Significantly improve performance by using a buffered writer

Before

```
Benchmark 1: seq 10000000 | bat
  Time (mean ± σ):      6.235 s ±  0.052 s    [User: 3.664 s, System: 2.714 s]
  Range (min … max):    6.172 s …  6.355 s    10 runs
```

After

```
Benchmark 1: seq 10000000 | ./target/release/bat
  Time (mean ± σ):     215.9 ms ±   5.1 ms    [User: 275.4 ms, System: 38.8 ms]
  Range (min … max):   210.3 ms … 224.9 ms    10 runs
```

Using `less` for comparison

```
Benchmark 1: seq 10000000 | less
  Time (mean ± σ):     637.3 ms ±  43.3 ms    [User: 642.1 ms, System: 95.6 ms]
  Range (min … max):   584.5 ms … 700.1 ms    10 runs
```

And raw

```
Benchmark 1: seq 10000000
  Time (mean ± σ):      63.1 ms ±   1.3 ms    [User: 57.1 ms, System: 5.9 ms]
  Range (min … max):    62.1 ms …  66.0 ms    10 runs
```

Signed-off-by: Mohammad AlSaleh <CE.Mohammad.AlSaleh@gmail.com>

CHANGELOG.md

@@ -44,6 +44,7 @@
 - Use bat's ANSI iterator during tab expansion, see #2998 (@eth-p)
 - Support 'statically linked binary' for aarch64 in 'Release' page, see #2992 (@tzq0301)
 - Update options in shell completions and the man page of `bat`, see #2995 (@akinomyoga)
+- Significantly improve performance by using a buffered writer, see #3101 (@MoSal)
 
 ## Syntaxes
 

src/controller.rs

@@ -1,4 +1,4 @@
-use std::io::{self, BufRead, Write};
+use std::io::{self, BufRead, BufWriter, Write};
 
 use crate::assets::HighlightingAssets;
 use crate::config::{Config, VisibleLines};
@@ -88,9 +88,12 @@ impl<'b> Controller<'b> {
             clircle::Identifier::stdout()
         };
 
+        const BUF_W_SZ: usize = 1 << 14;
         let mut writer = match output_buffer {
             Some(buf) => OutputHandle::FmtWrite(buf),
-            None => OutputHandle::IoWrite(output_type.handle()?),
+            None => {
+                OutputHandle::IoWrite(BufWriter::with_capacity(BUF_W_SZ, output_type.handle()?))
+            }
         };
         let mut no_errors: bool = true;
         let stderr = io::stderr();
@@ -124,10 +127,10 @@ impl<'b> Controller<'b> {
         Ok(no_errors)
     }
 
-    fn print_input<R: BufRead>(
+    fn print_input<R: BufRead, W: io::Write>(
         &self,
         input: Input,
-        writer: &mut OutputHandle,
+        writer: &mut OutputHandle<W>,
         stdin: R,
         stdout_identifier: Option<&Identifier>,
         is_first: bool,
@@ -174,7 +177,7 @@ impl<'b> Controller<'b> {
             None
         };
 
-        let mut printer: Box<dyn Printer> = if self.config.loop_through {
+        let mut printer: Box<dyn Printer<_>> = if self.config.loop_through {
             Box::new(SimplePrinter::new(self.config))
         } else {
             Box::new(InteractivePrinter::new(
@@ -196,10 +199,10 @@ impl<'b> Controller<'b> {
         )
     }
 
-    fn print_file(
+    fn print_file<W: io::Write>(
         &self,
-        printer: &mut dyn Printer,
+        printer: &mut dyn Printer<W>,
-        writer: &mut OutputHandle,
+        writer: &mut OutputHandle<W>,
         input: &mut OpenedInput,
         add_header_padding: bool,
         #[cfg(feature = "git")] line_changes: &Option<LineChanges>,
@@ -234,10 +237,10 @@ impl<'b> Controller<'b> {
         Ok(())
     }
 
-    fn print_file_ranges(
+    fn print_file_ranges<W: io::Write>(
         &self,
-        printer: &mut dyn Printer,
+        printer: &mut dyn Printer<W>,
-        writer: &mut OutputHandle,
+        writer: &mut OutputHandle<W>,
         reader: &mut InputReader,
         line_ranges: &LineRanges,
     ) -> Result<()> {
@@ -279,6 +282,7 @@ impl<'b> Controller<'b> {
             line_number += 1;
             line_buffer.clear();
         }
+        writer.flush()?;
         Ok(())
     }
 }

src/printer.rs

@@ -1,5 +1,5 @@
 use std::fmt;
-use std::io;
+use std::io::{self, BufWriter, Write};
 use std::vec::Vec;
 
 use nu_ansi_term::Color::{Fixed, Green, Red, Yellow};
@@ -67,35 +67,42 @@ const EMPTY_SYNTECT_STYLE: syntect::highlighting::Style = syntect::highlighting:
     font_style: FontStyle::empty(),
 };
 
-pub enum OutputHandle<'a> {
+pub enum OutputHandle<'a, W: io::Write> {
-    IoWrite(&'a mut dyn io::Write),
+    IoWrite(BufWriter<W>),
     FmtWrite(&'a mut dyn fmt::Write),
 }
 
-impl<'a> OutputHandle<'a> {
+impl<'a, W: io::Write> OutputHandle<'a, W> {
     fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> Result<()> {
         match self {
             Self::IoWrite(handle) => handle.write_fmt(args).map_err(Into::into),
             Self::FmtWrite(handle) => handle.write_fmt(args).map_err(Into::into),
         }
     }
+
+    pub(crate) fn flush(&mut self) -> Result<()> {
+        match self {
+            Self::IoWrite(handle) => handle.flush().map_err(Into::into),
+            Self::FmtWrite(_handle) => Ok(()),
+        }
+    }
 }
 
-pub(crate) trait Printer {
+pub(crate) trait Printer<W: io::Write> {
     fn print_header(
         &mut self,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         input: &OpenedInput,
         add_header_padding: bool,
     ) -> Result<()>;
-    fn print_footer(&mut self, handle: &mut OutputHandle, input: &OpenedInput) -> Result<()>;
+    fn print_footer(&mut self, handle: &mut OutputHandle<W>, input: &OpenedInput) -> Result<()>;
 
-    fn print_snip(&mut self, handle: &mut OutputHandle) -> Result<()>;
+    fn print_snip(&mut self, handle: &mut OutputHandle<W>) -> Result<()>;
 
     fn print_line(
         &mut self,
         out_of_range: bool,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         line_number: usize,
         line_buffer: &[u8],
     ) -> Result<()>;
@@ -115,28 +122,28 @@ impl<'a> SimplePrinter<'a> {
     }
 }
 
-impl<'a> Printer for SimplePrinter<'a> {
+impl<'a, W: io::Write> Printer<W> for SimplePrinter<'a> {
     fn print_header(
         &mut self,
-        _handle: &mut OutputHandle,
+        _handle: &mut OutputHandle<W>,
         _input: &OpenedInput,
         _add_header_padding: bool,
     ) -> Result<()> {
         Ok(())
     }
 
-    fn print_footer(&mut self, _handle: &mut OutputHandle, _input: &OpenedInput) -> Result<()> {
+    fn print_footer(&mut self, _handle: &mut OutputHandle<W>, _input: &OpenedInput) -> Result<()> {
         Ok(())
     }
 
-    fn print_snip(&mut self, _handle: &mut OutputHandle) -> Result<()> {
+    fn print_snip(&mut self, _handle: &mut OutputHandle<W>) -> Result<()> {
         Ok(())
     }
 
     fn print_line(
         &mut self,
         out_of_range: bool,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         _line_number: usize,
         line_buffer: &[u8],
     ) -> Result<()> {
@@ -321,9 +328,9 @@ impl<'a> InteractivePrinter<'a> {
         })
     }
 
-    fn print_horizontal_line_term(
+    fn print_horizontal_line_term<W: io::Write>(
         &mut self,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         style: Style,
     ) -> Result<()> {
         writeln!(
@@ -334,7 +341,11 @@ impl<'a> InteractivePrinter<'a> {
         Ok(())
     }
 
-    fn print_horizontal_line(&mut self, handle: &mut OutputHandle, grid_char: char) -> Result<()> {
+    fn print_horizontal_line<W: io::Write>(
+        &mut self,
+        handle: &mut OutputHandle<W>,
+        grid_char: char,
+    ) -> Result<()> {
         if self.panel_width == 0 {
             self.print_horizontal_line_term(handle, self.colors.grid)?;
         } else {
@@ -372,7 +383,10 @@ impl<'a> InteractivePrinter<'a> {
         }
     }
 
-    fn print_header_component_indent(&mut self, handle: &mut OutputHandle) -> Result<()> {
+    fn print_header_component_indent<W: io::Write>(
+        &mut self,
+        handle: &mut OutputHandle<W>,
+    ) -> Result<()> {
         if self.config.style_components.grid() {
             write!(
                 handle,
@@ -387,18 +401,18 @@ impl<'a> InteractivePrinter<'a> {
         }
     }
 
-    fn print_header_component_with_indent(
+    fn print_header_component_with_indent<W: io::Write>(
         &mut self,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         content: &str,
     ) -> Result<()> {
         self.print_header_component_indent(handle)?;
         writeln!(handle, "{content}")
     }
 
-    fn print_header_multiline_component(
+    fn print_header_multiline_component<W: io::Write>(
         &mut self,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         content: &str,
     ) -> Result<()> {
         let mut content = content;
@@ -446,10 +460,10 @@ impl<'a> InteractivePrinter<'a> {
     }
 }
 
-impl<'a> Printer for InteractivePrinter<'a> {
+impl<'a, W: io::Write> Printer<W> for InteractivePrinter<'a> {
     fn print_header(
         &mut self,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         input: &OpenedInput,
         add_header_padding: bool,
     ) -> Result<()> {
@@ -549,7 +563,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
         Ok(())
     }
 
-    fn print_footer(&mut self, handle: &mut OutputHandle, _input: &OpenedInput) -> Result<()> {
+    fn print_footer(&mut self, handle: &mut OutputHandle<W>, _input: &OpenedInput) -> Result<()> {
         if self.config.style_components.grid()
             && (self.content_type.map_or(false, |c| c.is_text()) || self.config.show_nonprintable)
         {
@@ -559,7 +573,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
         }
     }
 
-    fn print_snip(&mut self, handle: &mut OutputHandle) -> Result<()> {
+    fn print_snip(&mut self, handle: &mut OutputHandle<W>) -> Result<()> {
         let panel = self.create_fake_panel(" ...");
         let panel_count = panel.chars().count();
 
@@ -586,7 +600,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
     fn print_line(
         &mut self,
         out_of_range: bool,
-        handle: &mut OutputHandle,
+        handle: &mut OutputHandle<W>,
         line_number: usize,
         line_buffer: &[u8],
     ) -> Result<()> {