client.connected() return true when internet lost connection

[ruem2802]

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Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
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Platform

• Hardware: [ESP-12|ESP-01|ESP-07|ESP8285 device|other]
• Core Version: [latest git hash or date]
• Development Env: [Arduino IDE|Platformio|Make|other]
• Operating System: [Windows|Ubuntu|MacOS]

Settings in IDE

• Module: [Generic ESP8266 Module|Wemos D1 mini r2|Nodemcu|other]
• Flash Mode: [qio|dio|other]
• Flash Size: [4MB/1MB]
• lwip Variant: [v1.4|v2 Lower Memory|Higher Bandwidth]
• Reset Method: [ck|nodemcu]
• Flash Frequency: [40Mhz]
• CPU Frequency: [80Mhz|160MHz]
• Upload Using: [OTA|SERIAL]
• Upload Speed: [115200|other] (serial upload only)

Problem Description

Detailed problem description goes here.

MCVE Sketch

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#define BUTTON D1 
// WiFi
const char *ssid = "mousse"; // Enter your WiFi name
const char *password = "qweqweqwe";  // Enter WiFi password

// MQTT Broker
const char *mqtt_broker = "broker.emqx.io";
const char *topic = "esp8266/test";
const char *mqtt_username = "emqx";
const char *mqtt_password = "public";
const int mqtt_port = 1883;
bool status_internet = true ;

WiFiClient espClient;
PubSubClient client(espClient);

void setup() {
  // Set software serial baud to 115200;
  Serial.begin(115200);
   pinMode(BUTTON, INPUT); // Button 1 as input
  // connecting to a WiFi network
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
      delay(500);
      Serial.println("Connecting to WiFi..");
  }
  Serial.println("Connected to the WiFi network");
  //connecting to a mqtt broker
  client.setServer(mqtt_broker, mqtt_port);
  client.setCallback(callback);
  while (!client.connected()) {
      status_internet  = fail;
      String client_id = "esp8266-client-";
      client_id += String(WiFi.macAddress());
      Serial.printf("The client %s connects to the public mqtt broker\n", client_id.c_str());
      if (client.connect(client_id.c_str(), mqtt_username, mqtt_password)) {
          status_internet  = true;
          Serial.println("Public emqx mqtt broker connected");
      } else {    
          Serial.print("failed with state ");
          Serial.print(client.state());
          delay(2000);
      }
  }
  // publish and subscribe
  client.publish(topic, "hello emqx");
  client.subscribe(topic);
}

void callback(char *topic, byte *payload, unsigned int length) {
  Serial.print("Message arrived in topic: ");
  Serial.println(topic);
  Serial.print("Message:");
  for (int i = 0; i < length; i++) {
      Serial.print((char) payload[i]);
  }
  Serial.println();
  Serial.println("-----------------------");
}

void check_input()
{
  if(digitalRead(BUTTON_1) client.publish("state button", 1);
  else client.publish("state button", 0);
}
void loop() {
  client.loop();
check_input();
}

Debug Messages

Debug messages go here

When internet lost connection client.connected() return true so I continue to publish -> Error

[mcspr]

This is not related to Core though? Example code you provided deals with PubSubClient, which is an external library and is not maintained in this repo. Check out the example code dealing with disconnections, and if that does not work please report to the PubSubClient repo instead:
https://github.com/knolleary/pubsubclient
https://github.com/knolleary/pubsubclient/blob/master/examples/mqtt_reconnect_nonblocking/mqtt_reconnect_nonblocking.ino

[ruem2802]

@mcspr i checked pubsubclient.cpp, in function client.connected() they call core 's function: when lost connection (i unplug the network) -> function 's esp8266 (_client->connected) not return false state instantly

[mcspr]

Yes, but this does not happen immediately
https://arduino-esp8266.readthedocs.io/en/latest/esp8266wifi/client-class.html
https://www.arduino.cc/en/Reference/WiFiClientConnected

connected()
Whether or not the client is connected. Note that a client is considered connected if the connection has been closed but there is still unread data.

Arduino/libraries/ESP8266WiFi/src/WiFiClient.cpp

Lines 325 to 331 in 9d024d1

	uint8_t WiFiClient::connected()
	{
	if (!_client || _client->state() == CLOSED)
	return 0;
	return _client->state() == ESTABLISHED || available();
	}

_client->state() also does not change straight away when you hard-disconnect by unplugging the cable and thus wificlient will still think it is connected for a while (...at least 15min, iirc?). PubSubClient has an additional check for MQTT ping packets, see keepAlive (based on MQTT_KEEPALIVE) time checks at the top of the 'loop()'. It should notice that as there's no network activity and it will stop the underlying client in about 15seconds (default) and return 'false'.

[ruem2802]

@mcspr Thank for support!!

[d-a-v]

Regarding

connected()
Whether or not the client is connected. Note that a client is considered connected if the connection has been closed but there is still unread data.

While it is true that historically, ::connected() is true when ::available() is true, this assertion has been removed some time ago because it leaded to network issues.

Currently ::connected() is a synonym of Peer can still send us data in the future = the posix meaning or a connected tcp link. When it is false, no more new data can be received, but we can have unread data in the receive buffer, which ::available() is able to tell us.
This is described in our documentation and I can link to the history of this change on request (or update doc or whatever is needed to make things more clear).

[mcspr]

Currently ::connected() is a synonym of Peer can still send us data in the future = the posix meaning or a connected tcp link. When it is false, no more new data can be received, but we can have unread data in the receive buffer, which ::available() is able to tell us.
This is described in our documentation and I can link to the history of this change on request (or update doc or whatever is needed to make things more clear).

Then, should the notice be in the our client doc? 'git-blame' points to #4626, and there was at least one discussion related to the change at #6701 (which did not actually result in updating the docs... :/)

Something like

Whether or not the client is connected. Notice that a client is considered disconnected when the underlying connection is closed, even when there is still an unread data.

And replace the 'connected()' link with a html header link to the paragraph included in the wificlient class page

Also from cross-links, there's at least one patch to the pubsubclient that tweaks it's behaviour and uses ::available() before ::connected()
https://github.com/letscontrolit/ESPEasy/pull/2811/files
https://github.com/letscontrolit/ESPEasy/blob/mega/lib/pubsubclient/src/PubSubClient.cpp