Fix gethostbyaddr for IPv6 arguments, remove mutable state

caml_gethostbyaddr always calls gethostbyaddr with address type AF_INET,
i.e., IPv4, even when its argument is an IPv6 address. This commit also
removes a file-local mutable variable for the sake of domain safety.

otherlibs/unix/gethost.c

@@ -36,22 +36,22 @@
 #define GETHOSTBYNAME_IS_REENTRANT 1
 #endif
 
-static int entry_h_length;
-
-static value alloc_one_addr(char const *a)
+static value alloc_one_addr_ipv4(char const *a)
 {
   struct in_addr addr;
-#ifdef HAS_IPV6
-  struct in6_addr addr6;
-  if (entry_h_length == 16) {
-    memmove(&addr6, a, 16);
-    return caml_unix_alloc_inet6_addr(&addr6);
-  }
-#endif
   memmove (&addr, a, 4);
   return caml_unix_alloc_inet_addr(&addr);
 }
 
+#ifdef HAS_IPV6
+static value alloc_one_addr_ipv6(char const *a)
+{
+  struct in6_addr addr6;
+  memmove(&addr6, a, 16);
+  return caml_unix_alloc_inet6_addr(&addr6);
+}
+#endif
+
 static value alloc_host_entry(struct hostent *entry)
 {
   CAMLparam0();
@@ -65,9 +65,10 @@ static value alloc_host_entry(struct hostent *entry)
     aliases = caml_copy_string_array((const char**)entry->h_aliases);
   else
     aliases = Atom(0);
-  entry_h_length = entry->h_length;
   addr_list =
-    caml_alloc_array(alloc_one_addr, (const char**)entry->h_addr_list);
+    caml_alloc_array((entry->h_addrtype == AF_INET6) ?
+        alloc_one_addr_ipv6 : alloc_one_addr_ipv4,
+      (const char**)entry->h_addr_list);
   res = caml_alloc_small(4, 0);
   Field(res, 0) = name;
   Field(res, 1) = aliases;
@@ -84,28 +85,42 @@ CAMLprim value caml_unix_gethostbyaddr(value a)
 {
   struct in_addr adr = GET_INET_ADDR(a);
   struct hostent * hp;
+  int addr_type;
+  socklen_t addr_len;
+#if HAS_IPV6
+  if (caml_string_length(a) == 16) {
+    addr_type = AF_INET6;
+    addr_len = 16;
+  }
+  else {
+    addr_type = AF_INET;
+    addr_len = 4;
+  }
+#else
+  addr_type = AF_INET;
+#endif
 #if HAS_GETHOSTBYADDR_R == 7
   struct hostent h;
   char buffer[NETDB_BUFFER_SIZE];
   int h_errnop;
   caml_enter_blocking_section();
-  hp = gethostbyaddr_r((char *) &adr, 4, AF_INET,
+  hp = gethostbyaddr_r((char *) &adr, addr_len, addr_type,
                        &h, buffer, sizeof(buffer), &h_errnop);
   caml_leave_blocking_section();
 #elif HAS_GETHOSTBYADDR_R == 8
   struct hostent h;
   char buffer[NETDB_BUFFER_SIZE];
   int h_errnop, rc;
   caml_enter_blocking_section();
-  rc = gethostbyaddr_r((char *) &adr, 4, AF_INET,
+  rc = gethostbyaddr_r((char *) &adr, addr_len, addr_type,
                        &h, buffer, sizeof(buffer), &hp, &h_errnop);
   caml_leave_blocking_section();
   if (rc != 0) hp = NULL;
 #else
 #ifdef GETHOSTBYADDR_IS_REENTRANT
   caml_enter_blocking_section();
 #endif
-  hp = gethostbyaddr((char *) &adr, 4, AF_INET);
+  hp = gethostbyaddr((char *) &adr, addr_type, addr_type);
 #ifdef GETHOSTBYADDR_IS_REENTRANT
   caml_leave_blocking_section();
 #endif