Make UTC the default timestamps option, and change the output format to include the timezone

This works around the issue of potentially silently changing the
timezone used in logfiles (and not leaving the user any way to notice
the change) by changing the timezone format used from one that is
timezone agnostic to one that includes the timezone.

Since it's alreday changing from one that perfectly matches Supervisord,
this uses the well known RFC 3339 format that implements ISO 8601 (and
happens to currently be the only format provided by the `time` crate
that I don't have to implement myself).

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "simple_logger"
-version = "1.16.0"
+version = "2.0.0"
 license = "MIT"
 authors = ["Sam Clements <[email protected]>"]
 description = "A logger that prints all messages with a readable output format"

README.md

@@ -2,12 +2,17 @@
 
 A logger that prints all messages with a readable output format.
 
-The output format is based on the format used by [Supervisord](http://supervisord.org/).
+The output format is based on the format used by [Supervisord](http://supervisord.org/), with timestamps in [RFC 3339](https://datatracker.ietf.org/doc/html/rfc3339) format.
 
 * [Source on GitHub](https://github.com/borntyping/rust-simple_logger)
 * [Packages on Crates.io](https://crates.io/crates/simple_logger)
 * [Documentation on Docs.rs](https://docs.rs/simple_logger)
 
+Breaking changes
+----------------
+
+- **Version 2.0.0 changes the default from displaying timestamps in the local timezone to displaying timestamps in UTC.** See issue [#52](https://github.com/borntyping/rust-simple_logger/issues/52) for more information.
+
 Usage
 -----
 
@@ -24,7 +29,7 @@ fn main() {
 This outputs:
 
 ```
-2015-02-24 01:05:20 WARN [logging_example] This is an example message.
+2022-01-19T17:27:07.013874956Z WARN [logging_example] This is an example message.
 ```
 
 You can run the above example with:

src/lib.rs

@@ -35,12 +35,7 @@ use colored::*;
 use log::{Level, LevelFilter, Log, Metadata, Record, SetLoggerError};
 use std::collections::HashMap;
 #[cfg(feature = "timestamps")]
-use time::{format_description::FormatItem, OffsetDateTime};
-
-#[cfg(feature = "timestamps")]
-const TIMESTAMP_FORMAT: &[FormatItem] = time::macros::format_description!(
-    "[year]-[month]-[day] [hour]:[minute]:[second],[subsecond digits:3]"
-);
+use time::{format_description::well_known::Rfc3339, OffsetDateTime, UtcOffset};
 
 #[cfg(feature = "timestamps")]
 #[derive(PartialEq)]
@@ -48,6 +43,7 @@ enum Timestamps {
     None,
     Local,
     Utc,
+    UtcOffset(UtcOffset),
 }
 
 /// Implements [`Log`] and a set of simple builder methods for configuration.
@@ -105,7 +101,7 @@ impl SimpleLogger {
             threads: false,
 
             #[cfg(feature = "timestamps")]
-            timestamps: Timestamps::Local,
+            timestamps: Timestamps::Utc,
 
             #[cfg(feature = "colored")]
             colors: true,
@@ -292,6 +288,16 @@ impl SimpleLogger {
         self
     }
 
+    /// Display timestamps using a static UTC offset.
+    ///
+    /// This method is only available if the `timestamps` feature is enabled.
+    #[must_use = "You must call init() to begin logging"]
+    #[cfg(feature = "timestamps")]
+    pub fn with_utc_offset(mut self, offset: UtcOffset) -> SimpleLogger {
+        self.timestamps = Timestamps::UtcOffset(offset);
+        self
+    }
+
     /// Control whether messages are colored or not.
     ///
     /// This method is only available if the `colored` feature is enabled.
@@ -408,13 +414,15 @@ impl Log for SimpleLogger {
                     Timestamps::None => "".to_string(),
                     Timestamps::Local => format!("{} ", OffsetDateTime::now_local().expect(concat!(
                             "Could not determine the UTC offset on this system. ",
+                            "Consider displaying UTC time instead. ",
                             "Possible causes are that the time crate does not implement \"local_offset_at\" ",
                             "on your system, or that you are running in a multi-threaded environment and ",
                             "the time crate is returning \"None\" from \"local_offset_at\" to avoid unsafe ",
                             "behaviour. See the time crate's documentation for more information. ",
                             "(https://time-rs.github.io/internal-api/time/index.html#feature-flags)"
-                        )).format(&TIMESTAMP_FORMAT).unwrap()),
-                    Timestamps::Utc => format!("{} ", OffsetDateTime::now_utc().format(&TIMESTAMP_FORMAT).unwrap()),
+                        )).format(&Rfc3339).unwrap()),
+                    Timestamps::Utc => format!("{} ", OffsetDateTime::now_utc().format(&Rfc3339).unwrap()),
+                    Timestamps::UtcOffset(offset) => format!("{} ", OffsetDateTime::now_utc().to_offset(offset).format(&Rfc3339).unwrap()),
                 }
 
                 #[cfg(not(feature = "timestamps"))]
@@ -478,6 +486,17 @@ pub fn init() -> Result<(), SetLoggerError> {
     SimpleLogger::new().init()
 }
 
+/// Initialise the logger with it's default configuration.
+///
+/// Log messages will not be filtered.
+/// The `RUST_LOG` environment variable is not used.
+///
+/// This function is only available if the `timestamps` feature is enabled.
+#[cfg(feature = "timestamps")]
+pub fn init_utc() -> Result<(), SetLoggerError> {
+    SimpleLogger::new().with_utc_timestamps().init()
+}
+
 /// Initialise the logger with the `RUST_LOG` environment variable.
 ///
 /// Log messages will be filtered based on the `RUST_LOG` environment variable.
@@ -546,7 +565,7 @@ mod test {
     #[cfg(feature = "timestamps")]
     fn test_timestamps_defaults() {
         let builder = SimpleLogger::new();
-        assert!(builder.timestamps == Timestamps::Local);
+        assert!(builder.timestamps == Timestamps::Utc);
     }
 
     #[test]