first cut: establishes base helper classes and main

helpers.cc

Index: helpers.cc
diff --git a/helpers.cc b/helpers.cc
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+// 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.
+//
+// Provides the implementation of the helper functions for PlatformReader
+// and derived classes.
+
+#include "helpers.h"
+
+#include <stdio.h>
+#include <sys/types.h>
+
+#include "platform_reader.h"
+
+namespace cros_boot_mode {
+namespace helpers {
+
+size_t read_file(const char *path, char *buf, size_t max_bytes) {
+  if (!buf)
+    return 0;
+  ::FILE *fp = ::fopen(path, "r");
+  if (!fp || !max_bytes)
+    return 0;
+  size_t bytes_read = ::fread(buf, 1, max_bytes, fp);
+
+  // If max_bytes doesn't consume the entire file, return 0 bytes read.
+  // This is meant to ensure that unexpected platform changes appear as
+  // kUnsupported rather than randomly based on truncation.
+  if (::fgetc(fp) != EOF) {
+    bytes_read = 0;
+  }
+
+  ::fclose(fp);
+  return bytes_read;
+}
+
+int to_int(const char *file_contents, size_t length) {
+  if (!length)
+    return PlatformReader::kUnsupported;
+  int enum_value = PlatformReader::kUnsupported;
+  if (sscanf(file_contents, "%d", &enum_value) != 1 || enum_value < 0)
+    return PlatformReader::kUnsupported;
+  return enum_value;
+}
+
+}  // namespace helpers
+}  // namespace cros_boot_mode