I develop server app using boost asio. App works great. What doesn't work, is the the exclusive binding to the network port.
I launch one instance of the app - it starts listening to incoming connections.
I launch one more instance - it also starts listening to incoming connections on the same port. Handler that passed to async_accept do not invoked with error as expected.
Usually I just try to acquire the port. If operation fails - port is in use. With Asio this approach does not work. How to check availability of the port?
void TcpServerFactory::acceptConnectionsOnPort(int serverPort,
boost::shared_ptr<TcpConfigServerReceiver> tcpConfig,
boost::function<void(boost::shared_ptr<TcpServer>)> onSuccessfullyConnectedHandler)
{
// todo check is port not busy
FORMATTED_LOG(this->_log, info) << "Start to accept connections on port " << serverPort;
auto endpoint = boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), serverPort);
boost::shared_ptr<boost::asio::ip::tcp::acceptor> tcpAcceptor(new boost::asio::ip::tcp::acceptor(this->_ioService, endpoint));
this->acceptConnections(tcpAcceptor, tcpConfig, onSuccessfullyConnectedHandler);
}
void TcpServerFactory::acceptConnections(boost::shared_ptr<boost::asio::ip::tcp::acceptor> tcpAcceptor,
boost::shared_ptr<TcpConfigServerReceiver> tcpConfig,
boost::function<void(boost::shared_ptr<TcpServer>)> onSuccessfullyConnectedHandler)
{
boost::shared_ptr<boost::asio::ip::tcp::socket> tcpSocket(new boost::asio::ip::tcp::socket(this->_ioService));
boost::function<void(const boost::system::error_code &)> onAcceptOperationCompletedHandler =
boost::bind(&TcpServerFactory::onAcceptOperationCompleted, this->downcasted_shared_from_this<TcpServerFactory>(),
_1, tcpAcceptor, tcpSocket, tcpConfig, onSuccessfullyConnectedHandler);
tcpAcceptor.get()->async_accept(*tcpSocket, onAcceptOperationCompletedHandler);
}
void TcpServerFactory::onAcceptOperationCompleted(const boost::system::error_code & err,
boost::shared_ptr<boost::asio::ip::tcp::acceptor> tcpAcceptor,
boost::shared_ptr<boost::asio::ip::tcp::socket> tcpSocket,
boost::shared_ptr<TcpConfigServerReceiver> tcpConfig,
boost::function<void(boost::shared_ptr<TcpServer>)> onSuccessfullyConnectedHandler)
{
if (err)
{
FORMATTED_LOG(this->_log, info) << "Failed to accept connections on port " << tcpAcceptor->local_endpoint().port() << "due to error " << BOOST_ERROR_TO_STREAM(err);
return;
}
this->acceptConnections(tcpAcceptor, tcpConfig, onSuccessfullyConnectedHandler);
this->onConnectionEstablished(tcpSocket, tcpConfig, onSuccessfullyConnectedHandler);
}
Update
I tried to replace constructor of acceptor on series of commands. I expected that on tcpAcceptor->bind() exception will be raised, but that didn't happened.
// boost::shared_ptr<boost::asio::ip::tcp::acceptor> tcpAcceptor(new boost::asio::ip::tcp::acceptor(this->_ioService, endpoint));
boost::shared_ptr<boost::asio::ip::tcp::acceptor> tcpAcceptor(new boost::asio::ip::tcp::acceptor(this->_ioService));
tcpAcceptor->open(endpoint.protocol());
tcpAcceptor->set_option(boost::asio::socket_base::reuse_address(true));
tcpAcceptor->bind(endpoint);
boost::system::error_code err;
tcpAcceptor->listen(boost::asio::socket_base::max_connections, err);
reuse_address is not supposed to do that. Its meaning to avoid "wait" interval after port was freed.
Related
I'm new at IoT & MQTT communication protocol. I'm trying to connect my broker which runs at Amazon Ec2 from my Vue web app via Websockets. I have started mosquitto with:
root#ip-xxx-xx-xx-xx:~# mosquitto -c /etc/mosquitto/conf.d/default.conf
1618518468: mosquitto version 1.6.7 starting
1618518468: Config loaded from /etc/mosquitto/conf.d/default.conf.
1618518468: Opening ipv4 listen socket on port 1883.
1618518468: Opening ipv6 listen socket on port 1883.
1618518468: Opening websockets listen socket on port 9001.
/etc/mosquitto/conf.d/default.conf file contains:
listener 1883
protocol mqtt
allow_anonymous true
listener 9001
protocol websockets
allow_anonymous true
My test js file is:
var mqtt = require('mqtt');
var count =0;
var client = mqtt.connect("mqtt://xx.xxx.xxx.xxx",{clientId:"mqttjs01"});
console.log("connected flag " + client.connected);
//handle incoming messages
client.on('message',function(topic, message, packet){
console.log("message is "+ message);
console.log("topic is "+ topic);
});
client.on("connect",function(){
console.log("connected "+ client.connected);
})
//handle errors
client.on("error",function(error){
console.log("Can't connect" + error);
process.exit(1)});
//publish
function publish(topic,msg,options){
console.log("publishing",msg);
if (client.connected == true){
client.publish(topic,msg,options);
}
count+=1;
if (count==2) //ens script
clearTimeout(timer_id); //stop timer
client.end();
}
//////////////
var options={
retain:true,
qos:1};
var topic="acs";
var message="test message";
var topic_list=["topic2","topic3","topic4"];
var topic_o={"topic22":0,"topic33":1,"topic44":1};
console.log("subscribing to topics");
client.subscribe(topic,{qos:0}); //single topic
client.subscribe(topic_list,{qos:1}); //topic list
client.subscribe(topic_o); //object
var timer_id=setInterval(function(){publish(topic,message,options);},5000);
//notice this is printed even before we connect
console.log("end of script");
But I'm getting this error:
New client connected from 176.xxx.xxx.xx as mqttjs01 (p2, c1, k60).
1618518546: Socket error on client mqttjs01, disconnecting.
I have installed libwebsockets, I have tried with various mosquitto versions. Current version is: 1.6.7.
Is there any problem with my client or broker? How can I fix this?
At the end of the publish() function the if statement is missing enclosing braces so it doesn't do what you think it does.
function publish(topic,msg,options){
console.log("publishing",msg);
if (client.connected == true){
client.publish(topic,msg,options);
}
count+=1;
if (count==2) //ens script
clearTimeout(timer_id); //stop timer
client.end();
}
Lets fix the indentation so we can see more clearly.
function publish(topic,msg,options){
console.log("publishing",msg);
if (client.connected == true){
client.publish(topic,msg,options);
}
count+=1;
if (count==2) //ens script
clearTimeout(timer_id); //stop timer
client.end();
}
As you can see client.end() will ALWAYS be called when ever publish() is called. If you only want to publish twice you need to wrap the 2 statements in the braces (this is not python where whitespace has meaning)
if (count==2) { //ens script
clearTimeout(timer_id); //stop timer
client.end();
}
You really should indent all your code properly it will make it much easier to read and to spot errors like this.
Also as #JDAllen mentioned you are not making use of the WebSocket connection, unless this code is running in the browser, where the sandbox will force it to be a WebSocket connection even if you specify mqtt:// as the schema in the URL, and you will have to include the port number to make it actually connect. e.g.
ws://xxx.xxx.xxx.xxx:9001
I have an esp32 as STA in my network, collecting sensor data, that publishes through my wifi AP to my home network. Everything was working fine until we had a general power surge in the neighborhood. When power came back the esp32 was out of the network. I had to recycle its power to let it re-establish connection. Is there an explanation for this? Most probably it came up much faster than the wifi or the mqtt broker did. Could this be the issue? If this is the issue, is there a way to postpone booting of the esp32 just after wifi network and mqtt is available?
Edit: I return to my original post to add some code that I used.
void setup() {
Serial.begin(115200);
delay(10);
WiFi.mode(WIFI_STA);
// Configures static IP address
if (!WiFi.config(local_IP, gateway, subnet, primaryDNS, secondaryDNS)) {
Serial.println("STA Failed to configure");
}
// Connect to Wi-Fi network with SSID and password
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
// Print local IP address
Serial.println("");
Serial.println("WiFi connected.");
Serial.println("IP address: ");
...
client.setKeepAlive( MQTT_KEEPALIVE );
client.setServer(mqtt_server, 1883);
client.connect(aHostname);
if (!client.connected()) {
Serial.print("mqtt status in setup: ");
Serial.println(client.state());
reconnect();
} else {
client.setCallback(callback);
Serial.print("mqtt status in setup: ");
Serial.println(client.state());
client.setCallback(callback);
client.setKeepAlive( MQTT_KEEPALIVE );
}
Also if mqtt broker is lost there is a reconnection attempt in loop:
void loop(){
if (!client.connected()) {
reconnect();
}
..
}
If it's a question of ESP32 booting faster than the WiFi access point, then this has a very simple solution. Retry the WiFi connection in ESP32 until it succeeds. Then do the same with MQTT. If you think about it, the device is useless without WiFi&MQTT connections so feel free to just keep retrying forever (or until it's successful).
In your case the MQTT broker's retry in the loop() should be an obvious example of to add a similar retry for the WiFi. Since I don't use Arduino and I don't currently have the time to read the WiFi module's documentation, I'll leave the implementation to you.
Facing a issue if the client is started before server
Specs : ubuntu 16.04 with c++11,libzmq : 4.2.3
problem : sample codes
server.cpp
int main()
{
zmq::context_t context(1);
zmq::socket_t requester(context,ZMQ_ROUTER);
.
//code to get address
.
requester.bind(address);
while(true)
{
zmq::message_t message;
requester.recv(&message);
.
//remaining code
.
}
return 0;
}
client.cpp
int main()
{
zmq::context_t context(1);
zmq::socket_t requester(context,ZMQ_DEALER);
.
//code to get address
.
requester.connect(address);
zmq::message_t message;
.
//populate the message to send
.
requester.send(message);
return 0;
}
I know that in zmq i can start client even if the server is not running,but my client application has to include a safety check which requires the server to be started.Is there any way i can achieve by making connect fail or someother workaround.Timeout options doesnt work for me
Make the send non blocking, if there there is no server(s) available the send will fail and set an errno
http://api.zeromq.org/4-2:zmq-send
ZMQ_DONTWAIT
For socket types (DEALER, PUSH) that block when there are no available peers
(or all peers have full high-water mark), specifies that the operation should
be performed in non-blocking mode. If the message cannot be queued on the
socket, the zmq_send() function shall fail with errno set to EAGAIN.
I'm struggling with connecting two sockets:
frontend (ROUTER) - which handles clients request and forward them to backend
backend (ROUTER) - which receives request from frontend and deals with them with the use of number of workers ( which require some initialization, configuration etc).
The server code looks like this:
void server_task::run() {
frontend.bind("tcp://*:5570");
backend.bind("inproc://backend");
zmq::pollitem_t items[] = {
{ frontend, 0, ZMQ_POLLIN, 0 },
{ backend, 0, ZMQ_POLLIN, 0}
};
try {
while (true) {
zmq::poll(&items[0], 2, -1);
if (items[0].revents & ZMQ_POLLIN) {
frontend_h();
}
if (items[1].revents & ZMQ_POLLIN) {
backend_h();
}
}
}
catch (std::exception& e) {
LOG(info) << e.what();
}
}
frontend_h and backend_h are handler classes, each having access to both sockets.
The question is:
Considering synchronous execution of frontend_h() and backend_h() how can I forward the request dealt in frontend_h() to backend_h()?
I tried to simply re-send the message using backend socket like that:
void frontend_handler::handle_query(std::unique_ptr<zmq::message_t> identity, std::unique_ptr<zmq::message_t> request) {
zmq::message_t req_msg, req_identity;
req_msg.copy(request.get());
req_identity.copy(identity.get());
zmq::message_t header = create_header(request_type::REQ_QUERY);
backend.send(header, ZMQ_SNDMORE);
backend.send(message);
}
But it stucks on zmq::poll in run() after the execution of handle_query().
Stucks on zmq::poll()?
Your code has instructed the .poll() method to block, exactly as documentation states:
If the value of timeout is -1, zmq_poll() shall block indefinitely until a requested event has occurred...
How can I forward the request?
It seems pretty expensive to re-marshall each message ( +1 for using at least the .copy() method and avoiding re-packing overheads ) once your code is co-located and the first, receiving handler, can request and invoke any appropriate method of the latter directly ( and without any Context()-processing associated efforts and overheads.
Good day.
I'm trying to implement a question - answer logic using boost::asio.
On the Client I have:
void Send_Message()
{
....
boost::asio::async_write(server_socket, boost::asio::buffer(&Message, sizeof(Message)), boost::bind(&Client::Handle_Write_Message, this, boost::asio::placeholders::error));
....
}
void Handle_Write_Message(const boost::system::error_code& error)
{
....
std::cout << "Message was sent.\n";
....
boost::asio::async_read(server_socket_,boost::asio::buffer(&Message, sizeof(Message)), boost::bind(&Client::Handle_Read_Message, this, boost::asio::placeholders::error));
....
}
void Handle_Read_Message(const boost::system::error_code& error)
{
....
std::cout << "I have a new message.\n";
....
}
And on the Server i have the "same - logic" code:
void Read_Message()
{
....
boost::asio::async_read(client_socket, boost::asio::buffer(&Message, sizeof(Message)), boost::bind(&Server::Handle_Read_Message, this, boost::asio::placeholders::error));
....
}
void Handle_Read_Message(const boost::system::error_code& error)
{
....
std::cout << "I have a new message.\n";
....
boost::asio::async_write(client_socket_,boost::asio::buffer(&Message, sizeof(Message)), boost::bind(&Server::Handle_Write_Message, this, boost::asio::placeholders::error));
....
}
void Handle_Write_Message(const boost::system::error_code& error)
{
....
std::cout << "Message was sent back.\n";
....
}
Message it's just a structure.
And the output on the Client is: Message was sent.
Output on the Server is: I have a new message.
And that's all. After this both programs are still working but nothing happens.
I tried to implement code like:
if (!error)
{
....
}
else
{
// close sockets and etc.
}
But there are no errors in reading or writing. Both programs are just running normally, but doesn't interact with each other.
This code is quite obvious but i can't understand why it's not working.
Thanks in advance for any advice.
Is the underlying socket a unix or inet socket?
You might want to try a tool like tcpdump or wireshark to watch the exchange between the client and server.
I always forget to call run() or poll() on my boost::asio::io_service. Are you calling that? Because boost requires that called periodically in order to send/receive.