Fix logger initialization on readonly filesystems

Calling RollingFileAppender::new tries to create the directory for the log files even though logging is turned off by Logger.init('off', null). This change simply postpones the initialization of RollingFileAppender until it is actually needed. This way if we do eg. Logger.init("info", null) it works as expected and does not throw an error on readonly filesystems.

Fixes valkey-io#2387

logger_core/src/lib.rs

@@ -2,9 +2,12 @@
  * Copyright Valkey GLIDE Project Contributors - SPDX Identifier: Apache-2.0
  */
 use once_cell::sync::OnceCell;
-use std::sync::RwLock;
+use std::{
+    path::{Path, PathBuf},
+    sync::RwLock,
+};
 use tracing::{self, event};
-use tracing_appender::rolling::{RollingFileAppender, Rotation};
+use tracing_appender::rolling::{RollingFileAppender, RollingWriter, Rotation};
 use tracing_subscriber::{
     filter::Filtered,
     fmt::{
@@ -28,7 +31,7 @@ type InnerLayered = Layered<reload::Layer<InnerFiltered, Registry>, Registry>;
 // A reloadable layer of subscriber to a rolling file
 type FileReload = Handle<
     Filtered<
-        Layer<InnerLayered, DefaultFields, Format, RollingFileAppender>,
+        Layer<InnerLayered, DefaultFields, Format, LazyRollingFileAppender>,
         LevelFilter,
         InnerLayered,
     >,
@@ -48,6 +51,42 @@ pub static INITIATE_ONCE: InitiateOnce = InitiateOnce {
     init_once: OnceCell::new(),
 };
 
+struct LazyRollingFileAppender {
+    file_appender: OnceCell<RollingFileAppender>,
+    rotation: Rotation,
+    directory: PathBuf,
+    filename_prefix: PathBuf,
+}
+
+impl LazyRollingFileAppender {
+    fn new(
+        rotation: Rotation,
+        directory: impl AsRef<Path>,
+        filename_prefix: impl AsRef<Path>,
+    ) -> LazyRollingFileAppender {
+        LazyRollingFileAppender {
+            file_appender: OnceCell::new(),
+            rotation,
+            directory: directory.as_ref().to_path_buf(),
+            filename_prefix: filename_prefix.as_ref().to_path_buf(),
+        }
+    }
+}
+
+impl<'a> tracing_subscriber::fmt::writer::MakeWriter<'a> for LazyRollingFileAppender {
+    type Writer = RollingWriter<'a>;
+    fn make_writer(&'a self) -> Self::Writer {
+        let file_appender = self.file_appender.get_or_init(|| {
+            RollingFileAppender::new(
+                self.rotation.clone(),
+                self.directory.clone(),
+                self.filename_prefix.clone(),
+            )
+        });
+        file_appender.make_writer()
+    }
+}
+
 #[derive(Debug)]
 pub enum Level {
     Error = 0,
@@ -84,7 +123,7 @@ pub fn init(minimal_level: Option<Level>, file_name: Option<&str>) -> Level {
 
         let (stdout_layer, stdout_reload) = reload::Layer::new(stdout_fmt);
 
-        let file_appender = RollingFileAppender::new(
+        let file_appender = LazyRollingFileAppender::new(
             Rotation::HOURLY,
             "glide-logs",
             file_name.unwrap_or("output.log"),
@@ -130,7 +169,7 @@ pub fn init(minimal_level: Option<Level>, file_name: Option<&str>) -> Level {
                 });
         }
         Some(file) => {
-            let file_appender = RollingFileAppender::new(Rotation::HOURLY, "glide-logs", file);
+            let file_appender = LazyRollingFileAppender::new(Rotation::HOURLY, "glide-logs", file);
             let _ = reloads
                 .file_reload
                 .write()