2 * Copyright 2017-present Facebook, Inc.
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
20 #include <unordered_map>
23 #include <folly/CPortability.h>
24 #include <folly/Memory.h>
27 namespace experimental {
29 // Class to model the process environment in idiomatic C++
31 // Changes to the modeled environment do not change the process environment
32 // unless `setAsCurrentEnvironment()` is called.
33 struct EnvironmentState {
34 using EnvType = std::unordered_map<std::string, std::string>;
36 // Returns an EnvironmentState containing a copy of the current process
37 // environment. Subsequent changes to the process environment do not
38 // alter the stored model. If the process environment is altered during the
39 // execution of this method the results are not defined.
41 // Throws MalformedEnvironment if the process environment cannot be modeled.
42 static EnvironmentState fromCurrentEnvironment();
44 // Returns an empty EnvironmentState
45 static EnvironmentState empty() {
49 explicit EnvironmentState(EnvType const& env) : env_(env) {}
50 explicit EnvironmentState(EnvType&& env) : env_(std::move(env)) {}
52 // Get the model environment for querying.
53 EnvType const& operator*() const {
56 EnvType const* operator->() const {
60 // Get the model environment for mutation or querying.
61 EnvType& operator*() {
64 EnvType* operator->() {
68 // Update the process environment with the one in the stored model.
69 // Subsequent changes to the model do not alter the process environment. The
70 // state of the process environment during execution of this method is not
71 // defined. If the process environment is altered by another thread during the
72 // execution of this method the results are not defined.
73 void setAsCurrentEnvironment();
75 // Get a copy of the model environment in the form used by `folly::Subprocess`
76 std::vector<std::string> toVector() const;
78 // Get a copy of the model environment in the form commonly used by C routines
79 // such as execve, execle, etc. Example usage:
81 // EnvironmentState forChild{};
82 // ... manipulate `forChild` as needed ...
83 // execve("/bin/program",pArgs,forChild.toPointerArray().get());
84 std::unique_ptr<char*, void (*)(char**)> toPointerArray() const;
91 struct FOLLY_EXPORT MalformedEnvironment : std::runtime_error {
92 using std::runtime_error::runtime_error;
94 } // namespace experimental
97 // RAII class allowing scoped changes to the process environment. The
98 // environment state at the time of its construction is restored at the time
99 // of its destruction.
102 : state_(std::make_unique<experimental::EnvironmentState>(
103 experimental::EnvironmentState::fromCurrentEnvironment())) {}
105 EnvVarSaver(EnvVarSaver&& other) noexcept : state_(std::move(other.state_)) {}
107 EnvVarSaver& operator=(EnvVarSaver&& other) noexcept {
108 state_ = std::move(other.state_);
114 state_->setAsCurrentEnvironment();
119 std::unique_ptr<experimental::EnvironmentState> state_;