116 lines
3.9 KiB
Rust
116 lines
3.9 KiB
Rust
//! Helpers for daemons/services.
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use std::ffi::CString;
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use std::os::unix::ffi::OsStrExt;
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use std::panic::UnwindSafe;
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use failure::*;
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// Unfortunately FnBox is nightly-only and Box<FnOnce> is unusable, so just use Box<Fn>...
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pub type BoxedStoreFunc = Box<dyn Fn() -> Result<String, Error> + UnwindSafe + Send>;
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/// Helper trait to "store" something in the environment to be re-used after re-executing the
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/// service on a reload.
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pub trait ReexecContinue: Sized {
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fn restore(var: &str) -> Result<Self, Error>;
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fn get_store_func(&self) -> BoxedStoreFunc;
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}
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/// Manages things to be stored and reloaded upon reexec.
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/// Anything which should be restorable should be instantiated via this struct's `restore` method,
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pub struct ReexecStore {
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pre_exec: Vec<PreExecEntry>,
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}
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// Currently we only need environment variables for storage, but in theory we could also add
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// variants which need temporary files or pipes...
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struct PreExecEntry {
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name: &'static str, // Feel free to change to String if necessary...
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store_fn: BoxedStoreFunc,
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}
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impl ReexecStore {
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pub fn new() -> Self {
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Self {
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pre_exec: Vec::new(),
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}
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}
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/// Restore an object from an environment variable of the given name, or, if none exists, uses
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/// the function provided in the `or_create` parameter to instantiate the new "first" instance.
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///
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/// Values created via this method will be remembered for later re-execution.
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pub fn restore<T, F>(&mut self, name: &'static str, or_create: F) -> Result<T, Error>
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where
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T: ReexecContinue,
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F: FnOnce() -> Result<T, Error>,
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{
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let res = match std::env::var(name) {
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Ok(varstr) => T::restore(&varstr)?,
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Err(std::env::VarError::NotPresent) => or_create()?,
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Err(_) => bail!("variable {} has invalid value", name),
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};
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self.pre_exec.push(PreExecEntry {
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name,
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store_fn: res.get_store_func(),
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});
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Ok(res)
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}
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fn pre_exec(self) -> Result<(), Error> {
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for item in self.pre_exec {
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std::env::set_var(item.name, (item.store_fn)()?);
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}
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Ok(())
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}
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pub fn fork_restart(self) -> Result<(), Error> {
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// Get the path to our executable as CString
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let exe = CString::new(
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std::fs::read_link("/proc/self/exe")?
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.into_os_string()
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.as_bytes()
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)?;
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// Get our parameters as Vec<CString>
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let args = std::env::args_os();
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let mut new_args = Vec::with_capacity(args.len());
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for arg in args {
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new_args.push(CString::new(arg.as_bytes())?);
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}
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// Start ourselves in the background:
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use nix::unistd::{fork, ForkResult};
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match fork() {
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Ok(ForkResult::Child) => {
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// At this point we call pre-exec helpers. We must be certain that if they fail for
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// whatever reason we can still call `_exit()`, so use catch_unwind.
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match std::panic::catch_unwind(move || self.do_exec(exe, new_args)) {
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Ok(_) => eprintln!("do_exec returned unexpectedly!"),
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Err(_) => eprintln!("panic in re-exec"),
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}
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// No matter how we managed to get here, this is the time where we bail out quickly:
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unsafe {
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libc::_exit(-1)
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}
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}
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Ok(ForkResult::Parent { child }) => {
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eprintln!("forked off a new server (pid: {})", child);
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Ok(())
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}
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Err(e) => {
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eprintln!("fork() failed, restart delayed: {}", e);
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Ok(())
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}
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}
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}
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fn do_exec(self, exe: CString, args: Vec<CString>) -> Result<(), Error> {
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self.pre_exec()?;
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nix::unistd::setsid()?;
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nix::unistd::execvp(&exe, &args)?;
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Ok(())
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}
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}
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