add support for notifying SystemD when the push server is ready

This requires the optional feature `systemd` to be enabled and allows
the startup of units depending on e.g. Unix domain sockets to be delayed
until these are created.

Signed-off-by: Eric Wolf <robo-eric@gmx.de>

Cargo.toml

@@ -32,6 +32,7 @@ derivative = "2.2.0"
 nextcloud-config-parser = { version = "0.10.0", features = ["redis-connect"] }
 url = "2.5.0"
 clap = { version = "4.5.4", features = ["derive"] }
+sd-notify = { version = "0.4.1", optional = true }
 
 [dev-dependencies]
 mini-redis = "0.4.1"
@@ -49,3 +50,6 @@ opt-level = 3
 lto = true
 
 [workspace]
+
+[features]
+systemd = ["dep:sd-notify"]

README.md

@@ -60,12 +60,15 @@ Documentation=https://github.com/nextcloud/notify_push
 [Service]
 Environment = PORT=7867 # Change if you already have something running on this port
 ExecStart = /path/to/push/binary/notify_push /path/to/nextcloud/config/config.php
+Type=notify # requires the push server to have been build with the systemd feature
 User=www-data
 
 [Install]
 WantedBy = multi-user.target
 ```
 
+If the push server has not been compiled with the optional systemd feature the `Type=notify` line has to be removed.
+
 #### OpenRC
 
 For OpenRC based setups, you can create an OpenRC service by creating a file named `/etc/init.d/notify_push` with the following content.

src/error.rs

@@ -26,6 +26,9 @@ pub enum Error {
  Authentication(#[from] AuthenticationError),
  #[error("Error while communicating with Nextcloud: {0}")]
  NextCloud(#[from] NextCloudError),
+ #[cfg(feature = "systemd")]
+ #[error("Failed to notify SystemD: {0}")]
+ SystemD(#[from] std::io::Error),
 }
 
 #[derive(Debug, Error, Diagnostic)]

src/main.rs

@@ -6,6 +6,8 @@ use notify_push::error::ConfigError;
 use notify_push::message::DEBOUNCE_ENABLE;
 use notify_push::metrics::serve_metrics;
 use notify_push::{listen_loop, serve, App, Error};
+#[cfg(feature = "systemd")]
+use sd_notify;
 use std::sync::atomic::Ordering;
 use std::sync::Arc;
 use tokio::select;
@@ -97,6 +99,10 @@ async fn run(config: Config, log_handle: LoggerHandle) -> Result<()> {
  )?);
  }
 
+ // tell SystemD that sockets have been bound to their addresses
+ #[cfg(feature = "systemd")]
+ sd_notify::notify(true, &[sd_notify::NotifyState::Ready]).map_err(Error::SystemD)?;
+
  spawn(listen_loop(app, listen_cancel_handle));
 
  // wait for either a sigint or sigterm