Added a DNSServer library

libraries/DNSServer/src/DNSServer.cpp

@@ -0,0 +1,133 @@
+#include "DNSServer.h"
+#include <lwip/def.h>
+#include <Arduino.h>
+
+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() &&
+        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 = 0;
+
+  _udp.beginPacket(_udp.remoteIP(), _udp.remotePort());
+  _udp.write(_buffer, _currentPacketSize);
+  _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();
+}
+
+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();
+}

libraries/DNSServer/src/DNSServer.h

@@ -0,0 +1,72 @@
+#ifndef DNSServer_h
+#define DNSServer_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