Add libnettestutils as a networking test utility

The library provides a helper function that can retrieve dumpsys
results from a specific service. It can also take dumpsys arguments.

Bug: 29761778
Bug: 202086915
Test: test in Ib4aeb385ab80187feb39b659274a0aee20a4a5ed

Change-Id: Ib2ab8b6e4136bd3cbc52b025e53a1fa0c4e91709

staticlibs/native/nettestutils/DumpService.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2022 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 "nettestutils/DumpService.h"
+
+#include <android-base/file.h>
+
+#include <sstream>
+#include <thread>
+
+android::status_t dumpService(const android::sp<android::IBinder>& binder,
+                              const std::vector<std::string>& args,
+                              std::vector<std::string>& outputLines) {
+  if (!outputLines.empty()) return -EUCLEAN;
+
+  android::base::unique_fd localFd, remoteFd;
+  if (!Pipe(&localFd, &remoteFd)) return -errno;
+
+  android::Vector<android::String16> str16Args;
+  for (const auto& arg : args) {
+    str16Args.push(android::String16(arg.c_str()));
+  }
+  android::status_t ret;
+  // dump() blocks until another thread has consumed all its output.
+  std::thread dumpThread =
+      std::thread([&ret, binder, remoteFd{std::move(remoteFd)}, str16Args]() {
+        ret = binder->dump(remoteFd, str16Args);
+      });
+
+  std::string dumpContent;
+  if (!android::base::ReadFdToString(localFd.get(), &dumpContent)) {
+    return -errno;
+  }
+  dumpThread.join();
+  if (ret != android::OK) return ret;
+
+  std::stringstream dumpStream(std::move(dumpContent));
+  std::string line;
+  while (std::getline(dumpStream, line)) {
+    outputLines.push_back(line);
+  }
+
+  return android::OK;
+}