From 60cbb776f22e4ef2268c026e88a24d6ed75b3776 Mon Sep 17 00:00:00 2001
From: discord9 <55937128+discord9@users.noreply.github.com>
Date: Fri, 14 Nov 2025 17:52:50 +0800
Subject: [PATCH] fix: `BytesMut` only reuse if src has remaining (#803)

Signed-off-by: discord9 <discord9@163.com>
---
 src/bytes_mut.rs      | 7 +++++--
 tests/test_buf_mut.rs | 9 +++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/bytes_mut.rs b/src/bytes_mut.rs
index 333a0ae..565e91d 100644
--- a/src/bytes_mut.rs
+++ b/src/bytes_mut.rs
@@ -1202,8 +1202,11 @@ unsafe impl BufMut for BytesMut {
     where
         Self: Sized,
     {
-        // When capacity is zero, try reusing allocation of `src`.
-        if self.capacity() == 0 {
+        if !src.has_remaining() {
+            // prevent calling `copy_to_bytes`->`put`->`copy_to_bytes` infintely when src is empty
+            return;
+        } else if self.capacity() == 0 {
+            // When capacity is zero, try reusing allocation of `src`.
             let src_copy = src.copy_to_bytes(src.remaining());
             drop(src);
             match src_copy.try_into_mut() {
diff --git a/tests/test_buf_mut.rs b/tests/test_buf_mut.rs
index 9eb0bff..f1bd3b0 100644
--- a/tests/test_buf_mut.rs
+++ b/tests/test_buf_mut.rs
@@ -273,3 +273,12 @@ fn copy_from_slice_panics_if_different_length_2() {
     let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) };
     slice.copy_from_slice(b"abcd");
 }
+
+/// Test if with zero capacity BytesMut does not infinitely recurse in put from Buf
+#[test]
+fn test_bytes_mut_reuse() {
+    let mut buf = BytesMut::new();
+    buf.put(&[] as &[u8]);
+    let mut buf = BytesMut::new();
+    buf.put(&[1u8, 2, 3] as &[u8]);
+}