diff --git a/src/TinyMqtt.cpp b/src/TinyMqtt.cpp
index 9e164a7..9077ba9 100644
--- a/src/TinyMqtt.cpp
+++ b/src/TinyMqtt.cpp
@@ -59,7 +59,7 @@ void MqttClient::close(bool bSendDisconnect)
 {
 	debug("close " << id().c_str());
 	mqtt_connected = false;
-	if (client)
+	if (client)	// connected to a remote broker
 	{
 		if (bSendDisconnect and client->connected())
 		{
@@ -72,10 +72,16 @@ void MqttClient::close(bool bSendDisconnect)
 	if (parent)
 	{
 		parent->removeClient(this);
-		parent=nullptr;
+		parent = nullptr;
 	}
 }
 
+void MqttClient::connect(MqttBroker* parentBroker)
+{
+	close();
+	parent = parentBroker;
+}
+
 void MqttClient::connect(std::string broker, uint16_t port, uint16_t ka)
 {
 	debug("cnx: closing");
@@ -397,12 +403,13 @@ void MqttClient::processMessage(const MqttMessage* mesg)
 #ifdef TINY_MQTT_DEBUG
 if (mesg->type() != MqttMessage::Type::PingReq && mesg->type() != MqttMessage::Type::PingResp)
 {
-#ifdef NOT_ESP_CORE
-  Serial << "---> INCOMING " << _HEX(mesg->type()) << " client(" << (dbg_ptr)client << ':' << clientId << ") mem=" << " ESP.getFreeHeap() "<< endl;
-#else
-  Serial << "---> INCOMING " << _HEX(mesg->type()) << " client(" << (dbg_ptr)client << ':' << clientId << ") mem=" << ESP.getFreeHeap() << endl;
-#endif
+	#ifdef NOT_ESP_CORE
+		Serial << "---> INCOMING " << _HEX(mesg->type()) << " client(" << (dbg_ptr)client << ':' << clientId << ") mem=" << " ESP.getFreeHeap() "<< endl;
+	#else
+		Serial << "---> INCOMING " << _HEX(mesg->type()) << " client(" << (dbg_ptr)client << ':' << clientId << ") mem=" << ESP.getFreeHeap() << endl;
+	#endif
 	// mesg->hexdump("Incoming");
+	mesg->hexdump("Incoming");
 }
 #endif
   auto header = mesg->getVHeader();
@@ -544,6 +551,9 @@ if (mesg->type() != MqttMessage::Type::PingReq && mesg->type() != MqttMessage::T
 			break;
 
 		case MqttMessage::Type::Publish:
+			#ifdef TINY_MQTT_DEBUG
+				Serial << "publish " << mqtt_connected << '/' << (long) client << endl;
+			#endif
 			if (mqtt_connected or client == nullptr)
 			{
 				uint8_t qos = mesg->type() & 0x6;
@@ -558,8 +568,12 @@ if (mesg->type() != MqttMessage::Type::PingReq && mesg->type() != MqttMessage::T
 				// TODO reset DUP
 				// TODO reset RETAIN
 
-				if (client==nullptr)	// internal MqttClient receives publish
+				if (parent==nullptr or client==nullptr)	// internal MqttClient receives publish
 				{
+					#ifdef TINY_MQTT_DEBUG
+						Serial << (isSubscribedTo(published) ? "not" : "") << " subscribed.\n";
+						Serial << "has " << (callback ? "" : "no ") << " callback.\n";
+					#endif
 					if (callback and isSubscribedTo(published))
 					{
 						callback(this, published, payload, len);	// TODO send the real payload
@@ -613,7 +627,6 @@ MqttError MqttClient::publish(const Topic& topic, const char* payload, size_t pa
 	MqttMessage msg(MqttMessage::Publish);
 	msg.add(topic);
 	msg.add(payload, pay_length, false);
-	msg.complete();
 	if (parent)
 	{
 		return parent->publish(this, topic, msg);
@@ -637,6 +650,10 @@ MqttError MqttClient::publishIfSubscribed(const Topic& topic, const MqttMessage&
 		else
 		{
 			processMessage(&msg);
+
+			#ifdef TINY_MQTT_DEBUG
+				Serial << "Should call the callback ?\n";
+			#endif
 			// callback(this, topic, nullptr, 0);	// TODO Payload
 		}
 	}
@@ -714,7 +731,7 @@ void MqttMessage::incoming(char in_byte)
 			reset();
 			break;
 	}
-	if (buffer.length() > MaxBufferLength)	// TODO magic 256 ?
+	if (buffer.length() > MaxBufferLength)
 	{
 		debug("Too long " << state);
 		reset();
@@ -725,36 +742,47 @@ void MqttMessage::add(const char* p, size_t len, bool addLength)
 {
 	if (addLength)
 	{
-		buffer.reserve(buffer.length()+addLength+2);
+		buffer.reserve(buffer.length()+2);
 		incoming(len>>8);
 		incoming(len & 0xFF);
 	}
 	while(len--) incoming(*p++);
 }
 
-void MqttMessage::encodeLength(char* msb, int length) const
+void MqttMessage::encodeLength() const
 {
-	do
+	if (state != Complete)
 	{
-		uint8_t encoded(length & 0x7F);
-		length >>=7;
-		if (length) encoded |= 0x80;
-		*msb++ = encoded;
-	} while (length);
-};
+		int length = buffer.size()-2;	// 1 byte for header, 1 byte for pre-reserved length field.
+		std::string::size_type ins=1;
+		do
+		{
+			uint8_t encoded(length & 0x7F);
+			length >>=7;
+			if (length) encoded |= 0x80;
 
-void MqttMessage::complete()
-{
-		encodeLength(&buffer[1], buffer.size()-2);
+			if (ins==1)
+				buffer[ins]=encoded;
+			else
+				buffer.insert(ins, 1, encoded);
+			// On pourrait optimiser, cet insert est couteux, il faudrait en fait non pas
+			// insérer, mais réserver 4 octets  pour les remplir
+			// plus tard avec ke fixed header et la taille.
+			// Cela changerait en revanche le début du message qui ne serait plus
+			// buffer[0], mais buffer[0..3] selon la taille du message.
+			
+			++ins;
+		} while (length);
 		state = Complete;
-}
+	}
+};
 
 MqttError MqttMessage::sendTo(MqttClient* client) const
 {
 	if (buffer.size())
 	{
 		debug("sending " << buffer.size() << " bytes");
-		encodeLength(&buffer[1], buffer.size()-2);
+		encodeLength();
 		// hexdump("snd");
 		client->write(&buffer[0], buffer.size());
 	}
diff --git a/src/TinyMqtt.h b/src/TinyMqtt.h
index 27487dd..2a8d01a 100644
--- a/src/TinyMqtt.h
+++ b/src/TinyMqtt.h
@@ -101,8 +101,6 @@ class MqttMessage
 		void add(const Topic& t) { add(t.str()); }
 		const char* end() const { return &buffer[0]+buffer.size(); }
 		const char* getVHeader() const { return &buffer[vheader]; }
-		uint16_t length() const { return buffer.size(); }
-		void complete();
 
 		void reset();
 
@@ -127,12 +125,12 @@ class MqttMessage
 		void hexdump(const char* prefix=nullptr) const;
 
 	private:
-		void encodeLength(char* msb, int length) const;
+		void encodeLength() const;
 
 		mutable std::string buffer;	// mutable -> sendTo()
 		uint8_t vheader;
 		uint16_t size;	// bytes left to receive
-		State state;
+		mutable State state;	// mutable -> encodeLength()
 };
 
 class MqttBroker;
@@ -172,7 +170,14 @@ class MqttClient
 		/** Should be called in main loop() */
 		void loop();
 		void close(bool bSendDisconnect=true);
-		void setCallback(CallBack fun) {callback=fun; };
+		void setCallback(CallBack fun)
+		{
+			callback=fun;
+			#ifdef TINY_MQTT_DEBUG
+				Serial << "Callback set to " << (long)fun << endl;
+				if (callback) callback(this, "test/topic", "value", 5);
+			#endif
+		};
 
 		// Publish from client to the world
 		MqttError publish(const Topic&, const char* payload, size_t pay_length);
@@ -214,6 +219,8 @@ class MqttClient
 		static long counter;
 
 	private:
+
+		// event when tcp/ip link established (real or fake)
 		static void onConnect(void * client_ptr, TcpClient*);
 #ifdef TCP_ASYNC
 		static void onData(void* client_ptr, TcpClient*, void* data, size_t len);
@@ -240,7 +247,7 @@ class MqttClient
 		// (this is the case when MqttBroker isn't used except here)
 		MqttBroker* parent=nullptr;		// connection to local broker
 
-		TcpClient* client=nullptr;		// connection to mqtt client or to remote broker
+		TcpClient* client=nullptr;		// connection to remote broker
 		std::set<Topic>	subscriptions;
 		std::string clientId;
 		CallBack callback = nullptr;