[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/include/netdutils/MemBlock.h

@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#ifndef NETUTILS_MEMBLOCK_H
+#define NETUTILS_MEMBLOCK_H
+
+#include <memory>
+#include "netdutils/Slice.h"
+
+namespace android {
+namespace netdutils {
+
+// A class to encapsulate self-deleting byte arrays while preserving access
+// to the underlying length (without the length being part of the type, e.g.
+// std::array<>). By design, the only interface to the underlying bytes is
+// via Slice, to encourage safer memory access usage.
+//
+// No thread-safety guarantees whatsoever.
+class MemBlock {
+  public:
+    MemBlock() : MemBlock(0U) {}
+    explicit MemBlock(size_t len)
+            : mData((len > 0U) ? new uint8_t[len]{} : nullptr),
+              mLen(len) {}
+    // Allocate memory of size src.size() and copy src into this MemBlock.
+    explicit MemBlock(Slice src) : MemBlock(src.size()) {
+        copy(get(), src);
+    }
+
+    // No copy construction or assignment.
+    MemBlock(const MemBlock&) = delete;
+    MemBlock& operator=(const MemBlock&) = delete;
+
+    // Move construction and assignment are okay.
+    MemBlock(MemBlock&&) = default;
+    MemBlock& operator=(MemBlock&&) = default;
+
+    // Even though this method is const, the memory wrapped by the
+    // returned Slice is mutable.
+    Slice get() const noexcept { return Slice(mData.get(), mLen); }
+
+    // Implicit cast to Slice.
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator const Slice() const noexcept { return get(); }
+
+  private:
+    std::unique_ptr<uint8_t[]> mData;
+    size_t mLen;
+};
+
+}  // namespace netdutils
+}  // namespace android
+
+#endif /* NETUTILS_MEMBLOCK_H */