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-rw-r--r--apt-pkg/contrib/srvrec.cc211
1 files changed, 211 insertions, 0 deletions
diff --git a/apt-pkg/contrib/srvrec.cc b/apt-pkg/contrib/srvrec.cc
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+++ b/apt-pkg/contrib/srvrec.cc
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+// -*- mode: cpp; mode: fold -*-
+// Description /*{{{*/
+/* ######################################################################
+
+ SRV record support
+
+ ##################################################################### */
+ /*}}}*/
+#include <config.h>
+
+#include <netdb.h>
+
+#include <ctime>
+#include <arpa/inet.h>
+#include <arpa/nameser.h>
+#include <netinet/in.h>
+#include <resolv.h>
+
+#include <algorithm>
+#include <memory>
+#include <tuple>
+
+#include <apt-pkg/configuration.h>
+#include <apt-pkg/error.h>
+#include <apt-pkg/strutl.h>
+
+#include "srvrec.h"
+
+bool SrvRec::operator==(SrvRec const &other) const
+{
+ return (std::tie(target, priority, weight, port) ==
+ std::tie(other.target, other.priority, other.weight, other.port));
+}
+
+bool GetSrvRecords(std::string host, int port, std::vector<SrvRec> &Result)
+{
+ // try SRV only for hostnames, not for IP addresses
+ {
+ struct in_addr addr4;
+ struct in6_addr addr6;
+ if (inet_pton(AF_INET, host.c_str(), &addr4) == 1 ||
+ inet_pton(AF_INET6, host.c_str(), &addr6) == 1)
+ return true;
+ }
+
+ std::string target;
+ int res;
+ struct servent s_ent_buf;
+ struct servent *s_ent = nullptr;
+ std::vector<char> buf(1024);
+
+ res = getservbyport_r(htons(port), "tcp", &s_ent_buf, buf.data(), buf.size(), &s_ent);
+ if (res != 0 || s_ent == nullptr)
+ 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 >= 19991006
+ struct __res_state res;
+
+ if (res_ninit(&res) != 0)
+ return _error->Errno("res_init", "Failed to init resolver");
+
+ // Close on return
+ std::shared_ptr<void> guard(&res, res_nclose);
+
+ answer_len = res_nquery(&res, name.c_str(), C_IN, T_SRV, answer, sizeof(answer));
+#else
+ 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));
+#endif //__RES >= 19991006
+ 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)
+ {
+ 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
+ Result.emplace_back(buf, priority, weight, port);
+ }
+
+ // implement load balancing as specified in RFC-2782
+
+ // sort them by priority
+ std::stable_sort(Result.begin(), Result.end());
+
+ if (_config->FindB("Debug::Acquire::SrvRecs", false))
+ for(auto const &R : Result)
+ std::cerr << "SrvRecs: got " << R.target
+ << " prio: " << R.priority
+ << " weight: " << R.weight
+ << '\n';
+
+ 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 = Recs.begin();
+ std::vector<SrvRec>::iterator const J = std::find_if(Recs.begin(), Recs.end(),
+ [&I](SrvRec const &J) { return I->priority != J.priority; });
+
+ // clock seems random enough.
+ I += std::max(static_cast<clock_t>(0), clock()) % std::distance(I, J);
+ SrvRec const selected = std::move(*I);
+ Recs.erase(I);
+
+ if (_config->FindB("Debug::Acquire::SrvRecs", false) == true)
+ std::cerr << "PopFromSrvRecs: selecting " << selected.target << std::endl;
+
+ return selected;
+}