properly allocate read buffer

actix-http/src/h1/mod.rs

@@ -1,5 +1,5 @@
 //! HTTP/1 implementation
-use bytes::Bytes;
+use bytes::{Bytes, BytesMut};
 
 mod client;
 mod codec;
@@ -38,6 +38,16 @@ pub enum MessageType {
     Stream,
 }
 
+const LW: usize = 2 * 1024;
+const HW: usize = 32 * 1024;
+
+pub(crate) fn reserve_readbuf(src: &mut BytesMut) {
+    let cap = src.capacity();
+    if cap < LW {
+        src.reserve(HW - cap);
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;