Support date/time in log file name

docs/Configuration.md

@@ -131,6 +131,9 @@ my_console_appender:
 The _path_ field is required and accepts environment variables of the form
 `$ENV{name_here}`. The path can be relative or absolute.
 
+The _path_ field also supports date/time formats such as `$TIME{chrono_format}`. Refer
+to [chrono format](https://docs.rs/chrono/latest/chrono/format/strftime/index.html) for date and time formatting syntax
+
 The _encoder_ field is optional and can consist of multiple fields. Refer to
 the [encoder](#encoder) documention.
 
@@ -140,7 +143,7 @@ append to the log file if it exists, false will truncate the existing file.
 ```yml
 my_file_appender:
   kind: file
-  path: $ENV{PWD}/log/test.log
+  path: $ENV{PWD}/log/test_$TIME{%Y-%m-%d_%H-%M-%S}.log
   append: true
 ```
 

examples/sample_config.yml

@@ -8,7 +8,7 @@ appenders:
               level: info
     file:
         kind: file
-        path: "log/file.log"
+        path: "log/file-$TIME{%Y-%m-%d_%H-%M-%S}.log"
         encoder:
             pattern: "[{d(%Y-%m-%dT%H:%M:%S%.6f)} {h({l}):<5.5} {M}] {m}{n}"
     rollingfile:

src/append/file.rs

@@ -2,6 +2,7 @@
 //!
 //! Requires the `file_appender` feature.
 
+use chrono::prelude::Local;
 use derivative::Derivative;
 use log::Record;
 use parking_lot::Mutex;
@@ -11,6 +12,11 @@ use std::{
     path::{Path, PathBuf},
 };
 
+const TIME_PREFIX: &str = "$TIME{";
+const TIME_PREFIX_LEN: usize = TIME_PREFIX.len();
+const TIME_SUFFIX: char = '}';
+const TIME_SUFFIX_LEN: usize = 1;
+
 #[cfg(feature = "config_parsing")]
 use crate::config::{Deserialize, Deserializers};
 #[cfg(feature = "config_parsing")]
@@ -84,31 +90,63 @@ impl FileAppenderBuilder {
     }
 
     /// Consumes the `FileAppenderBuilder`, producing a `FileAppender`.
-    /// The path argument can contain environment variables of the form $ENV{name_here},
-    /// where 'name_here' will be the name of the environment variable that
-    /// will be resolved. Note that if the variable fails to resolve,
-    /// $ENV{name_here} will NOT be replaced in the path.
+    /// The path argument can contain special patterns that will be resolved:
+    ///
+    /// - `$ENV{name_here}`: This pattern will be replaced by `name_here`.
+    ///   where 'name_here' will be the name of the environment variable that
+    ///   will be resolved. Note that if the variable fails to resolve,
+    ///   $ENV{name_here} will NOT be replaced in the path.
+    /// - `$TIME{chrono_format}`: This pattern will be replaced by `chrono_format`.
+    ///   where 'chrono_format' will be date/time format from chrono crate. Note
+    ///   that if the chrono_format fails to resolve, $TIME{chrono_format} will
+    ///   NOT be replaced in the path.
     pub fn build<P: AsRef<Path>>(self, path: P) -> io::Result<FileAppender> {
         let path_cow = path.as_ref().to_string_lossy();
-        let path: PathBuf = expand_env_vars(path_cow).as_ref().into();
-        if let Some(parent) = path.parent() {
+        // Expand environment variables in the path
+        let expanded_env_path: PathBuf = expand_env_vars(path_cow).as_ref().into();
+        // Apply the date/time format to the path
+        let final_path = self.date_time_format(expanded_env_path);
+
+        if let Some(parent) = final_path.parent() {
             fs::create_dir_all(parent)?;
         }
         let file = OpenOptions::new()
             .write(true)
             .append(self.append)
             .truncate(!self.append)
             .create(true)
-            .open(&path)?;
+            .open(&final_path)?;
 
         Ok(FileAppender {
-            path,
+            path: final_path,
             file: Mutex::new(SimpleWriter(BufWriter::with_capacity(1024, file))),
             encoder: self
                 .encoder
                 .unwrap_or_else(|| Box::<PatternEncoder>::default()),
         })
     }
+
+    fn date_time_format(&self, path: PathBuf) -> PathBuf {
+        let mut date_time_path = path.to_str().unwrap().to_string();
+        // Locate the start and end of the placeholder
+        while let Some(start) = date_time_path.find(TIME_PREFIX) {
+            if let Some(end) = date_time_path[start..].find(TIME_SUFFIX) {
+                let end = start + end;
+                // Extract the date format string
+                let date_format = &date_time_path[start + TIME_PREFIX_LEN..end];
+
+                // Get the current date and time
+                let now = Local::now();
+
+                // Format the current date and time
+                let formatted_date = now.format(date_format).to_string();
+
+                // replacing the placeholder with the formatted date
+                date_time_path.replace_range(start..end + TIME_SUFFIX_LEN, &formatted_date);
+            }
+        }
+        PathBuf::from(date_time_path)
+    }
 }
 
 /// A deserializer for the `FileAppender`.
@@ -180,4 +218,69 @@ mod test {
             .build(tempdir.path().join("foo.log"))
             .unwrap();
     }
+
+    #[test]
+    fn test_date_time_format_with_valid_format() {
+        let current_time = Local::now().format("%Y-%m-%d").to_string();
+        let tempdir = tempfile::tempdir().unwrap();
+        let builder = FileAppender::builder()
+            .build(
+                tempdir
+                    .path()
+                    .join("foo")
+                    .join("bar")
+                    .join("logs/log-$TIME{%Y-%m-%d}.log"),
+            )
+            .unwrap();
+        let expected_path = tempdir
+            .path()
+            .join(format!("foo/bar/logs/log-{}.log", current_time));
+        assert_eq!(builder.path, expected_path);
+    }
+
+    #[test]
+    fn test_date_time_format_with_invalid_format() {
+        let tempdir = tempfile::tempdir().unwrap();
+        let builder = FileAppender::builder()
+            .build(
+                tempdir
+                    .path()
+                    .join("foo")
+                    .join("bar")
+                    .join("logs/log-$TIME{INVALID}.log"),
+            )
+            .unwrap();
+        let expected_path = tempdir.path().join("foo/bar/logs/log-INVALID.log");
+        assert_eq!(builder.path, expected_path);
+    }
+
+    #[test]
+    fn test_date_time_format_without_placeholder() {
+        let tempdir = tempfile::tempdir().unwrap();
+        let builder = FileAppender::builder()
+            .build(tempdir.path().join("foo").join("bar").join("bar.log"))
+            .unwrap();
+        let expected_path = tempdir.path().join("foo/bar/bar.log");
+        assert_eq!(builder.path, expected_path);
+    }
+
+    #[test]
+    fn test_date_time_format_with_multiple_placeholders() {
+        let current_time = Local::now().format("%Y-%m-%d").to_string();
+        let tempdir = tempfile::tempdir().unwrap();
+        let builder = FileAppender::builder()
+            .build(
+                tempdir
+                    .path()
+                    .join("foo")
+                    .join("bar")
+                    .join("logs-$TIME{%Y-%m-%d}/log-$TIME{%Y-%m-%d}.log"),
+            )
+            .unwrap();
+        let expected_path = tempdir.path().join(format!(
+            "foo/bar/logs-{}/log-{}.log",
+            current_time, current_time
+        ));
+        assert_eq!(builder.path, expected_path);
+    }
 }