1 /*
2  * Copyright (C) 2022 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef ART_LIBARTTOOLS_INCLUDE_TOOLS_SYSTEM_PROPERTIES_H_
18 #define ART_LIBARTTOOLS_INCLUDE_TOOLS_SYSTEM_PROPERTIES_H_
19 
20 #include <string>
21 
22 #include "android-base/parsebool.h"
23 #include "android-base/properties.h"
24 
25 namespace art {
26 namespace tools {
27 
28 // A class for getting system properties with fallback lookup support. Different from
29 // android::base::GetProperty, this class is mockable.
30 class SystemProperties {
31  public:
32   SystemProperties() = default;
33   SystemProperties(const SystemProperties& other) = default;
34   SystemProperties& operator=(const SystemProperties& other) = default;
35   SystemProperties(SystemProperties&& other) = default;
36   SystemProperties& operator=(SystemProperties&& other) = default;
37   virtual ~SystemProperties() = default;
38 
39   // Returns the current value of the system property `key`, or `default_value` if the property
40   // doesn't have a value.
Get(const std::string & key,const std::string & default_value)41   std::string Get(const std::string& key, const std::string& default_value) const {
42     std::string value = GetProperty(key);
43     if (!value.empty()) {
44       return value;
45     }
46     return default_value;
47   }
48 
49   // Same as above, but allows specifying one or more fallback keys. The last argument is a string
50   // default value that will be used if none of the given keys has a value.
51   //
52   // Usage:
53   //
54   // Look up for "key_1", then "key_2", then "key_3". If none of them has a value, return "default":
55   //   Get("key_1", "key_2", "key_3", /*default_value=*/"default")
56   template <typename... Args>
Get(const std::string & key,const std::string & fallback_key,Args...args)57   std::string Get(const std::string& key, const std::string& fallback_key, Args... args) const {
58     return Get(key, Get(fallback_key, args...));
59   }
60 
61   // Returns the current value of the system property `key` with zero or more fallback keys, or an
62   // empty string if none of the given keys has a value.
63   //
64   // Usage:
65   //
66   // Look up for "key_1". If it doesn't have a value, return an empty string:
67   //  GetOrEmpty("key_1")
68   //
69   // Look up for "key_1", then "key_2", then "key_3". If none of them has a value, return an empty
70   // string:
71   //  GetOrEmpty("key_1", "key_2", "key_3")
72   template <typename... Args>
GetOrEmpty(const std::string & key,Args...fallback_keys)73   std::string GetOrEmpty(const std::string& key, Args... fallback_keys) const {
74     return Get(key, fallback_keys..., /*default_value=*/"");
75   }
76 
77   // Returns the current value of the boolean system property `key`, or `default_value` if the
78   // property doesn't have a value. See `android::base::ParseBool` for how the value is parsed.
GetBool(const std::string & key,bool default_value)79   bool GetBool(const std::string& key, bool default_value) const {
80     android::base::ParseBoolResult result = android::base::ParseBool(GetProperty(key));
81     if (result != android::base::ParseBoolResult::kError) {
82       return result == android::base::ParseBoolResult::kTrue;
83     }
84     return default_value;
85   }
86 
87   // Same as above, but allows specifying one or more fallback keys. The last argument is a bool
88   // default value that will be used if none of the given keys has a value.
89   //
90   // Usage:
91   //
92   // Look up for "key_1", then "key_2", then "key_3". If none of them has a value, return true:
93   //   Get("key_1", "key_2", "key_3", /*default_value=*/true)
94   template <typename... Args>
GetBool(const std::string & key,const std::string & fallback_key,Args...args)95   bool GetBool(const std::string& key, const std::string& fallback_key, Args... args) const {
96     return GetBool(key, GetBool(fallback_key, args...));
97   }
98 
99  protected:
100   // The single source of truth of system properties. Can be mocked in unit tests.
GetProperty(const std::string & key)101   virtual std::string GetProperty(const std::string& key) const {
102     return android::base::GetProperty(key, /*default_value=*/"");
103   }
104 };
105 
106 }  // namespace tools
107 }  // namespace art
108 
109 #endif  // ART_LIBARTTOOLS_INCLUDE_TOOLS_SYSTEM_PROPERTIES_H_
110