---
<a id="en"></a>
# self_cmd: Self-Executing Command Builder
- [Overview](#overview)
- [Features](#features)
- [Usage](#usage)
- [Design Philosophy](#design-philosophy)
- [Technical Stack](#technical-stack)
- [Project Structure](#project-structure)
- [API Reference](#api-reference)
- [Error Handling](#error-handling)
## Overview
`self_cmd` is a Rust library that creates Command instances for re-executing the current program with identical arguments and stdio inheritance. On Linux, it provides additional support for systemd socket activation by preserving file descriptor mappings through the `LISTEN_FDS` protocol.
## Features
- **Self-Replication**: Generate Command objects that execute the current program
- **Argument Preservation**: Automatically captures and forwards command-line arguments
- **Stdio Inheritance**: Maintains stdin, stdout, and stderr connections
- **Socket Activation Support**: Linux-specific file descriptor mapping for systemd integration
- **Robust Error Handling**: Custom error types with proper error propagation
- **Logging Integration**: Built-in logging support for debugging and monitoring
## Usage
Add to your `Cargo.toml`:
```toml
[dependencies]
self_cmd = "0.1.7"
```
```rust
use self_cmd;
fn main() -> self_cmd::Result<()> {
// Create and execute a command that re-runs this program
// Automatically handles stdio inheritance and Linux FD mappings for systemd socket activation
let mut cmd = self_cmd::get()?;
let status = cmd.status()?;
println!("Child process exited with: {status}");
Ok(())
}
```
On Linux systems, the library automatically handles systemd socket activation by checking `LISTEN_FDS`, duplicating file descriptors starting from FD 3, and configuring the child process environment. This makes it seamless for services that need to restart while maintaining their listening sockets.
## Design Philosophy
The library follows a minimalist approach with a single public function that encapsulates the complexity of self-execution:
```mermaid
graph TD
A[Program Start] --> B["self_cmd::get()"]
B --> C["env::current_exe()"]
C --> D["env::args().skip(1)"]
D --> E["Command::new(program)"]
E --> F["cmd.args(args)"]
F --> G[Configure Stdio Inheritance]
G --> H{Linux?}
H -->|Yes| I["fd_mapping()"]
I --> J[Check LISTEN_FDS env]
J --> K[Duplicate FDs 3+]
K --> L[Create FdMapping]
L --> M[Set LISTEN_FDS for child]
M --> N[Remove LISTEN_PID]
N --> O[Return Command]
H -->|No| O
O --> P[Execute Command]
```
The design ensures:
- **Simplicity**: Single function interface
- **Reliability**: Proper error handling without panics
- **Flexibility**: Returns Command for further customization
- **Performance**: Minimal overhead with lazy evaluation
## Technical Stack
- **Language**: Rust 2024 Edition
- **Core Dependencies**:
- `log` for logging functionality
- `thiserror` for structured error handling
- **Linux Dependencies**:
- `command-fds` for file descriptor mapping
- `libc` for low-level system calls
- **Error Handling**: Custom `Error` type with `thiserror` integration
- **Process Management**: `std::process::Command` with FD mapping extensions
- **Environment Access**: `std::env` for executable path and arguments
## Project Structure
```
self_cmd/
├── src/
│ ├── lib.rs # Core implementation and public API
│ ├── error.rs # Error types and handling
│ └── fd_mapping.rs # Linux-specific FD mapping (conditional)
├── tests/
│ └── main.rs # Integration tests
├── readme/
│ ├── en.md # English documentation
│ └── zh.md # Chinese documentation
├── Cargo.toml # Project configuration
└── test.sh # Test runner script
```
## API Reference
### `get() -> Result<Command>`
Creates a Command instance configured to re-execute the current program with full context preservation.
**Returns:**
- `Ok(Command)`: Configured command ready for execution
- `Err(Error)`: If unable to determine executable path or configure FD mappings
**Behavior:**
- Captures current executable path via `env::current_exe()`
- Preserves all command-line arguments except program name
- Configures stdio inheritance (stdin, stdout, stderr)
- **Linux only**: Handles systemd socket activation FD mapping
- Returns Command for further customization before execution
**Example:**
```rust
match self_cmd::get() {
Ok(mut cmd) => {
// Command is ready to use with full context preservation
cmd.status()?;
}
Err(e) => {
eprintln!("Failed to create self command: {e}");
}
}
```
### `fd_mapping() -> Result<Vec<FdMapping>>` (Linux only)
**Available on Linux only** - Creates file descriptor mappings for systemd socket activation.
**Returns:**
- `Ok(Vec<FdMapping>)`: List of FD mappings for socket activation
- `Err(Error)`: If FD duplication or validation fails
This function is automatically called by `get()` on Linux systems and typically doesn't need to be used directly.
## Error Handling
The library uses a custom `Error` type built with `thiserror` for comprehensive error handling:
```rust
use self_cmd::{Error, Result};
#[derive(Error, Debug)]
pub enum Error {
#[error("IO error: {0}")]
Io(#[from] std::io::Error),
#[error("FD mapping collision: {0}")]
FdMappingCollision(#[from] command_fds::FdMappingCollision),
}
```
All public functions return `Result<T>` which is an alias for `std::result::Result<T, Error>`. This provides:
- **Structured Errors**: Clear error types for different failure modes
- **Error Chaining**: Automatic conversion from underlying error types
- **Debugging Support**: Rich error messages with context
- **Integration**: Seamless integration with `?` operator and error handling patterns
---
## About
This project is an open-source component of [js0.site ⋅ Refactoring the Internet Plan](https://js0.site).
We are redefining the development paradigm of the Internet in a componentized way. Welcome to follow us:
* [Google Group](https://groups.google.com/g/js0-site)
* [js0site.bsky.social](https://bsky.app/profile/js0site.bsky.social)
---
<a id="zh"></a>
# self_cmd: 自执行命令构建器
- [概述](#概述)
- [功能特性](#功能特性)
- [使用方法](#使用方法)
- [设计理念](#设计理念)
- [技术栈](#技术栈)
- [项目结构](#项目结构)
- [API 参考](#api-参考)
- [错误处理](#错误处理)
## 概述
`self_cmd` 是 Rust 库，用于创建重新执行当前程序的 Command 实例，保持相同参数和标准输入输出继承。在 Linux 系统上，通过 `LISTEN_FDS` 协议保持文件描述符映射，提供对 systemd 套接字激活的额外支持。
## 功能特性
- **自我复制**: 生成执行当前程序的 Command 对象
- **参数保持**: 自动捕获并转发命令行参数
- **标准输入输出继承**: 维持 stdin、stdout、stderr 连接
- **套接字激活支持**: Linux 特定的文件描述符映射，用于 systemd 集成
- **健壮的错误处理**: 自定义错误类型与正确的错误传播
- **日志集成**: 内置日志支持，用于调试和监控
## 使用方法
添加到 `Cargo.toml`:
```toml
[dependencies]
self_cmd = "0.1.7"
```
```rust
use self_cmd;
fn main() -> self_cmd::Result<()> {
// 创建并执行重新运行此程序的命令
// 自动处理标准输入输出继承和 Linux systemd 套接字激活的 FD 映射
let mut cmd = self_cmd::get()?;
let status = cmd.status()?;
println!("子进程退出状态: {status}");
Ok(())
}
```
在 Linux 系统上，库自动处理 systemd 套接字激活，通过检查 `LISTEN_FDS`、从 FD 3 开始复制文件描述符并配置子进程环境。使需要重启但保持监听套接字的服务变得无缝。
## 设计理念
库采用极简主义方法，通过单个公共函数封装自执行的复杂性:
```mermaid
graph TD
A[程序启动] --> B["self_cmd::get()"]
B --> C["env::current_exe()"]
C --> D["env::args().skip(1)"]
D --> E["Command::new(program)"]
E --> F["cmd.args(args)"]
F --> G[配置标准输入输出继承]
G --> H{Linux?}
H -->|是| I["fd_mapping()"]
I --> J[检查 LISTEN_FDS 环境变量]
J --> K[复制 FD 3+]
K --> L[创建 FdMapping]
L --> M[为子进程设置 LISTEN_FDS]
M --> N[移除 LISTEN_PID]
N --> O[返回 Command]
H -->|否| O
O --> P[执行命令]
```
设计确保:
- **简洁性**: 单函数接口
- **可靠性**: 无恐慌的错误处理
- **灵活性**: 返回 Command 供进一步定制
- **性能**: 惰性求值的最小开销
## 技术栈
- **语言**: Rust 2024 版本
- **核心依赖**:
- `log` 用于日志功能
- `thiserror` 用于结构化错误处理
- **Linux 依赖**:
- `command-fds` 用于文件描述符映射
- `libc` 用于底层系统调用
- **错误处理**: 自定义 `Error` 类型与 `thiserror` 集成
- **进程管理**: `std::process::Command` 与 FD 映射扩展
- **环境访问**: `std::env` 获取可执行文件路径和参数
## 项目结构
```
self_cmd/
├── src/
│ ├── lib.rs # 核心实现和公共 API
│ ├── error.rs # 错误类型和处理
│ └── fd_mapping.rs # Linux 特定的 FD 映射（条件编译）
├── tests/
│ └── main.rs # 集成测试
├── readme/
│ ├── en.md # 英文文档
│ └── zh.md # 中文文档
├── Cargo.toml # 项目配置
└── test.sh # 测试运行脚本
```
## API 参考
### `get() -> Result<Command>`
创建配置为重新执行当前程序的 Command 实例，完整保持上下文。
**返回值:**
- `Ok(Command)`: 配置好的命令，可直接执行
- `Err(Error)`: 无法确定可执行文件路径或配置 FD 映射时
**行为:**
- 通过 `env::current_exe()` 捕获当前可执行文件路径
- 保留除程序名外的所有命令行参数
- 配置标准输入输出继承 (stdin, stdout, stderr)
- **仅 Linux**: 处理 systemd 套接字激活 FD 映射
- 返回 Command 供执行前进一步定制
**示例:**
```rust
match self_cmd::get() {
Ok(mut cmd) => {
// 命令已准备就绪，完整保持上下文
cmd.status()?;
}
Err(e) => {
eprintln!("创建自执行命令失败: {e}");
}
}
```
### `fd_mapping() -> Result<Vec<FdMapping>>` (仅 Linux)
**仅在 Linux 上可用** - 为 systemd 套接字激活创建文件描述符映射。
**返回值:**
- `Ok(Vec<FdMapping>)`: 套接字激活的 FD 映射列表
- `Err(Error)`: FD 复制或验证失败时
此函数在 Linux 系统上由 `get()` 自动调用，通常不需要直接使用。
## 错误处理
库使用基于 `thiserror` 构建的自定义 `Error` 类型进行全面的错误处理:
```rust
use self_cmd::{Error, Result};
#[derive(Error, Debug)]
pub enum Error {
#[error("IO error: {0} / IO 错误: {0}")]
Io(#[from] std::io::Error),
#[error("FD mapping collision: {0} / FD 映射冲突: {0}")]
FdMappingCollision(#[from] command_fds::FdMappingCollision),
}
```
所有公共函数返回 `Result<T>`，这是 `std::result::Result<T, Error>` 的别名。这提供了:
- **结构化错误**: 不同失败模式的清晰错误类型
- **错误链**: 从底层错误类型的自动转换
- **调试支持**: 带有上下文的丰富错误消息
- **集成**: 与 `?` 操作符和错误处理模式的无缝集成
---
## 关于
本项目为 [js0.site ⋅ 重构互联网计划](https://js0.site) 的开源组件。
我们正在以组件化的方式重新定义互联网的开发范式，欢迎关注：
* [谷歌邮件列表](https://groups.google.com/g/js0-site)
* [js0site.bsky.social](https://bsky.app/profile/js0site.bsky.social)