rust: use 'tracing' as the logs system

rust/agama-server/Cargo.toml

@@ -11,8 +11,6 @@ anyhow = "1.0"
 agama-locale-data = { path = "../agama-locale-data" }
 agama-lib = { path = "../agama-lib" }
 log = "0.4"
-simplelog = "0.12.1"
-systemd-journal-logger = "1.0"
 zbus = { version = "3", default-features = false, features = ["tokio"] }
 zbus_macros = "3"
 uuid = { version = "1.3.4", features = ["v4"] }
@@ -53,7 +51,10 @@ openssl = "0.10.64"
 hyper = "1.2.0"
 hyper-util = "0.1.3"
 tokio-openssl = "0.6.4"
-futures-util = { version = "0.3.30", default-features = false, features = ["alloc"] }
+futures-util = { version = "0.3.30", default-features = false, features = [
+  "alloc",
+] }
+libsystemd = "0.7.0"
 
 [[bin]]
 name = "agama-dbus-server"

rust/agama-server/src/agama-web-server.rs

@@ -28,7 +28,6 @@ use openssl::ssl::{Ssl, SslAcceptor, SslFiletype, SslMethod};
 use tokio::sync::broadcast::channel;
 use tokio_openssl::SslStream;
 use tower::Service;
-use tracing_subscriber::prelude::*;
 use utoipa::OpenApi;
 
 const DEFAULT_WEB_UI_DIR: &str = "/usr/share/agama/web_ui";
@@ -294,8 +293,6 @@ async fn start_server(address: String, service: Router, ssl_acceptor: SslAccepto
 /// `options`: command-line arguments.
 async fn serve_command(args: ServeArgs) -> anyhow::Result<()> {
     start_logging().context("Could not initialize the logger")?;
-    let journald = tracing_journald::layer().context("could not connect to journald")?;
-    tracing_subscriber::registry().with(journald).init();
 
     let (tx, _) = channel(16);
     run_monitor(tx.clone()).await?;

rust/agama-server/src/logs.rs

@@ -1,17 +1,18 @@
-use log::{self, LevelFilter, SetLoggerError};
+//! Functions to work with logs.
 
-pub fn start_logging() -> Result<(), SetLoggerError> {
-    if systemd_journal_logger::connected_to_journal() {
-        // unwrap here is intentional as we are sure no other logger is active yet
-        systemd_journal_logger::JournalLog::default().install()?;
-        log::set_max_level(LevelFilter::Info); // log only info for journal logger
+use anyhow::Context;
+use libsystemd::logging;
+use tracing_subscriber::prelude::*;
+
+/// Initializes the logging mechanism.
+///
+/// It is based on [Tracing](https://github.com/tokio-rs/tracing), part of the Tokio ecosystem.
+pub fn start_logging() -> anyhow::Result<()> {
+    if logging::connected_to_journal() {
+        let journald = tracing_journald::layer().context("could not connect to journald")?;
+        tracing_subscriber::registry().with(journald).init();
     } else {
-        simplelog::TermLogger::init(
-            LevelFilter::Info, // lets use info, trace provides too much output from libraries
-            simplelog::Config::default(),
-            simplelog::TerminalMode::Stderr, // only stderr output for easier filtering
-            simplelog::ColorChoice::Auto,
-        )?;
+        tracing_subscriber::fmt::init();
     }
     Ok(())
 }