lokinet/llarp/dns.cpp

#include <string.h>
#include "dnsd.hpp"  // for llarp_handle_dnsd_recvfrom, dnsc
#include "logger.hpp"

#ifdef _WIN32
#define uint UINT
#endif

extern "C"
{
  uint16_t
  get16bits(const char *&buffer) throw()
  {
    uint16_t value = static_cast< unsigned char >(buffer[0]);
    value          = value << 8;
    value += static_cast< unsigned char >(buffer[1]);
    buffer += 2;
    return value;
  }

  // uint32_t
  uint32_t
  get32bits(const char *&buffer) throw()
  {
    uint32_t value = uint32_t(
        (unsigned char)(buffer[0]) << 24 | (unsigned char)(buffer[1]) << 16
        | (unsigned char)(buffer[2]) << 8 | (unsigned char)(buffer[3]));
    buffer += 4;
    return value;
  }

  dns_msg_header *
  decode_hdr(const char *buffer)
  {
    dns_msg_header *hdr = new dns_msg_header;
    hdr->id             = get16bits(buffer);
    uint fields         = get16bits(buffer);
    uint8_t lFields     = (fields & 0x00FF) >> 0;
    uint8_t hFields     = (fields & 0xFF00) >> 8;
    // hdr->qr      = fields & 0x8000;
    hdr->qr     = (hFields >> 7) & 0x1;
    hdr->opcode = fields & 0x7800;
    hdr->aa     = fields & 0x0400;
    hdr->tc     = fields & 0x0200;
    hdr->rd     = fields & 0x0100;

    hdr->ra = (lFields >> 7) & 0x1;
    // hdr->z       = (lFields >> 6) & 0x1;
    // hdr->ad      = (lFields >> 5) & 0x1;
    // hdr->cd      = (lFields >> 4) & 0x1;
    hdr->rcode = lFields & 0xf;

    hdr->qdCount = get16bits(buffer);
    hdr->anCount = get16bits(buffer);
    hdr->nsCount = get16bits(buffer);
    hdr->arCount = get16bits(buffer);
    return hdr;
  }

  dns_msg_question *
  decode_question(const char *buffer)
  {
    dns_msg_question *question = new dns_msg_question;
    std::string m_qName        = "";
    int length                 = *buffer++;
    // llarp::LogInfo("qNamLen", length);
    while(length != 0)
    {
      for(int i = 0; i < length; i++)
      {
        char c = *buffer++;
        m_qName.append(1, c);
      }
      length = *buffer++;
      if(length != 0)
        m_qName.append(1, '.');
    }
    question->name   = m_qName;
    question->type   = get16bits(buffer);
    question->qClass = get16bits(buffer);
    return question;
  }

  dns_msg_answer *
  decode_answer(const char *buffer)
  {
    dns_msg_answer *answer = new dns_msg_answer;
    answer->type           = get16bits(buffer);
    // assert(answer->type < 259);
    if(answer->type > 259)
    {
      llarp::LogWarn("Answer type is off the charts");
    }
    answer->aClass = get16bits(buffer);
    answer->ttl    = get32bits(buffer);
    answer->rdLen  = get16bits(buffer);
    if(answer->rdLen == 4)
    {
      answer->rData = new uint8_t[answer->rdLen];
      memcpy(answer->rData, buffer, answer->rdLen);
    }
    else
    {
      llarp::LogWarn("Unknown Type ", answer->type);
    }
    return answer;
  }

  void
  put16bits(char *&buffer, uint16_t value) throw()
  {
    buffer[0] = (value & 0xFF00) >> 8;
    buffer[1] = value & 0xFF;
    buffer += 2;
  }

  void
  put32bits(char *&buffer, uint32_t value) throw()
  {
    buffer[0] = (value & 0xFF000000) >> 24;
    buffer[1] = (value & 0x00FF0000) >> 16;
    buffer[2] = (value & 0x0000FF00) >> 8;
    buffer[3] = (value & 0x000000FF) >> 0;
    buffer += 4;
  }

  void
  code_domain(char *&buffer, const std::string &domain) throw()
  {
    std::string::size_type start(0);
    std::string::size_type end;  // indexes
    // llarp::LogInfo("domain [", domain, "]");
    while((end = domain.find('.', start)) != std::string::npos)
    {
      *buffer++ = end - start;  // label length octet
      for(std::string::size_type i = start; i < end; i++)
      {
        *buffer++ = domain[i];  // label octets
        // llarp::LogInfo("Writing ", domain[i], " at ", i);
      }
      start = end + 1;  // Skip '.'
    }

    // llarp::LogInfo("start ", start, " domain size ", domain.size());

    *buffer++ = domain.size() - start;  // last label length octet
    for(uint i = start; i < domain.size(); i++)
    {
      *buffer++ = domain[i];  // last label octets
      // llarp::LogInfo("Writing ", domain[i], " at ", i);
    }

    *buffer++ = 0;
  }

  void
  llarp_handle_dns_recvfrom(struct llarp_udp_io *udp,
                            const struct sockaddr *saddr, const void *buf,
                            ssize_t sz)
  {
    unsigned char *castBuf = (unsigned char *)buf;
    // auto buffer = llarp::StackBuffer< decltype(castBuf) >(castBuf);
    dns_msg_header *hdr = decode_hdr((const char *)castBuf);
    // castBuf += 12;
    llarp::LogDebug("msg id ", hdr->id);
    llarp::LogDebug("msg qr ", (uint8_t)hdr->qr);
    if(hdr->qr)
    {
      llarp::LogDebug("handling as dnsc answer");
      llarp_handle_dnsc_recvfrom(udp, saddr, buf, sz);
    }
    else
    {
      llarp::LogDebug("handling as dnsd question");
      llarp_handle_dnsd_recvfrom(udp, saddr, buf, sz);
    }
    /*
     llarp::LogInfo("msg op ", hdr->opcode);
     llarp::LogInfo("msg rc ", hdr->rcode);

     for(uint i = 0; i < hdr->qdCount; i++)
     {
     dns_msg_question *question = decode_question((const char*)castBuf);
     llarp::LogInfo("Read a question");
     castBuf += question->name.length() + 8;
     }

     for(uint i = 0; i < hdr->anCount; i++)
     {
     dns_msg_answer *answer = decode_answer((const char*)castBuf);
     llarp::LogInfo("Read an answer");
     castBuf += answer->name.length() + 4 + 4 + 4 + answer->rdLen;
     }
     */
  }
}