Captive Portal for WiFi AP

/*
  AccesPoint Server with Captive Portal

  John V - Jan 2019
  Version 0.1.0 - WIP
  Build for MKR Wifi 1000 with uBlox Nina W10
  Build from the basic AP Webserver demo from Arduino website.

  Setting DNS and Gateway IUP to own AP-IPaddress
  Checking first 16 DNS requests via UDP port 53
  Send Respond on DNS requests with redirected IP-adress of own AP : your landing page
  WebServer is a simple main page with a Text-box (php-POST), entered answer is read back from the received data.
  <yourIP>/SECRETS sends the list of answers to the serial - just a test

  Tested with Samsung S7 S5mini Phone with Firefox/Chrome.
  Win10 and iExplore / Chrome gives a problem  - WIP to test others, especialy on HTML replies for connectivity check ???? - how to handle these beyond the CaptivePortal check ?
  
  Serial Debug info is everywhere- feel free to cut ut out to make a leaner code
  btw ... When connecting your phone, you wil see a spam of DNS request data comming in :), its limited to 16 DNS requests, - changed in #define DNSMAXREQUESTS XX 

 */

#include <SPI.h>
#include <WiFiNINA.h>
#include <WiFiUdp.h>
#include "arduino_secrets.h" 

char ssid[] = SECRET_SSID;     // your network SSID (name)
char pass[] = SECRET_PASS;     // your network password (use for WPA, or use as key for WEP)
int keyIndex = 0;              // your network key Index number (needed only for WEP)

// Define Wifi Client parameters
         
IPAddress gwip(172,128, 128, 1);         // GW fixed IP adress
IPAddress apip(172,128, 128, 100);         // AP fixed IP adress
uint8_t apChannel = 2;                  // AP wifi channel
String answerLine = "";                   // make a String to hold incoming php-data from the client
String answerList1[32];                   // store of answerList SSID
String answerList2[32];                   // store of answerList answers
int answerCounter =0;                     

int status = WL_IDLE_STATUS;
WiFiServer server(80);

// Define UDP settings for DNS 
#define UDP_PACKET_SIZE 128           // MAX UDP packaet size = 512
#define DNSHEADER_SIZE 12             // DNS Header
#define DNSANSWER_SIZE 16             // DNS Answer = standard set with Packet Compression
#define DNSMAXREQUESTS 16             // trigger first DNS requests, to redirect to own web-page
byte packetBuffer[ UDP_PACKET_SIZE];  // buffer to hold incoming and outgoing packets
byte dnsReplyHeader[DNSHEADER_SIZE] = { 
  0x00,0x00,   // ID, to be filled in #offset 0
  0x81,0x80,   // answer header Codes
  0x00,0x01,   //QDCOUNT = 1 question
  0x00,0x01,   //ANCOUNT = 1 answer
  0x00,0x00,   //NSCOUNT / ignore
  0x00,0x00    //ARCOUNT / ignore
  };
byte dnsReplyAnswer[DNSANSWER_SIZE] = {   
  0xc0,0x0c,  // pointer to pos 12 : NAME Labels
  0x00,0x01,  // TYPE
  0x00,0x01,  // CLASS
  0x00,0x00,  // TTL
  0x00,0x3c,  // TLL 1 hour
  0x00,0x04,   // RDLENGTH = 4
  0x00,0x00,  // IP adress octets to be filled #offset 12
  0x00,0x00   // IP adress octeds to be filled
  } ;
byte dnsReply[UDP_PACKET_SIZE];       // buffer to hold the send DNS repluy
IPAddress dnsclientIp;
unsigned int dnsclientPort;
unsigned int udpPort = 53;            // local port to listen for UDP packets
WiFiUDP Udp;                          // A UDP instance to let us send and receive packets over UDP
int dnsreqCount=0;

void setup() {
  //Initialize serial and wait for port to open:
  Serial.begin(9600);
  Serial.println("Access Point Web Server with CaptivePortal");

  // check for the WiFi module:
  if (WiFi.status() == WL_NO_MODULE) {
    Serial.println("Communication with WiFi module failed!");
    // don't continue
    while (true);
  }

  String fv = WiFi.firmwareVersion();
  if (fv < "1.0.0") {
    Serial.println("Please upgrade the firmware");
  }

  // by default the local IP address of will be 192.168.4.1
  // Create open network. Change this line if you want to create an WEP network:
  Serial.print("Creating access point named: ");
  Serial.println(ssid);
  WiFi.disconnect();
  WiFi.config(apip,apip,gwip,IPAddress(255,255,255,0));
  //WiFi.setHostname(myHost);
  status = WiFi.beginAP(ssid,apChannel); // setup AP 
  if (status != WL_AP_LISTENING) {
    Serial.println("Creating access point failed");
    // don't continue
    while (true) ;  
  }
    // wait 10 seconds for connection:
  delay(10000);

  // you're connected now, so print out the status
  printWiFiStatus();

  // start the web server on port 80
  Udp.begin(udpPort);
  server.begin();


}


void loop() {
int t;
char c;
// compare the previous AP status to the current status
  IPAddress ip = WiFi.localIP();
  if (status != WiFi.status()) {
    // it has changed update the variable
    status = WiFi.status();

    if (status == WL_AP_CONNECTED) {
      // a device has connected to the AP
      Serial.println("Device connected to AP");
      dnsreqCount=0; 
      udpScan(); // scan DNS request for redirect
    }
    else {
      // a device has disconnected from the AP, and we are back in listening mode
      Serial.println("Device disconnected from AP");
    }
  }
// Wifi Server check
  WiFiClient client = server.available();   // listen for incoming clients
  if (client) {                             // if you get a client,
    Serial.println("new client");           // print a message out the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    while (client.connected()) {            // loop while the client's connected
      if (client.available()) {             // if there's bytes to read from the client,
        c = client.read();             // read a byte, then
        Serial.write(c);                    // print it out the serial monitor
        if (c == '\n') {                    // if the byte is a newline character

          // if the current line is blank, you got two newline characters in a row.
          // that's the end of the client HTTP request, so send a response:
          if (currentLine.length() == 0) {
            // HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
            // and a content-type so the client knows what's coming, then a blank line:
            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println();
            // the content of the HTTP response follows the header:
            client.println("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">"); // metaview
            client.println("<body style=\"background-color:black\">"); // set color CCS HTML5 style
            client.print( "<h2 style=\"font-family:verdana; color:GoldenRod\">Demo Access Point ");client.print(WiFi.SSID());client.println("</h2>");
            client.print("<p style=\"font-family:verdana; color:Goldenrod\">IP-address :"); client.print(WiFi.localIP());client.print("<br>");
            client.print("<p style=\"font-family:verdana; color:Goldenrod\">Enter your Name:<br>");
            client.println("<form method=POST action=\"checkpass.php\">");
            client.println("<input type=text name=data>");
            client.println("<input type=submit name=action value=Submit>");
            client.println("</form></p><br><br>");
            client.print("<h3 style=\"font-family:verdana; color:GoldenRod\">Click <a href=\"http://");client.print(WiFi.localIP());client.print("\">here</a> to goto landing page</h3><br>");
            // The HTTP response ends with another blank line:
            client.println();
            // break out of the while loop:

            break;
          }
          else {      // if you got a newline, then clear currentLine:
            currentLine = "";
          }
        }
        else if (c != '\r') {    // if you got anything else but a carriage return character,
          currentLine += c;      // add it to the end of the currentLine
        }

        // Check to see if the client request was a post
        if (currentLine.endsWith("POST /checkpass.php")) {
                Serial.println("** found POST");  
                currentLine = ""; 
                while (client.connected()) {                 // loop while the client's connected
                if (client.available()) {                    // if there's bytes to read from the client,
                   c = client.read();                        // read a byte, then
                   Serial.write(c);                          // print it out the serial monitor
                    if (c == '\n') {                          // if the byte is a newline character
                       //if (currentLine.length() == 0) break; // no lenght :  end of data request
                       currentLine = "";                      // if you got a newline, then clear currentLine:
                       }
                    else if (c != '\r') currentLine += c;     // if you got anything else but a carriage return character, add to string
  
               if (currentLine.endsWith("&action")) {         // Check read line on &action = posted PhP data
                    t = currentLine.length()-12;              // count 12 back to get answer
                    Serial.print("** found pass, length("); Serial.print(t);Serial.print("):");
                    answerLine = currentLine.substring(4, t+5);  // save answers
                    Serial.println(answerLine); 
                    answerList1[answerCounter]=WiFi.SSID();  // manage list of answers and SSID's
                    answerList2[answerCounter]=answerLine;
                    answerCounter= (answerCounter+1)%32;
                     break;
                    }
    
                 } 
            }
            delay(1000);
            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println();
            client.println("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">"); // metaview
            client.println("<body style=\"background-color:black\">"); // set color CCS HTML5 style
            client.print( "<h2 style=\"font-family:verdana; color:GoldenRod\">Access Router ");client.print(WiFi.SSID());client.println("</h2>");
            client.print("<p style=\"font-family:verdana; color:indianred\">Thank you, analysing Post request.<br>");
            client.print("<meta http-equiv=\"refresh\" content=\"4;url=/\" />");
            client.println();  
            break;
        } // end loop POST /checkpass.php check

        if (currentLine.endsWith("GET /SECRETS")) {
            client.println("HTTP/1.1 200 OK"); 
            client.println("Content-type:text/html");
            client.println();    
            client.println("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">"); // metaview    
            client.println("<body style=\"background-color:black\">"); // set color CCS HTML5 style
            client.print( "<h2 style=\"font-family:verdana; color:GoldenRod\">Demo Access Point ");client.print(WiFi.SSID());client.println("</h2>");
            client.print("<p style=\"font-family:verdana; color:indianred\">Thank you, list is Serial send.<br>");
            client.print("<meta http-equiv=\"refresh\" content=\"4;url=/\" />");
            client.println();  
            printAnswers();
          break;
        }
/*
        if (currentLine.endsWith("GET /connecttest")) {              // HTTP redirect for browsers with connect-test ?
            // client.println("HTTP/1.1 302 found");
            // client.print("Location: http://");client.print(WiFi.localIP());client.println("/");
            client.println("HTTP/1.1 204 No Content");
            client.println();  

          break;
        }

        if (currentLine.endsWith("GET /generate_204")) {              // HTTP generate 204 ?
            // client.println("HTTP/1.1 302 found");
            // client.print("Location: http://");client.print(WiFi.localIP());client.println("/");
            client.println("HTTP/1.1 204 No Content");
            client.println();  
          break;
        }

*/
        
      } // end loop client avaialbe    
    } // end loo client connected
    
    // close the connection:
    client.stop();
    Serial.println("**client disconnected");
  }
  else udpScan();
}



void printWiFiStatus() {
  IPAddress ip;
  // print the SSID of the network you're attached to:
 
  Serial.print("Nina W10 firmware: ");Serial.println(WiFi.firmwareVersion());
  Serial.print("SSID: "); Serial.println(WiFi.SSID());

  // print your WiFi shield's IP address:
  ip = WiFi.localIP();
  Serial.print("IP Address  : ");  Serial.println(ip);
  // print your WiFi shield's gateway:
  ip = WiFi.gatewayIP();
  Serial.print("IP Gateway  : ");  Serial.println(ip);
  // print your WiFi shield's gateway:
  ip = WiFi.subnetMask();
  Serial.print("Subnet Mask : ");  Serial.println(ip);
  // print where to go in a browser:
  ip = WiFi.localIP();
  Serial.print("To see this page in action, open a browser to http://");  Serial.println(ip);
}



void printAnswers() {
int t;
Serial.println("answerList:\n----------");
for (t=0;t<32;++t){
  Serial.print("Pass");Serial.print(t+1);Serial.print(":");
  Serial.print(answerList1[t]);;Serial.print(":"); Serial.println(answerList2[t]);
  }
Serial.println("----------");  
}




// UIDP port 53 - DNS - Scan
void udpScan()
{
int t=0;  // generic loop counter
int r,p;  // reply and packet counters
unsigned int packetSize=0;
unsigned int replySize=0;
  packetSize = Udp.parsePacket();
  if ( (packetSize!=0) && (packetSize<UDP_PACKET_SIZE) )  //only packets with small size
    {
    // We've received a packet, read the data from it
    Udp.read(packetBuffer, packetSize); // read the packet into the buffer
    dnsclientIp = Udp.remoteIP();
    dnsclientPort = Udp.remotePort();
    if ( (dnsclientIp != apip) && (dnsreqCount<=DNSMAXREQUESTS) ) // only non-local IP and only the first few DNSMAXREQUESTS x times
    {
    // DEBUG : Serial Print received Packet
    Serial.print("DNS-packets (");Serial.print(packetSize);
    Serial.print(") from ");Serial.print(dnsclientIp);
    Serial.print(" port ");Serial.println(dnsclientPort);
      for (t=0;t<packetSize;++t){
      Serial.print(packetBuffer[t],HEX);Serial.print(":");
      }
      Serial.println(" ");
      for (t=0;t<packetSize;++t){
      Serial.print( (char) packetBuffer[t]);//Serial.print("");
      }
    Serial.println("");
    
    //Copy Packet ID and IP into DNS header and DNS answer
    dnsReplyHeader[0] = packetBuffer[0];dnsReplyHeader[1] = packetBuffer[1]; // Copy ID of Packet offset 0 in Header
    dnsReplyAnswer[12] = apip[0];dnsReplyAnswer[13] = apip[1];dnsReplyAnswer[14] = apip[2];dnsReplyAnswer[15] = apip[3]; // copy AP Ip adress offset 12 in Answer
    r=0; // set reply buffer counter
    p=12; // set packetbuffer counter @ QUESTION QNAME section
    // copy Header into reply
    for (t=0;t<DNSHEADER_SIZE;++t) dnsReply[r++]=dnsReplyHeader[t];
    // copy Qusetion into reply:  Name labels till octet=0x00
    while (packetBuffer[p]!=0) dnsReply[r++]=packetBuffer[p++];
    // copy end of question plus Qtype and Qclass 5 octets
    for(t=0;t<5;++t)  dnsReply[r++]=packetBuffer[p++];
    //copy Answer into reply
    for (t=0;t<DNSANSWER_SIZE;++t) dnsReply[r++]=dnsReplyAnswer[t];
    replySize=r;
    
    // DEBUG : Serial print DSN reply
        Serial.print("DNS-Reply (");Serial.print(replySize);
        Serial.print(") from ");Serial.print(apip);
        Serial.print(" port ");Serial.println(udpPort);
        for (t=0;t<replySize;++t){
        Serial.print(dnsReply[t],HEX);Serial.print(":");
        }
        Serial.println(" ");
        for (t=0;t<replySize;++t){
        Serial.print( (char) dnsReply[t]);//Serial.print("");
        }
    Serial.println("");  
  // Send DSN UDP packet
  Udp.beginPacket(dnsclientIp, dnsclientPort); //reply DNSquestion
  Udp.write(dnsReply, replySize);
  Udp.endPacket();
  dnsreqCount++;
    } // end loop correct IP
 } // end loop received packet
  
}