diff --git a/lib/redis_client/redis_client.dart b/lib/redis_client/redis_client.dart
index 6c1de83..a9fa855 100644
--- a/lib/redis_client/redis_client.dart
+++ b/lib/redis_client/redis_client.dart
@@ -2,6 +2,8 @@ part of redis_client;
 
 const exclusive = '(';
 
+typedef SubscriptionCallback = Function(Receiver receiver);
+
 /**
  * The [RedisClient] is a high level class to access your redis server.
  *
@@ -62,6 +64,8 @@ class RedisClient {
   Map get stats => connection.stats;
 
   Future close() => connection.close();
+  
+  bool get isConnected => connection.isConnected;
 
 
 
@@ -284,7 +288,17 @@ class RedisClient {
   Future<String> getset(String key, String value) => connection.sendCommand(RedisCommand.GETSET, [ key, value ]).receiveBulkString();
 
   /// Sets the value of given key.
-  Future set(String key, String value) => connection.sendCommand(RedisCommand.SET, [ key, value ]).receiveStatus("OK");
+  Future<bool> set(String key, String value, {bool ifNotExists = false, Duration expiration}) async {
+    final list = [key, value];
+    if (expiration != null) list.addAll(['PX', (expiration.inMilliseconds).toString()]);
+    if (ifNotExists) list.add('NX');
+    try {
+      final reply = await connection.sendCommand(RedisCommand.SET, list).receiveStatus('OK');
+      return reply == 'OK';
+    } on RedisClientException catch (e) {
+      return false;
+    }
+  }
 
   /**
    * Sets a value and the expiration in one step.
@@ -305,6 +319,14 @@ class RedisClient {
       connection.sendCommand(RedisCommand.PSETEX, 
           [ key, expireInMs.toString(), value ]).receiveStatus("OK");
 
+  /// If [key] does not exist, the key is added with the value of [value],
+  /// and true is returned.
+  ///
+  /// If [key] does exist, this operation has no effect and false is returned.
+  Future<bool> setnx(String key, Object value) =>
+      connection.sendCommandWithVariadicValues(RedisCommand.SETNX, [ key ],
+          serializer.serializeToList(value)).receiveBool();
+
   /**
    * Remove the existing timeout on key.
    *
@@ -1447,7 +1469,7 @@ class RedisClient {
    * If field already exists, this operation has no effect.
    */
   Future<bool> hsetnx(String hashId, String key, Object value) => 
-      connection.sendCommandWithVariadicValues(RedisCommand.HSETNX, [ key ], 
+      connection.sendCommandWithVariadicValues(RedisCommand.HSETNX, [ hashId, key ], 
           serializer.serializeToList(value)).receiveBool();
   
   /**
@@ -1567,7 +1589,7 @@ class RedisClient {
    * Subscribes to [List<String> ] channels 
    * with [Function] onMessage handler
    */
-  Future subscribe(List<String> channels, Function onMessage) => connection.subscribe(channels, onMessage);      
+  Future subscribe(List<String> channels, SubscriptionCallback onMessage) => connection.subscribe(channels, onMessage);      
   
   /**
    * Unubscribes from [List<String>] channels 
@@ -1578,7 +1600,7 @@ class RedisClient {
    * Publishes [String] message to [String] channel 
    * map when key does not exist.
    */
-  Future publish(String channel, String message) => 
+  Future<int> publish(String channel, String message) => 
       connection.sendCommand(RedisCommand.PUBLISH, [channel,message])
         .receiveInteger();
   
diff --git a/lib/redis_client/redis_connection.dart b/lib/redis_client/redis_connection.dart
index 6bbdf72..255287d 100644
--- a/lib/redis_client/redis_connection.dart
+++ b/lib/redis_client/redis_connection.dart
@@ -73,11 +73,13 @@ abstract class RedisConnection {
 
 
   /// Subscribes to [List<String>] channels with [Function] onMessage handler
-  Future subscribe(List<String> channels, Function onMessage);
+  Future subscribe(List<String> channels, SubscriptionCallback onMessage);
 
 
   /// Unubscribes from [List<String>] channels
   Future unsubscribe(List<String> channels);
+  
+  var isConnected = false;
 }
 
 
@@ -169,6 +171,8 @@ class _RedisConnection extends RedisConnection {
             .transform(_streamTransformerHandler.createTransformer())
             .listen(_onRedisReply, onError: _onStreamError, onDone: _onStreamDone);
 
+          isConnected = true;
+
           if (password != null) return _authenticate(password);
         })
         .then((_) {
@@ -189,6 +193,7 @@ class _RedisConnection extends RedisConnection {
   /// Closes the connection.
   Future close() {
     logger.fine("Closing connection.");
+    isConnected = false;
     return this.connected.then((_) => _socket.close());
   }
 
@@ -209,12 +214,13 @@ class _RedisConnection extends RedisConnection {
   /// Gets called when the socket has an error.
   void _onSocketError(err) {
     logger.warning("Socket error $err.");
+    close();
     throw new RedisClientException("Socket error $err.");
   }
 
-  Function _subscriptionHandler = null;
+  SubscriptionCallback _subscriptionHandler = null;
 
-  Future subscribe(List<String> channels, Function onMessage){
+  Future subscribe(List<String> channels, SubscriptionCallback onMessage){
 
     Completer subscribeCompleter = new Completer();
     List<String> args = new List <String>()
@@ -269,11 +275,13 @@ class _RedisConnection extends RedisConnection {
   void _onStreamError(err) {
     logger.warning("Stream error $err");
     _socket.close();
+    isConnected = false;
     throw new RedisClientException("Received stream error $err.");
   }
 
   /// Gets called when the stream closes.
   void _onStreamDone() {
+    isConnected = false;
     logger.fine("Stream finished.");
   }
 
@@ -321,6 +329,10 @@ class _RedisConnection extends RedisConnection {
    *     rawSend([ "GET".codeUnits, UTF8.encode("keyname") ]).receiveBulkString().then((String value) { });
    */
   Receiver rawSend(List<List<int>> cmdWithArgs) {
+    
+    if (!isConnected)
+      throw new RedisClientException('redis socket not connected');
+
     var response = new Receiver();