#include "byte.h"
#include "dnsresolv.h"
#include "env.h"
#include "ip.h"
#include "readclose.h"
#include "socket_if.h"
#include "taia.h"

/**
  @file dns_rcip.c
  @author djb, fefe, feh
  @source ucspi-tcp
  @brief DNS receive for query
*/

static stralloc data = {0};
static stralloc ifname = {0};

static int init(char ip[QUERY_MAXIPLEN], uint32 sid[QUERY_MAXNS])
{
  int i;
  int j;
  int k = 0;
  int iplen = 0;
  char *x;
  char ip4[4];

  /* Read (compactified) IPv4|v6 addresses of resolvers
     Store them in array IP with fixed length:
     ip(64) -> 16 IPv4 addresses (not used anymore)
     ip(512) -> 16*2 IPv6 addresses (we use IPv4 mapped IPv6 addresses)
     sid(32) -> the scope for the respective IPv6 or 0
  */
  for (i = 0; i < QUERY_MAXNS; ++i) sid[i] = 0;

  x = env_get("DNSCACHEIP");
  if (x) {
    while (iplen <= 240 && *x != '\0') {
      if (*x == ' ') {
        ++x;
      } else if ((i = ip6_ifscan(x, ip + iplen, &ifname))) {
        if (ifname.len > 2) sid[k] = socket_getifidx(ifname.s);
        iplen += 16;
        k++;
        if (*(x += i) == '\0') break;
      }
    }
  }

  if (!iplen) {
    i = openreadclose("/etc/resolv.conf", &data, 64);
    if (i == -1) return DNS_INT;
    if (i) {
      if (!stralloc_append(&data, "\n")) return DNS_MEM;
      i = 0;
      for (j = 0; j < data.len; ++j) {
        if (data.s[j] == '\n') {
          if (byte_equal("nameserver ", 11, data.s + i) || byte_equal("nameserver\t", 11, data.s + i)) {
            i += 10;
            while ((data.s[i] == ' ') || (data.s[i] == '\t')) i++;
            if (iplen <= 240) {
              data.s[j] = '\0'; /* ip6_ifscan needs terminated string on input */
              if (ip4_scan(data.s + i, ip4)) {
                if (byte_equal(ip4, 4, "\0\0\0\0")) byte_copy(ip4, 4, "\177\0\0\1");
                byte_copy(ip + iplen, 12, V4mappedprefix);
                byte_copy(ip + iplen + 12, 4, ip4);
                sid[k] = 0;
                iplen += 16;
                k++;
              } else if (ip6_ifscan(data.s + i, ip + iplen, &ifname)) {
                if (ifname.len > 2) sid[k] = socket_getifidx(ifname.s);
                iplen += 16;
                k++;
              }
            }
          }
          i = j + 1;
        }
      }
    }
  }

  if (!iplen) {
    byte_copy(ip, 16, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1");
    iplen = 16;
  }
  byte_zero(ip + iplen, QUERY_MAXIPLEN - iplen);
  return 0;
}

static int ok = 0;
static unsigned int uses;
static struct taia deadline;
static char ip[QUERY_MAXIPLEN]; /* defined if ok */
static uint32 scopes[QUERY_MAXNS];

int dns_resolvconfip(char s[QUERY_MAXIPLEN], uint32 scope[QUERY_MAXNS])
{
  struct taia now;

  taia_now(&now);
  if (taia_less(&deadline, &now)) ok = 0;
  if (!uses) ok = 0;

  if (!ok) {
    if (init(ip, scopes) < 0) return DNS_INT;
    taia_uint(&deadline, 600);
    taia_add(&deadline, &now, &deadline);
    uses = 10000;
    ok = 1;
  }

  --uses;
  byte_copy(s, QUERY_MAXIPLEN, ip);
  byte_copy(scope, 128, scopes);
  return 0;
}