2 * Copyright 2017 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.
19 #include <folly/Memory.h>
22 #include <unordered_map>
26 namespace experimental {
28 // Class to model the process environment in idiomatic C++
30 // Changes to the modeled environment do not change the process environment
31 // unless `setAsCurrentEnvironment()` is called.
32 struct EnvironmentState {
33 using EnvType = std::unordered_map<std::string, std::string>;
35 // Returns an EnvironmentState containing a copy of the current process
36 // environment. Subsequent changes to the process environment do not
37 // alter the stored model. If the process environment is altered during the
38 // execution of this method the results are not defined.
40 // Throws MalformedEnvironment if the process environment cannot be modeled.
41 static EnvironmentState fromCurrentEnvironment();
43 // Returns an empty EnvironmentState
44 static EnvironmentState empty() {
48 explicit EnvironmentState(EnvType const& env) : env_(env) {}
49 explicit EnvironmentState(EnvType&& env) : env_(std::move(env)) {}
51 // Get the model environment for querying.
52 EnvType const& operator*() const {
55 EnvType const* operator->() const {
59 // Get the model environment for mutation or querying.
60 EnvType& operator*() {
63 EnvType* operator->() {
67 // Update the process environment with the one in the stored model.
68 // Subsequent changes to the model do not alter the process environment. The
69 // state of the process environment during execution of this method is not
70 // defined. If the process environment is altered by another thread during the
71 // execution of this method the results are not defined.
72 void setAsCurrentEnvironment();
74 // Get a copy of the model environment in the form used by `folly::Subprocess`
75 std::vector<std::string> toVector() const;
77 // Get a copy of the model environment in the form commonly used by C routines
78 // such as execve, execle, etc. Example usage:
80 // EnvironmentState forChild{};
81 // ... manipulate `forChild` as needed ...
82 // execve("/bin/program",pArgs,forChild.toPointerArray().get());
83 std::unique_ptr<char*, void (*)(char**)> toPointerArray() const;
90 struct MalformedEnvironment : std::runtime_error {
91 using std::runtime_error::runtime_error;
93 } // namespace experimental
96 // RAII class allowing scoped changes to the process environment. The
97 // environment state at the time of its construction is restored at the time
98 // of its destruction.
101 : state_(make_unique<experimental::EnvironmentState>(
102 experimental::EnvironmentState::fromCurrentEnvironment())) {}
104 EnvVarSaver(EnvVarSaver&& other) noexcept : state_(std::move(other.state_)) {}
106 EnvVarSaver& operator=(EnvVarSaver&& other) noexcept {
107 state_ = std::move(other.state_);
113 state_->setAsCurrentEnvironment();
118 std::unique_ptr<experimental::EnvironmentState> state_;