From 84f307643811f5eb6fb85facc603a16eb7c3eaa0 Mon Sep 17 00:00:00 2001
From: Sean McArthur <sean@seanmonstar.com>
Date: Tue, 30 Jan 2018 14:58:51 -0800
Subject: [PATCH] perf(client): don't make a copy of Headers each Request

---
 src/client/mod.rs               | 14 ++++++++------
 src/header/internals/vec_map.rs |  5 +++++
 src/header/mod.rs               |  8 ++++++++
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/client/mod.rs b/src/client/mod.rs
index dec8a91d..509dd564 100644
--- a/src/client/mod.rs
+++ b/src/client/mod.rs
@@ -14,7 +14,7 @@ use http;
 use tokio::reactor::Handle;
 pub use tokio_service::Service;
 
-use header::{Headers, Host};
+use header::{Host};
 use proto;
 use proto::request;
 use method::Method;
@@ -180,12 +180,14 @@ where C: Connect,
                 ))));
             }
         };
-        let host = Host::new(domain.host().expect("authority implies host").to_owned(), domain.port());
         let (mut head, body) = request::split(req);
-        let mut headers = Headers::new();
-        headers.set(host);
-        headers.extend(head.headers.iter());
-        head.headers = headers;
+        if !head.headers.has::<Host>() {
+            let host = Host::new(
+                domain.host().expect("authority implies host").to_owned(),
+                domain.port(),
+            );
+            head.headers.set_pos(0, host);
+        }
 
         use futures::Sink;
         use futures::sync::{mpsc, oneshot};
diff --git a/src/header/internals/vec_map.rs b/src/header/internals/vec_map.rs
index a1e70d54..8ddc6a5a 100644
--- a/src/header/internals/vec_map.rs
+++ b/src/header/internals/vec_map.rs
@@ -23,6 +23,11 @@ impl<K: PartialEq, V> VecMap<K, V> {
         self.vec.push((key, value));
     }
 
+    pub fn insert_pos(&mut self, key: K, value: V, pos: usize) {
+        debug_assert!(!self.contains_key(&key));
+        self.vec.insert(pos, (key, value))
+    }
+
     #[inline]
     pub fn append(&mut self, key: K, value: V) {
         self.vec.push((key, value));
diff --git a/src/header/mod.rs b/src/header/mod.rs
index 0dc3a30b..866d2521 100644
--- a/src/header/mod.rs
+++ b/src/header/mod.rs
@@ -392,6 +392,14 @@ impl Headers {
                          Item::new_typed(value));
     }
 
+    pub(crate) fn set_pos<H: Header>(&mut self, pos: usize, value: H) {
+        self.data.insert_pos(
+            HeaderName(Ascii::new(Cow::Borrowed(header_name::<H>()))),
+            Item::new_typed(value),
+            pos,
+        );
+    }
+
     /// Get a reference to the header field's value, if it exists.
     pub fn get<H: Header>(&self) -> Option<&H> {
         self.data.get(&HeaderName(Ascii::new(Cow::Borrowed(header_name::<H>()))))