Add compatibility check for ::config() method with arduino arg order (#3860)

Author: devyte

libraries/ESP8266WiFi/src/ESP8266WiFiSTA.cpp

@@ -195,6 +195,14 @@ wl_status_t ESP8266WiFiSTAClass::begin() {
     return status();
 }
 
+static void
+swap(IPAddress &lhs, IPAddress &rhs)
+{
+  IPAddress tmp = lhs;
+  lhs = rhs;
+  rhs = tmp;
+}
+
 
 /**
  * Change IP configuration settings disabling the dhcp client
@@ -210,6 +218,22 @@ bool ESP8266WiFiSTAClass::config(IPAddress local_ip, IPAddress gateway, IPAddres
         return false;
     }
 
+    //Arduino has a different arg order: ip, dns, gateway, subnet. To allow compatibility, check first octet of 3rd arg. If 255, interpret as ESP order, otherwise Arduino order.
+    if(subnet[0] != 255)
+    {
+      //octet is not 255 => interpret as Arduino order
+
+      if(dns1[0] == 0)
+      {
+        //arg order is arduino and 4th arg not given => assign it arduino default
+        dns1 = IPAddress(255,255,255,0);
+      }
+
+      //current order is arduino:                   ip-dns-gway-subnet
+      swap(gateway, subnet); //after this, order is ip-gway-dns-subnet
+      swap(subnet, dns1);    //after this, order is ip-gway-subnet-dns (correct ESP order)
+    } 
+
     struct ip_info info;
     info.ip.addr = static_cast<uint32_t>(local_ip);
     info.gw.addr = static_cast<uint32_t>(gateway);

libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h

@@ -39,6 +39,9 @@ class ESP8266WiFiSTAClass {
         wl_status_t begin(char* ssid, char *passphrase = NULL, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
         wl_status_t begin();
 
+        //The argument order for ESP is not the same as for Arduino. However, there is compatibility code under the hood 
+        //to detect Arduino arg order, and handle it correctly. Be aware that the Arduino default value handling doesn't 
+        //work here (see Arduino docs for gway/subnet defaults). In other words: at least 3 args must always be given.
         bool config(IPAddress local_ip, IPAddress gateway, IPAddress subnet, IPAddress dns1 = (uint32_t)0x00000000, IPAddress dns2 = (uint32_t)0x00000000);
 
         bool reconnect();