Make getdnsnetid returning app_netId instead of dns_netId and fix nits

1. getdnsnetid command return app_netId instead of dns_netId.
2. fix nits for ag/7691940
3. Add more tests

Bug: 129530368
Test: built, flashed, booted
          system/netd/tests/runtests.sh

Change-Id: Ifd1345e1124088179e38346e3693957a8b5ef63b
diff --git a/client/NetdClientTest.cpp b/client/NetdClientTest.cpp
new file mode 100644
index 0000000..6f2fc09
--- /dev/null
+++ b/client/NetdClientTest.cpp
@@ -0,0 +1,75 @@
+/*
+ * 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 <poll.h> /* poll */
+#include <sys/socket.h>
+
+#include <thread>
+
+#include <android-base/parseint.h>
+#include <android-base/unique_fd.h>
+#include <gtest/gtest.h>
+
+#include "NetdClient.h"
+#include "netdclient_priv.h"
+
+namespace {
+
+// Keep in sync with FrameworkListener.cpp (500, "Command not recognized")
+constexpr char NOT_SUPPORT_MSG[] = "500 Command not recognized";
+
+void serverLoop(int dnsProxyFd) {
+    while (true) {
+        pollfd fds[1] = {{.fd = dnsProxyFd, .events = POLLIN}};
+        enum { SERVERFD = 0 };
+
+        const int s = TEMP_FAILURE_RETRY(poll(fds, std::size(fds), -1));
+        if (s <= 0) break;
+
+        if (fds[SERVERFD].revents & POLLIN) {
+            char buf[4096];
+            TEMP_FAILURE_RETRY(read(fds[SERVERFD].fd, &buf, sizeof(buf)));
+            // TODO: verify command
+            TEMP_FAILURE_RETRY(write(fds[SERVERFD].fd, NOT_SUPPORT_MSG, sizeof(NOT_SUPPORT_MSG)));
+        }
+    }
+}
+
+}  // namespace
+
+TEST(NetdClientTest, getNetworkForDnsInternal) {
+    // Test invalid fd
+    unsigned dnsNetId = 0;
+    const int invalidFd = -1;
+    EXPECT_EQ(-EBADF, getNetworkForDnsInternal(invalidFd, &dnsNetId));
+
+    // Test what the client does if the resolver does not support the "getdnsnetid" command.
+    android::base::unique_fd clientFd, serverFd;
+    ASSERT_TRUE(android::base::Socketpair(AF_UNIX, &clientFd, &serverFd));
+
+    std::thread serverThread = std::thread(serverLoop, serverFd.get());
+
+    EXPECT_EQ(-EOPNOTSUPP, getNetworkForDnsInternal(clientFd.get(), &dnsNetId));
+
+    clientFd.reset();  // Causes serverLoop() to exit
+    serverThread.join();
+}
+
+TEST(NetdClientTest, getNetworkForDns) {
+    // Test null input
+    unsigned* testNull = nullptr;
+    EXPECT_EQ(-EFAULT, getNetworkForDns(testNull));
+}