I have a method which basically forwards any URL coming from the user when it connects to the ESP as an access point. This could of course also be an empty URL. I set to a website alias, which does complicate things a bit because a phone will start to look through it's search engine to see if it can resolve it, so it may require 5G to be turned off.
Anyway, it sounds like that would do the trick for you, but i can not find or remember where i got it from It was a modification of DNSserver.h / .cpp
It required renaming it (i went for patchDNSserver.h /.cpp ) to make it includable.
the .h
#ifndef PatchDNSServer_h
#define PatchDNSServer_h
#include <WiFiUdp.h>
#define DNS_QR_QUERY 0
#define DNS_QR_RESPONSE 1
#define DNS_OPCODE_QUERY 0
enum class DNSReplyCode
{
NoError = 0,
FormError = 1,
ServerFailure = 2,
NonExistentDomain = 3,
NotImplemented = 4,
Refused = 5,
YXDomain = 6,
YXRRSet = 7,
NXRRSet = 8
};
struct DNSHeader
{
uint16_t ID; // identification number
unsigned char RD : 1; // recursion desired
unsigned char TC : 1; // truncated message
unsigned char AA : 1; // authoritive answer
unsigned char OPCode : 4; // message_type
unsigned char QR : 1; // query/response flag
unsigned char RCode : 4; // response code
unsigned char Z : 3; // its z! reserved
unsigned char RA : 1; // recursion available
uint16_t QDCount; // number of question entries
uint16_t ANCount; // number of answer entries
uint16_t NSCount; // number of authority entries
uint16_t ARCount; // number of resource entries
};
class DNSServer
{
public:
DNSServer();
void processNextRequest();
void setErrorReplyCode(const DNSReplyCode &replyCode);
void setTTL(const uint32_t &ttl);
// Returns true if successful, false if there are no sockets available
bool start(const uint16_t &port,
const String &domainName,
const IPAddress &resolvedIP);
// stops the DNS server
void stop();
private:
WiFiUDP _udp;
uint16_t _port;
String _domainName;
unsigned char _resolvedIP[4];
int _currentPacketSize;
unsigned char* _buffer;
DNSHeader* _dnsHeader;
uint32_t _ttl;
DNSReplyCode _errorReplyCode;
void downcaseAndRemoveWwwPrefix(String &domainName);
String getDomainNameWithoutWwwPrefix();
bool requestIncludesOnlyOneQuestion();
void replyWithIP();
void replyWithCustomCode();
};
#endif
the .cpp
#include "PatchDNSServer.h"
#include <lwip/def.h>
#include <Arduino.h>
//#define DEBUG
//#define DEBUG_OUTPUT Serial
DNSServer::DNSServer()
{
_ttl = htonl(60);
_errorReplyCode = DNSReplyCode::NonExistentDomain;
}
bool DNSServer::start(const uint16_t &port, const String &domainName,
const IPAddress &resolvedIP)
{
_port = port;
_domainName = domainName;
_resolvedIP[0] = resolvedIP[0];
_resolvedIP[1] = resolvedIP[1];
_resolvedIP[2] = resolvedIP[2];
_resolvedIP[3] = resolvedIP[3];
downcaseAndRemoveWwwPrefix(_domainName);
return _udp.begin(_port) == 1;
}
void DNSServer::setErrorReplyCode(const DNSReplyCode &replyCode)
{
_errorReplyCode = replyCode;
}
void DNSServer::setTTL(const uint32_t &ttl)
{
_ttl = htonl(ttl);
}
void DNSServer::stop()
{
_udp.stop();
}
void DNSServer::downcaseAndRemoveWwwPrefix(String &domainName)
{
domainName.toLowerCase();
domainName.replace("www.", "");
}
void DNSServer::processNextRequest()
{
_currentPacketSize = _udp.parsePacket();
if (_currentPacketSize)
{
_buffer = (unsigned char*)malloc(_currentPacketSize * sizeof(char));
_udp.read(_buffer, _currentPacketSize);
_dnsHeader = (DNSHeader*) _buffer;
if (_dnsHeader->QR == DNS_QR_QUERY &&
_dnsHeader->OPCode == DNS_OPCODE_QUERY &&
requestIncludesOnlyOneQuestion() &&
(_domainName == "*" || getDomainNameWithoutWwwPrefix() == _domainName)
)
{
replyWithIP();
}
else if (_dnsHeader->QR == DNS_QR_QUERY)
{
replyWithCustomCode();
}
free(_buffer);
}
}
bool DNSServer::requestIncludesOnlyOneQuestion()
{
return ntohs(_dnsHeader->QDCount) == 1 &&
_dnsHeader->ANCount == 0 &&
_dnsHeader->NSCount == 0 &&
_dnsHeader->ARCount == 0;
}
String DNSServer::getDomainNameWithoutWwwPrefix()
{
String parsedDomainName = "";
unsigned char *start = _buffer + 12;
if (*start == 0)
{
return parsedDomainName;
}
int pos = 0;
while(true)
{
unsigned char labelLength = *(start + pos);
for(int i = 0; i < labelLength; i++)
{
pos++;
parsedDomainName += (char)*(start + pos);
}
pos++;
if (*(start + pos) == 0)
{
downcaseAndRemoveWwwPrefix(parsedDomainName);
return parsedDomainName;
}
else
{
parsedDomainName += ".";
}
}
}
void DNSServer::replyWithIP()
{
_dnsHeader->QR = DNS_QR_RESPONSE;
_dnsHeader->ANCount = _dnsHeader->QDCount;
_dnsHeader->QDCount = _dnsHeader->QDCount;
//_dnsHeader->RA = 1;
_udp.beginPacket(_udp.remoteIP(), _udp.remotePort());
_udp.write(_buffer, _currentPacketSize);
_udp.write((uint8_t)192); // answer name is a pointer
_udp.write((uint8_t)12); // pointer to offset at 0x00c
_udp.write((uint8_t)0); // 0x0001 answer is type A query (host address)
_udp.write((uint8_t)1);
_udp.write((uint8_t)0); //0x0001 answer is class IN (internet address)
_udp.write((uint8_t)1);
_udp.write((unsigned char*)&_ttl, 4);
// Length of RData is 4 bytes (because, in this case, RData is IPv4)
_udp.write((uint8_t)0);
_udp.write((uint8_t)4);
_udp.write(_resolvedIP, sizeof(_resolvedIP));
_udp.endPacket();
#ifdef DEBUG
DEBUG_OUTPUT.print("DNS responds: ");
DEBUG_OUTPUT.print(_resolvedIP[0]);
DEBUG_OUTPUT.print(".");
DEBUG_OUTPUT.print(_resolvedIP[1]);
DEBUG_OUTPUT.print(".");
DEBUG_OUTPUT.print(_resolvedIP[2]);
DEBUG_OUTPUT.print(".");
DEBUG_OUTPUT.print(_resolvedIP[3]);
DEBUG_OUTPUT.print(" for ");
DEBUG_OUTPUT.println(getDomainNameWithoutWwwPrefix());
#endif
}
void DNSServer::replyWithCustomCode()
{
_dnsHeader->QR = DNS_QR_RESPONSE;
_dnsHeader->RCode = (unsigned char)_errorReplyCode;
_dnsHeader->QDCount = 0;
_udp.beginPacket(_udp.remoteIP(), _udp.remotePort());
_udp.write(_buffer, sizeof(DNSHeader));
_udp.endPacket();
}
And the implementation is easy enough.
#include <PatchDNSServer.h>
#define DNS_PORT 53
DNSServer dnsServer;
void setup() {
dnsServer.start(DNS_PORT, "*", IPAddress(192, 168, 4, 1));
// dnsServer.start(DNS_PORT, "blabla.com", IPAddress(192, 168, 4, 1));
}
void loop() {
dnsServer.processNextRequest();
}
This works for connecting to it as an AP. Through the router it is a different matter. There may be newer ways to do the same, i think it was more or less a fix to part of a core that wasn't working properly.
Anyway, provided as is (compiles and works on all ESP cores i have used)
) but it does not always work because it depends on the router's configuration
