systemd: Add module for logging to the journal

Cargo.lock

@@ -2782,6 +2782,10 @@ dependencies = [
 [[package]]
 name = "radicle-systemd"
 version = "0.9.0"
+dependencies = [
+ "log",
+ "systemd-journal-logger",
+]
 
 [[package]]
 name = "radicle-term"
@@ -3432,6 +3436,16 @@ dependencies = [
  "syn 2.0.89",
 ]
 
+[[package]]
+name = "systemd-journal-logger"
+version = "2.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7266304d24ca5a4b230545fc558c80e18bd3e1d2eb1be149b6bcd04398d3e79c"
+dependencies = [
+ "log",
+ "rustix 1.0.7",
+]
+
 [[package]]
 name = "tar"
 version = "0.4.40"

crates/radicle-systemd/Cargo.toml

@@ -8,6 +8,11 @@ edition.workspace = true
 version = "0.9.0"
 rust-version.workspace = true
 
+[dependencies]
+log = { workspace = true, optional = true }
+systemd-journal-logger = { version = "2.2.2", optional = true }
+
 [features]
-default = ["listen"]
+default = ["journal", "listen"]
+journal = ["dep:log", "dep:systemd-journal-logger"]
 listen = []

crates/radicle-systemd/src/journal.rs

@@ -0,0 +1,23 @@
+use systemd_journal_logger::{connected_to_journal, current_exe_identifier, JournalLog};
+
+/// If the current process is directly connected to the systemd journal,
+/// return a logger that will write to it.
+pub fn logger<K, V, I>(
+    default_identifier: String,
+    extra_fields: I,
+) -> std::io::Result<Option<Box<dyn log::Log>>>
+where
+    I: IntoIterator<Item = (K, V)>,
+    K: AsRef<str>,
+    V: AsRef<[u8]>,
+{
+    if !connected_to_journal() {
+        return Ok(None);
+    }
+
+    Ok(Some(Box::new(
+        JournalLog::new()?
+            .with_syslog_identifier(current_exe_identifier().unwrap_or(default_identifier))
+            .with_extra_fields(extra_fields),
+    )))
+}

crates/radicle-systemd/src/lib.rs

@@ -1,4 +1,7 @@
 //! Library for interaction with systemd, specialized for Radicle.
 
+#[cfg(feature = "journal")]
+pub mod journal;
+
 #[cfg(feature = "listen")]
 pub mod listen;