From baa5053572ed9e88ca1058ec2b5a3f08046c5a40 Mon Sep 17 00:00:00 2001
From: Paolo Barbolini <paolo@paolo565.org>
Date: Thu, 25 Apr 2024 09:08:16 +0200
Subject: [PATCH] Reuse capacity when possible in <BytesMut as Buf>::advance
 impl (#698)

---
 src/bytes_mut.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/bytes_mut.rs b/src/bytes_mut.rs
index 0ea0272c5..35e19005a 100644
--- a/src/bytes_mut.rs
+++ b/src/bytes_mut.rs
@@ -1066,6 +1066,14 @@ impl Buf for BytesMut {
 
     #[inline]
     fn advance(&mut self, cnt: usize) {
+        // Advancing by the length is the same as resetting the length to 0,
+        // except this way we get to reuse the full capacity.
+        if cnt == self.remaining() {
+            // SAFETY: Zero is not greater than the capacity.
+            unsafe { self.set_len(0) };
+            return;
+        }
+
         assert!(
             cnt <= self.remaining(),
             "cannot advance past `remaining`: {:?} <= {:?}",