cashew: add local byte counters

src/byte_counter.h

+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SRC_BYTE_COUNTER_H_
+#define SRC_BYTE_COUNTER_H_
+
+#include <string>
+
+#include <base/basictypes.h>  // NOLINT
+
+namespace cashew {
+
+class ByteCounterDelegate;
+
+// interface for byte counter
+class ByteCounter {
+  public:
+    virtual ~ByteCounter() {}
+
+    // to what interface is this counter attached?
+    virtual const std::string& GetInterface() const = 0;
+
+    // received bytes
+    virtual uint64 GetRxBytes() const = 0;
+
+    // transmitted bytes
+    virtual uint64 GetTxBytes() const = 0;
+
+    // set delegate interface that will receive counter updates
+    // it's ok to clear this by setting it to NULL
+    virtual void SetDelegate(ByteCounterDelegate *delegate) = 0;
+
+    // factory
+    // return appropriate concrete impl
+    // caller owns returned ByteCounter and is responsible for deleting it
+    static ByteCounter* NewByteCounter(const std::string& interface);
+};
+
+// interface for delegates
+class ByteCounterDelegate {
+  public:
+    virtual ~ByteCounterDelegate() {}
+
+    // called when byte counter is updated
+    virtual void OnByteCounterUpdate(const ByteCounter *counter,
+                                     uint64 rx_bytes, uint64 tx_bytes) = 0;
+};
+
+}  // namespace cashew
+
+#endif  // SRC_BYTE_COUNTER_H_