feat: Syslog-adapted formating and auto-detection

Author: djugei

src/fmt/mod.rs

@@ -63,7 +63,6 @@ use std::io::prelude::Write;
 use std::rc::Rc;
 use std::{fmt, io};
 
-#[cfg(feature = "color")]
 use log::Level;
 use log::Record;
 
@@ -243,6 +242,28 @@ impl<T: Display> Display for StyledValue<T> {
 #[cfg(not(feature = "color"))]
 type StyledValue<T> = T;
 
+pub struct SyslogFormatter;
+
+impl SyslogFormatter {
+    pub(crate) fn build(&mut self) -> FormatFn {
+        Box::new(|buf: &mut Formatter, record: &Record<'_>| {
+            writeln!(
+                buf,
+                "<{}>{}: {}",
+                match record.level() {
+                    Level::Error => 3,
+                    Level::Warn => 4,
+                    Level::Info => 6,
+                    Level::Debug => 7,
+                    Level::Trace => 7,
+                },
+                record.target(),
+                record.args()
+            )
+        })
+    }
+}
+
 /// A [custom format][crate::Builder::format] with settings for which fields to show
 pub struct ConfigurableFormat {
     // This format needs to work with any combination of crate features.
@@ -258,6 +279,13 @@ pub struct ConfigurableFormat {
     pub(crate) kv_format: Option<Box<KvFormatFn>>,
 }
 
+impl ConfigurableFormat {
+    /// Convert the format into a callable function.
+    pub(crate) fn build(&mut self) -> FormatFn {
+        Box::new(std::mem::take(self))
+    }
+}
+
 impl ConfigurableFormat {
     /// Format the [`Record`] as configured for outputting
     pub fn format(&self, formatter: &mut Formatter, record: &Record<'_>) -> io::Result<()> {

src/logger.rs

@@ -40,6 +40,7 @@ pub struct Builder {
     writer: writer::Builder,
     format: fmt::ConfigurableFormat,
     built: bool,
+    is_syslog: bool,
 }
 
 impl Builder {
@@ -160,6 +161,10 @@ impl Builder {
             self.parse_write_style(&s);
         }
 
+        if env.is_daemon() {
+            self.is_syslog = true;
+        }
+
         self
     }
 
@@ -291,6 +296,13 @@ impl Builder {
         self
     }
 
+    /// If set to true, format log messages in a Syslog-adapted format.
+    /// Overrides the auto-detected value.
+    pub fn format_syslog(&mut self, syslog: bool) -> &mut Self {
+        self.is_syslog = syslog;
+        self
+    }
+
     /// Set the format for structured key/value pairs in the log record
     ///
     /// With the default format, this function is called for each record and should format
@@ -480,7 +492,11 @@ impl Builder {
         Logger {
             writer: self.writer.build(),
             filter: self.filter.build(),
-            format: Box::new(std::mem::take(&mut self.format)),
+            format: if self.is_syslog {
+                fmt::SyslogFormatter.build()
+            } else {
+                self.format.build()
+            },
         }
     }
 
@@ -822,6 +838,11 @@ impl<'a> Env<'a> {
     fn get_write_style(&self) -> Option<String> {
         self.write_style.get()
     }
+
+    fn is_daemon(&self) -> bool {
+        //TODO: support more logging systems
+        Var::new("JOURNAL_STREAM").get().is_some()
+    }
 }
 
 impl<'a, T> From<T> for Env<'a>