Expose ParseBool from libbase

Also change the properties implementation to call the new API.  We use
this ParseBool API in the new SystemProperties implementation, with
which we want the libbase property API to be consistent.

Test: included
Change-Id: I89cb3eb4e1203a6bb0da41914dad720e44c00303

base/Android.bp

@@ -58,6 +58,7 @@ cc_defaults {
         "file.cpp",
         "logging.cpp",
         "mapped_file.cpp",
+        "parsebool.cpp",
         "parsenetaddress.cpp",
         "process.cpp",
         "properties.cpp",
@@ -149,6 +150,7 @@ cc_test {
         "macros_test.cpp",
         "mapped_file_test.cpp",
         "parsedouble_test.cpp",
+        "parsebool_test.cpp",
         "parseint_test.cpp",
         "parsenetaddress_test.cpp",
         "process_test.cpp",

base/include/android-base/parsebool.h

@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <string_view>
+
+namespace android {
+namespace base {
+
+// Parse the given string as yes or no inactivation of some sort. Return one of the
+// ParseBoolResult enumeration values.
+//
+// The following values parse as true:
+//
+//   1
+//   on
+//   true
+//   y
+//   yes
+//
+//
+// The following values parse as false:
+//
+//   0
+//   false
+//   n
+//   no
+//   off
+//
+// Anything else is a parse error.
+//
+// The purpose of this function is to have a single canonical parser for yes-or-no indications
+// throughout the system.
+
+enum class ParseBoolResult {
+  kError,
+  kFalse,
+  kTrue,
+};
+
+ParseBoolResult ParseBool(std::string_view s);
+
+}  // namespace base
+}  // namespace android

base/parsebool.cpp

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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 "android-base/parsebool.h"
+#include <errno.h>
+
+namespace android {
+namespace base {
+
+ParseBoolResult ParseBool(std::string_view s) {
+  if (s == "1" || s == "y" || s == "yes" || s == "on" || s == "true") {
+    return ParseBoolResult::kTrue;
+  }
+  if (s == "0" || s == "n" || s == "no" || s == "off" || s == "false") {
+    return ParseBoolResult::kFalse;
+  }
+  return ParseBoolResult::kError;
+}
+
+}  // namespace base
+}  // namespace android

base/parsebool_test.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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 "android-base/parsebool.h"
+
+#include <errno.h>
+
+#include <gtest/gtest.h>
+#include <string_view>
+
+using android::base::ParseBool;
+using android::base::ParseBoolResult;
+
+TEST(parsebool, true_) {
+  static const char* yes[] = {
+      "1", "on", "true", "y", "yes",
+  };
+  for (const char* s : yes) {
+    ASSERT_EQ(ParseBoolResult::kTrue, ParseBool(s));
+  }
+}
+
+TEST(parsebool, false_) {
+  static const char* no[] = {
+      "0", "false", "n", "no", "off",
+  };
+  for (const char* s : no) {
+    ASSERT_EQ(ParseBoolResult::kFalse, ParseBool(s));
+  }
+}
+
+TEST(parsebool, invalid) {
+  ASSERT_EQ(ParseBoolResult::kError, ParseBool("blarg"));
+  ASSERT_EQ(ParseBoolResult::kError, ParseBool(""));
+}

base/properties.cpp

@@ -28,19 +28,22 @@
 #include <map>
 #include <string>
 
+#include <android-base/parsebool.h>
 #include <android-base/parseint.h>
 
 namespace android {
 namespace base {
 
 bool GetBoolProperty(const std::string& key, bool default_value) {
-  std::string value = GetProperty(key, "");
-  if (value == "1" || value == "y" || value == "yes" || value == "on" || value == "true") {
-    return true;
-  } else if (value == "0" || value == "n" || value == "no" || value == "off" || value == "false") {
-    return false;
+  switch (ParseBool(GetProperty(key, ""))) {
+    case ParseBoolResult::kError:
+      return default_value;
+    case ParseBoolResult::kFalse:
+      return false;
+    case ParseBoolResult::kTrue:
+      return true;
   }
-  return default_value;
+  __builtin_unreachable();
 }
 
 template <typename T>