lokinet/llarp/dnsd.cpp

#include "dnsd.hpp"
#include "logger.hpp"
#include "net.hpp"
#include <string>

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

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

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

dns_msg *decode_hdr(const char *buffer)
{
  dns_msg *hdr = new dns_msg;
  hdr->id = get16bits(buffer);
  uint fields = get16bits(buffer);
  hdr->qr = fields & 0x8000;
  hdr->opcode = fields & 0x7800;
  hdr->aa = fields & 0x0400;
  hdr->tc = fields & 0x0200;
  hdr->rd = fields & 0x0100;
  hdr->ra = fields & 0x8000;

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

void code_domain(char*& buffer, const std::string& domain) throw()
{

  int start(0), end; // indexes
  //llarp::LogInfo("domain [", domain, "]");
  while ((end = domain.find('.', start)) != std::string::npos)
  {

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

  *buffer++ = 0;
}

ssize_t
raw_sendto_dns_hook_func(void *sock, const struct sockaddr *from, const void *buffer, size_t length)
{
  int *fd = (int *)sock;
  // how do we get to these??
  socklen_t addrLen = sizeof (struct sockaddr_in);
  return sendto(*fd, buffer, length, 0, from, addrLen);
}

ssize_t
llarp_sendto_dns_hook_func(void *sock, const struct sockaddr *from, const void *buffer, size_t length)
{
  struct llarp_udp_io *udp = (struct llarp_udp_io *)sock;
  if (!udp)
  {
    return 0;
  }
  return llarp_ev_udp_sendto(udp, from, buffer, length);
}

bool forward_dns_request(std::string request)
{
  return true;
}

void
writesend_dnss_response(struct sockaddr *hostRes, const struct sockaddr *from, dns_request *request)
{
  if (!hostRes)
  {
    llarp::LogWarn("Failed to resolve");
    // FIXME: actually return correct packet
    return;
  }

  const size_t BUFFER_SIZE = 1024;
  char buf[BUFFER_SIZE];
  memset(buf, 0, BUFFER_SIZE);
  char* write_buffer = buf;
  char* bufferBegin = buf;
  // build header
  put16bits(write_buffer, request->id);
  int fields = (1 << 15); // QR => message type, 1 = response
  fields += (0 << 14); // I think opcode is always 0
  fields += 0; // response code (3 => not found, 0 = Ok)
  put16bits(write_buffer, fields);

  put16bits(write_buffer, 1); // QD (number of questions)
  put16bits(write_buffer, 1); // AN (number of answers)
  put16bits(write_buffer, 0); // NS (number of auth RRs)
  put16bits(write_buffer, 0); // AR (number of Additional RRs)

  // code question
  code_domain(write_buffer, request->m_qName);
  put16bits(write_buffer, request->m_qType);
  put16bits(write_buffer, request->m_qClass);

  // code answer
  code_domain(write_buffer, request->m_qName); // com, type=6, ttl=0
  put16bits(write_buffer, request->m_qType);
  put16bits(write_buffer, request->m_qClass);
  put32bits(write_buffer, 1453); // ttl

  // has to be a string of 4 bytes
  struct sockaddr_in *sin = (struct sockaddr_in *)hostRes;
  unsigned char *ip = (unsigned char *)&sin->sin_addr.s_addr;

  put16bits(write_buffer, 4); // rdLength
  *write_buffer++ = ip[0];
  *write_buffer++ = ip[1];
  *write_buffer++ = ip[2];
  *write_buffer++ = ip[3];

  uint out_bytes = write_buffer - bufferBegin;
  llarp::LogInfo("Sending ", out_bytes, " bytes");
  //struct llarp_udp_io *udp = (struct llarp_udp_io *)request->user;
  request->hook(request->user, from, buf, out_bytes);
}

void phase2(dns_client_request *client_request, struct sockaddr *result)
{
  llarp::LogInfo("phase2");
  //writesend_dnss_response(struct sockaddr *hostRes, const struct sockaddr *from, dns_request *request)
  dns_request *server_request = (dns_request *)client_request->user;
  writesend_dnss_response(result, server_request->from, server_request);
}

void
handle_recvfrom(const char *buffer, ssize_t nbytes, const struct sockaddr *from, dns_request *request)
{
  const size_t HDR_OFFSET = 12;
  const char* p_buffer = buffer;

  dns_msg *msg = decode_hdr(p_buffer);
  //llarp::LogInfo("DNS_MSG size", sizeof(dns_msg));
  p_buffer += HDR_OFFSET;
  request->id = msg->id;
  std::string m_qName = "";
  int length = *p_buffer++;
  //llarp::LogInfo("qNamLen", length);
  while (length != 0) {
    for (int i = 0; i < length; i++) {
      char c = *p_buffer++;
      m_qName.append(1, c);
    }
    length = *p_buffer++;
    if (length != 0) m_qName.append(1,'.');
  }
  request->m_qName = m_qName;
  request->m_qType = get16bits(p_buffer);
  request->m_qClass = get16bits(p_buffer);
  llarp::LogInfo("qName  ", m_qName);
  llarp::LogInfo("qType  ", request->m_qType);
  llarp::LogInfo("qClass ", request->m_qClass);

  if (!forward_dns_request(m_qName))
  {
    // told that hook will handle overrides
    return;
  }

  sockaddr *hostRes = nullptr;
  if (0)
  {
    hostRes = resolveHost(m_qName.c_str());
    llarp::Addr anIp(*hostRes);
    llarp::LogInfo("DNS got ", anIp);
    //writesend_dnss_response(struct sockaddr *hostRes, const struct sockaddr *from, dns_request *request)
    writesend_dnss_response(hostRes, from, request);
  }
  else
  {
    llarp::Addr anIp;
    struct llarp_udp_io *udp = (struct llarp_udp_io *)request->user;
    //hostRes = llarp_resolveHost(udp->parent, m_qName.c_str());
    llarp_resolve_host(udp->parent, m_qName.c_str(), &phase2, (void *)request);
  }
}

// this is called in net threadpool
void
llarp_handle_recvfrom(struct llarp_udp_io *udp, const struct sockaddr *saddr,
                const void *buf, ssize_t sz)
{
  //llarp_link *link = static_cast< llarp_link * >(udp->user);
  llarp::LogInfo("Received Bytes ", sz);
  dns_request llarp_dns_request;
  llarp_dns_request.from = (struct sockaddr *)saddr;
  llarp_dns_request.user = (void *)udp;
  llarp_dns_request.hook = &llarp_sendto_dns_hook_func;
  handle_recvfrom((char *)buf, sz, saddr, &llarp_dns_request);
}

void
raw_handle_recvfrom(int *sockfd, const struct sockaddr *saddr,
           const void *buf, ssize_t sz)
{
  llarp::LogInfo("Received Bytes ", sz);
  dns_request llarp_dns_request;
  llarp_dns_request.from = (struct sockaddr *)saddr;
  llarp_dns_request.user = (void *)sockfd;
  llarp_dns_request.hook = &raw_sendto_dns_hook_func;
  handle_recvfrom((char *)buf, sz, saddr, &llarp_dns_request);
}