/* 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA */ #include <config.h> #ifdef USE_DNS_SRV #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 "memory.h" #include "types.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)) 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=m_realloc(*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: m_free(*list); *list=NULL; return 0; fail: m_free(*list); *list=NULL; return -1; } #endif /* USE_DNS_SRV */ #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=%d\n",srv[i].priority); printf("weight=%d\n",srv[i].weight); printf("port=%d\n",srv[i].port); printf("target=%s\n",srv[i].target); printf("\n"); } m_free(srv); return 0; } #endif /* TEST */