Dependencies+Main: Add sd-notify and idle feature back

This patch reverts 6959e6c3a6,
32a2492425 and
7f7b6b4e29 on top of the
current tree, adding back their features.

Cargo.lock

@@ -288,6 +288,15 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f3cb5ba0dc43242ce17de99c180e96db90b235b8a9fdc9543c96d2209116bd9f"
 
+[[package]]
+name = "sd-notify"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b943eadf71d8b69e661330cb0e2656e31040acf21ee7708e2c238a0ec6af2bf4"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "secrets-file-builder"
 version = "0.6.0"
@@ -295,6 +304,7 @@ dependencies = [
  "anyhow",
  "clap",
  "handlebars",
+ "sd-notify",
  "serde_json",
  "url-escape",
 ]

Cargo.toml

@@ -12,5 +12,6 @@ repository = "https://git.nwex.de/networkException/secrets-file-builder"
 anyhow = "1.0.88"
 clap = { version = "4.5.17", features = ["derive"] }
 handlebars = "5.1.0"
+sd-notify = "0.4.5"
 serde_json = "1.0.114"
 url-escape = "0.1.1"

src/main.rs

@@ -1,6 +1,7 @@
 use std::env;
 use std::fs;
 use std::path::PathBuf;
+use std::thread;
 
 use anyhow::Result;
 
@@ -8,6 +9,8 @@ use clap::Parser;
 use serde_json::{Map, Value};
 use url_escape;
 
+use sd_notify::NotifyState;
+
 use handlebars::{Context, Handlebars, Helper, HelperResult, JsonRender, Output, RenderContext, RenderErrorReason};
 
 #[derive(clap::Parser)]
@@ -18,12 +21,18 @@ struct Arguments {
 
     /// The path to write the built secret file to
     output_path: PathBuf,
+
+    /// If the process should keep running without doing anything. This is used to keep a systemd service
+    /// running this and the associated RuntimeDirectory alive.
+    #[clap(long, default_value_t = false)]
+    idle: bool,
 }
 
 fn main() -> Result<()> {
     let Arguments {
         contents_path,
         output_path,
+        idle,
     } = Arguments::parse();
 
     let mut handlebars = Handlebars::new();
@@ -96,5 +105,13 @@ fn main() -> Result<()> {
 
     println!("Wrote secret file to '{}'", output_path.to_string_lossy());
 
+    sd_notify::notify(true, &[NotifyState::Ready])?;
+
+    if idle {
+        loop {
+            thread::park();
+        }
+    }
+
     Ok(())
 }