Add trigger onstartup

Cargo.toml

@@ -26,6 +26,7 @@ delete_roller = []
 fixed_window_roller = []
 size_trigger = []
 time_trigger = ["rand"]
+onstartup_trigger = []
 json_encoder = ["serde", "serde_json", "chrono", "log-mdc", "log/serde", "thread-id"]
 pattern_encoder = ["chrono", "log-mdc", "thread-id"]
 ansi_writer = []
@@ -43,6 +44,7 @@ all_components = [
     "fixed_window_roller",
     "size_trigger",
     "time_trigger",
+    "onstartup_trigger",
     "json_encoder",
     "pattern_encoder",
     "threshold_filter"

docs/Configuration.md

@@ -172,7 +172,7 @@ The new component is the _policy_ field. A policy must have the _kind_ field lik
 other components, the default (and only supported) policy is `kind: compound`.
 
 The _trigger_ field is used to dictate when the log file should be rolled. It
-supports two types: `size`, and `time`.
+supports three types: `size`, `time` and `onstartup`.
 
 For `size`, it require a _limit_ field. The _limit_ field is a string which defines the maximum file size
 prior to a rolling of the file. The limit field requires one of the following
@@ -233,6 +233,16 @@ trigger:
     max_random_delay: 0
 ```
 
+For `onstartup`, it has an optional field, _min_size_. It indicates the minimum size the file must have to roll over. A size of zero will cause a roll over no matter what the file size is. The default value is 1, which will prevent rolling over an empty file.
+
+i.e.
+
+```yml
+trigger:
+    kind: onstartup
+    min_size: 1
+```
+
 The _roller_ field supports two types: delete, and fixed_window. The delete
 roller does not take any other configuration fields. The fixed_window roller
 supports three fields: pattern, base, and count. The most current log file will

src/append/rolling_file/policy/compound/trigger/mod.rs

@@ -12,6 +12,9 @@ pub mod size;
 #[cfg(feature = "time_trigger")]
 pub mod time;
 
+#[cfg(feature = "onstartup_trigger")]
+pub mod onstartup;
+
 /// A trait which identifies if the active log file should be rolled over.
 pub trait Trigger: fmt::Debug + Send + Sync + 'static {
     /// Determines if the active log file should be rolled over.

src/append/rolling_file/policy/compound/trigger/onstartup.rs

@@ -0,0 +1,119 @@
+//! The OnStartUp trigger.
+//!
+//! Requires the `onstartup_trigger` feature.
+
+use std::sync::Once;
+
+use crate::append::rolling_file::{policy::compound::trigger::Trigger, LogFile};
+
+#[cfg(feature = "config_parsing")]
+use crate::config::{Deserialize, Deserializers};
+
+/// Configuration for the onstartup trigger.
+#[cfg(feature = "config_parsing")]
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug, Default, serde::Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct OnStartUpTriggerConfig {
+    #[serde(default = "default_min_size")]
+    min_size: u64,
+}
+
+#[cfg(feature = "config_parsing")]
+fn default_min_size() -> u64 {
+    1
+}
+
+/// A trigger which rolls the log on startup.
+#[derive(Debug)]
+pub struct OnStartUpTrigger {
+    min_size: u64,
+    initial: Once,
+}
+
+impl OnStartUpTrigger {
+    /// Returns a new trigger which rolls the log on startup.
+    pub fn new(min_size: u64) -> OnStartUpTrigger {
+        OnStartUpTrigger {
+            min_size,
+            initial: Once::new(),
+        }
+    }
+}
+
+impl Trigger for OnStartUpTrigger {
+    fn trigger(&self, file: &LogFile) -> anyhow::Result<bool> {
+        let mut result = false;
+        self.initial.call_once(|| {
+            if file.len_estimate() >= self.min_size {
+                result = true;
+            }
+        });
+        Ok(result)
+    }
+
+    fn is_pre_process(&self) -> bool {
+        true
+    }
+}
+
+/// A deserializer for the `OnStartUpTrigger`.
+///
+/// # Configuration
+///
+/// ```yaml
+/// kind: onstartup
+///
+/// ```
+#[cfg(feature = "config_parsing")]
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug, Default)]
+pub struct OnStartUpTriggerDeserializer;
+
+#[cfg(feature = "config_parsing")]
+impl Deserialize for OnStartUpTriggerDeserializer {
+    type Trait = dyn Trigger;
+
+    type Config = OnStartUpTriggerConfig;
+
+    fn deserialize(
+        &self,
+        config: OnStartUpTriggerConfig,
+        _: &Deserializers,
+    ) -> anyhow::Result<Box<dyn Trigger>> {
+        Ok(Box::new(OnStartUpTrigger::new(config.min_size)))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn pre_process() {
+        let trigger = OnStartUpTrigger::new(0);
+        assert!(trigger.is_pre_process());
+    }
+
+    fn trigger_with_file_size(file_size: u64) -> (bool, bool) {
+        let file = tempfile::tempdir().unwrap();
+        let logfile = LogFile {
+            writer: &mut None,
+            path: file.path(),
+            len: file_size,
+        };
+
+        let trigger = OnStartUpTrigger::new(1); // default
+        let result1 = trigger.trigger(&logfile).unwrap();
+        let result2 = trigger.trigger(&logfile).unwrap();
+        (result1, result2)
+    }
+
+    #[test]
+    fn trigger() {
+        // When the file size < min_size, the trigger should return false.
+        assert_eq!(trigger_with_file_size(0), (false, false));
+        // When the file size == min_size, the trigger should return true for the first time.
+        assert_eq!(trigger_with_file_size(1), (true, false));
+        // When the file size >= min_size, the trigger should return true for the first time.
+        assert_eq!(trigger_with_file_size(2), (true, false));
+    }
+}

src/config/raw.rs

@@ -219,6 +219,12 @@ impl Default for Deserializers {
             append::rolling_file::policy::compound::trigger::time::TimeTriggerDeserializer,
         );
 
+        #[cfg(feature = "onstartup_trigger")]
+        d.insert(
+            "onstartup",
+            append::rolling_file::policy::compound::trigger::onstartup::OnStartUpTriggerDeserializer,
+        );
+
         #[cfg(feature = "json_encoder")]
         d.insert("json", encode::json::JsonEncoderDeserializer);
 
@@ -265,6 +271,8 @@ impl Deserializers {
     ///         * Requires the `size_trigger` feature.
     ///     * "time" -> `TimeTriggerDeserializer`
     ///         * Requires the `time_trigger` feature.
+    ///     * "onstartup" -> `OnStartUpTriggerDeserializer`
+    ///         * Requires the `onstartup_trigger` feature.
     pub fn new() -> Deserializers {
         Deserializers::default()
     }

src/lib.rs

@@ -22,6 +22,7 @@
 //!       - Triggers
 //!         - [size](append/rolling_file/policy/compound/trigger/size/struct.SizeTriggerDeserializer.html#configuration): requires the `size_trigger` feature
 //!         - [time](append/rolling_file/policy/compound/trigger/tine/struct.TimeTriggerDeserializer.html#configuration): requires the `time_trigger` feature
+//!         - [onstartup](append/rolling_file/policy/compound/trigger/tine/struct.OnStartUpTriggerDeserializer.html#configuration): requires the `onstartup_trigger` feature
 //!
 //! ## Encoders
 //!