DNS: zero out res_state

This is needed to avoid segfault on some OS.
Also free the state resources on error.

src/dns.c

@@ -310,6 +310,7 @@ SEXP r_nsl(SEXP hostname, SEXP server, SEXP class, SEXP type) {
 
   struct __res_state state;
   res_state statep = &state;
+  memset(statep, 0, sizeof(state));
   ret = res_ninit(statep);
   if (ret) R_THROW_SYSTEM_ERROR("Failed to initialize resolver library");
 
@@ -328,10 +329,16 @@ SEXP r_nsl(SEXP hostname, SEXP server, SEXP class, SEXP type) {
     INTEGER(type)[0],
     answer,
     sizeof answer);
-  if (ret == -1) R_THROW_SYSTEM_ERROR("DNS query failed");
+  if (ret == -1) {
+    res_nclose(statep);
+    R_THROW_SYSTEM_ERROR("DNS query failed");
+  }
 
   ret = ns_initparse(answer, ret, &msg);
-  if (ret == -1) R_THROW_SYSTEM_ERROR("Cannot parse DNS answer");
+  if (ret == -1) {
+    res_nclose(statep);
+    R_THROW_SYSTEM_ERROR("Cannot parse DNS answer");
+  }
 
   LOGICAL(VECTOR_ELT(result, 1))[0] = ns_msg_getflag(msg, ns_f_aa);
   LOGICAL(VECTOR_ELT(result, 1))[1] = ns_msg_getflag(msg, ns_f_tc);
@@ -361,7 +368,10 @@ SEXP r_nsl(SEXP hostname, SEXP server, SEXP class, SEXP type) {
     SEXP rawdata;
 
     ret = ns_parserr(&msg, ns_s_an, i, &rec);
-    if (ret == -1) R_THROW_SYSTEM_ERROR("Cannot parse DNS record");
+    if (ret == -1) {
+      res_nclose(statep);
+      R_THROW_SYSTEM_ERROR("Cannot parse DNS record");
+    }
     class = ns_rr_class(rec);
     type = ns_rr_type(rec);
     data = ns_rr_rdata(rec);
@@ -406,7 +416,10 @@ SEXP r_nsl(SEXP hostname, SEXP server, SEXP class, SEXP type) {
       int len, j;
       ret = xxns_name_uncompress(ns_msg_base(msg), ns_msg_end(msg),
                                  data, buf, sizeof buf);
-      if (ret < 0) R_THROW_SYSTEM_ERROR("Cannot parse SOA DNS record");
+      if (ret < 0) {
+        res_nclose(statep);
+        R_THROW_SYSTEM_ERROR("Cannot parse SOA DNS record");
+      }
 
       data += ret; len = strlen(buf2); buf2 += len; bufsize -= len;
       if (bufsize > 2) {
@@ -415,14 +428,18 @@ SEXP r_nsl(SEXP hostname, SEXP server, SEXP class, SEXP type) {
 
       ret = xxns_name_uncompress(ns_msg_base(msg), ns_msg_end(msg),
                                  data, buf2, bufsize);
-      if (ret < 0) R_THROW_SYSTEM_ERROR("Cannot parse SOA DNS record");
+      if (ret < 0) {
+        res_nclose(statep);
+        R_THROW_SYSTEM_ERROR("Cannot parse SOA DNS record");
+      }
 
       data += ret; len = strlen(buf2); buf2 += len; bufsize -= len;
       if (bufsize > 2) {
         *buf2 = '.'; buf2++; bufsize--; *buf2 = ' '; buf2++; bufsize--;
       }
 
       if (ns_msg_end(msg) - data < 5*NS_INT32SZ) {
+        res_nclose(statep);
         R_THROW_ERROR("Cannot parse SOA DNS record");
       }
       for (j = 0; j < 5; j++) NS_GET32(soa[j], data);
@@ -440,6 +457,7 @@ SEXP r_nsl(SEXP hostname, SEXP server, SEXP class, SEXP type) {
     }
 
     if (ret < 0) {
+      res_nclose(statep);
       R_THROW_SYSTEM_ERROR("Cannot parse NS/PTR/CNAME DNS record");
     }