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