diff options
Diffstat (limited to 'apt-pkg/contrib/srvrec.cc')
| -rw-r--r-- | apt-pkg/contrib/srvrec.cc | 196 |
1 files changed, 196 insertions, 0 deletions
diff --git a/apt-pkg/contrib/srvrec.cc b/apt-pkg/contrib/srvrec.cc new file mode 100644 index 000000000..b4a3d97d2 --- /dev/null +++ b/apt-pkg/contrib/srvrec.cc @@ -0,0 +1,196 @@ +// -*- mode: cpp; mode: fold -*- +// Description /*{{{*/ +/* ###################################################################### + + SRV record support + + ##################################################################### */ + /*}}}*/ +#include <config.h> + +#include <netdb.h> + +#include <netinet/in.h> +#include <arpa/nameser.h> +#include <resolv.h> +#include <chrono> + +#include <algorithm> + +#include <apt-pkg/configuration.h> +#include <apt-pkg/error.h> +#include <apt-pkg/strutl.h> + + +#include "srvrec.h" + + +bool GetSrvRecords(std::string host, int port, std::vector<SrvRec> &Result) +{ + std::string target; + struct servent *s_ent = getservbyport(htons(port), "tcp"); + if (s_ent == NULL) + return false; + + strprintf(target, "_%s._tcp.%s", s_ent->s_name, host.c_str()); + return GetSrvRecords(target, Result); +} + +bool GetSrvRecords(std::string name, std::vector<SrvRec> &Result) +{ + unsigned char answer[PACKETSZ]; + int answer_len, compressed_name_len; + int answer_count; + + if (res_init() != 0) + return _error->Errno("res_init", "Failed to init resolver"); + + answer_len = res_query(name.c_str(), C_IN, T_SRV, answer, sizeof(answer)); + if (answer_len == -1) + return false; + if (answer_len < (int)sizeof(HEADER)) + return _error->Warning("Not enough data from res_query (%i)", answer_len); + + // check the header + HEADER *header = (HEADER*)answer; + if (header->rcode != NOERROR) + return _error->Warning("res_query returned rcode %i", header->rcode); + answer_count = ntohs(header->ancount); + if (answer_count <= 0) + return _error->Warning("res_query returned no answers (%i) ", answer_count); + + // skip the header + compressed_name_len = dn_skipname(answer+sizeof(HEADER), answer+answer_len); + if(compressed_name_len < 0) + return _error->Warning("dn_skipname failed %i", compressed_name_len); + + // pt points to the first answer record, go over all of them now + unsigned char *pt = answer+sizeof(HEADER)+compressed_name_len+QFIXEDSZ; + while ((int)Result.size() < answer_count && pt < answer+answer_len) + { + SrvRec rec; + u_int16_t type, klass, priority, weight, port, dlen; + char buf[MAXDNAME]; + + compressed_name_len = dn_skipname(pt, answer+answer_len); + if (compressed_name_len < 0) + return _error->Warning("dn_skipname failed (2): %i", + compressed_name_len); + pt += compressed_name_len; + if (((answer+answer_len) - pt) < 16) + return _error->Warning("packet too short"); + + // extract the data out of the result buffer + #define extract_u16(target, p) target = *p++ << 8; target |= *p++; + + extract_u16(type, pt); + if(type != T_SRV) + return _error->Warning("Unexpected type excepted %x != %x", + T_SRV, type); + extract_u16(klass, pt); + if(klass != C_IN) + return _error->Warning("Unexpected class excepted %x != %x", + C_IN, klass); + pt += 4; // ttl + extract_u16(dlen, pt); + extract_u16(priority, pt); + extract_u16(weight, pt); + extract_u16(port, pt); + + #undef extract_u16 + + compressed_name_len = dn_expand(answer, answer+answer_len, pt, buf, sizeof(buf)); + if(compressed_name_len < 0) + return _error->Warning("dn_expand failed %i", compressed_name_len); + pt += compressed_name_len; + + // add it to our class + rec.priority = priority; + rec.weight = weight; + rec.port = port; + rec.target = buf; + Result.push_back(rec); + } + + // implement load balancing as specified in RFC-2782 + + // sort them by priority + std::stable_sort(Result.begin(), Result.end()); + + for(std::vector<SrvRec>::iterator I = Result.begin(); + I != Result.end(); ++I) + { + if (_config->FindB("Debug::Acquire::SrvRecs", false) == true) + { + std::cerr << "SrvRecs: got " << I->target + << " prio: " << I->priority + << " weight: " << I->weight + << std::endl; + } + } + + return true; +} + +SrvRec PopFromSrvRecs(std::vector<SrvRec> &Recs) +{ + // FIXME: instead of the simplistic shuffle below use the algorithm + // described in rfc2782 (with weights) + // and figure out how the weights need to be adjusted if + // a host refuses connections + +#if 0 // all code below is only needed for the weight adjusted selection + // assign random number ranges + int prev_weight = 0; + int prev_priority = 0; + for(std::vector<SrvRec>::iterator I = Result.begin(); + I != Result.end(); ++I) + { + if(prev_priority != I->priority) + prev_weight = 0; + I->random_number_range_start = prev_weight; + I->random_number_range_end = prev_weight + I->weight; + prev_weight = I->random_number_range_end; + prev_priority = I->priority; + + if (_config->FindB("Debug::Acquire::SrvRecs", false) == true) + std::cerr << "SrvRecs: got " << I->target + << " prio: " << I->priority + << " weight: " << I->weight + << std::endl; + } + + // go over the code in reverse order and note the max random range + int max = 0; + prev_priority = 0; + for(std::vector<SrvRec>::iterator I = Result.end(); + I != Result.begin(); --I) + { + if(prev_priority != I->priority) + max = I->random_number_range_end; + I->random_number_range_max = max; + } +#endif + + // shuffle in a very simplistic way for now (equal weights) + std::vector<SrvRec>::iterator I, J; + I = J = Recs.begin(); + for(;I != Recs.end(); ++I) + { + if(I->priority != J->priority) + break; + } + + // FIXME: meeeeh, where to init this properly + unsigned seed = std::chrono::system_clock::now().time_since_epoch().count(); + std::shuffle(J, I, std::default_random_engine(seed)); + + // meh, no pop_front() in std::vector? + SrvRec selected = *Recs.begin(); + Recs.erase(Recs.begin()); + + if (_config->FindB("Debug::Acquire::SrvRecs", false) == true) + std::cerr << "PopFromSrvRecs: selecting " << selected.target << std::endl; + + return selected; +} |