Flush the IO writer after each log message

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased]
+### Added
+
+* Option `flush` to enable flushing of the `io::Write` after each record.
+
 ## 2.2.0 - 2017-12-10
 ### Added
 

lib.rs

@@ -168,6 +168,7 @@ impl<S> slog::Serializer for SerdeSerializer<S>
 /// to a given `io`
 pub struct Json<W: io::Write> {
     newlines: bool,
+    flush: bool,
     values: Vec<OwnedKVList>,
     io: RefCell<W>,
     pretty: bool,
@@ -238,6 +239,9 @@ impl<W> slog::Drain for Json<W>
         if self.newlines {
             try!(io.write_all("\n".as_bytes()));
         }
+        if self.flush {
+            io.flush()?;
+        }
         Ok(())
     }
 }
@@ -250,6 +254,7 @@ impl<W> slog::Drain for Json<W>
 /// Create with `Json::new`.
 pub struct JsonBuilder<W: io::Write> {
     newlines: bool,
+    flush: bool,
     values: Vec<OwnedKVList>,
     io: W,
     pretty: bool,
@@ -261,6 +266,7 @@ impl<W> JsonBuilder<W>
     fn new(io: W) -> Self {
         JsonBuilder {
             newlines: true,
+            flush: false,
             values: vec![],
             io: io,
             pretty: false,
@@ -274,6 +280,7 @@ impl<W> JsonBuilder<W>
         Json {
             values: self.values,
             newlines: self.newlines,
+            flush: self.flush,
             io: RefCell::new(self.io),
             pretty: self.pretty,
         }
@@ -285,6 +292,12 @@ impl<W> JsonBuilder<W>
         self
     }
 
+    /// Enable flushing of the `io::Write` after every log record
+    pub fn set_flush(mut self, enabled: bool) -> Self {
+        self.flush = enabled;
+        self
+    }
+
     /// Set whether or not pretty formatted logging should be used
     pub fn set_pretty(mut self, enabled: bool) -> Self {
         self.pretty = enabled;