add a config FieldConvertor for parsing nanoseconds

Summary:
Add a `FieldConvertor` implementation allowing a config field to be parsed
into a `std::chrono::nanoseconds` value.

Reviewed By: strager

Differential Revision: D15428932

fbshipit-source-id: d3ace45a2986717c798897534e7b3015eda35fa9

eden/fs/config/FieldConverter.cpp

@@ -9,6 +9,8 @@
  */
 #include "eden/fs/config/FieldConverter.h"
 
+#include "eden/fs/utils/ChronoParse.h"
+
 using folly::Expected;
 using std::string;
 
@@ -80,5 +82,21 @@ Expected<string, string> FieldConverter<string>::fromString(
   return folly::makeExpected<string, string>(value.toString());
 }
 
+Expected<std::chrono::nanoseconds, string>
+FieldConverter<std::chrono::nanoseconds>::fromString(
+    folly::StringPiece value,
+    const std::map<string, string>& /* unused */) const {
+  auto result = stringToDuration(value);
+  if (result.hasValue()) {
+    return result.value();
+  }
+  return folly::makeUnexpected(chronoParseErrorToString(result.error()).str());
+}
+
+std::string FieldConverter<std::chrono::nanoseconds>::toDebugString(
+    std::chrono::nanoseconds value) const {
+  return durationToString(value);
+}
+
 } // namespace eden
 } // namespace facebook

eden/fs/config/FieldConverter.h

@@ -9,6 +9,7 @@
  */
 #pragma once
 
+#include <chrono>
 #include <map>
 #include <string>
 #include <type_traits>
@@ -90,5 +91,23 @@ class FieldConverter<
   }
 };
 
+/*
+ * FieldConverter implementation for nanoseconds.
+ *
+ * We could fairly easily implement this for other duration types, but we would
+ * have to decide what to do if the config specifies a more granular input
+ * value.  e.g., if we wanted to parse a config field as `std::chrono::minutes`
+ * what should we do if the value in the config file was "10s"?
+ */
+template <>
+class FieldConverter<std::chrono::nanoseconds> {
+ public:
+  folly::Expected<std::chrono::nanoseconds, std::string> fromString(
+      folly::StringPiece value,
+      const std::map<std::string, std::string>& convData) const;
+
+  std::string toDebugString(std::chrono::nanoseconds value) const;
+};
+
 } // namespace eden
 } // namespace facebook

eden/fs/config/test/ConfigSettingTest.cpp

@@ -19,6 +19,7 @@ using folly::StringPiece;
 
 using namespace facebook::eden;
 using namespace folly::string_piece_literals;
+using namespace std::chrono_literals;
 
 TEST(ConfigSettingTest, initStateCheck) {
   AbsolutePath defaultDir{"/DEFAULT_DIR"};
@@ -285,7 +286,7 @@ void checkSet(
   auto setResult =
       setting.setStringValue(str, attrMap, ConfigSource::UserConfig);
   ASSERT_FALSE(setResult.hasError()) << setResult.error();
-  if (std::is_floating_point<T>::value) {
+  if constexpr (std::is_floating_point<T>::value) {
     EXPECT_FLOAT_EQ(expected, setting.getValue());
   } else {
     EXPECT_EQ(expected, setting.getValue());
@@ -361,3 +362,15 @@ TEST(ConfigSettingTest, setArithmetic) {
       "Non-whitespace character found after end of conversion: \"0.001.9\"",
       "0.001.9");
 }
+
+TEST(ConfigSettingTest, setDuration) {
+  ConfigSetting<std::chrono::nanoseconds> setting{"test:value", 5ms, nullptr};
+  EXPECT_EQ(5ms, setting.getValue());
+  checkSet(setting, 90s, "1m30s");
+  checkSet(setting, -90s, "-1m30s");
+  checkSet(setting, 42ns, "42ns");
+  checkSet(setting, 300s, "5m");
+  checkSetError(setting, "empty input string", "");
+  checkSetError(setting, "unknown duration unit specifier", "90");
+  checkSetError(setting, "non-digit character found", "bogus");
+}