From 81844d2b65e5b5fab28caec29d1ff6c7d680c34a Mon Sep 17 00:00:00 2001
From: David Shaw <dshaw@jabberwocky.com>
Date: Tue, 11 Mar 2003 22:04:53 +0000
Subject: * http.c (connect_server): Use DNS SRV to get a server list.  Fail
 over to A records if necessary.

* Makefile.am, srv.h, srv.c: New DNS SRV handling code.
---
 util/srv.c | 246 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 246 insertions(+)
 create mode 100644 util/srv.c

(limited to 'util/srv.c')

diff --git a/util/srv.c b/util/srv.c
new file mode 100644
index 000000000..8fc0ca0de
--- /dev/null
+++ b/util/srv.c
@@ -0,0 +1,246 @@
+/* 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>
+#include <netinet/in.h>
+#include <arpa/nameser.h>
+#include <resolv.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include "memory.h"
+#include "types.h"
+#include "srv.h"
+
+#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)
+{
+  char answer[PACKETSZ];
+  int r,srvcount=0;
+  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.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 */
-- 
cgit