Add WiFiServer hasClient and WiFiTelnetToSerial example (#394)

WiFiTelnetToSerial is also a test for hasClient().

libraries/WiFi/examples/WiFiTelnetToSerial/WiFiTelnetToSerial.ino

+/*
+  WiFiTelnetToSerial - Example Transparent UART to Telnet Server for ESP32
+
+  Copyright (c) 2017 Hristo Gochkov. All rights reserved.
+  This file is part of the ESP32 WiFi library for Arduino environment.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+#include <WiFi.h>
+#include <WiFiMulti.h>
+
+WiFiMulti wifiMulti;
+
+//how many clients should be able to telnet to this ESP32
+#define MAX_SRV_CLIENTS 1
+const char* ssid = "**********";
+const char* password = "**********";
+
+WiFiServer server(23);
+WiFiClient serverClients[MAX_SRV_CLIENTS];
+
+HardwareSerial Serial1(2);  // UART1/Serial1 pins 16,17
+
+void setup() {
+  Serial.begin(115200);
+  Serial.println("\nConnecting");
+
+  wifiMulti.addAP(ssid, password);
+  wifiMulti.addAP("ssid_from_AP_2", "your_password_for_AP_2");
+  wifiMulti.addAP("ssid_from_AP_3", "your_password_for_AP_3");
+
+  Serial.println("Connecting Wifi ");
+  for (int loops = 10; loops > 0; loops--) {
+    if (wifiMulti.run() == WL_CONNECTED) {
+      Serial.println("");
+      Serial.print("WiFi connected ");
+      Serial.print("IP address: ");
+      Serial.println(WiFi.localIP());
+      break;
+    }
+    else {
+      Serial.println(loops);
+      delay(1000);
+    }
+  }
+  if (wifiMulti.run() != WL_CONNECTED) {
+    Serial.println("WiFi connect failed");
+    delay(1000);
+    ESP.restart();
+  }
+
+  //start UART and the server
+  Serial1.begin(9600);
+  server.begin();
+  server.setNoDelay(true);
+
+  Serial.print("Ready! Use 'telnet ");
+  Serial.print(WiFi.localIP());
+  Serial.println(" 23' to connect");
+}
+
+void loop() {
+  uint8_t i;
+  if (wifiMulti.run() == WL_CONNECTED) {
+    //check if there are any new clients
+    if (server.hasClient()){
+      for(i = 0; i < MAX_SRV_CLIENTS; i++){
+        //find free/disconnected spot
+        if (!serverClients[i] || !serverClients[i].connected()){
+          if(serverClients[i]) serverClients[i].stop();
+          serverClients[i] = server.available();
+          if (!serverClients[i]) Serial.println("available broken");
+          Serial.print("New client: ");
+          Serial.print(i); Serial.print(' ');
+          Serial.println(serverClients[i].remoteIP());
+          break;
+        }
+      }
+      if (i >= MAX_SRV_CLIENTS) {
+        //no free/disconnected spot so reject
+        server.available().stop();
+      }
+    }
+    //check clients for data
+    for(i = 0; i < MAX_SRV_CLIENTS; i++){
+      if (serverClients[i] && serverClients[i].connected()){
+        if(serverClients[i].available()){
+          //get data from the telnet client and push it to the UART
+          while(serverClients[i].available()) Serial1.write(serverClients[i].read());
+        }
+      }
+      else {
+        if (serverClients[i]) {
+          serverClients[i].stop();
+        }
+      }
+    }
+    //check UART for data
+    if(Serial1.available()){
+      size_t len = Serial1.available();
+      uint8_t sbuf[len];
+      Serial1.readBytes(sbuf, len);
+      //push UART data to all connected telnet clients
+      for(i = 0; i < MAX_SRV_CLIENTS; i++){
+        if (serverClients[i] && serverClients[i].connected()){
+          serverClients[i].write(sbuf, len);
+          delay(1);
+        }
+      }
+    }
+  }
+  else {
+    Serial.println("WiFi not connected!");
+    for(i = 0; i < MAX_SRV_CLIENTS; i++) {
+      if (serverClients[i]) serverClients[i].stop();
+    }
+    delay(1000);
+  }
+}

libraries/WiFi/src/WiFiServer.cpp

@@ -40,9 +40,16 @@ void WiFiServer::stopAll(){}
 WiFiClient WiFiServer::available(){
   if(!_listening)
     return WiFiClient();
+  int client_sock;
+  if (_accepted_sockfd >= 0) {
+    client_sock = _accepted_sockfd;
+    _accepted_sockfd = -1;
+  }
+  else {
   struct sockaddr_in _client;
   int cs = sizeof(struct sockaddr_in);
-  int client_sock = accept(sockfd, (struct sockaddr *)&_client, (socklen_t*)&cs);
+    client_sock = accept(sockfd, (struct sockaddr *)&_client, (socklen_t*)&cs);
+  }
   if(client_sock >= 0){
     int val = 1;
     if(setsockopt(client_sock, SOL_SOCKET, SO_KEEPALIVE, (char*)&val, sizeof(int)) == ESP_OK) {
@@ -70,6 +77,8 @@ void WiFiServer::begin(){
     return;
   fcntl(sockfd, F_SETFL, O_NONBLOCK);
   _listening = true;
+  _noDelay = false;
+  _accepted_sockfd = -1;
 }
 
 void WiFiServer::setNoDelay(bool nodelay) {
@@ -80,6 +89,19 @@ bool WiFiServer::getNoDelay() {
     return _noDelay;
 }
 
+bool WiFiServer::hasClient() {
+    if (_accepted_sockfd >= 0) {
+      return true;
+    }
+    struct sockaddr_in _client;
+    int cs = sizeof(struct sockaddr_in);
+    _accepted_sockfd = accept(sockfd, (struct sockaddr *)&_client, (socklen_t*)&cs);
+    if (_accepted_sockfd >= 0) {
+      return true;
+    }
+    return false;
+}
+
 void WiFiServer::end(){
   close(sockfd);
   sockfd = -1;

libraries/WiFi/src/WiFiServer.h

@@ -26,6 +26,7 @@
 class WiFiServer : public Server {
   private:
     int sockfd;
+    int _accepted_sockfd = -1;
     uint16_t _port;
     uint8_t _max_clients;
     bool _listening;
@@ -34,13 +35,14 @@ class WiFiServer : public Server {
   public:
     void listenOnLocalhost(){}
 
-    WiFiServer(uint16_t port=80, uint8_t max_clients=4):sockfd(-1),_port(port),_max_clients(max_clients),_listening(false){}
+    WiFiServer(uint16_t port=80, uint8_t max_clients=4):sockfd(-1),_accepted_sockfd(-1),_port(port),_max_clients(max_clients),_listening(false),_noDelay(false){}
     ~WiFiServer(){ end();}
     WiFiClient available();
     WiFiClient accept(){return available();}
     void begin();
     void setNoDelay(bool nodelay);
     bool getNoDelay();
+    bool hasClient();
     size_t write(const uint8_t *data, size_t len);
     size_t write(uint8_t data){
       return write(&data, 1);