esp8266/libraries/lwIP_Ethernet/examples/LegacyAdvancedChatServer/LegacyAdvancedChatServer.ino

/*
 Advanced Chat Server

 A more advanced server that distributes any incoming messages
 to all connected clients but the client the message comes from.
 To use, telnet to your device's IP address and type.
 You can see the client's input in the serial monitor as well.
 Using an Arduino Wiznet Ethernet shield.

 Circuit:
 * Ethernet Wiznet5500/Wiznet5100/ENC28J60 on esp8266

 created 18 Dec 2009
 by David A. Mellis
 modified 9 Apr 2012
 by Tom Igoe
 redesigned to make use of operator== 25 Nov 2013
 by Norbert Truchsess

 */

// specific to esp8266 w/lwIP
#include <EthernetCompat.h>
ArduinoWiznet5500lwIP Ethernet(/*SS*/ 16);  // <== adapt to your hardware
// ArduinoWiznet5100lwIP Ethernet(/*SS*/ 16);  // <== adapt to your hardware
// ArduinoENC28J60lwIP Ethernet(/*SS*/ 16);  // <== adapt to your hardware



// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network.
// gateway and subnet are optional:
byte notNeededButAllowed_mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};
byte* mac = nullptr;  // automatic mac
IPAddress ip(192, 168, 1, 177);
IPAddress myDns(192, 168, 1, 1);
IPAddress gateway(192, 168, 1, 1);
IPAddress subnet(255, 255, 0, 0);


// telnet defaults to port 23
EthernetServer server(23);

EthernetClient clients[8];

void setup() {
  // You can use Ethernet.init(pin) to configure the CS pin
  // Ethernet.init(10);  // Most Arduino shields
  // Ethernet.init(5);   // MKR ETH shield
  // Ethernet.init(0);   // Teensy 2.0
  // Ethernet.init(20);  // Teensy++ 2.0
  // Ethernet.init(15);  // ESP8266 with Adafruit Featherwing Ethernet
  // Ethernet.init(33);  // ESP32 with Adafruit Featherwing Ethernet
  //                     // esp8266 w/lwIP: SS set in Ethernet constructor

  // initialize the Ethernet device
  Ethernet.begin(mac, ip, myDns, gateway, subnet);

  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ;  // wait for serial port to connect. Needed for native USB port only
  }

  // Check for Ethernet hardware present
  if (Ethernet.hardwareStatus() == EthernetNoHardware) {
    Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
    while (true) {
      delay(1);  // do nothing, no point running without Ethernet hardware
    }
  }
  if (Ethernet.linkStatus() == LinkOFF) {
    Serial.println("Ethernet cable is not connected.");
  }

  // start listening for clients
  server.begin();

  Serial.print("Chat server address:");
  Serial.println(Ethernet.localIP());
}

void loop() {
  // check for any new client connecting, and say hello (before any incoming data)
  EthernetClient newClient = server.accept();
  if (newClient) {
    for (byte i = 0; i < 8; i++) {
      if (!clients[i]) {
        Serial.print("We have a new client #");
        Serial.println(i);
        newClient.print("Hello, client number: ");
        newClient.println(i);
        // Once we "accept", the client is no longer tracked by EthernetServer
        // so we must store it into our list of clients
        clients[i] = newClient;
        break;
      }
    }
  }

  // check for incoming data from all clients
  for (byte i = 0; i < 8; i++) {
    if (clients[i] && clients[i].available() > 0) {
      // read bytes from a client
      byte buffer[80];
      int count = clients[i].read(buffer, 80);
      // write the bytes to all other connected clients
      for (byte j = 0; j < 8; j++) {
        if (j != i && clients[j].connected()) {
          clients[j].write(buffer, count);
        }
      }
    }
  }

  // stop any clients which disconnect
  for (byte i = 0; i < 8; i++) {
    if (clients[i] && !clients[i].connected()) {
      Serial.print("disconnect client #");
      Serial.println(i);
      clients[i].stop();
    }
  }
}