From 7e7a2f2058690e8286187c1bd7ac999dcfa506b6 Mon Sep 17 00:00:00 2001
From: Ryan Fowler <ryan.fowler19@gmail.com>
Date: Tue, 26 Jul 2022 10:45:58 -0400
Subject: [PATCH] Create BytesMut for Json with initial capacity (#1196)

* Create BytesMut for Json with initial capacity

* Add a comment explaining BytesMut initial capacity

* Update link to serde_json::to_vec function to docs.rs
---
 axum/src/json.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/axum/src/json.rs b/axum/src/json.rs
index d496f607..6f4b0988 100644
--- a/axum/src/json.rs
+++ b/axum/src/json.rs
@@ -186,7 +186,9 @@ where
     T: Serialize,
 {
     fn into_response(self) -> Response {
-        let mut buf = BytesMut::new().writer();
+        // Use a small initial capacity of 128 bytes like serde_json::to_vec
+        // https://docs.rs/serde_json/1.0.82/src/serde_json/ser.rs.html#2189
+        let mut buf = BytesMut::with_capacity(128).writer();
         match serde_json::to_writer(&mut buf, &self.0) {
             Ok(()) => (
                 [(