apt-pkg/contrib/srvrec.cc

   1 // -*- mode: cpp; mode: fold -*-
   2 // Description                                                          /*{{{*/
   3 /* ######################################################################
   4
   5    SRV record support
   6
   7    ##################################################################### */
   8                                                                         /*}}}*/
   9 #include <config.h>
  10
  11 #include <netdb.h>
  12
  13 #include <netinet/in.h>
  14 #include <arpa/nameser.h>
  15 #include <resolv.h>
  16 #include <time.h>
  17
  18 #include <algorithm>
  19 #include <tuple>
  20
  21 #include <apt-pkg/configuration.h>
  22 #include <apt-pkg/error.h>
  23 #include <apt-pkg/strutl.h>
  24
  25
  26 #include "srvrec.h"
  27
  28
  29 bool SrvRec::operator==(SrvRec const &other) const
  30 {
  31    return (std::tie(target, priority, weight, port) ==
  32            std::tie(other.target, other.priority, other.weight, other.port));
  33 }
  34
  35 bool GetSrvRecords(std::string host, int port, std::vector<SrvRec> &Result)
  36 {
  37    std::string target;
  38    int res;
  39    struct servent s_ent_buf;
  40    struct servent *s_ent = nullptr;
  41    std::vector<char> buf(1024);
  42
  43    res = getservbyport_r(htons(port), "tcp", &s_ent_buf, buf.data(), buf.size(), &s_ent);
  44    if (res != 0 || s_ent == nullptr)
  45       return false;
  46
  47    strprintf(target, "_%s._tcp.%s", s_ent->s_name, host.c_str());
  48    return GetSrvRecords(target, Result);
  49 }
  50
  51 bool GetSrvRecords(std::string name, std::vector<SrvRec> &Result)
  52 {
  53    unsigned char answer[NS_PACKETSZ];
  54    int answer_len, compressed_name_len;
  55    int answer_count;
  56
  57    if (res_init() != 0)
  58       return _error->Errno("res_init", "Failed to init resolver");
  59
  60    answer_len = res_query(name.c_str(), C_IN, T_SRV, answer, sizeof(answer));
  61    if (answer_len == -1)
  62       return false;
  63    if (answer_len < (int)sizeof(HEADER))
  64       return _error->Warning("Not enough data from res_query (%i)", answer_len);
  65
  66    // check the header
  67    HEADER *header = (HEADER*)answer;
  68    if (header->rcode != NOERROR)
  69       return _error->Warning("res_query returned rcode %i", header->rcode);
  70    answer_count = ntohs(header->ancount);
  71    if (answer_count <= 0)
  72       return _error->Warning("res_query returned no answers (%i) ", answer_count);
  73
  74    // skip the header
  75    compressed_name_len = dn_skipname(answer+sizeof(HEADER), answer+answer_len);
  76    if(compressed_name_len < 0)
  77       return _error->Warning("dn_skipname failed %i", compressed_name_len);
  78
  79    // pt points to the first answer record, go over all of them now
  80    unsigned char *pt = answer+sizeof(HEADER)+compressed_name_len+NS_QFIXEDSZ;
  81    while ((int)Result.size() < answer_count && pt < answer+answer_len)
  82    {
  83       u_int16_t type, klass, priority, weight, port, dlen;
  84       char buf[MAXDNAME];
  85
  86       compressed_name_len = dn_skipname(pt, answer+answer_len);
  87       if (compressed_name_len < 0)
  88          return _error->Warning("dn_skipname failed (2): %i",
  89                                 compressed_name_len);
  90       pt += compressed_name_len;
  91       if (((answer+answer_len) - pt) < 16)
  92          return _error->Warning("packet too short");
  93
  94       // extract the data out of the result buffer
  95       #define extract_u16(target, p) target = *p++ << 8; target |= *p++;
  96
  97       extract_u16(type, pt);
  98       if(type != T_SRV)
  99          return _error->Warning("Unexpected type excepted %x != %x",
 100                                 T_SRV, type);
 101       extract_u16(klass, pt);
 102       if(klass != C_IN)
 103          return _error->Warning("Unexpected class excepted %x != %x",
 104                                 C_IN, klass);
 105       pt += 4;  // ttl
 106       extract_u16(dlen, pt);
 107       extract_u16(priority, pt);
 108       extract_u16(weight, pt);
 109       extract_u16(port, pt);
 110
 111       #undef extract_u16
 112
 113       compressed_name_len = dn_expand(answer, answer+answer_len, pt, buf, sizeof(buf));
 114       if(compressed_name_len < 0)
 115          return _error->Warning("dn_expand failed %i", compressed_name_len);
 116       pt += compressed_name_len;
 117
 118       // add it to our class
 119       Result.emplace_back(buf, priority, weight, port);
 120    }
 121
 122    // implement load balancing as specified in RFC-2782
 123
 124    // sort them by priority
 125    std::stable_sort(Result.begin(), Result.end());
 126
 127    for(std::vector<SrvRec>::iterator I = Result.begin();
 128       I != Result.end(); ++I)
 129    {
 130       if (_config->FindB("Debug::Acquire::SrvRecs", false) == true)
 131       {
 132          std::cerr << "SrvRecs: got " << I->target
 133                    << " prio: " << I->priority
 134                    << " weight: " << I->weight
 135                    << std::endl;
 136       }
 137    }
 138
 139    return true;
 140 }
 141
 142 SrvRec PopFromSrvRecs(std::vector<SrvRec> &Recs)
 143 {
 144    // FIXME: instead of the simplistic shuffle below use the algorithm
 145    //        described in rfc2782 (with weights)
 146    //        and figure out how the weights need to be adjusted if
 147    //        a host refuses connections
 148
 149 #if 0  // all code below is only needed for the weight adjusted selection
 150    // assign random number ranges
 151    int prev_weight = 0;
 152    int prev_priority = 0;
 153    for(std::vector<SrvRec>::iterator I = Result.begin();
 154       I != Result.end(); ++I)
 155    {
 156       if(prev_priority != I->priority)
 157          prev_weight = 0;
 158       I->random_number_range_start = prev_weight;
 159       I->random_number_range_end = prev_weight + I->weight;
 160       prev_weight = I->random_number_range_end;
 161       prev_priority = I->priority;
 162
 163       if (_config->FindB("Debug::Acquire::SrvRecs", false) == true)
 164          std::cerr << "SrvRecs: got " << I->target
 165                    << " prio: " << I->priority
 166                    << " weight: " << I->weight
 167                    << std::endl;
 168    }
 169
 170    // go over the code in reverse order and note the max random range
 171    int max = 0;
 172    prev_priority = 0;
 173    for(std::vector<SrvRec>::iterator I = Result.end();
 174       I != Result.begin(); --I)
 175    {
 176       if(prev_priority != I->priority)
 177          max = I->random_number_range_end;
 178       I->random_number_range_max = max;
 179    }
 180 #endif
 181
 182    // shuffle in a very simplistic way for now (equal weights)
 183    std::vector<SrvRec>::iterator I = Recs.begin();
 184    std::vector<SrvRec>::iterator const J = std::find_if(Recs.begin(), Recs.end(),
 185          [&I](SrvRec const &J) { return I->priority != J.priority; });
 186
 187    // clock seems random enough.
 188    I += std::max(static_cast<clock_t>(0), clock()) % std::distance(I, J);
 189    SrvRec const selected = std::move(*I);
 190    Recs.erase(I);
 191
 192    if (_config->FindB("Debug::Acquire::SrvRecs", false) == true)
 193       std::cerr << "PopFromSrvRecs: selecting " << selected.target << std::endl;
 194
 195    return selected;
 196 }