[native] Add support for env vars providing property values

This allows a user to configure the value of an environment
variable to be used as value for a configuration property.
For example, the configuration file may contain keys that
would be hard coded. The values can now be replaced by
environment variables that are read at startup time and
the keys don't require hard coding in the configuration file.

Author: czentgr

presto-native-execution/presto_cpp/main/common/ConfigReader.cpp

@@ -19,6 +19,25 @@
 #include "velox/common/config/Config.h"
 
 namespace facebook::presto::util {
+
+namespace {
+// Replaces strings of the form "${VAR}"
+// with the value of the environment variable "VAR" (if it exists).
+// Does nothing if the input doesn't look like "${...}".
+std::string replaceIfEnvironmentVariable(std::string_view str) {
+  if (str.size() >= 3 && str.substr(0, 2) == "${" &&
+      str[str.size() - 1] == '}') {
+    auto env_name = std::string(str.substr(2, str.size() - 3));
+
+    char* envval = std::getenv(env_name.c_str());
+    if (envval) {
+      return std::string(envval);
+    }
+  }
+  return std::string(str);
+}
+} // namespace
+
 std::unordered_map<std::string, std::string> readConfig(
     const std::string& filePath) {
   // https://teradata.github.io/presto/docs/141t/configuration/configuration.html
@@ -45,7 +64,8 @@ std::unordered_map<std::string, std::string> readConfig(
     const auto name = line.substr(0, delimiterPos);
     VELOX_CHECK(!name.empty(), "property pair '{}' has empty key", line);
     const auto value = line.substr(delimiterPos + 1);
-    properties.emplace(name, value);
+    const auto adjustedValue = replaceIfEnvironmentVariable(value);
+    properties.emplace(name, adjustedValue);
   }
 
   return properties;

presto-native-execution/presto_cpp/main/common/tests/ConfigTest.cpp

@@ -255,4 +255,33 @@ TEST_F(ConfigTest, optionalNodeId) {
   EXPECT_EQ(nodeId, config.nodeId());
 }
 
+TEST_F(ConfigTest, readConfigEnvVarTest) {
+  char path[] = "/tmp/velox_system_config_test_XXXXXX";
+  const char* tempDirectoryPath = mkdtemp(path);
+  if (tempDirectoryPath == nullptr) {
+    throw std::logic_error("Cannot open temp directory");
+  }
+
+  std::string propFilePath = tempDirectoryPath;
+  propFilePath += "/envtest.properties";
+  std::string ENV_VAR = "PRESTO_READ_CONFIG_TEST_VAR";
+
+  std::ofstream propFile (propFilePath);
+  propFile << fmt::format("{}={}\n", "plain-text", "plain-text-value");
+  propFile << fmt::format("{}=${{{}}}\n", "env-var", ENV_VAR);
+  propFile << fmt::format("{}=${{{}\n", "env-var2", ENV_VAR);
+  propFile << fmt::format("{}={}}}\n", "env-var3", ENV_VAR);
+  propFile << fmt::format("{}=${{}}\n", "no-env-var");
+  propFile.close();
+
+  setenv(ENV_VAR.c_str(), "env-var-value", 1);
+  auto properties = facebook::presto::util::readConfig(propFilePath);
+  ASSERT_EQ(properties["plain-text"], "plain-text-value");
+  ASSERT_EQ(properties["env-var"], "env-var-value");
+  ASSERT_EQ(properties["env-var2"], "${PRESTO_READ_CONFIG_TEST_VAR");
+  ASSERT_EQ(properties["env-var3"], "PRESTO_READ_CONFIG_TEST_VAR}");
+  ASSERT_EQ(properties["no-env-var"], "${}");
+  unsetenv(ENV_VAR.c_str());
+}
+
 } // namespace facebook::presto::test