feat: Support logging to journald with tracing-journald

This stubs out on non-unix platforms.

src/core/config/mod.rs

@@ -811,6 +811,24 @@ pub struct Config {
 	#[serde(default)]
 	pub log_thread_ids: bool,
 
+	/// Enable journald logging on Unix platforms
+	///
+	/// When enabled, log output will be sent to the systemd journal
+	/// This is only supported on Unix platforms
+	///
+	/// default: false
+	#[cfg(target_family = "unix")]
+	#[serde(default)]
+	pub log_to_journald: bool,
+
+	/// The syslog identifier to use with journald logging
+	///
+	/// Only used when journald logging is enabled
+	///
+	/// Defaults to the binary name
+	#[cfg(target_family = "unix")]
+	pub journald_identifier: Option<String>,
+
 	/// OpenID token expiration/TTL in seconds.
 	///
 	/// These are the OpenID tokens that are primarily used for Matrix account

src/main/Cargo.toml

@@ -43,6 +43,7 @@ default = [
 	"io_uring",
 	"jemalloc",
 	"jemalloc_conf",
+	"journald",
 	"media_thumbnail",
 	"release_max_log_level",
 	"systemd",
@@ -130,6 +131,11 @@ sentry_telemetry = [
 systemd = [
 	"conduwuit-router/systemd",
 ]
+journald = [ # This is a stub on non-unix platforms
+	"dep:tracing-journald",
+]
+
+
 # enable the tokio_console server ncompatible with release_max_log_level
 tokio_console = [
 	"dep:console-subscriber",
@@ -183,6 +189,7 @@ tracing-opentelemetry.optional = true
 tracing-opentelemetry.workspace = true
 tracing-subscriber.workspace = true
 tracing.workspace = true
+tracing-journald = { workspace = true, optional = true }
 
 [target.'cfg(all(not(target_env = "msvc"), target_os = "linux"))'.dependencies]
 hardened_malloc-rs.workspace = true

src/main/logging.rs

@@ -46,6 +46,16 @@ pub(crate) fn init(
 		.with(console_layer.with_filter(console_reload_filter))
 		.with(cap_layer);
 
+	// If journald logging is enabled on Unix platforms, create a separate
+	// subscriber for it
+	#[cfg(all(target_family = "unix", feature = "journald"))]
+	if config.log_to_journald {
+		println!("Initialising journald logging");
+		if let Err(e) = init_journald_logging(config) {
+			eprintln!("Failed to initialize journald logging: {e}");
+		}
+	}
+
 	#[cfg(feature = "sentry_telemetry")]
 	let subscriber = {
 		let sentry_filter = EnvFilter::try_new(&config.sentry_filter)
@@ -135,6 +145,28 @@ pub(crate) fn init(
 	Ok(ret)
 }
 
+#[cfg(all(target_family = "unix", feature = "journald"))]
+fn init_journald_logging(config: &Config) -> Result<()> {
+	use tracing_journald::Layer as JournaldLayer;
+
+	let journald_filter =
+		EnvFilter::try_new(&config.log).map_err(|e| err!(Config("log", "{e}.")))?;
+
+	let mut journald_layer = JournaldLayer::new()
+		.map_err(|e| err!(Config("journald", "Failed to initialize journald layer: {e}.")))?;
+
+	if let Some(ref identifier) = config.journald_identifier {
+		journald_layer = journald_layer.with_syslog_identifier(identifier.to_owned());
+	}
+
+	let journald_subscriber =
+		Registry::default().with(journald_layer.with_filter(journald_filter));
+
+	let _guard = tracing::subscriber::set_default(journald_subscriber);
+
+	Ok(())
+}
+
 fn tokio_console_enabled(config: &Config) -> (bool, &'static str) {
 	if !cfg!(all(feature = "tokio_console", tokio_unstable)) {
 		return (false, "");
@@ -154,7 +186,10 @@ fn tokio_console_enabled(config: &Config) -> (bool, &'static str) {
 	(true, "")
 }
 
-fn set_global_default<S: SubscriberExt + Send + Sync>(subscriber: S) {
+fn set_global_default<S>(subscriber: S)
+where
+	S: tracing::Subscriber + Send + Sync + 'static,
+{
 	tracing::subscriber::set_global_default(subscriber)
 		.expect("the global default tracing subscriber failed to be initialized");
 }