1 files changed, 82 insertions, 0 deletions
diff --git a/dnsserver.cpp b/dnsserver.cpp
new file mode 100644
index 0000000..9fe1925
--- /dev/null
+++ b/dnsserver.cpp
@@ -0,0 +1,82 @@
+#include "dnsserver.h"
+
+DNSServer::DNSServer()
+{
+  _ttl = htonl(600);
+  _errorReplyCode = DNSReplyCode::NonExistentDomain;
+}
+
+bool DNSServer::start(const IPAddress &resolvedIP)
+{
+  _buffer = NULL;
+  _resolvedIP[0] = resolvedIP[0];
+  _resolvedIP[1] = resolvedIP[1];
+  _resolvedIP[2] = resolvedIP[2];
+  _resolvedIP[3] = resolvedIP[3];
+  return _udp.begin(53) == 1;
+}
+
+void DNSServer::stop()
+{
+  _udp.stop();
+  free(_buffer);
+  _buffer = NULL;
+}
+
+void DNSServer::processNextRequest()
+{
+  _currentPacketSize = _udp.parsePacket();
+  if (_currentPacketSize)
+  {
+    if (_buffer != NULL) free(_buffer);
+    _buffer = (unsigned char*)malloc(_currentPacketSize * sizeof(char));
+    if (_buffer == NULL) return;
+    _udp.read(_buffer, _currentPacketSize);
+
+    _dnsHeader = (DNSHeader*) _buffer;
+
+    if (_dnsHeader->QR == DNS_QR_QUERY &&
+        _dnsHeader->OPCode == DNS_OPCODE_QUERY &&
+        requestIncludesOnlyOneQuestion())
+    {
+      replyWithIP();  // reply with the same ip regardless of request
+    }
+  }
+}
+
+bool DNSServer::requestIncludesOnlyOneQuestion()
+{
+  return ntohs(_dnsHeader->QDCount) == 1 &&
+         _dnsHeader->ANCount == 0 &&
+         _dnsHeader->NSCount == 0 &&
+         _dnsHeader->ARCount == 0;
+}
+
+void DNSServer::replyWithIP()
+{
+  if (_buffer == NULL) return;
+  _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();
+}