Add multi-destination logging: syslog and file support

Implement logging infrastructure for non-systemd platforms:

- Add src/logging.rs with syslog and file logging support
- New CLI flags: --syslog, --log-file, --log-file-daily
- Syslog uses libc directly with LOG_DAEMON facility
- File logging via tracing-appender with optional daily rotation

Update service scripts:
- OpenRC and FreeBSD rc.d now use --syslog by default
- Ensures logs are captured on platforms without journald

Default (stderr) behavior unchanged for systemd compatibility.
Log destination is selected at startup based on CLI flags.

Signed-off-by: Vladimir Krivopalov <argenet@yandex.ru>

src/logging.rs

@@ -0,0 +1,291 @@
+//! Logging configuration for telemt.
+//!
+//! Supports multiple log destinations:
+//! - stderr (default, works with systemd journald)
+//! - syslog (Unix only, for traditional init systems)
+//! - file (with optional rotation)
+
+#![allow(dead_code)] // Infrastructure module - used via CLI flags
+
+use std::path::Path;
+
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+use tracing_subscriber::{EnvFilter, fmt, reload};
+
+/// Log destination configuration.
+#[derive(Debug, Clone, Default)]
+pub enum LogDestination {
+    /// Log to stderr (default, captured by systemd journald).
+    #[default]
+    Stderr,
+    /// Log to syslog (Unix only).
+    #[cfg(unix)]
+    Syslog,
+    /// Log to a file with optional rotation.
+    File {
+        path: String,
+        /// Rotate daily if true.
+        rotate_daily: bool,
+    },
+}
+
+/// Logging options parsed from CLI/config.
+#[derive(Debug, Clone, Default)]
+pub struct LoggingOptions {
+    /// Where to send logs.
+    pub destination: LogDestination,
+    /// Disable ANSI colors.
+    pub disable_colors: bool,
+}
+
+/// Guard that must be held to keep file logging active.
+/// When dropped, flushes and closes log files.
+pub struct LoggingGuard {
+    _guard: Option<tracing_appender::non_blocking::WorkerGuard>,
+}
+
+impl LoggingGuard {
+    fn new(guard: Option<tracing_appender::non_blocking::WorkerGuard>) -> Self {
+        Self { _guard: guard }
+    }
+
+    /// Creates a no-op guard for stderr/syslog logging.
+    pub fn noop() -> Self {
+        Self { _guard: None }
+    }
+}
+
+/// Initialize the tracing subscriber with the specified options.
+///
+/// Returns a reload handle for dynamic log level changes and a guard
+/// that must be kept alive for file logging.
+pub fn init_logging(
+    opts: &LoggingOptions,
+    initial_filter: &str,
+) -> (reload::Handle<EnvFilter, impl tracing::Subscriber + Send + Sync>, LoggingGuard) {
+    let (filter_layer, filter_handle) = reload::Layer::new(EnvFilter::new(initial_filter));
+
+    match &opts.destination {
+        LogDestination::Stderr => {
+            let fmt_layer = fmt::Layer::default()
+                .with_ansi(!opts.disable_colors)
+                .with_target(true);
+
+            tracing_subscriber::registry()
+                .with(filter_layer)
+                .with(fmt_layer)
+                .init();
+
+            (filter_handle, LoggingGuard::noop())
+        }
+
+        #[cfg(unix)]
+        LogDestination::Syslog => {
+            // Use a custom fmt layer that writes to syslog
+            let fmt_layer = fmt::Layer::default()
+                .with_ansi(false)
+                .with_target(true)
+                .with_writer(SyslogWriter::new);
+
+            tracing_subscriber::registry()
+                .with(filter_layer)
+                .with(fmt_layer)
+                .init();
+
+            (filter_handle, LoggingGuard::noop())
+        }
+
+        LogDestination::File { path, rotate_daily } => {
+            let (non_blocking, guard) = if *rotate_daily {
+                // Extract directory and filename prefix
+                let path = Path::new(path);
+                let dir = path.parent().unwrap_or(Path::new("/var/log"));
+                let prefix = path.file_name()
+                    .and_then(|s| s.to_str())
+                    .unwrap_or("telemt");
+
+                let file_appender = tracing_appender::rolling::daily(dir, prefix);
+                tracing_appender::non_blocking(file_appender)
+            } else {
+                let file = std::fs::OpenOptions::new()
+                    .create(true)
+                    .append(true)
+                    .open(path)
+                    .expect("Failed to open log file");
+                tracing_appender::non_blocking(file)
+            };
+
+            let fmt_layer = fmt::Layer::default()
+                .with_ansi(false)
+                .with_target(true)
+                .with_writer(non_blocking);
+
+            tracing_subscriber::registry()
+                .with(filter_layer)
+                .with(fmt_layer)
+                .init();
+
+            (filter_handle, LoggingGuard::new(Some(guard)))
+        }
+    }
+}
+
+/// Syslog writer for tracing.
+#[cfg(unix)]
+struct SyslogWriter {
+    _private: (),
+}
+
+#[cfg(unix)]
+impl SyslogWriter {
+    fn new() -> Self {
+        // Open syslog connection on first use
+        static INIT: std::sync::Once = std::sync::Once::new();
+        INIT.call_once(|| {
+            unsafe {
+                // Open syslog with ident "telemt", LOG_PID, LOG_DAEMON facility
+                let ident = b"telemt\0".as_ptr() as *const libc::c_char;
+                libc::openlog(ident, libc::LOG_PID | libc::LOG_NDELAY, libc::LOG_DAEMON);
+            }
+        });
+        Self { _private: () }
+    }
+}
+
+#[cfg(unix)]
+impl std::io::Write for SyslogWriter {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        // Convert to C string, stripping newlines
+        let msg = String::from_utf8_lossy(buf);
+        let msg = msg.trim_end();
+
+        if msg.is_empty() {
+            return Ok(buf.len());
+        }
+
+        // Determine priority based on log level in the message
+        let priority = if msg.contains(" ERROR ") || msg.contains(" error ") {
+            libc::LOG_ERR
+        } else if msg.contains(" WARN ") || msg.contains(" warn ") {
+            libc::LOG_WARNING
+        } else if msg.contains(" INFO ") || msg.contains(" info ") {
+            libc::LOG_INFO
+        } else if msg.contains(" DEBUG ") || msg.contains(" debug ") {
+            libc::LOG_DEBUG
+        } else {
+            libc::LOG_INFO
+        };
+
+        // Write to syslog
+        let c_msg = std::ffi::CString::new(msg.as_bytes())
+            .unwrap_or_else(|_| std::ffi::CString::new("(invalid utf8)").unwrap());
+
+        unsafe {
+            libc::syslog(priority, b"%s\0".as_ptr() as *const libc::c_char, c_msg.as_ptr());
+        }
+
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
+#[cfg(unix)]
+impl<'a> tracing_subscriber::fmt::MakeWriter<'a> for SyslogWriter {
+    type Writer = SyslogWriter;
+
+    fn make_writer(&'a self) -> Self::Writer {
+        SyslogWriter::new()
+    }
+}
+
+/// Parse log destination from CLI arguments.
+pub fn parse_log_destination(args: &[String]) -> LogDestination {
+    let mut i = 0;
+    while i < args.len() {
+        match args[i].as_str() {
+            #[cfg(unix)]
+            "--syslog" => {
+                return LogDestination::Syslog;
+            }
+            "--log-file" => {
+                i += 1;
+                if i < args.len() {
+                    return LogDestination::File {
+                        path: args[i].clone(),
+                        rotate_daily: false,
+                    };
+                }
+            }
+            s if s.starts_with("--log-file=") => {
+                return LogDestination::File {
+                    path: s.trim_start_matches("--log-file=").to_string(),
+                    rotate_daily: false,
+                };
+            }
+            "--log-file-daily" => {
+                i += 1;
+                if i < args.len() {
+                    return LogDestination::File {
+                        path: args[i].clone(),
+                        rotate_daily: true,
+                    };
+                }
+            }
+            s if s.starts_with("--log-file-daily=") => {
+                return LogDestination::File {
+                    path: s.trim_start_matches("--log-file-daily=").to_string(),
+                    rotate_daily: true,
+                };
+            }
+            _ => {}
+        }
+        i += 1;
+    }
+    LogDestination::Stderr
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_log_destination_default() {
+        let args: Vec<String> = vec![];
+        assert!(matches!(parse_log_destination(&args), LogDestination::Stderr));
+    }
+
+    #[test]
+    fn test_parse_log_destination_file() {
+        let args = vec!["--log-file".to_string(), "/var/log/telemt.log".to_string()];
+        match parse_log_destination(&args) {
+            LogDestination::File { path, rotate_daily } => {
+                assert_eq!(path, "/var/log/telemt.log");
+                assert!(!rotate_daily);
+            }
+            _ => panic!("Expected File destination"),
+        }
+    }
+
+    #[test]
+    fn test_parse_log_destination_file_daily() {
+        let args = vec!["--log-file-daily=/var/log/telemt".to_string()];
+        match parse_log_destination(&args) {
+            LogDestination::File { path, rotate_daily } => {
+                assert_eq!(path, "/var/log/telemt");
+                assert!(rotate_daily);
+            }
+            _ => panic!("Expected File destination"),
+        }
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn test_parse_log_destination_syslog() {
+        let args = vec!["--syslog".to_string()];
+        assert!(matches!(parse_log_destination(&args), LogDestination::Syslog));
+    }
+}