[sensors](CrOS/Linux) Implement Sensor device manager for sensors

device/generic_sensor/linux/platform_sensor_utils_linux.cc

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "device/generic_sensor/linux/platform_sensor_utils_linux.h"
-
-#include "base/files/file_enumerator.h"
-#include "base/files/file_util.h"
-#include "base/strings/string_number_conversions.h"
-#include "base/strings/string_util.h"
-#include "base/threading/thread_restrictions.h"
-#include "device/generic_sensor/public/cpp/sensor_reading.h"
-
-namespace device {
-
-namespace {
-
-bool InitSensorPaths(const std::vector<std::string>& input_names,
-                     const char* base_path,
-                     std::vector<base::FilePath>* sensor_paths) {
-  // Search the iio/devices directory for a subdirectory (eg "device0" or
-  // "iio:device0") that contains the specified input_name file (eg
-  // "in_illuminance_input" or "in_illuminance0_input").
-  base::FileEnumerator dir_enumerator(base::FilePath(base_path), false,
-                                      base::FileEnumerator::DIRECTORIES);
-  for (base::FilePath check_path = dir_enumerator.Next(); !check_path.empty();
-       check_path = dir_enumerator.Next()) {
-    for (auto const& file_name : input_names) {
-      base::FilePath full_path = check_path.Append(file_name);
-      if (base::PathExists(full_path)) {
-        sensor_paths->push_back(full_path);
-        return true;
-      }
-    }
-  }
-  return false;
-}
-
-bool GetSensorFilePaths(const SensorDataLinux& data,
-                        std::vector<base::FilePath>* sensor_paths) {
-  DCHECK(sensor_paths->empty());
-  // Depending on a sensor, there can be up to three sets of files that need
-  // to be checked. If one of three files is not found, a sensor is
-  // treated as a non-existing one.
-  for (auto const& file_names : data.sensor_file_names) {
-    // Supply InitSensorPaths() with a set of files.
-    // Only one file from each set should be found.
-    if (!InitSensorPaths(file_names, data.base_path_sensor_linux, sensor_paths))
-      return false;
-  }
-  return true;
-}
-
-// Returns -1 if unable to read a scaling value.
-// Otherwise, returns a scaling value read from a file.
-double ReadSensorScalingValue(const base::FilePath& scale_file_path) {
-  std::string value;
-  if (!base::ReadFileToString(scale_file_path, &value))
-    return -1;
-
-  double scaling_value;
-  base::TrimWhitespaceASCII(value, base::TRIM_ALL, &value);
-  if (!base::StringToDouble(value, &scaling_value))
-    return -1;
-  return scaling_value;
-}
-
-}  // namespace
-
-// static
-std::unique_ptr<SensorReader> SensorReader::Create(
-    const SensorDataLinux& data) {
-  base::ThreadRestrictions::AssertIOAllowed();
-  std::vector<base::FilePath> sensor_paths;
-  if (!GetSensorFilePaths(data, &sensor_paths))
-    return nullptr;
-
-  DCHECK(!sensor_paths.empty());
-  // Scaling value is 1 if scaling file is not specified is |data| or scaling
-  // file is not found.
-  double scaling_value = 1;
-  if (!data.sensor_scale_name.empty()) {
-    const base::FilePath scale_file_path =
-        sensor_paths.back().DirName().Append(data.sensor_scale_name);
-    if (base::PathExists(scale_file_path))
-      scaling_value = ReadSensorScalingValue(scale_file_path);
-  }
-
-  // A file with a scaling value is found, but couldn't be read.
-  if (scaling_value == -1)
-    return nullptr;
-
-  return base::WrapUnique(new SensorReader(
-      std::move(sensor_paths), scaling_value, data.apply_scaling_func));
-}
-
-SensorReader::SensorReader(
-    std::vector<base::FilePath> sensor_paths,
-    double scaling_value,
-    const SensorDataLinux::ReaderFunctor& apply_scaling_func)
-    : sensor_paths_(std::move(sensor_paths)),
-      scaling_value_(scaling_value),
-      apply_scaling_func_(apply_scaling_func) {
-  DCHECK(!sensor_paths_.empty());
-}
-
-SensorReader::~SensorReader() = default;
-
-bool SensorReader::ReadSensorReading(SensorReading* reading) {
-  base::ThreadRestrictions::AssertIOAllowed();
-  SensorReading readings;
-  DCHECK_LE(sensor_paths_.size(), arraysize(readings.values));
-  int i = 0;
-  for (const auto& path : sensor_paths_) {
-    std::string new_read_value;
-    if (!base::ReadFileToString(path, &new_read_value))
-      return false;
-
-    double new_value = 0;
-    base::TrimWhitespaceASCII(new_read_value, base::TRIM_ALL, &new_read_value);
-    if (!base::StringToDouble(new_read_value, &new_value))
-      return false;
-    readings.values[i++] = new_value;
-  }
-  if (!apply_scaling_func_.is_null())
-    apply_scaling_func_.Run(scaling_value_, readings);
-  *reading = readings;
-  return true;
-}
-
-}  // namespace device