From cada71e3f4a0bcd2886b278523dd07eeff2e3e8e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20du=20Garreau?= <bdgdlm@outlook.com>
Date: Mon, 19 Dec 2022 20:16:49 +0100
Subject: [PATCH] `io::Chain`: specialize some `Read` methods

---
 library/std/src/io/mod.rs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 23a13523fc27..23159459a70e 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -2389,6 +2389,39 @@ impl<T: Read, U: Read> Read for Chain<T, U> {
         }
         self.second.read_vectored(bufs)
     }
+
+    #[inline]
+    fn is_read_vectored(&self) -> bool {
+        self.first.is_read_vectored() || self.second.is_read_vectored()
+    }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
+        let mut read = 0;
+        if !self.done_first {
+            read += self.first.read_to_end(buf)?;
+            self.done_first = true;
+        }
+        read += self.second.read_to_end(buf)?;
+        Ok(read)
+    }
+
+    fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> Result<()> {
+        if buf.capacity() == 0 {
+            return Ok(());
+        }
+
+        if !self.done_first {
+            let old_len = buf.written();
+            self.first.read_buf(buf.reborrow())?;
+
+            if buf.written() != old_len {
+                return Ok(());
+            } else {
+                self.done_first = true;
+            }
+        }
+        self.second.read_buf(buf)
+    }
 }
 
 #[stable(feature = "chain_bufread", since = "1.9.0")]