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/* srv.c - DNS SRV code
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* Copyright (C) 2003 Free Software Foundation, Inc.
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* This file is part of GNUPG.
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* GNUPG is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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* GNUPG is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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#include <sys/types.h>
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#include <netinet/in.h>
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#include <arpa/nameser.h>
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/* Not every installation has gotten around to supporting SRVs
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priosort(const void *a,const void *b)
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const struct srventry *sa=a,*sb=b;
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if(sa->priority>sb->priority)
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else if(sa->priority<sb->priority)
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getsrv(const char *name,struct srventry **list)
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unsigned char answer[PACKETSZ];
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unsigned char *pt,*emsg;
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r=res_query(name,C_IN,T_SRV,answer,PACKETSZ);
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if(r<sizeof(HEADER) || r>PACKETSZ)
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if((((HEADER *)answer)->rcode)==NOERROR &&
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(count=ntohs(((HEADER *)answer)->ancount)))
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pt=&answer[sizeof(HEADER)];
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/* Skip over the query */
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rc=dn_skipname(pt,emsg);
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while(count-->0 && pt<emsg)
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struct srventry *srv=NULL;
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*list=xrealloc(*list,(srvcount+1)*sizeof(struct srventry));
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memset(&(*list)[srvcount],0,sizeof(struct srventry));
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srv=&(*list)[srvcount];
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rc=dn_skipname(pt,emsg); /* the name we just queried for */
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/* Truncated message? */
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/* We asked for SRV and got something else !? */
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/* We asked for IN and got something else !? */
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srv->priority=*pt++ << 8;
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srv->priority|=*pt++;
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srv->weight=*pt++ << 8;
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srv->port=*pt++ << 8;
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/* Get the name. 2782 doesn't allow name compression, but
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dn_expand still works to pull the name out of the
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rc=dn_expand(answer,emsg,pt,srv->target,MAXDNAME);
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if(rc==1 && srv->target[0]==0) /* "." */
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/* Corrupt packet? */
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printf("count=%d\n",srvcount);
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printf("priority=%d\n",srv->priority);
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printf("weight=%d\n",srv->weight);
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printf("port=%d\n",srv->port);
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printf("target=%s\n",srv->target);
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/* Now we have an array of all the srv records. */
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/* Order by priority */
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qsort(*list,srvcount,sizeof(struct srventry),priosort);
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/* For each priority, move the zero-weighted items first. */
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for(i=0;i<srvcount;i++)
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for(j=i;j<srvcount && (*list)[i].priority==(*list)[j].priority;j++)
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if((*list)[j].weight==0)
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struct srventry temp;
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memcpy(&temp,&(*list)[j],sizeof(struct srventry));
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memcpy(&(*list)[j],&(*list)[i],sizeof(struct srventry));
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memcpy(&(*list)[i],&temp,sizeof(struct srventry));
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/* Run the RFC-2782 weighting algorithm. We don't need very
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high quality randomness for this, so regular libc srand/rand
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srand(time(NULL)*getpid());
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for(i=0;i<srvcount;i++)
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float prio_count=0,chose;
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for(j=i;j<srvcount && (*list)[i].priority==(*list)[j].priority;j++)
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prio_count+=(*list)[j].weight;
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(*list)[j].run_count=prio_count;
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chose=prio_count*rand()/RAND_MAX;
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for(j=i;j<srvcount && (*list)[i].priority==(*list)[j].priority;j++)
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if(chose<=(*list)[j].run_count)
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struct srventry temp;
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memcpy(&temp,&(*list)[j],sizeof(struct srventry));
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memcpy(&(*list)[j],&(*list)[i],sizeof(struct srventry));
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memcpy(&(*list)[i],&temp,sizeof(struct srventry));
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main(int argc,char *argv[])
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struct srventry *srv;
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rc=getsrv("_hkp._tcp.wwwkeys.pgp.net",&srv);
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printf("Count=%d\n\n",rc);
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printf("priority=%hu\n",srv[i].priority);
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printf("weight=%hu\n",srv[i].weight);
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printf("port=%hu\n",srv[i].port);
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printf("target=%s\n",srv[i].target);
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compile-command: "cc -DTEST -I.. -I../include -Wall -g -o srv srv.c -lresolv libutil.a"
added
removed
common/srv.c
