[NETD-BPF#1] Move libnetdutils to frameworks/libs/net/...

libnetdutils is referenced by netd.c and TrafficController.cpp, which
are going to be mainlined. Therefore, move libnetdutils to a common
place where both mainline module and platform code (Netd) can refer to.

Bug: 202086915
Test: build; flash; cd system/netd; atest
Ignore-AOSP-First: the netd change(same topic) would not automerge from
aosp.
No-Typo-Check: Clean code move with no other changes.
BYPASS_INCLUSIVE_LANGUAGE_REASON=Clean code move with no other changes.
Change-Id: I645bfe35f6543149c9a9f894cd4158d27a481abe

staticlibs/netd/libnetdutils/DumpWriter.cpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2016 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 "netdutils/DumpWriter.h"
+
+#include <unistd.h>
+#include <limits>
+
+#include <android-base/stringprintf.h>
+#include <utils/String8.h>
+
+using android::base::StringAppendV;
+
+namespace android {
+namespace netdutils {
+
+namespace {
+
+const char kIndentString[] = "  ";
+const size_t kIndentStringLen = strlen(kIndentString);
+
+}  // namespace
+
+DumpWriter::DumpWriter(int fd) : mIndentLevel(0), mFd(fd) {}
+
+void DumpWriter::incIndent() {
+    if (mIndentLevel < std::numeric_limits<decltype(mIndentLevel)>::max()) {
+        mIndentLevel++;
+    }
+}
+
+void DumpWriter::decIndent() {
+    if (mIndentLevel > std::numeric_limits<decltype(mIndentLevel)>::min()) {
+        mIndentLevel--;
+    }
+}
+
+void DumpWriter::println(const std::string& line) {
+    if (!line.empty()) {
+        for (int i = 0; i < mIndentLevel; i++) {
+            ::write(mFd, kIndentString, kIndentStringLen);
+        }
+        ::write(mFd, line.c_str(), line.size());
+    }
+    ::write(mFd, "\n", 1);
+}
+
+// NOLINTNEXTLINE(cert-dcl50-cpp): Grandfathered C-style variadic function.
+void DumpWriter::println(const char* fmt, ...) {
+    std::string line;
+    va_list ap;
+    va_start(ap, fmt);
+    StringAppendV(&line, fmt, ap);
+    va_end(ap);
+    println(line);
+}
+
+}  // namespace netdutils
+}  // namespace android