/** @file

  A brief file description

  @section license License

  Licensed to the Apache Software Foundation (ASF) under one
  or more contributor license agreements.  See the NOTICE file
  distributed with this work for additional information
  regarding copyright ownership.  The ASF licenses this file
  to you under the Apache License, Version 2.0 (the
  "License"); you may not use this file except in compliance
  with the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
 */

/*****************************************************************************
 *
 *  SplitDNS.cc - Implementation of "split" DNS (as the name says)
 *
 *
 ****************************************************************************/

#include "ts/ink_platform.h"
#include "ts/Tokenizer.h"

#ifdef SPLIT_DNS
#include <sys/types.h>
#include "P_SplitDNS.h"
#include "ts/MatcherUtils.h"
#include "ts/HostLookup.h"

/* --------------------------------------------------------------
   this file is built using "ParentSelection.cc as a template.
   -------------    ------------------------------------------------- */

/* --------------------------------------------------------------
   globals
   -------------------------------------------------------------- */
static const char modulePrefix[] = "[SplitDNS]";

ConfigUpdateHandler<SplitDNSConfig> *SplitDNSConfig::splitDNSUpdate = nullptr;

static ClassAllocator<DNSRequestData> DNSReqAllocator("DNSRequestDataAllocator");

/* --------------------------------------------------------------
   used by a lot of protocols. We do not have dest ip in most
   cases.
   -------------------------------------------------------------- */
const matcher_tags sdns_dest_tags = {"dest_host", "dest_domain", nullptr, "url_regex", "url", nullptr, true};

/* --------------------------------------------------------------
   config Callback Prototypes
   -------------------------------------------------------------- */
enum SplitDNSCB_t {
  SDNS_FILE_CB,
  SDNS_ENABLE_CB,
};

static const char *SDNSResultStr[] = {"DNSServer_Undefined", "DNSServer_Specified", "DNSServer_Failed"};

int SplitDNSConfig::m_id               = 0;
int SplitDNSConfig::gsplit_dns_enabled = 0;
int splitDNSFile_CB(const char *name, RecDataT data_type, RecData data, void *cookie);
Ptr<ProxyMutex> SplitDNSConfig::dnsHandler_mutex;

/* --------------------------------------------------------------
   SplitDNSResult::SplitDNSResult()
   -------------------------------------------------------------- */
inline SplitDNSResult::SplitDNSResult() : r(DNS_SRVR_UNDEFINED), m_line_number(0), m_rec(nullptr), m_wrap_around(false)
{
}

/* --------------------------------------------------------------
   SplitDNS::SplitDNS()
   -------------------------------------------------------------- */
SplitDNS::SplitDNS() : m_DNSSrvrTable(nullptr), m_SplitDNSlEnable(0), m_bEnableFastPath(false), m_pxLeafArray(nullptr), m_numEle(0)
{
}

SplitDNS::~SplitDNS()
{
  if (m_DNSSrvrTable) {
    delete m_DNSSrvrTable;
  }
}

/* --------------------------------------------------------------
   SplitDNSConfig::acquire()
   -------------------------------------------------------------- */
SplitDNS *
SplitDNSConfig::acquire()
{
  return (SplitDNS *)configProcessor.get(SplitDNSConfig::m_id);
}

/* --------------------------------------------------------------
   SplitDNSConfig::release()
   -------------------------------------------------------------- */
void
SplitDNSConfig::release(SplitDNS *params)
{
  configProcessor.release(SplitDNSConfig::m_id, params);
}

/* --------------------------------------------------------------
   SplitDNSConfig::startup()
   -------------------------------------------------------------- */
void
SplitDNSConfig::startup()
{
  dnsHandler_mutex = new_ProxyMutex();

  // startup just check gsplit_dns_enabled
  REC_ReadConfigInt32(gsplit_dns_enabled, "proxy.config.dns.splitDNS.enabled");
  SplitDNSConfig::splitDNSUpdate = new ConfigUpdateHandler<SplitDNSConfig>();
  SplitDNSConfig::splitDNSUpdate->attach("proxy.config.cache.splitdns.filename");
}

/* --------------------------------------------------------------
   SplitDNSConfig::reconfigure()
   -------------------------------------------------------------- */
void
SplitDNSConfig::reconfigure()
{
  if (0 == gsplit_dns_enabled)
    return;

  SplitDNS *params = new SplitDNS;

  params->m_SplitDNSlEnable = gsplit_dns_enabled;
  params->m_DNSSrvrTable    = new DNS_table("proxy.config.dns.splitdns.filename", modulePrefix, &sdns_dest_tags);

  params->m_numEle = params->m_DNSSrvrTable->getEntryCount();
  if (nullptr == params->m_DNSSrvrTable || (0 == params->m_numEle)) {
    Warning("No NAMEDs provided! Disabling SplitDNS");
    gsplit_dns_enabled = 0;
    delete params;
    return;
  }

  if (nullptr != params->m_DNSSrvrTable->getHostMatcher() && nullptr == params->m_DNSSrvrTable->getReMatcher() &&
      nullptr == params->m_DNSSrvrTable->getIPMatcher() && 4 >= params->m_numEle) {
    HostLookup *pxHL          = params->m_DNSSrvrTable->getHostMatcher()->getHLookup();
    params->m_pxLeafArray     = (void *)pxHL->getLArray();
    params->m_bEnableFastPath = true;
  }

  m_id = configProcessor.set(m_id, params);

  if (is_debug_tag_set("splitdns_config")) {
    SplitDNSConfig::print();
  }
}

/* --------------------------------------------------------------
   SplitDNSConfig::print()
   -------------------------------------------------------------- */
void
SplitDNSConfig::print()
{
  SplitDNS *params = SplitDNSConfig::acquire();

  Debug("splitdns_config", "DNS Server Selection Config");
  Debug("splitdns_config", "\tEnabled=%d", params->m_SplitDNSlEnable);

  params->m_DNSSrvrTable->Print();
  SplitDNSConfig::release(params);
}

/* --------------------------------------------------------------
   SplitDNS::getDNSRecord()
   -------------------------------------------------------------- */
void *
SplitDNS::getDNSRecord(const char *hostname)
{
  Debug("splitdns", "Called SplitDNS::getDNSRecord(%s)", hostname);

  DNSRequestData *pRD = DNSReqAllocator.alloc();
  pRD->m_pHost        = hostname;

  SplitDNSResult res;
  findServer(pRD, &res);

  DNSReqAllocator.free(pRD);

  if (DNS_SRVR_SPECIFIED == res.r) {
    return (void *)&(res.m_rec->m_servers);
  }

  Debug("splitdns", "Fail to match a valid splitdns rule, fallback to default dns resolver");
  return nullptr;
}

/* --------------------------------------------------------------
   SplitDNS::findServer()
   -------------------------------------------------------------- */
void
SplitDNS::findServer(RequestData *rdata, SplitDNSResult *result)
{
  DNS_table *tablePtr = m_DNSSrvrTable;
  SplitDNSRecord *rec;

  ink_assert(result->r == DNS_SRVR_UNDEFINED);

  if (m_SplitDNSlEnable == 0) {
    result->r = DNS_SRVR_UNDEFINED;
    return;
  }

  result->m_rec         = nullptr;
  result->m_line_number = 0xffffffff;
  result->m_wrap_around = false;

  /* ---------------------------
     the 'alleged' fast path ...
     --------------------------- */
  if (m_bEnableFastPath) {
    SplitDNSRecord *data_ptr = nullptr;
    char *pHost              = (char *)rdata->get_host();
    if (nullptr == pHost) {
      Warning("SplitDNS: No host to match !");
      return;
    }

    int len        = strlen(pHost);
    HostLeaf *pxHL = (HostLeaf *)m_pxLeafArray;
    for (int i = 0; i < m_numEle; i++) {
      if (nullptr == pxHL)
        break;

      if (false == pxHL[i].isNot && pxHL[i].len > len)
        continue;

      int idx      = len - pxHL[i].len;
      char *pH     = &pHost[idx];
      char *pMatch = (char *)pxHL[i].match;
      char cNot    = *pMatch;

      if ('!' == cNot)
        pMatch++;

      int res = memcmp(pH, pMatch, pxHL[i].len);

      if ((0 != res && '!' == cNot) || (0 == res && '!' != cNot)) {
        data_ptr = (SplitDNSRecord *)pxHL[i].opaque_data;
        data_ptr->UpdateMatch(result, rdata);
        break;
      }
    }
  } else {
    tablePtr->Match(rdata, result);
  }

  rec = result->m_rec;
  if (rec == nullptr) {
    result->r = DNS_SRVR_UNDEFINED;
    return;
  } else {
    result->r = DNS_SRVR_SPECIFIED;
  }

  if (is_debug_tag_set("splitdns_config")) {
    const char *host = rdata->get_host();

    switch (result->r) {
    case DNS_SRVR_FAIL:
      Debug("splitdns_config", "Result for %s was %s", host, SDNSResultStr[result->r]);
      break;
    case DNS_SRVR_SPECIFIED:
      Debug("splitdns_config", "Result for %s was dns servers", host);
      result->m_rec->Print();
      break;
    default:
      // DNS_SRVR_UNDEFINED
      break;
    }
  }
}

/* --------------------------------------------------------------
   SplitDNSRecord::ProcessDNSHosts()
   -------------------------------------------------------------- */
const char *
SplitDNSRecord::ProcessDNSHosts(char *val)
{
  Tokenizer pTok(",; \t\r");
  int numTok;
  const char *current;
  int port = 0;
  char *tmp;
  int totsz = 0, sz = 0;

  numTok = pTok.Initialize(val, SHARE_TOKS);
  if (MAXNS < numTok) {
    numTok = MAXNS;
    Warning("Only first %d DNS servers are tracked", numTok);
  }
  if (numTok == 0) {
    return "No servers specified";
  }

  /* ------------------------------------------------
     Allocate the servers array and Loop through the
     set of servers specified
     ------------------------------------------------ */
  for (int i = 0; i < numTok; i++) {
    current = pTok[i];
    tmp     = (char *)strchr(current, ':');
    // coverity[secure_coding]
    if (tmp != nullptr && sscanf(tmp + 1, "%d", &port) != 1) {
      return "Malformed DNS port";
    }

    /* ----------------------------------------
       Make sure that is no garbage beyond the
       server port
       ---------------------------------------- */
    if (tmp) {
      char *scan = tmp + 1;
      for (; *scan != '\0' && ParseRules::is_digit(*scan); scan++)
        ;
      for (; *scan != '\0' && ParseRules::is_wslfcr(*scan); scan++)
        ;

      if (*scan != '\0') {
        return "Garbage trailing entry or invalid separator";
      }

      if (tmp - current > (MAXDNAME - 1)) {
        return "DNS server name (ip) is too long";
      } else if (tmp - current == 0) {
        return "server string is emtpy";
      }
      *tmp = 0;
    }

    if (0 != ats_ip_pton(current, &m_servers.x_server_ip[i].sa)) {
      return "invalid IP address given for a DNS server";
    }

    ats_ip_port_cast(&m_servers.x_server_ip[i].sa) = htons(port ? port : NAMESERVER_PORT);

    if ((MAXDNAME * 2 - 1) > totsz) {
      sz = strlen(current);
      memcpy((m_servers.x_dns_ip_line + totsz), current, sz);
      totsz += sz;
    }
  }

  m_dnsSrvr_cnt = numTok;
  return nullptr;
}

/* --------------------------------------------------------------
   SplitDNSRecord::ProcessDefDomain()
   -------------------------------------------------------------- */
const char *
SplitDNSRecord::ProcessDefDomain(char *val)
{
  Tokenizer pTok(",; \t\r");
  int numTok;

  numTok = pTok.Initialize(val, SHARE_TOKS);

  if (numTok > 1) {
    return "more than one default domain name specified";
  }

  if (numTok == 0) {
    return "no default domain name specified";
  }

  int len = 0;
  if (pTok[0] && 0 != (len = strlen(pTok[0]))) {
    memcpy(&m_servers.x_def_domain[0], pTok[0], len);
    m_servers.x_def_domain[len] = '\0';
  }

  return nullptr;
}

/* --------------------------------------------------------------
   SplitDNSRecord::ProcessDomainSrchList()
   -------------------------------------------------------------- */
const char *
SplitDNSRecord::ProcessDomainSrchList(char *val)
{
  Tokenizer pTok(",; \t\r");
  int numTok;
  int cnt = 0, sz = 0;
  char *pSp = nullptr;
  const char *current;

  numTok = pTok.Initialize(val, SHARE_TOKS);

  if (numTok == 0) {
    return "No servers specified";
  }

  pSp = &m_servers.x_domain_srch_list[0];

  for (int i = 0; i < numTok; i++) {
    current = pTok[i];
    cnt     = sz += strlen(current);

    if (MAXDNAME - 1 < sz)
      break;

    memcpy(pSp, current, cnt);
    pSp += (cnt + 1);
  }

  m_domain_srch_list = numTok;
  return nullptr;
}

/* --------------------------------------------------------------
   SplitDNSRecord::Init()

   matcher_line* line_info - contains parsed label/value pairs
   of the current split.config line
   -------------------------------------------------------------- */
config_parse_error
SplitDNSRecord::Init(matcher_line *line_info)
{
  const char *errPtr = nullptr;
  const char *tmp;
  char *label;
  char *val;

  this->line_num = line_info->line_num;
  for (int i = 0; i < MATCHER_MAX_TOKENS; i++) {
    label = line_info->line[0][i];
    val   = line_info->line[1][i];

    if (label == nullptr) {
      continue;
    }

    if (strcasecmp(label, "def_domain") == 0) {
      if (nullptr != (errPtr = ProcessDefDomain(val))) {
        return config_parse_error("%s %s at line %d", modulePrefix, errPtr, line_num);
      }
      line_info->line[0][i] = nullptr;
      line_info->num_el--;
      continue;
    }

    if (strcasecmp(label, "search_list") == 0) {
      if (nullptr != (errPtr = ProcessDomainSrchList(val))) {
        return config_parse_error("%s %s at line %d", modulePrefix, errPtr, line_num);
      }
      line_info->line[0][i] = nullptr;
      line_info->num_el--;
      continue;
    }

    if (strcasecmp(label, "named") == 0) {
      if (nullptr != (errPtr = ProcessDNSHosts(val))) {
        return config_parse_error("%s %s at line %d", modulePrefix, errPtr, line_num);
      }
      line_info->line[0][i] = nullptr;
      line_info->num_el--;
      continue;
    }
  }

  if (!ats_is_ip(&m_servers.x_server_ip[0].sa)) {
    return config_parse_error("%s No server specified in splitdns.config at line %d", modulePrefix, line_num);
  }

  DNSHandler *dnsH  = new DNSHandler;
  ink_res_state res = new ts_imp_res_state;

  memset(res, 0, sizeof(ts_imp_res_state));
  if ((-1 == ink_res_init(res, m_servers.x_server_ip, m_dnsSrvr_cnt, dns_search, m_servers.x_def_domain,
                          m_servers.x_domain_srch_list, nullptr))) {
    char ab[INET6_ADDRPORTSTRLEN];
    return config_parse_error("Failed to build res record for the servers %s ...",
                              ats_ip_ntop(&m_servers.x_server_ip[0].sa, ab, sizeof ab));
  }

  dnsH->m_res = res;
  dnsH->mutex = SplitDNSConfig::dnsHandler_mutex;
  ats_ip_invalidate(&dnsH->ip.sa); // Mark to use default DNS.

  m_servers.x_dnsH = dnsH;

  SET_CONTINUATION_HANDLER(dnsH, &DNSHandler::startEvent_sdns);
  (eventProcessor.eventthread[ET_DNS][0])->schedule_imm(dnsH);

  /* -----------------------------------------------------
     Process any modifiers to the directive, if they exist
     ----------------------------------------------------- */
  if (line_info->num_el > 0) {
    tmp = ProcessModifiers(line_info);
    if (tmp != nullptr) {
      return config_parse_error("%s %s at line %d in splitdns.config", modulePrefix, tmp, line_num);
    }
  }

  return config_parse_error::ok();
}

/* --------------------------------------------------------------
    SplitDNSRecord::UpdateMatch()
   -------------------------------------------------------------- */
void
SplitDNSRecord::UpdateMatch(SplitDNSResult *result, RequestData * /* rdata ATS_UNUSED */)
{
  int last_number = result->m_line_number;

  if ((last_number < 0) || (last_number > this->line_num)) {
    result->m_rec         = this;
    result->m_line_number = this->line_num;

    Debug("splitdns_config", "Matched with %p dns node from line %d", this, this->line_num);
  }
}

/* --------------------------------------------------------------
    SplitDNSRecord::Print()
   -------------------------------------------------------------- */
void
SplitDNSRecord::Print()
{
  for (int i = 0; i < m_dnsSrvr_cnt; i++) {
    char ab[INET6_ADDRPORTSTRLEN];
    Debug("splitdns_config", " %s", ats_ip_ntop(&m_servers.x_server_ip[i].sa, ab, sizeof ab));
  }
}

void
ink_split_dns_init(ModuleVersion v)
{
  static int init_called = 0;

  ink_release_assert(!checkModuleVersion(v, SPLITDNS_MODULE_VERSION));
  if (init_called)
    return;

  init_called = 1;
}

#endif // SPLIT_DNS
