/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * SPDX-License-Identifier: curl
 *
 ***************************************************************************/
#include "first.h"

static int dnsd_wrotepidfile = 0;
static int dnsd_wroteportfile = 0;

static unsigned short get16bit(const unsigned char **pkt, size_t *size)
{
  const unsigned char *p = *pkt;
  (*pkt) += 2;
  *size -= 2;
  return (unsigned short)((p[0] << 8) | p[1]);
}

static char name[256];

static int qname(const unsigned char **pkt, size_t *size)
{
  unsigned char length;
  int o = 0;
  const unsigned char *p = *pkt;
  do {
    int i;
    length = *p++;
    if(*size < length)
      /* too long */
      return 1;
    if(length && o)
      name[o++] = '.';
    for(i = 0; i < length; i++) {
      name[o++] = *p++;
    }
  } while(length);
  *size -= (p - *pkt);
  *pkt = p;
  name[o++] = '\0';
  return 0;
}

#define QTYPE_A     1
#define QTYPE_AAAA  28
#define QTYPE_HTTPS 0x41

static const char *type2string(unsigned short qtype)
{
  switch(qtype) {
  case QTYPE_A:
    return "A";
  case QTYPE_AAAA:
    return "AAAA";
  case QTYPE_HTTPS:
    return "HTTPS";
  }
  return "<unknown>";
}

/*
 * Handle initial connection protocol.
 *
 * Return query (qname + type + class), type and id.
 */
static int store_incoming(const unsigned char *data, size_t size,
                          unsigned char *qbuf, size_t qbuflen, size_t *qlen,
                          unsigned short *qtype, unsigned short *idp)
{
  FILE *server;
  char dumpfile[256];
#if 0
  size_t i;
#endif
  unsigned short qd;
  const unsigned char *qptr;
  size_t qsize;

  *qlen = 0;
  *qtype = 0;
  *idp = 0;

  snprintf(dumpfile, sizeof(dumpfile), "%s/dnsd.input", logdir);

  /* Open request dump file. */
  server = curlx_fopen(dumpfile, "ab");
  if(!server) {
    char errbuf[STRERROR_LEN];
    int error = errno;
    logmsg("fopen() failed with error (%d) %s",
           error, curlx_strerror(error, errbuf, sizeof(errbuf)));
    logmsg("Error opening file '%s'", dumpfile);
    return -1;
  }

  /*
                                    1  1  1  1  1  1
      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                      ID                       |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |QR|   Opcode  |AA|TC|RD|RA|   Z    |   RCODE   |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    QDCOUNT                    |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    ANCOUNT                    |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    NSCOUNT                    |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    ARCOUNT                    |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   */
  *idp = get16bit(&data, &size);
  data += 2; /* skip the next 16 bits */
  size -= 2;
#if 0
  fprintf(server, "QR: %x\n", (id & 0x8000) > 15);
  fprintf(server, "OPCODE: %x\n", (id & 0x7800) >> 11);
  fprintf(server, "TC: %x\n", (id & 0x200) >> 9);
  fprintf(server, "RD: %x\n", (id & 0x100) >> 8);
  fprintf(server, "Z: %x\n", (id & 0x70) >> 4);
  fprintf(server, "RCODE: %x\n", (id & 0x0f));
#endif
  (void)get16bit(&data, &size);

  data += 6; /* skip ANCOUNT, NSCOUNT and ARCOUNT */
  size -= 6;

  /* store pointer and size at the QD point */
  qsize = size;
  qptr = data;

  if(!qname(&data, &size)) {
    qd = get16bit(&data, &size);
    fprintf(server, "QNAME %s QTYPE %s\n", name, type2string(qd));
    *qtype = qd;
    logmsg("Question for '%s' type %x / %s", name, qd, type2string(qd));

    (void)get16bit(&data, &size);

    *qlen = qsize - size; /* total size of the query */
    if(*qlen > qbuflen) {
      logmsg("dnsd: query too large: %lu > %lu",
             (unsigned long)*qlen, (unsigned long)qbuflen);
      curlx_fclose(server);
      return -1;
    }
    memcpy(qbuf, qptr, *qlen);
  }
  else
    logmsg("Bad input qname");
#if 0
  for(i = 0; i < size; i++) {
    fprintf(server, "%02d", (unsigned int)data[i]);
  }
  fprintf(server, "\n");
#endif

  curlx_fclose(server);

  return 0;
}

static void add_answer(unsigned char *bytes, size_t *w,
                       const unsigned char *a, size_t alen,
                       unsigned short qtype)
{
  size_t i = *w;

  /* add answer */
  bytes[i++] = 0xc0;
  bytes[i++] = 0x0c; /* points to the query at this fixed packet index */

  /* QTYPE */
  bytes[i++] = (unsigned char)(qtype >> 8);
  bytes[i++] = (unsigned char)(qtype & 0xff);

  /* QCLASS IN */
  bytes[i++] = 0x00;
  bytes[i++] = 0x01;

  /* TTL, Time to live: 2580 (43 minutes) */
  bytes[i++] = 0x00;
  bytes[i++] = 0x00;
  bytes[i++] = 0x0a;
  bytes[i++] = 0x14;

  /* QTYPE size */
  bytes[i++] = (unsigned char)(alen >> 8);
  bytes[i++] = (unsigned char)(alen & 0xff);

  memcpy(&bytes[i], a, alen);
  i += alen;

  *w = i;
}

#ifdef _WIN32
#define SENDTO3 int
#else
#define SENDTO3 size_t
#endif

#define INSTRUCTIONS "dnsd.cmd"

#define MAX_ALPN 5

static unsigned char ipv4_pref[4];
static unsigned char ipv6_pref[16];
static unsigned char alpn_pref[MAX_ALPN];
static int alpn_count;
static unsigned char ancount_a;
static unsigned char ancount_aaaa;

/* this is an answer to a question */
static int send_response(curl_socket_t sock,
                         const struct sockaddr *addr, curl_socklen_t addrlen,
                         const unsigned char *qbuf, size_t qlen,
                         unsigned short qtype, unsigned short id)
{
  ssize_t rc;
  size_t i;
  int a;
  char addrbuf[128]; /* IP address buffer */
  unsigned char bytes[256] = {
    0x80, 0xea, /* ID, overwrite */
    0x81, 0x80,
    /*
    Flags: 0x8180 Standard query response, No error
        1... .... .... .... = Response: Message is a response
        .000 0... .... .... = Opcode: Standard query (0)
        .... .0.. .... .... = Authoritative: Server is not an authority for
                              domain
        .... ..0. .... .... = Truncated: Message is not truncated
        .... ...1 .... .... = Recursion desired: Do query recursively
        .... .... 1... .... = Recursion available: Server can do recursive
                              queries
        .... .... .0.. .... = Z: reserved (0)
        .... .... ..0. .... = Answer authenticated: Answer/authority portion
                              was not authenticated by the server
        .... .... ...0 .... = Non-authenticated data: Unacceptable
        .... .... .... 0000 = Reply code: No error (0)
    */
    0x0, 0x1, /* QDCOUNT a single question */
    0x0, 0x0, /* ANCOUNT number of answers */
    0x0, 0x0, /* NSCOUNT */
    0x0, 0x0  /* ARCOUNT */
  };

  bytes[0] = (unsigned char)(id >> 8);
  bytes[1] = (unsigned char)(id & 0xff);

  if(qlen > (sizeof(bytes) - 12))
    return -1;

  /* append query, includes QTYPE and QCLASS */
  memcpy(&bytes[12], qbuf, qlen);

  i = 12 + qlen;

  switch(qtype) {
  case QTYPE_A:
    bytes[7] = ancount_a;
    for(a = 0; a < ancount_a; a++) {
      const unsigned char *store = ipv4_pref;
      add_answer(bytes, &i, store, sizeof(ipv4_pref), QTYPE_A);
      logmsg("Sending back A (%x) '%s'", QTYPE_A,
             curlx_inet_ntop(AF_INET, store, addrbuf, sizeof(addrbuf)));
    }
    break;
  case QTYPE_AAAA:
    bytes[7] = ancount_aaaa;
    for(a = 0; a < ancount_aaaa; a++) {
      const unsigned char *store = ipv6_pref;
      add_answer(bytes, &i, store, sizeof(ipv6_pref), QTYPE_AAAA);
      logmsg("Sending back AAAA (%x) '%s'", QTYPE_AAAA,
             curlx_inet_ntop(AF_INET6, store, addrbuf, sizeof(addrbuf)));
    }
    break;
  case QTYPE_HTTPS:
    bytes[7] = 1; /* one answer */
    break;
  }

#ifdef __AMIGA__
  /* Amiga breakage */
  (void)rc;
  (void)sock;
  (void)addr;
  (void)addrlen;
  fprintf(stderr, "Not working\n");
  return -1;
#else
  rc = sendto(sock, (const void *)bytes, (SENDTO3)i, 0, addr, addrlen);
  if(rc != (ssize_t)i) {
    fprintf(stderr, "failed sending %d bytes\n", (int)i);
  }
#endif
  return 0;
}

static void read_instructions(void)
{
  char file[256];
  FILE *f;
  snprintf(file, sizeof(file), "%s/" INSTRUCTIONS, logdir);
  f = curlx_fopen(file, FOPEN_READTEXT);
  if(f) {
    char buf[256];
    ancount_aaaa = ancount_a = 0;
    alpn_count = 0;
    while(fgets(buf, sizeof(buf), f)) {
      char *p = strchr(buf, '\n');
      if(p) {
        int rc;
        *p = 0;
        if(!strncmp("A: ", buf, 3)) {
          rc = curlx_inet_pton(AF_INET, &buf[3], ipv4_pref);
          ancount_a = (rc == 1);
        }
        else if(!strncmp("AAAA: ", buf, 6)) {
          char *p6 = &buf[6];
          if(*p6 == '[') {
            char *pt = strchr(p6, ']');
            if(pt)
              *pt = 0;
            p6++;
          }
          rc = curlx_inet_pton(AF_INET6, p6, ipv6_pref);
          ancount_aaaa = (rc == 1);
        }
        else if(!strncmp("ALPN: ", buf, 6)) {
          char *ap = &buf[6];
          rc = 0;
          while(*ap) {
            if('h' == *ap) {
              ap++;
              if(*ap >= '1' && *ap <= '3') {
                if(alpn_count < MAX_ALPN)
                  alpn_pref[alpn_count++] = *ap;
              }
              else
                break;
            }
            else
              break;
          }
        }
        else {
          /* accept empty line */
          rc = buf[0] ? 0 : 1;
        }
        if(rc != 1) {
          logmsg("Bad line in %s: '%s'\n", file, buf);
        }
      }
    }
    curlx_fclose(f);
  }
  else
    logmsg("Error opening file '%s'", file);
}

static int test_dnsd(int argc, const char **argv)
{
  srvr_sockaddr_union_t me;
  ssize_t n = 0;
  int arg = 1;
  unsigned short port = 9123; /* UDP */
  curl_socket_t sock = CURL_SOCKET_BAD;
  int flag;
  int rc;
  int error;
  char errbuf[STRERROR_LEN];
  int result = 0;

  pidname = ".dnsd.pid";
  serverlogfile = "log/dnsd.log";
  serverlogslocked = 0;

  while(argc > arg) {
    const char *opt;
    curl_off_t num;
    if(!strcmp("--verbose", argv[arg])) {
      arg++;
      /* nothing yet */
    }
    else if(!strcmp("--version", argv[arg])) {
      printf("dnsd IPv4%s\n",
#ifdef USE_IPV6
             "/IPv6"
#else
             ""
#endif
      );
      return 0;
    }
    else if(!strcmp("--pidfile", argv[arg])) {
      arg++;
      if(argc > arg)
        pidname = argv[arg++];
    }
    else if(!strcmp("--portfile", argv[arg])) {
      arg++;
      if(argc > arg)
        portname = argv[arg++];
    }
    else if(!strcmp("--logfile", argv[arg])) {
      arg++;
      if(argc > arg)
        serverlogfile = argv[arg++];
    }
    else if(!strcmp("--logdir", argv[arg])) {
      arg++;
      if(argc > arg)
        logdir = argv[arg++];
    }
    else if(!strcmp("--ipv4", argv[arg])) {
#ifdef USE_IPV6
      ipv_inuse = "IPv4";
      use_ipv6 = FALSE;
#endif
      arg++;
    }
    else if(!strcmp("--ipv6", argv[arg])) {
#ifdef USE_IPV6
      ipv_inuse = "IPv6";
      use_ipv6 = TRUE;
#endif
      arg++;
    }
    else if(!strcmp("--port", argv[arg])) {
      arg++;
      if(argc > arg) {
        opt = argv[arg];
        if(!curlx_str_number(&opt, &num, 0xffff))
          port = (unsigned short)num;
        arg++;
      }
    }
    else {
      if(argv[arg])
        fprintf(stderr, "unknown option: %s\n", argv[arg]);
      puts("Usage: dnsd [option]\n"
           " --version\n"
           " --logfile [file]\n"
           " --logdir [directory]\n"
           " --pidfile [file]\n"
           " --portfile [file]\n"
           " --ipv4\n"
           " --ipv6\n"
           " --port [port]\n");
      return 0;
    }
  }

  snprintf(loglockfile, sizeof(loglockfile), "%s/%s/dnsd-%s.lock",
           logdir, SERVERLOGS_LOCKDIR, ipv_inuse);

#ifdef USE_IPV6
  if(!use_ipv6)
#endif
    sock = socket(AF_INET, SOCK_DGRAM, 0);
#ifdef USE_IPV6
  else
    sock = socket(AF_INET6, SOCK_DGRAM, 0);
#endif

  if(sock == CURL_SOCKET_BAD) {
    error = SOCKERRNO;
    logmsg("Error creating socket (%d) %s",
           error, curlx_strerror(error, errbuf, sizeof(errbuf)));
    result = 1;
    goto dnsd_cleanup;
  }

  flag = 1;
  if(setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&flag, sizeof(flag))) {
    error = SOCKERRNO;
    logmsg("setsockopt(SO_REUSEADDR) failed with error (%d) %s",
           error, curlx_strerror(error, errbuf, sizeof(errbuf)));
    result = 1;
    goto dnsd_cleanup;
  }

#ifdef USE_IPV6
  if(!use_ipv6) {
#endif
    memset(&me.sa4, 0, sizeof(me.sa4));
    me.sa4.sin_family = AF_INET;
    me.sa4.sin_addr.s_addr = INADDR_ANY;
    me.sa4.sin_port = htons(port);
    rc = bind(sock, &me.sa, sizeof(me.sa4));
#ifdef USE_IPV6
  }
  else {
    memset(&me.sa6, 0, sizeof(me.sa6));
    me.sa6.sin6_family = AF_INET6;
    me.sa6.sin6_addr = in6addr_any;
    me.sa6.sin6_port = htons(port);
    rc = bind(sock, &me.sa, sizeof(me.sa6));
  }
#endif /* USE_IPV6 */
  if(rc) {
    error = SOCKERRNO;
    logmsg("Error binding socket on port %hu (%d) %s", port,
           error, curlx_strerror(error, errbuf, sizeof(errbuf)));
    result = 1;
    goto dnsd_cleanup;
  }

  if(!port) {
    /* The system was supposed to choose a port number, figure out which
       port we actually got and update the listener port value with it. */
    curl_socklen_t la_size;
    srvr_sockaddr_union_t localaddr;
    memset(&localaddr, 0, sizeof(localaddr));
#ifdef USE_IPV6
    if(!use_ipv6)
#endif
      la_size = sizeof(localaddr.sa4);
#ifdef USE_IPV6
    else
      la_size = sizeof(localaddr.sa6);
#endif
    if(getsockname(sock, &localaddr.sa, &la_size) < 0) {
      error = SOCKERRNO;
      logmsg("getsockname() failed with error (%d) %s",
             error, curlx_strerror(error, errbuf, sizeof(errbuf)));
      sclose(sock);
      goto dnsd_cleanup;
    }
    switch(localaddr.sa.sa_family) {
    case AF_INET:
      port = ntohs(localaddr.sa4.sin_port);
      break;
#ifdef USE_IPV6
    case AF_INET6:
      port = ntohs(localaddr.sa6.sin6_port);
      break;
#endif
    default:
      break;
    }
    if(!port) {
      /* Real failure, listener port shall not be zero beyond this point. */
      logmsg("Apparently getsockname() succeeded, with listener port zero.");
      logmsg("A valid reason for this failure is a binary built without");
      logmsg("proper network library linkage. This might not be the only");
      logmsg("reason, but double check it before anything else.");
      result = 2;
      goto dnsd_cleanup;
    }
  }

  dnsd_wrotepidfile = write_pidfile(pidname);
  if(!dnsd_wrotepidfile) {
    result = 1;
    goto dnsd_cleanup;
  }

  if(portname) {
    dnsd_wroteportfile = write_portfile(portname, port);
    if(!dnsd_wroteportfile) {
      result = 1;
      goto dnsd_cleanup;
    }
  }

  logmsg("Running %s version on port UDP/%d", ipv_inuse, (int)port);

  for(;;) {
    unsigned short id = 0;
    unsigned char inbuffer[1500];
    srvr_sockaddr_union_t from;
    curl_socklen_t fromlen;
    unsigned char qbuf[256]; /* query storage */
    size_t qlen = 0; /* query size */
    unsigned short qtype = 0;
    fromlen = sizeof(from);
#ifdef USE_IPV6
    if(!use_ipv6)
#endif
      fromlen = sizeof(from.sa4);
#ifdef USE_IPV6
    else
      fromlen = sizeof(from.sa6);
#endif
    n = (ssize_t)recvfrom(sock, (char *)inbuffer, sizeof(inbuffer), 0,
                          &from.sa, &fromlen);
    if(got_exit_signal)
      break;
    if(n < 0) {
      logmsg("recvfrom");
      result = 3;
      break;
    }

    /* read once per incoming query, which is probably more than one
       per test case */
    read_instructions();

    store_incoming(inbuffer, n, qbuf, sizeof(qbuf), &qlen, &qtype, &id);

    set_advisor_read_lock(loglockfile);
    serverlogslocked = 1;

    send_response(sock, &from.sa, fromlen, qbuf, qlen, qtype, id);

    if(got_exit_signal)
      break;

    if(serverlogslocked) {
      serverlogslocked = 0;
      clear_advisor_read_lock(loglockfile);
    }

#if 0
    logmsg("end of one transfer");
#endif
  }

dnsd_cleanup:

#if 0
  if((peer != sock) && (peer != CURL_SOCKET_BAD))
    sclose(peer);
#endif

  if(sock != CURL_SOCKET_BAD)
    sclose(sock);

  if(got_exit_signal)
    logmsg("signalled to die");

  if(dnsd_wrotepidfile)
    unlink(pidname);
  if(dnsd_wroteportfile)
    unlink(portname);

  if(serverlogslocked) {
    serverlogslocked = 0;
    clear_advisor_read_lock(loglockfile);
  }

  restore_signal_handlers(true);

  if(got_exit_signal) {
    logmsg("========> %s dnsd (port: %d pid: %ld) exits with signal (%d)",
           ipv_inuse, (int)port, (long)our_getpid(), exit_signal);
    /*
     * To properly set the return status of the process we
     * must raise the same signal SIGINT or SIGTERM that we
     * caught and let the old handler take care of it.
     */
    raise(exit_signal);
  }

  logmsg("========> dnsd quits");
  return result;
}
