DNS-message.cpp

   1 #include "DNS-message.hpp"
   2
   3 #include "DNS-iostream.hpp"
   4 #include "Domain.hpp"
   5
   6 #include <arpa/nameser.h>
   7
   8 namespace {
   9 using octet = unsigned char;
  10
  11 octet constexpr lo(uint16_t n) { return octet(n & 0xFF); }
  12 octet constexpr hi(uint16_t n) { return octet((n >> 8) & 0xFF); }
  13
  14 uint16_t constexpr as_u16(octet hi, octet lo)
  15 {
  16   return (uint16_t(hi) << 8) + lo;
  17 }
  18
  19 /*
  20                                            1  1  1  1  1  1
  21              0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
  22             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  23             |                      ID                       |
  24             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  25             |QR|   Opcode  |AA|TC|RD|RA| Z|AD|CD|   RCODE   |
  26             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  27             |                    QDCOUNT                    |
  28             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  29             |                    ANCOUNT                    |
  30             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  31             |                    NSCOUNT                    |
  32             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  33             |                    ARCOUNT                    |
  34             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  35
  36  */
  37
  38 class header {
  39   octet id_hi_;
  40   octet id_lo_;
  41
  42   octet flags_0_{1}; // recursion desired
  43   octet flags_1_{0};
  44
  45   octet qdcount_hi_{0};
  46   octet qdcount_lo_{1}; // 1 question
  47
  48   octet ancount_hi_{0};
  49   octet ancount_lo_{0};
  50
  51   octet nscount_hi_{0};
  52   octet nscount_lo_{0};
  53
  54   octet arcount_hi_{0};
  55   octet arcount_lo_{1}; // 1 additional for the OPT
  56
  57 public:
  58   explicit header(uint16_t id)
  59     : id_hi_(hi(id))
  60     , id_lo_(lo(id))
  61   {
  62     static_assert(sizeof(header) == 12);
  63   }
  64
  65   uint16_t id() const { return as_u16(id_hi_, id_lo_); }
  66
  67   uint16_t qdcount() const { return as_u16(qdcount_hi_, qdcount_lo_); }
  68   uint16_t ancount() const { return as_u16(ancount_hi_, ancount_lo_); }
  69   uint16_t nscount() const { return as_u16(nscount_hi_, nscount_lo_); }
  70   uint16_t arcount() const { return as_u16(arcount_hi_, arcount_lo_); }
  71
  72   // clang-format off
  73   bool truncation()          const { return (flags_0_ & 0x02) != 0; }
  74
  75   bool checking_disabled()   const { return (flags_1_ & 0x10) != 0; }
  76   bool authentic_data()      const { return (flags_1_ & 0x20) != 0; }
  77   bool recursion_available() const { return (flags_1_ & 0x80) != 0; }
  78   // clang-format on
  79
  80   uint16_t rcode() const { return flags_1_ & 0xf; }
  81 };
  82
  83 class question {
  84   octet qtype_hi_;
  85   octet qtype_lo_;
  86
  87   octet qclass_hi_;
  88   octet qclass_lo_;
  89
  90 public:
  91   explicit question(DNS::RR_type qtype, uint16_t qclass)
  92     : qtype_hi_(hi(static_cast<uint16_t>(qtype)))
  93     , qtype_lo_(lo(static_cast<uint16_t>(qtype)))
  94     , qclass_hi_(hi(qclass))
  95     , qclass_lo_(lo(qclass))
  96   {
  97     static_assert(sizeof(question) == 4);
  98   }
  99
 100   DNS::RR_type qtype() const
 101   {
 102     return static_cast<DNS::RR_type>(as_u16(qtype_hi_, qtype_lo_));
 103   }
 104   uint16_t qclass() const { return as_u16(qclass_hi_, qclass_lo_); }
 105 };
 106
 107 /*
 108
 109 <https://tools.ietf.org/html/rfc6891#section-6.1.2>
 110
 111        +------------+--------------+------------------------------+
 112        | Field Name | Field Type   | Description                  |
 113        +------------+--------------+------------------------------+
 114        | NAME       | domain name  | MUST be 0 (root domain)      |
 115        | TYPE       | u_int16_t    | OPT (41)                     |
 116        | CLASS      | u_int16_t    | requestor's UDP payload size |
 117        | TTL        | u_int32_t    | extended RCODE and flags     |
 118        | RDLEN      | u_int16_t    | length of all RDATA          |
 119        | RDATA      | octet stream | {attribute,value} pairs      |
 120        +------------+--------------+------------------------------+
 121
 122 <https://tools.ietf.org/html/rfc3225>
 123
 124 3. Protocol Changes, in place of TTL
 125
 126                 +0 (MSB)                +1 (LSB)
 127          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 128       0: |   EXTENDED-RCODE      |       VERSION         |
 129          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 130       2: |DO|                    Z                       |
 131          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 132
 133 */
 134
 135 class edns0_opt_meta_rr {
 136   octet root_domain_name_{0}; // must be zero
 137
 138   octet type_hi_{0};
 139   octet type_lo_{ns_t_opt};
 140
 141   octet class_hi_; // UDP payload size
 142   octet class_lo_;
 143
 144   octet extended_rcode_{0};
 145   octet version_{0};
 146
 147   octet z_hi_{0x80}; // "DNSSEC OK" (DO) bit
 148   octet z_lo_{0};
 149
 150   octet rdlen_hi_{0};
 151   octet rdlen_lo_{0};
 152
 153 public:
 154   explicit edns0_opt_meta_rr(uint16_t max_udp_sz)
 155     : class_hi_(hi(max_udp_sz))
 156     , class_lo_(lo(max_udp_sz))
 157   {
 158     static_assert(sizeof(edns0_opt_meta_rr) == 11);
 159   }
 160
 161   uint16_t extended_rcode() const { return extended_rcode_; }
 162 };
 163
 164 /*
 165
 166 <https://tools.ietf.org/html/rfc1035>
 167
 168 4.1.3. Resource record format
 169                                     1  1  1  1  1  1
 170       0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
 171     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 172     |                                               |
 173     /                                               /
 174     /                      NAME                     /
 175     |                                               |
 176     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 177     |                      TYPE                     |
 178     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 179     |                     CLASS                     |
 180     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 181     |                      TTL                      |
 182     |                                               |
 183     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 184     |                   RDLENGTH                    |
 185     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
 186     /                     RDATA                     /
 187     /                                               /
 188     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 189
 190  */
 191
 192 class rr {
 193   octet type_hi_;
 194   octet type_lo_;
 195
 196   octet class_hi_;
 197   octet class_lo_;
 198
 199   octet ttl_0_;
 200   octet ttl_1_;
 201   octet ttl_2_;
 202   octet ttl_3_;
 203
 204   octet rdlength_hi_;
 205   octet rdlength_lo_;
 206
 207 public:
 208   rr() { static_assert(sizeof(rr) == 10); }
 209
 210   uint16_t rr_type() const { return as_u16(type_hi_, type_lo_); }
 211   uint16_t rr_class() const { return as_u16(class_hi_, class_lo_); }
 212   uint32_t rr_ttl() const
 213   {
 214     return (uint32_t(ttl_0_) << 24) + (uint32_t(ttl_1_) << 16) +
 215            (uint32_t(ttl_2_) << 8) + (uint32_t(ttl_3_));
 216   }
 217
 218   uint16_t rdlength() const { return as_u16(rdlength_hi_, rdlength_lo_); }
 219
 220   auto cdata() const
 221   {
 222     return reinterpret_cast<char const*>(this) + sizeof(rr);
 223   }
 224   auto rddata() const { return reinterpret_cast<octet const*>(cdata()); }
 225   auto next_rr_name() const { return rddata() + rdlength(); }
 226 };
 227
 228 // name processing code mostly adapted from c-ares
 229
 230 auto uztosl(size_t uznum)
 231 {
 232   CHECK_LE(uznum, size_t(std::numeric_limits<long>::max()));
 233   return static_cast<long>(uznum);
 234 }
 235
 236 // return the length of the expansion of an encoded domain name, or -1
 237 // if the encoding is invalid
 238
 239 int name_length(octet const* encoded, DNS::message const& pkt)
 240 {
 241   // Allow the caller to pass us buf + len and have us check for it.
 242   if (encoded >= end(pkt))
 243     return -1;
 244
 245   int length = 0;
 246   int nindir = 0; // count indirections
 247
 248   while (*encoded) {
 249
 250     auto const top = (*encoded & NS_CMPRSFLGS);
 251
 252     if (top == NS_CMPRSFLGS) {
 253       // Check the offset and go there.
 254       if (encoded + 1 >= end(pkt))
 255         return -1;
 256
 257       auto const offset = (*encoded & ~NS_CMPRSFLGS) << 8 | *(encoded + 1);
 258       if (offset >= size(pkt))
 259         return -1;
 260
 261       encoded = begin(pkt) + offset;
 262
 263       ++nindir;
 264
 265       auto constexpr max_indirs = 50; // maximum indirections allowed for a name
 266
 267       // If we've seen more indirects than the message length, or over
 268       // some limit, then there's a loop.
 269       if (nindir > size(pkt) || nindir > max_indirs)
 270         return -1;
 271     }
 272     else if (top == 0) {
 273       auto offset = *encoded;
 274       if (encoded + offset + 1 >= end(pkt))
 275         return -1;
 276
 277       ++encoded;
 278
 279       while (offset--) {
 280         length += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
 281         encoded++;
 282       }
 283
 284       ++length;
 285     }
 286     else {
 287       // RFC 1035 4.1.4 says other options (01, 10) for top 2
 288       // bits are reserved.
 289       return -1;
 290     }
 291   }
 292
 293   // If there were any labels at all, then the number of dots is one
 294   // less than the number of labels, so subtract one.
 295
 296   return length ? length - 1 : length;
 297 }
 298
 299 bool expand_name(octet const*        encoded,
 300                  DNS::message const& pkt,
 301                  std::string&        name,
 302                  int&                enc_len)
 303 {
 304   name.clear();
 305
 306   auto indir = false;
 307
 308   auto const nlen = name_length(encoded, pkt);
 309   if (nlen < 0) {
 310     LOG(WARNING) << "bad name";
 311     return false;
 312   }
 313
 314   name.reserve(nlen);
 315
 316   if (nlen == 0) {
 317     // RFC 2181 says this should be ".": the root of the DNS tree.
 318     // Since this function strips trailing dots though, it becomes ""s
 319
 320     // indirect root label (like 0xc0 0x0c) is 2 bytes long
 321     if ((*encoded & NS_CMPRSFLGS) == NS_CMPRSFLGS)
 322       enc_len = 2;
 323     else
 324       enc_len = 1; // the caller should move one byte to get past this
 325
 326     return true;
 327   }
 328
 329   // error-checking done by name_length()
 330   auto p = encoded;
 331   while (*p) {
 332     if ((*p & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
 333       if (!indir) {
 334         enc_len = uztosl(p + 2 - encoded);
 335         indir   = true;
 336       }
 337       p = begin(pkt) + ((*p & ~NS_CMPRSFLGS) << 8 | *(p + 1));
 338     }
 339     else {
 340       int len = *p;
 341       p++;
 342       while (len--) {
 343         if (*p == '.' || *p == '\\')
 344           name += '\\';
 345         name += static_cast<char>(*p);
 346         p++;
 347       }
 348       name += '.';
 349     }
 350   }
 351
 352   if (!indir)
 353     enc_len = uztosl(p + 1 - encoded);
 354
 355   if (name.length() && (name.back() == '.')) {
 356     name.pop_back();
 357   }
 358
 359   return true;
 360 }
 361
 362 // return the length of the encoded name
 363
 364 int name_put(octet* bfr, char const* name)
 365 {
 366   auto q = bfr;
 367
 368   if ((name[0] == '.') && (name[1] == '\0'))
 369     name++;
 370
 371   while (*name) {
 372     if (*name == '.') {
 373       LOG(WARNING) << "zero length label";
 374       return -1;
 375     }
 376
 377     uint8_t     len = 0;
 378     char const* p;
 379
 380     for (p = name; *p && *p != '.'; p++) {
 381       if (*p == '\\' && *(p + 1) != 0)
 382         p++;
 383       len++;
 384     }
 385     if (len > 63) {
 386       // RFC-1035 Section 2.3.4. Size limits
 387       LOG(WARNING) << "label exceeds 63 octets";
 388       return -1;
 389     }
 390
 391     *q++ = len;
 392     for (p = name; *p && *p != '.'; p++) {
 393       if (*p == '\\' && *(p + 1) != 0)
 394         p++;
 395       *q++ = *p;
 396     }
 397
 398     if (!*p)
 399       break;
 400
 401     name = p + 1;
 402   }
 403
 404   // Add the zero-length label at the end.
 405   *q++ = 0;
 406
 407   auto const sz = q - bfr;
 408   if (sz > 255) {
 409     // RFC-1035 Section 2.3.4. Size limits
 410     LOG(WARNING) << "domain name exceeds 255 octets";
 411     return -1;
 412   }
 413
 414   return sz;
 415 }
 416 } // namespace
 417
 418 namespace DNS {
 419
 420 uint16_t message::id() const
 421 {
 422   auto const hdr_p = reinterpret_cast<header const*>(begin());
 423   return hdr_p->id();
 424 }
 425
 426 size_t min_message_sz() { return sizeof(header); }
 427
 428 DNS::message
 429 create_question(char const* name, DNS::RR_type type, uint16_t cls, uint16_t id)
 430 {
 431   // size to allocate may be larger than needed if backslash escapes
 432   // are used in domain name
 433
 434   auto const sz_alloc = strlen(name) + 2 + // clang-format off
 435                         sizeof(header)   +
 436                         sizeof(question) +
 437                         sizeof(edns0_opt_meta_rr); // clang-format on
 438
 439   DNS::message::container_t bfr(sz_alloc);
 440
 441   auto q = bfr.data();
 442
 443   new (q) header(id);
 444   q += sizeof(header);
 445
 446   auto const len = name_put(q, name);
 447   CHECK_GE(len, 1) << "malformed domain name " << name;
 448   q += len;
 449
 450   new (q) question(type, cls);
 451   q += sizeof(question);
 452
 453   new (q) edns0_opt_meta_rr(Config::max_udp_sz);
 454   q += sizeof(edns0_opt_meta_rr);
 455
 456   // verify constructed size is less than or equal to allocated size
 457   auto const sz = q - bfr.data();
 458   CHECK_LE(sz, sz_alloc);
 459
 460   bfr.resize(sz);
 461   bfr.shrink_to_fit();
 462
 463   return DNS::message{std::move(bfr)};
 464 }
 465
 466 void check_answer(bool& nx_domain,
 467                   bool& bogus_or_indeterminate,
 468
 469                   uint16_t& rcode,
 470                   uint16_t& extended_rcode,
 471
 472                   bool& truncation,
 473                   bool& authentic_data,
 474                   bool& has_record,
 475
 476                   DNS::message const& q,
 477                   DNS::message const& a,
 478
 479                   DNS::RR_type type,
 480                   char const*  name)
 481 {
 482   // We grab some stuff from the question we generated.  This is not
 483   // an un-trusted datum from afar.
 484
 485   auto const cls{[type = type, &q]() {
 486     auto       q_p     = begin(q);
 487     auto const q_hdr_p = reinterpret_cast<header const*>(q_p);
 488     CHECK_EQ(q_hdr_p->qdcount(), uint16_t(1));
 489     q_p += sizeof(header);
 490     std::string qname;
 491     int         name_len;
 492     CHECK(expand_name(q_p, q, qname, name_len));
 493     q_p += name_len;
 494     auto const question_p = reinterpret_cast<question const*>(q_p);
 495     CHECK(question_p->qtype() == type)
 496         << question_p->qtype() << " != " << type << '\n';
 497     return question_p->qclass();
 498   }()};
 499
 500   auto const hdr_p = reinterpret_cast<header const*>(begin(a));
 501
 502   rcode = hdr_p->rcode();
 503   switch (rcode) {
 504   case ns_r_noerror: break;
 505   case ns_r_nxdomain: nx_domain = true; break;
 506   case ns_r_servfail: bogus_or_indeterminate = true; break;
 507   default:
 508     bogus_or_indeterminate = true;
 509     LOG(WARNING) << "name lookup error: " << DNS::rcode_c_str(rcode) << " for "
 510                  << name << '/' << type;
 511     break;
 512   }
 513
 514   truncation     = hdr_p->truncation();
 515   authentic_data = hdr_p->authentic_data();
 516   has_record     = hdr_p->ancount() != 0;
 517
 518   if (truncation) {
 519     bogus_or_indeterminate = true;
 520     LOG(WARNING) << "DNS answer truncated for " << name << '/' << type;
 521     return;
 522   }
 523
 524   // check the question part of the reply
 525
 526   if (hdr_p->qdcount() != 1) {
 527     bogus_or_indeterminate = true;
 528     LOG(WARNING) << "question not copied into answer for " << name << '/'
 529                  << type;
 530     return;
 531   }
 532
 533   // p is a pointer that pushes forward in the message as we process
 534   // each section
 535   auto p = begin(a) + sizeof(header);
 536
 537   { // make sure the question name matches
 538     std::string qname;
 539     auto        enc_len = 0;
 540     if (!expand_name(p, a, qname, enc_len)) {
 541       bogus_or_indeterminate = true;
 542       LOG(WARNING) << "bad message";
 543       return;
 544     }
 545     p += enc_len;
 546     if (p >= end(a)) {
 547       bogus_or_indeterminate = true;
 548       LOG(WARNING) << "bad message";
 549       return;
 550     }
 551     if (!Domain::match(qname, name)) {
 552       bogus_or_indeterminate = true;
 553       LOG(WARNING) << "names don't match, " << qname << " != " << name;
 554       return;
 555     }
 556   }
 557
 558   if ((p + sizeof(question)) >= end(a)) {
 559     bogus_or_indeterminate = true;
 560     LOG(WARNING) << "bad message";
 561     return;
 562   }
 563
 564   auto question_p = reinterpret_cast<question const*>(p);
 565   p += sizeof(question);
 566
 567   if (question_p->qtype() != type) {
 568     bogus_or_indeterminate = true;
 569     LOG(WARNING) << "qtypes don't match, " << question_p->qtype()
 570                  << " != " << type;
 571     return;
 572   }
 573   if (question_p->qclass() != cls) {
 574     bogus_or_indeterminate = true;
 575     LOG(WARNING) << "qclasses don't match, " << question_p->qclass()
 576                  << " != " << cls;
 577     return;
 578   }
 579
 580   // answers and nameservers
 581   for (auto i = 0; i < (hdr_p->ancount() + hdr_p->nscount()); ++i) {
 582     std::string x;
 583     auto        enc_len = 0;
 584     if (!expand_name(p, a, x, enc_len) ||
 585         ((p + enc_len + sizeof(rr)) > end(a))) {
 586       bogus_or_indeterminate = true;
 587       LOG(WARNING) << "bad message in answer or nameserver section for " << name
 588                    << '/' << type;
 589       return;
 590     }
 591     p += enc_len;
 592     auto const rr_p = reinterpret_cast<rr const*>(p);
 593     p               = rr_p->next_rr_name();
 594   }
 595
 596   // check additional section for OPT record
 597   for (auto i = 0; i < hdr_p->arcount(); ++i) {
 598     std::string x;
 599     auto        enc_len = 0;
 600     if (!expand_name(p, a, x, enc_len) ||
 601         ((p + enc_len + sizeof(rr)) > end(a))) {
 602       bogus_or_indeterminate = true;
 603       LOG(WARNING) << "bad message in additional section for " << name << '/'
 604                    << type;
 605       return;
 606     }
 607     p += enc_len;
 608     auto const rr_p = reinterpret_cast<rr const*>(p);
 609
 610     switch (rr_p->rr_type()) {
 611     case ns_t_opt: {
 612       auto opt_p     = reinterpret_cast<edns0_opt_meta_rr const*>(p);
 613       extended_rcode = (opt_p->extended_rcode() << 4) + hdr_p->rcode();
 614       break;
 615     }
 616
 617     case ns_t_a:
 618     case ns_t_aaaa:
 619     case ns_t_ns:
 620     case ns_t_rrsig:
 621       // nameserver records often included with associated address info
 622       break;
 623
 624     default:
 625       LOG(INFO) << "unknown additional record, name == " << name;
 626       LOG(INFO) << "rr_p->type()  == " << rr_p->rr_type();
 627       LOG(INFO) << "rr_p->class() == " << rr_p->rr_class();
 628       LOG(INFO) << "rr_p->ttl()   == " << rr_p->rr_ttl();
 629       break;
 630     }
 631
 632     p = rr_p->next_rr_name();
 633   }
 634
 635   auto size_check = p - begin(a);
 636   if (size_check != size(a)) {
 637     bogus_or_indeterminate = true;
 638     LOG(WARNING) << "bad message size for " << name << '/' << type;
 639     return;
 640   }
 641 }
 642
 643 std::optional<RR> get_A(rr const* rr_p, DNS::message const& pkt, bool& err)
 644 {
 645   if (rr_p->rdlength() != 4) {
 646     LOG(WARNING) << "bogus A record";
 647     err = true;
 648     return {};
 649   }
 650   return RR_A{rr_p->rddata(), rr_p->rdlength()};
 651 }
 652
 653 std::optional<RR> get_CNAME(rr const* rr_p, DNS::message const& pkt, bool& err)
 654 {
 655   std::string name;
 656   int         enc_len;
 657   if (!expand_name(rr_p->rddata(), pkt, name, enc_len)) {
 658     LOG(WARNING) << "bogus CNAME record";
 659     err = true;
 660     return {};
 661   }
 662   return RR_CNAME{name};
 663 }
 664
 665 std::optional<RR> get_PTR(rr const* rr_p, DNS::message const& pkt, bool& err)
 666 {
 667   std::string name;
 668   int         enc_len;
 669   if (!expand_name(rr_p->rddata(), pkt, name, enc_len)) {
 670     LOG(WARNING) << "bogus PTR record";
 671     err = true;
 672     return {};
 673   }
 674   return RR_PTR{name};
 675 }
 676
 677 std::optional<RR> get_MX(rr const* rr_p, DNS::message const& pkt, bool& err)
 678 {
 679   std::string name;
 680   int         enc_len;
 681   if (rr_p->rdlength() < 3) {
 682     LOG(WARNING) << "bogus MX record";
 683     err = true;
 684     return {};
 685   }
 686   auto       p          = rr_p->rddata();
 687   auto const preference = as_u16(p[0], p[1]);
 688   p += 2;
 689   if (!expand_name(p, pkt, name, enc_len)) {
 690     LOG(WARNING) << "bogus MX record";
 691     err = true;
 692     return {};
 693   }
 694   return RR_MX{name, preference};
 695 }
 696
 697 std::optional<RR> get_TXT(rr const* rr_p, DNS::message const& pkt, bool& err)
 698 {
 699   if (rr_p->rdlength() < 1) {
 700     LOG(WARNING) << "bogus TXT record";
 701     err = true;
 702     return {};
 703   }
 704   std::string str;
 705   auto        p = rr_p->rddata();
 706   do {
 707     if ((p + 1 + *p) > rr_p->next_rr_name()) {
 708       LOG(WARNING) << "bogus string in TXT record";
 709       err = true;
 710       return {};
 711     }
 712     str.append(reinterpret_cast<char const*>(p) + 1, *p);
 713     p = p + *p + 1;
 714   } while (p < rr_p->next_rr_name());
 715   return RR_TXT{str};
 716 }
 717
 718 std::optional<RR> get_AAAA(rr const* rr_p, DNS::message const& pkt, bool& err)
 719 {
 720   if (rr_p->rdlength() != 16) {
 721     LOG(WARNING) << "bogus AAAA record";
 722     err = true;
 723     return {};
 724   }
 725   return RR_AAAA{rr_p->rddata(), rr_p->rdlength()};
 726 }
 727
 728 std::optional<RR> get_RRSIG(rr const* rr_p, DNS::message const& pkt, bool& err)
 729 {
 730   // LOG(WARNING) << "#### FIXME! RRSIG";
 731   // return RR_RRSIG{rr_p->rddata(), rr_p->rdlength()});
 732   return {};
 733 }
 734
 735 std::optional<RR> get_TLSA(rr const* rr_p, DNS::message const& pkt, bool& err)
 736 {
 737   if (rr_p->rdlength() < 4) {
 738     LOG(WARNING) << "bogus TLSA record";
 739     err = true;
 740     return {};
 741   }
 742
 743   auto p = rr_p->rddata();
 744
 745   uint8_t cert_usage    = *p++;
 746   uint8_t selector      = *p++;
 747   uint8_t matching_type = *p++;
 748
 749   uint8_t const* assoc_data    = p;
 750   size_t         assoc_data_sz = rr_p->rdlength() - 3;
 751
 752   return RR_TLSA{cert_usage, selector, matching_type, assoc_data,
 753                  assoc_data_sz};
 754 }
 755
 756 std::optional<RR> get_rr(rr const* rr_p, DNS::message const& pkt, bool& err)
 757 {
 758   auto const typ = static_cast<DNS::RR_type>(rr_p->rr_type());
 759
 760   switch (typ) { // clang-format off
 761   case DNS::RR_type::A:     return get_A    (rr_p, pkt, err);
 762   case DNS::RR_type::CNAME: return get_CNAME(rr_p, pkt, err);
 763   case DNS::RR_type::PTR:   return get_PTR  (rr_p, pkt, err);
 764   case DNS::RR_type::MX:    return get_MX   (rr_p, pkt, err);
 765   case DNS::RR_type::TXT:   return get_TXT  (rr_p, pkt, err);
 766   case DNS::RR_type::AAAA:  return get_AAAA (rr_p, pkt, err);
 767   case DNS::RR_type::RRSIG: return get_RRSIG(rr_p, pkt, err);
 768   case DNS::RR_type::TLSA:  return get_TLSA (rr_p, pkt, err);
 769   default: break;
 770   } // clang-format on
 771
 772   LOG(WARNING) << "unsupported RR type " << typ;
 773   return {};
 774 }
 775
 776 RR_collection get_records(message const& pkt, bool& bogus_or_indeterminate)
 777 {
 778   RR_collection ret;
 779
 780   auto const hdr_p = reinterpret_cast<header const*>(begin(pkt));
 781
 782   auto p = begin(pkt) + sizeof(header);
 783
 784   // skip queries
 785   for (auto i = 0; i < hdr_p->qdcount(); ++i) {
 786     std::string qname;
 787     auto        enc_len = 0;
 788
 789     CHECK(expand_name(p, pkt, qname, enc_len));
 790     p += enc_len;
 791     // auto question_p = reinterpret_cast<question const*>(p);
 792     p += sizeof(question);
 793   }
 794
 795   // get answers
 796   for (auto i = 0; i < hdr_p->ancount(); ++i) {
 797     std::string name;
 798     auto        enc_len = 0;
 799     CHECK(expand_name(p, pkt, name, enc_len));
 800     p += enc_len;
 801     if ((p + sizeof(rr)) > end(pkt)) {
 802       bogus_or_indeterminate = true;
 803       LOG(WARNING) << "bad message";
 804       return RR_collection{};
 805     }
 806     auto rr_p = reinterpret_cast<rr const*>(p);
 807     if ((p + rr_p->rdlength()) > end(pkt)) {
 808       bogus_or_indeterminate = true;
 809       LOG(WARNING) << "bad message";
 810       return RR_collection{};
 811     }
 812
 813     auto rr_ret = get_rr(rr_p, pkt, bogus_or_indeterminate);
 814
 815     if (bogus_or_indeterminate)
 816       return RR_collection{};
 817
 818     if (rr_ret)
 819       ret.emplace_back(*rr_ret);
 820
 821     p = rr_p->next_rr_name();
 822   }
 823
 824   return ret;
 825 }
 826
 827 } // namespace DNS