceptor::intercept($channel, new Grpc\Interceptor());
+        $now = Grpc\Timeval::now();
+        $deadline = $now->add(new Grpc\Timeval(100*1000));
+        $state = $interceptor_channel->watchConnectivityState(1, $deadline);
+        $this->assertTrue($state);
+        unset($time);
+        unset($deadline);
+        $channel->close();
+    }
+
+    public function testInterceptorChannelClose()
+    {
+        $channel = new Grpc\Channel(
+            'localhost:0',
+            ['credentials' => Grpc\ChannelCredentials::createInsecure()]
+        );
+        $interceptor_channel = Grpc\Interceptor::intercept($channel, new Grpc\Interceptor());
+        $this->assertNotNull($interceptor_channel);
+        $channel->close();
+    }
+
+    public function testInterceptorChannelGetTarget()
+    {
+        $channel = new Grpc\Channel(
+            'localhost:8888',
+            ['credentials' => Grpc\ChannelCredentials::createInsecure()]
+        );
+        $interceptor_channel = Grpc\Interceptor::intercept($channel, new Grpc\Interceptor());
+        $target = $interceptor_channel->getTarget();
+        $this->assertTrue(is_string($target));
+        $channel->close();
+    }
+}