Merge remote-tracking branch 'mvo/feature/srv-records' into debian/experimental

3 files changed, 244 insertions, 1 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;
+}
diff --git a/apt-pkg/contrib/srvrec.h b/apt-pkg/contrib/srvrec.h
new file mode 100644
index 000000000..e07edc683
--- /dev/null
+++ b/apt-pkg/contrib/srvrec.h
@@ -0,0 +1,47 @@
+// -*- mode: cpp; mode: fold -*-
+// Description								/*{{{*/
+/* ######################################################################
+
+   SRV record support
+
+   ##################################################################### */
+									/*}}}*/
+#ifndef SRVREC_H
+#define SRVREC_H
+
+#include <arpa/nameser.h>
+#include <vector>
+#include <string>
+
+class SrvRec
+{
+ public:
+   std::string target;
+   u_int16_t priority;
+   u_int16_t weight;
+   u_int16_t port;
+
+   // each server is assigned a interval [start, end] in the space of [0, max]
+   int random_number_range_start;
+   int random_number_range_end;
+   int random_number_range_max;
+
+   bool operator<(SrvRec const &other) const { 
+      return this->priority < other.priority; 
+   }
+};
+
+/** \brief Get SRV records from host/port (builds the query string internally) 
+ */
+bool GetSrvRecords(std::string name, std::vector<SrvRec> &Result);
+
+/** \brief Get SRV records for query string like: _http._tcp.example.com
+ */
+bool GetSrvRecords(std::string host, int port, std::vector<SrvRec> &Result);
+
+/** \brief Pop a single SRV record from the vector of SrvRec taking
+ *         priority and weight into account
+ */
+SrvRec PopFromSrvRecs(std::vector<SrvRec> &Recs);
+
+#endif
diff --git a/apt-pkg/makefile b/apt-pkg/makefile
index 5603b51ed..45dcddfe3 100644
--- a/apt-pkg/makefile
+++ b/apt-pkg/makefile
@@ -15,7 +15,7 @@ include ../buildlib/libversion.mak
 LIBRARY=apt-pkg
 MAJOR=$(LIBAPTPKG_MAJOR)
 MINOR=$(LIBAPTPKG_RELEASE)
-SLIBS=$(PTHREADLIB) $(INTLLIBS) -lutil -ldl
+SLIBS=$(PTHREADLIB) $(INTLLIBS) -lutil -ldl -lresolv
 ifeq ($(HAVE_ZLIB),yes)
 SLIBS+= -lz
 endif