/*
 * This file is part of PowerDNS or dnsdist.
 * Copyright -- PowerDNS.COM B.V. and its contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * In addition, for the avoidance of any doubt, permission is granted to
 * link this program with OpenSSL and to (re)distribute the binaries
 * produced as the result of such linking.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <string>
#include <map>
#include <unistd.h>
#include <stdlib.h>
#include <sstream>
#include "coprocess.hh"

#include "pdns/namespaces.hh"

#include "pdns/dns.hh"
#include "pdns/dnsbackend.hh"
#include "pdns/dnspacket.hh"
#include "pdns/pdnsexception.hh"
#include "pdns/logger.hh"
#include "pdns/arguments.hh"
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "pipebackend.hh"

// The following requirement guarantees UnknownDomainID will get output as "-1"
// for compatibility.
static_assert(std::is_signed<domainid_t>::value);

static const char* kBackendId = "[PIPEBackend]";

CoWrapper::CoWrapper(const string& command, int timeout, int abiVersion)
{
  d_command = command;
  d_timeout = timeout;
  d_abiVersion = abiVersion;
  launch(); // let exceptions fall through - if initial launch fails, we want to die
  // I think
}

CoWrapper::~CoWrapper() = default;

void CoWrapper::launch()
{
  if (d_cp)
    return;

  if (d_command.empty())
    throw ArgException("pipe-command is not specified");

  if (isUnixSocket(d_command)) {
    d_cp = std::make_unique<UnixRemote>(d_command);
  }
  else {
    auto coprocess = std::make_unique<CoProcess>(d_command, d_timeout);
    coprocess->launch();
    d_cp = std::move(coprocess);
  }

  d_cp->send("HELO\t" + std::to_string(d_abiVersion));
  string banner;
  d_cp->receive(banner);
  g_log << Logger::Error << "Backend launched with banner: " << banner << endl;
}

void CoWrapper::send(const string& line)
{
  launch();
  try {
    d_cp->send(line);
    return;
  }
  catch (PDNSException& ae) {
    d_cp.reset();
    throw;
  }
}
void CoWrapper::receive(string& line)
{
  launch();
  try {
    d_cp->receive(line);
    return;
  }
  catch (PDNSException& ae) {
    g_log << Logger::Warning << kBackendId << " Unable to receive data from coprocess. " << ae.reason << endl;
    d_cp.reset();
    throw;
  }
}

PipeBackend::PipeBackend(const string& suffix)
{
  d_disavow = false;
  signal(SIGCHLD, SIG_IGN);
  setArgPrefix("pipe" + suffix);
  try {
    launch();
  }
  catch (const ArgException& A) {
    g_log << Logger::Error << kBackendId << " Unable to launch, fatal argument error: " << A.reason << endl;
    throw;
  }
  catch (...) {
    throw;
  }
}

void PipeBackend::launch()
{
  if (d_coproc)
    return;

  try {
    if (!getArg("regex").empty()) {
      d_regex = std::make_unique<Regex>(getArg("regex"));
    }
    d_regexstr = getArg("regex");
    d_abiVersion = getArgAsNum("abi-version");
    d_coproc = std::make_unique<CoWrapper>(getArg("command"), getArgAsNum("timeout"), getArgAsNum("abi-version"));
  }

  catch (const ArgException& A) {
    cleanup();
    throw;
  }
}

/*
 * Cleans up the co-process wrapper
 */
void PipeBackend::cleanup()
{
  d_coproc.reset(nullptr);
  d_regex.reset();
  d_regexstr = string();
  d_abiVersion = 0;
}

void PipeBackend::lookup(const QType& qtype, const DNSName& qname, domainid_t zoneId, DNSPacket* pkt_p)
{
  try {
    launch();
    d_disavow = false;
    if (d_regex && !d_regex->match(qname.toStringRootDot())) {
      if (::arg().mustDo("query-logging"))
        g_log << Logger::Error << "Query for '" << qname << "' failed regex '" << d_regexstr << "'" << endl;
      d_disavow = true; // don't pass to backend
    }
    else {
      ostringstream query;
      string localIP = "0.0.0.0";
      string remoteIP = "0.0.0.0";
      Netmask realRemote("0.0.0.0/0");
      if (pkt_p) {
        localIP = pkt_p->getLocal().toString();
        realRemote = pkt_p->getRealRemote();
        remoteIP = pkt_p->getInnerRemote().toString();
      }
      // abi-version = 1
      // type    qname           qclass  qtype   id      remote-ip-address
      query << "Q\t" << qname.toStringRootDot() << "\tIN\t" << qtype.toString() << "\t" << zoneId << "\t" << remoteIP;

      // add the local-ip-address if abi-version is set to 2
      if (d_abiVersion >= 2)
        query << "\t" << localIP;
      if (d_abiVersion >= 3)
        query << "\t" << realRemote.toString();

      if (::arg().mustDo("query-logging"))
        g_log << Logger::Error << "Query: '" << query.str() << "'" << endl;
      d_coproc->send(query.str());
    }
  }
  catch (PDNSException& pe) {
    g_log << Logger::Error << kBackendId << " Error from coprocess: " << pe.reason << endl;
    d_disavow = true;
  }
  d_qtype = qtype;
  d_qname = qname;
}

bool PipeBackend::list(const ZoneName& target, domainid_t domain_id, bool /* include_disabled */)
{
  try {
    launch();
    d_disavow = false;
    ostringstream query;
    // The question format:

    // type    qname           qclass  qtype   id      ip-address
    if (d_abiVersion >= 4)
      query << "AXFR\t" << domain_id << "\t" << target.toStringRootDot();
    else
      query << "AXFR\t" << domain_id;

    d_coproc->send(query.str());
  }
  catch (PDNSException& ae) {
    g_log << Logger::Error << kBackendId << " Error from coprocess: " << ae.reason << endl;
  }
  d_qname = DNSName(std::to_string(domain_id)); // why do we store a number here??
  return true;
}

string PipeBackend::directBackendCmd(const string& query)
{
  if (d_abiVersion < 5)
    return "not supported on ABI version " + std::to_string(d_abiVersion) + " (use ABI version 5 or later)\n";

  try {
    launch();
    ostringstream oss;
    oss << "CMD\t" << query;
    d_coproc->send(oss.str());
  }
  catch (PDNSException& ae) {
    g_log << Logger::Error << kBackendId << " Error from coprocess: " << ae.reason << endl;
    cleanup();
  }

  ostringstream oss;
  while (true) {
    string line;
    d_coproc->receive(line);
    if (line == "END")
      break;
    oss << line << std::endl;
  };

  return oss.str();
}

//! For the dynamic loader
DNSBackend* PipeBackend::maker()
{
  try {
    return new PipeBackend();
  }
  catch (...) {
    g_log << Logger::Error << kBackendId << " Unable to instantiate a pipebackend!" << endl;
    return nullptr;
  }
}

PipeBackend::~PipeBackend()
{
  cleanup();
}

bool PipeBackend::get(DNSResourceRecord& r)
{
  if (d_disavow) // this query has been blocked
    return false;

  string line;

  // The answer format:
  // DATA    qname           qclass  qtype   ttl     id      content
  unsigned int extraFields = 0;
  if (d_abiVersion >= 3)
    extraFields = 2;

  try {
    launch();
    for (;;) {
      d_coproc->receive(line);
      vector<string> parts;
      stringtok(parts, line, "\t");
      if (parts.empty()) {
        g_log << Logger::Error << kBackendId << " Coprocess returned empty line in query for " << d_qname << endl;
        throw PDNSException("Format error communicating with coprocess");
      }
      else if (parts[0] == "FAIL") {
        throw DBException("coprocess returned a FAIL");
      }
      else if (parts[0] == "END") {
        return false;
      }
      else if (parts[0] == "LOG") {
        g_log << Logger::Error << "Coprocess: " << line.substr(4) << endl;
        continue;
      }
      else if (parts[0] == "DATA") { // yay
        if (parts.size() < 7 + extraFields) {
          g_log << Logger::Error << kBackendId << " Coprocess returned incomplete or empty line in data section for query for " << d_qname << endl;
          throw PDNSException("Format error communicating with coprocess in data section");
          // now what?
        }

        if (d_abiVersion >= 3) {
          r.scopeMask = std::stoi(parts[1]);
          r.auth = (parts[2] == "1");
        }
        else {
          r.scopeMask = 0;
          r.auth = true;
        }
        r.qname = DNSName(parts[1 + extraFields]);
        r.qtype = parts[3 + extraFields];
        pdns::checked_stoi_into(r.ttl, parts[4 + extraFields]);
        pdns::checked_stoi_into(r.domain_id, parts[5 + extraFields]);

        if (r.qtype.getCode() != QType::MX && r.qtype.getCode() != QType::SRV) {
          r.content.clear();
          for (unsigned int n = 6 + extraFields; n < parts.size(); ++n) {
            if (n != 6 + extraFields)
              r.content.append(1, ' ');
            r.content.append(parts[n]);
          }
        }
        else {
          if (parts.size() < 8 + extraFields) {
            g_log << Logger::Error << kBackendId << " Coprocess returned incomplete MX/SRV line in data section for query for " << d_qname << endl;
            throw PDNSException("Format error communicating with coprocess in data section of MX/SRV record");
          }

          r.content = parts[6 + extraFields] + " " + parts[7 + extraFields];
        }
        break;
      }
      else
        throw PDNSException("Coprocess backend sent incorrect response '" + line + "'");
    }
  }
  catch (DBException& dbe) {
    g_log << Logger::Error << kBackendId << " " << dbe.reason << endl;
    throw;
  }
  catch (PDNSException& pe) {
    g_log << Logger::Error << kBackendId << " " << pe.reason << endl;
    cleanup();
    throw;
  }
  return true;
}

//
// Magic class that is activated when the dynamic library is loaded
//

class PipeFactory : public BackendFactory
{
public:
  PipeFactory() :
    BackendFactory("pipe") {}

  void declareArguments(const string& suffix = "") override
  {
    declare(suffix, "command", "Command to execute for piping questions to", "");
    declare(suffix, "timeout", "Number of milliseconds to wait for an answer", "2000");
    declare(suffix, "regex", "Regular expression of queries to pass to coprocess", "");
    declare(suffix, "abi-version", "Version of the pipe backend ABI", "1");
  }

  DNSBackend* make(const string& suffix = "") override
  {
    return new PipeBackend(suffix);
  }
};

class PipeLoader
{
public:
  PipeLoader()
  {
    BackendMakers().report(std::make_unique<PipeFactory>());
    g_log << Logger::Info << kBackendId << " This is the pipe backend version " VERSION
#ifndef REPRODUCIBLE
          << " (" __DATE__ " " __TIME__ ")"
#endif
          << " reporting" << endl;
  }
};

static PipeLoader pipeloader;