for injection, add handler: add unit-tests

Add a handler to enable dependency injection for testing.  This is a
required step to use mocks.
Add the unit-tests.

Tested: Verified the new unit-tests ran.
Change-Id: I991849e6df2c3e74f59145a966048fc6825560db
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/handler.cpp b/handler.cpp
new file mode 100644
index 0000000..d34b7fc
--- /dev/null
+++ b/handler.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2019 Google Inc.
+ *
+ * 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 "handler.hpp"
+
+#include <cstdint>
+#include <cstdio>
+#include <filesystem>
+#include <fstream>
+#include <string>
+
+namespace ethstats
+{
+
+bool EthStats::validIfNameAndField(const std::string& path) const
+{
+    namespace fs = std::filesystem;
+
+    // TODO: Transition to using the netlink api.
+    std::error_code ec;
+    if (!fs::exists(path, ec))
+    {
+        std::fprintf(stderr, "Path: '%s' doesn't exist. ec(%d, %s)\n",
+                     path.c_str(), ec.value(), ec.message().c_str());
+        return false;
+    }
+
+    return true;
+}
+
+std::uint64_t EthStats::readStatistic(const std::string& path) const
+{
+    // We know the file exists, so just read it.
+    std::uint64_t value = 0;
+    std::ifstream ifs;
+
+    ifs.open(path);
+    ifs >> value;
+
+    return value;
+}
+
+EthStats handler;
+
+} // namespace ethstats