Remove private system API calls in dns_config_service_posix on iOS

net/dns/dns_config_watcher_mac.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/dns/dns_config_watcher_mac.h"
+
+#include <dlfcn.h>
+
+#include "base/lazy_instance.h"
+#include "third_party/apple_apsl/dnsinfo.h"
+
+namespace {
+
+// dnsinfo symbols are available via libSystem.dylib, but can also be present in
+// SystemConfiguration.framework. To avoid confusion, load them explicitly from
+// libSystem.dylib.
+class DnsInfoApi {
+ public:
+  typedef const char* (*dns_configuration_notify_key_t)();
+  typedef dns_config_t* (*dns_configuration_copy_t)();
+  typedef void (*dns_configuration_free_t)(dns_config_t*);
+
+  DnsInfoApi()
+      : dns_configuration_notify_key(NULL),
+        dns_configuration_copy(NULL),
+        dns_configuration_free(NULL) {
+    handle_ = dlopen("/usr/lib/libSystem.dylib",
+                     RTLD_LAZY | RTLD_NOLOAD);
+    if (!handle_)
+      return;
+    dns_configuration_notify_key =
+        reinterpret_cast<dns_configuration_notify_key_t>(
+            dlsym(handle_, "dns_configuration_notify_key"));
+    dns_configuration_copy =
+        reinterpret_cast<dns_configuration_copy_t>(
+            dlsym(handle_, "dns_configuration_copy"));
+    dns_configuration_free =
+        reinterpret_cast<dns_configuration_free_t>(
+            dlsym(handle_, "dns_configuration_free"));
+  }
+
+  ~DnsInfoApi() {
+    if (handle_)
+      dlclose(handle_);
+  }
+
+  dns_configuration_notify_key_t dns_configuration_notify_key;
+  dns_configuration_copy_t dns_configuration_copy;
+  dns_configuration_free_t dns_configuration_free;
+
+ private:
+  void* handle_;
+};
+
+const DnsInfoApi& GetDnsInfoApi() {
+  static base::LazyInstance<DnsInfoApi>::Leaky api = LAZY_INSTANCE_INITIALIZER;
+  return api.Get();
+}
+
+struct DnsConfigTDeleter {
+  inline void operator()(dns_config_t* ptr) const {
+    if (GetDnsInfoApi().dns_configuration_free)
+      GetDnsInfoApi().dns_configuration_free(ptr);
+  }
+};
+
+}  // namespace
+
+namespace net {
+namespace internal {
+
+bool DnsConfigWatcher::Watch(
+    const base::Callback<void(bool succeeded)>& callback) {
+  if (!GetDnsInfoApi().dns_configuration_notify_key)
+    return false;
+  return watcher_.Watch(GetDnsInfoApi().dns_configuration_notify_key(),
+                        callback);
+}
+
+// static
+ConfigParsePosixResult DnsConfigWatcher::CheckDnsConfig() {
+  if (!GetDnsInfoApi().dns_configuration_copy)
+    return CONFIG_PARSE_POSIX_NO_DNSINFO;
+  scoped_ptr<dns_config_t, DnsConfigTDeleter> dns_config(
+      GetDnsInfoApi().dns_configuration_copy());
+  if (!dns_config)
+    return CONFIG_PARSE_POSIX_NO_DNSINFO;
+
+  // TODO(szym): Parse dns_config_t for resolvers rather than res_state.
+  // DnsClient can't handle domain-specific unscoped resolvers.
+  unsigned num_resolvers = 0;
+  for (int i = 0; i < dns_config->n_resolver; ++i) {
+    dns_resolver_t* resolver = dns_config->resolver[i];
+    if (!resolver->n_nameserver)
+      continue;
+    if (resolver->options && !strcmp(resolver->options, "mdns"))
+      continue;
+    ++num_resolvers;
+  }
+  if (num_resolvers > 1)
+    return CONFIG_PARSE_POSIX_UNHANDLED_OPTIONS;
+  return CONFIG_PARSE_POSIX_OK;
+}
+
+}  // naespace internal
+}  // namespace net