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/* srv.c - DNS SRV code
* Copyright (C) 2003 Free Software Foundation, Inc.
*
* This file is part of GNUPG.
*
* GNUPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GNUPG is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*/
#include <config.h>
#include <sys/types.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#endif
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "util.h"
#include "srv.h"
/* Not every installation has gotten around to supporting SRVs
yet... */
#ifndef T_SRV
#define T_SRV 33
#endif
static int
priosort(const void *a,const void *b)
{
const struct srventry *sa=a,*sb=b;
if(sa->priority>sb->priority)
return 1;
else if(sa->priority<sb->priority)
return -1;
else
return 0;
}
int
getsrv(const char *name,struct srventry **list)
{
unsigned char answer[PACKETSZ];
int r,srvcount=0;
unsigned char *pt,*emsg;
u16 count,dlen;
*list=NULL;
r=res_query(name,C_IN,T_SRV,answer,PACKETSZ);
if(r<sizeof(HEADER) || r>PACKETSZ)
return -1;
if((((HEADER *)answer)->rcode)==NOERROR &&
(count=ntohs(((HEADER *)answer)->ancount)))
{
int i,rc;
emsg=&answer[r];
pt=&answer[sizeof(HEADER)];
/* Skip over the query */
rc=dn_skipname(pt,emsg);
if(rc==-1)
goto fail;
pt+=rc+QFIXEDSZ;
while(count-->0 && pt<emsg)
{
struct srventry *srv=NULL;
u16 type,class;
*list=xrealloc(*list,(srvcount+1)*sizeof(struct srventry));
memset(&(*list)[srvcount],0,sizeof(struct srventry));
srv=&(*list)[srvcount];
srvcount++;
rc=dn_skipname(pt,emsg); /* the name we just queried for */
if(rc==-1)
goto fail;
pt+=rc;
/* Truncated message? */
if((emsg-pt)<16)
goto fail;
type=*pt++ << 8;
type|=*pt++;
/* We asked for SRV and got something else !? */
if(type!=T_SRV)
goto fail;
class=*pt++ << 8;
class|=*pt++;
/* We asked for IN and got something else !? */
if(class!=C_IN)
goto fail;
pt+=4; /* ttl */
dlen=*pt++ << 8;
dlen|=*pt++;
srv->priority=*pt++ << 8;
srv->priority|=*pt++;
srv->weight=*pt++ << 8;
srv->weight|=*pt++;
srv->port=*pt++ << 8;
srv->port|=*pt++;
/* Get the name. 2782 doesn't allow name compression, but
dn_expand still works to pull the name out of the
packet. */
rc=dn_expand(answer,emsg,pt,srv->target,MAXDNAME);
if(rc==1 && srv->target[0]==0) /* "." */
goto noanswer;
if(rc==-1)
goto fail;
pt+=rc;
/* Corrupt packet? */
if(dlen!=rc+6)
goto fail;
#if 0
printf("count=%d\n",srvcount);
printf("priority=%d\n",srv->priority);
printf("weight=%d\n",srv->weight);
printf("port=%d\n",srv->port);
printf("target=%s\n",srv->target);
#endif
}
/* Now we have an array of all the srv records. */
/* Order by priority */
qsort(*list,srvcount,sizeof(struct srventry),priosort);
/* For each priority, move the zero-weighted items first. */
for(i=0;i<srvcount;i++)
{
int j;
for(j=i;j<srvcount && (*list)[i].priority==(*list)[j].priority;j++)
{
if((*list)[j].weight==0)
{
/* Swap j with i */
if(j!=i)
{
struct srventry temp;
memcpy(&temp,&(*list)[j],sizeof(struct srventry));
memcpy(&(*list)[j],&(*list)[i],sizeof(struct srventry));
memcpy(&(*list)[i],&temp,sizeof(struct srventry));
}
break;
}
}
}
/* Run the RFC-2782 weighting algorithm. We don't need very
high quality randomness for this, so regular libc srand/rand
is sufficient. */
srand(time(NULL)*getpid());
for(i=0;i<srvcount;i++)
{
int j;
float prio_count=0,chose;
for(j=i;j<srvcount && (*list)[i].priority==(*list)[j].priority;j++)
{
prio_count+=(*list)[j].weight;
(*list)[j].run_count=prio_count;
}
chose=prio_count*rand()/RAND_MAX;
for(j=i;j<srvcount && (*list)[i].priority==(*list)[j].priority;j++)
{
if(chose<=(*list)[j].run_count)
{
/* Swap j with i */
if(j!=i)
{
struct srventry temp;
memcpy(&temp,&(*list)[j],sizeof(struct srventry));
memcpy(&(*list)[j],&(*list)[i],sizeof(struct srventry));
memcpy(&(*list)[i],&temp,sizeof(struct srventry));
}
break;
}
}
}
}
return srvcount;
noanswer:
xfree(*list);
*list=NULL;
return 0;
fail:
xfree(*list);
*list=NULL;
return -1;
}
#ifdef TEST
int
main(int argc,char *argv[])
{
struct srventry *srv;
int rc,i;
rc=getsrv("_hkp._tcp.wwwkeys.pgp.net",&srv);
printf("Count=%d\n\n",rc);
for(i=0;i<rc;i++)
{
printf("priority=%hu\n",srv[i].priority);
printf("weight=%hu\n",srv[i].weight);
printf("port=%hu\n",srv[i].port);
printf("target=%s\n",srv[i].target);
printf("\n");
}
xfree(srv);
return 0;
}
#endif /* TEST */
/*
Local Variables:
compile-command: "cc -DTEST -I.. -I../include -Wall -g -o srv srv.c -lresolv libutil.a"
End:
*/
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