Revert D4832473: [Folly] Disable EnvUtil::setAsCurrentEnvironment() on platforms...

[folly.git] / folly / experimental / EnvUtil.h

diff --git a/folly/experimental/EnvUtil.h b/folly/experimental/EnvUtil.h
index a44e07bc249a7e744d3fff43f7c72e5dc56b38a4..3ab3b16af726bf35aa4add3cdcca6da28318cf15 100644 (file)
--- a/folly/experimental/EnvUtil.h
+++ b/folly/experimental/EnvUtil.h
@@ -16,19 +16,106 @@
 
 #pragma once
 
 
 #pragma once
 

+#include <folly/Memory.h>

 #include <map>
 #include <string>
 #include <map>
 #include <string>

+#include <unordered_map>
+#include <vector>

 
 namespace folly {
 
 namespace folly {

+namespace experimental {
+
+// Class to model the process environment in idiomatic C++
+//
+// Changes to the modeled environment do not change the process environment
+// unless `setAsCurrentEnvironment()` is called.
+struct EnvironmentState {
+  using EnvType = std::unordered_map<std::string, std::string>;
+
+  // Returns an EnvironmentState containing a copy of the current process
+  // environment. Subsequent changes to the process environment do not
+  // alter the stored model. If the process environment is altered during the
+  // execution of this method the results are not defined.
+  //
+  // Throws MalformedEnvironment if the process environment cannot be modeled.
+  static EnvironmentState fromCurrentEnvironment();
+
+  // Returns an empty EnvironmentState
+  static EnvironmentState empty() {
+    return {};
+  }
+
+  explicit EnvironmentState(EnvType const& env) : env_(env) {}
+  explicit EnvironmentState(EnvType&& env) : env_(std::move(env)) {}
+
+  // Get the model environment for querying.
+  EnvType const& operator*() const {
+    return env_;
+  }
+  EnvType const* operator->() const {
+    return &env_;
+  }
+
+  // Get the model environment for mutation or querying.
+  EnvType& operator*() {
+    return env_;
+  }
+  EnvType* operator->() {
+    return &env_;
+  }
+
+  // Update the process environment with the one in the stored model.
+  // Subsequent changes to the model do not alter the process environment. The
+  // state of the process environment during execution of this method is not
+  // defined. If the process environment is altered by another thread during the
+  // execution of this method the results are not defined.
+  void setAsCurrentEnvironment();
+
+  // Get a copy of the model environment in the form used by `folly::Subprocess`
+  std::vector<std::string> toVector() const;
+
+  // Get a copy of the model environment in the form commonly used by C routines
+  // such as execve, execle, etc. Example usage:
+  //
+  // EnvironmentState forChild{};
+  // ... manipulate `forChild` as needed ...
+  // execve("/bin/program",pArgs,forChild.toPointerArray().get());
+  std::unique_ptr<char*, void (*)(char**)> toPointerArray() const;
+
+ private:
+  EnvironmentState() {}
+  EnvType env_;
+};
+
+struct MalformedEnvironment : std::runtime_error {
+  using std::runtime_error::runtime_error;
+};
+} // namespace experimental
+

 namespace test {
 namespace test {

+// RAII class allowing scoped changes to the process environment. The
+// environment state at the time of its construction is restored at the time
+// of its destruction.
+struct EnvVarSaver {
+  EnvVarSaver()
+      : state_(make_unique<experimental::EnvironmentState>(
+            experimental::EnvironmentState::fromCurrentEnvironment())) {}
+
+  EnvVarSaver(EnvVarSaver&& other) noexcept : state_(std::move(other.state_)) {}
+
+  EnvVarSaver& operator=(EnvVarSaver&& other) noexcept {
+    state_ = std::move(other.state_);
+    return *this;
+  }

 
 

-class EnvVarSaver {
- public:
-  EnvVarSaver();
-  ~EnvVarSaver();
+  ~EnvVarSaver() {
+    if (state_) {
+      state_->setAsCurrentEnvironment();
+    }
+  }

 
  private:
 
  private:

-  std::map<std::string, std::string> saved_;
+  std::unique_ptr<experimental::EnvironmentState> state_;

 };
 };

-}
-}
+} // namespace test
+} // namespace folly