From 47ae565ed4f1b2a7cc754d4cf0af520b5e6841b9 Mon Sep 17 00:00:00 2001
From: Andreas Molzer <andreas.molzer@gmx.de>
Date: Sun, 26 Jan 2020 21:52:04 +0100
Subject: [PATCH] Add a method to query the capacity of a BufWriter

---
 src/libstd/io/buffered.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index 9e6849ba5bc..3d644b13f43 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -576,6 +576,25 @@ pub fn buffer(&self) -> &[u8] {
         &self.buf
     }
 
+    /// Returns the number of bytes the internal buffer can hold without flushing.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use std::io::BufWriter;
+    /// use std::net::TcpStream;
+    ///
+    /// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
+    ///
+    /// // Check the capacity of the inner buffer
+    /// let capacity = buf_writer.capacity();
+    /// // Calculate how many bytes can be written without flushing
+    /// let without_flush = capacity - buf_writer.buffer().len();
+    /// ```
+    pub fn capacity(&self) -> usize {
+        self.buf.capacity()
+    }
+
     /// Unwraps this `BufWriter<W>`, returning the underlying writer.
     ///
     /// The buffer is written out before returning the writer.