From cba6e102ec49d81086a780c12ef3a51f1c2bd340 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20du=20Garreau?= <bdgdlm@outlook.com>
Date: Mon, 19 Dec 2022 20:36:21 +0100
Subject: [PATCH] `io::Chain`: specialize some `BufRead` methods

---
 library/std/src/io/mod.rs | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 23159459a70..3617b956e80 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -2429,9 +2429,7 @@ impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
     fn fill_buf(&mut self) -> Result<&[u8]> {
         if !self.done_first {
             match self.first.fill_buf()? {
-                buf if buf.is_empty() => {
-                    self.done_first = true;
-                }
+                buf if buf.is_empty() => self.done_first = true,
                 buf => return Ok(buf),
             }
         }
@@ -2441,6 +2439,21 @@ fn fill_buf(&mut self) -> Result<&[u8]> {
     fn consume(&mut self, amt: usize) {
         if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
     }
+
+    fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
+        let mut read = 0;
+        if !self.done_first {
+            let n = self.first.read_until(byte, buf)?;
+            read += n;
+
+            match buf.last() {
+                Some(b) if *b == byte && n != 0 => return Ok(read),
+                _ => self.done_first = true,
+            }
+        }
+        read += self.second.read_until(byte, buf)?;
+        Ok(read)
+    }
 }
 
 impl<T, U> SizeHint for Chain<T, U> {