Move resolv_init out and make callbacks of libnetd_resolv global

1. Revise init flow of libnetd_resolv
   - A better and generic design for it
2. Rename and make callbacks from netd global
   - libnetd_resolv has multiple components need to use it
   - res* component could use it easily

Bug: 126141549
Test: built, flashed, booted
      system/netd/tests/runtests.sh pass

Change-Id: Iacb4fd708a26fd9c9139a606f0320fc12b4fc7e1
diff --git a/resolv/DnsResolver.cpp b/resolv/DnsResolver.cpp
new file mode 100644
index 0000000..a9d2f85
--- /dev/null
+++ b/resolv/DnsResolver.cpp
@@ -0,0 +1,79 @@
+/**
+ * Copyright (c) 2019, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "DnsResolver.h"
+
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+
+#include <resolv.h>
+#include "DnsProxyListener.h"
+#include "DnsResolverService.h"
+#include "resolv_private.h"
+
+bool resolv_init(const ResolverNetdCallbacks& callbacks) {
+    android::base::InitLogging(/*argv=*/nullptr);
+    android::base::SetDefaultTag("libnetd_resolv");
+    LOG(INFO) << "Initializing resolver";
+    const std::string logSeverityStr =
+            android::base::GetProperty("persist.sys.nw_dns_resolver_log", "WARNING");
+    android::base::SetMinimumLogSeverity(logSeverityStrToEnum(logSeverityStr));
+
+    android::net::gResNetdCallbacks = callbacks;
+    android::net::gDnsResolv = android::net::DnsResolver::getInstance();
+    return android::net::gDnsResolv->start();
+}
+
+namespace android {
+namespace net {
+
+namespace {
+
+bool verifyCallbacks() {
+    return gResNetdCallbacks.check_calling_permission && gResNetdCallbacks.get_network_context &&
+           gResNetdCallbacks.get_dns64_prefix;
+}
+
+}  // namespace
+
+DnsResolver* gDnsResolv = nullptr;
+ResolverNetdCallbacks gResNetdCallbacks;
+
+DnsResolver* DnsResolver::getInstance() {
+    // Instantiated on first use.
+    static DnsResolver instance;
+    return &instance;
+}
+
+bool DnsResolver::start() {
+    if (!verifyCallbacks()) {
+        LOG(ERROR) << "Callback verification failed";
+        return false;
+    }
+    if (mDnsProxyListener.startListener()) {
+        PLOG(ERROR) << "Unable to start DnsProxyListener";
+        return false;
+    }
+    binder_status_t ret;
+    if ((ret = DnsResolverService::start()) != STATUS_OK) {
+        LOG(ERROR) << "Unable to start DnsResolverService: " << ret;
+        return false;
+    }
+    return true;
+}
+
+}  // namespace net
+}  // namespace android