feat(connlib): always symlink to latest log file (#8400)

When debugging Firezone, it is useful to use `tail -f` on the current
logfile to see what `connlib` is doing. This is quite annoying to do
however because the log file rolls over with every restart of the
application. As a small QoL improvement, we always symlink the latest
log file to a link called `latest`. Therefore, all one needs to do is
re-run the latest `tail -f ./latest` command to get the new logs.

Resolves: #8388

rust/logging/src/file.rs

@@ -19,11 +19,14 @@ use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use std::{fs, io};
 
+use anyhow::Context;
 use time::OffsetDateTime;
 use tracing::Subscriber;
 use tracing_appender::non_blocking::{NonBlocking, WorkerGuard};
 use tracing_subscriber::Layer;
 
+use crate::unwrap_or_debug;
+
 pub const TIME_FORMAT: &str = "[year]-[month]-[day]-[hour]-[minute]-[second]";
 
 /// How many lines we will at most buffer in the channel with the background thread that writes to disk.
@@ -130,6 +133,7 @@ impl Appender {
         let filename = format!("{}.{date}.{}", self.file_base_name, self.file_extension);
 
         let path = self.directory.join(&filename);
+        let latest = self.directory.join("latest");
         let mut open_options = fs::OpenOptions::new();
         open_options.append(true).create(true);
 
@@ -146,6 +150,21 @@ impl Appender {
         let file = new_file?;
         Self::set_permissions(&file)?;
 
+        let _ = std::fs::remove_file(&latest);
+
+        #[cfg(unix)]
+        unwrap_or_debug!(
+            std::os::unix::fs::symlink(path, latest)
+                .context("Failed to create `latest` link to log file"),
+            "{}"
+        );
+        #[cfg(windows)]
+        unwrap_or_debug!(
+            std::os::windows::fs::symlink_file(path, latest)
+                .context("Failed to create `latest` link to log file"),
+            "{}"
+        );
+
         Ok((file, filename))
     }