res_send() doesn't work with osquery enabled

[pseudo at egg6 dot net]

Currently res_init() checks for availability of the native windows
function DnsQuery_A. If the function is found, it's preferred over the
cygwin implementation and res_query is set up to use it.
As DnsQuery_A finds the configured name servers itself, the current code
assumes we can avoid loading the dns server list with GetNetworkParams().

However, the assumption that everybody would use res_query is wrong. Some
programs may use res_mkquery() and res_send() or may only read the list of
servers from _res.nsaddr_list and send/receive the queries/replies
themselves. res_send() also relies on nsaddr_list.

The following patch makes get_dns_info() always try to populate
nsaddr_list if empty. If resolv.conf exists and provides nameservers, they
will be used as usual. Otherwise, GetNetworkParams() will be called to get
the servers from the operating system.

2010-08-26  Rumen Stoyanov <pseudo@egg6.net>

     * libc/minires-os-if.c (get_dns_info): Always populate nsaddr_list
     if empty, regardless of the availability of os_query.
     * libc/minires.c (res_nsend): Make sure there is atleast one
     nameserver in nsaddr_list or return.


Index: winsup/cygwin/libc/minires-os-if.c
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/libc/minires-os-if.c,v
retrieving revision 1.8
diff -u -p -r1.8 minires-os-if.c
--- winsup/cygwin/libc/minires-os-if.c  3 Jan 2009 05:12:22 -0000       1.8
+++ winsup/cygwin/libc/minires-os-if.c  26 Aug 2010 15:28:32 -0000
@@ -405,13 +405,16 @@ void get_dns_info(res_state statp)
   {
     DPRINTF(debug, "using dnsapi.dll %d\n", dwRetVal);
     statp->os_query = (typeof(statp->os_query)) cygwin_query;
-    /* We just need the search list. Avoid loading iphlpapi. */
-    statp->nscount = -1;
   }

   if (statp->nscount != 0)
     goto use_registry;

+  /* Some applications use res_send() or access the dns server list
+     directly, In both cases the list needs to get populated
+     regardless of the availability of a native os query. */
+  DPRINTF(debug, "no servers. falling back to iphlpapi.dll\n");
+
   /* First call to get the buffer length we need */
   dwRetVal = GetNetworkParams((FIXED_INFO *) 0, &ulOutBufLen);
   if (dwRetVal != ERROR_BUFFER_OVERFLOW) {
Index: winsup/cygwin/libc/minires.c
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/libc/minires.c,v
retrieving revision 1.8
diff -u -p -r1.8 minires.c
--- winsup/cygwin/libc/minires.c        6 May 2009 12:03:32 -0000       1.8
+++ winsup/cygwin/libc/minires.c        26 Aug 2010 15:28:32 -0000
@@ -436,6 +436,10 @@ int res_nsend( res_state statp, const un
   statp->res_h_errno = NETDB_SUCCESS;
   if (((statp->options & RES_INIT) == 0) && (res_ninit(statp) != 0))
     return -1;
+
+  /* successful res_ninit() doesn't guarantee we have servers to send to */
+  if (statp->nscount == 0)
+    return -1;

   /* Close the socket if it had been opened before a fork.
      Reuse of pid's cannot hurt */