feat(client): add http1_writev configuration option

Setting this to false will force HTTP/1 connections to always flatten
all buffers (headers and body) before writing to the transport. The
default is true.

src/client/mod.rs

@@ -42,6 +42,7 @@ pub mod compat;
 pub struct Client<C, B = proto::Body> {
     connector: C,
     executor: Exec,
+    h1_writev: bool,
     pool: Pool<HyperClient<B>>,
 }
 
@@ -96,6 +97,7 @@ impl<C, B> Client<C, B> {
         Client {
             connector: config.connector,
             executor: exec,
+            h1_writev: config.h1_writev,
             pool: Pool::new(config.keep_alive, config.keep_alive_timeout)
         }
     }
@@ -197,6 +199,7 @@ where C: Connect,
             let executor = self.executor.clone();
             let pool = self.pool.clone();
             let pool_key = Rc::new(domain.to_string());
+            let h1_writev = self.h1_writev;
             self.connector.connect(url)
                 .and_then(move |io| {
                     let (tx, rx) = dispatch::channel();
@@ -205,7 +208,10 @@ where C: Connect,
                         should_close: Cell::new(true),
                     };
                     let pooled = pool.pooled(pool_key, tx);
-                    let conn = proto::Conn::<_, _, proto::ClientTransaction, _>::new(io, pooled.clone());
+                    let mut conn = proto::Conn::<_, _, proto::ClientTransaction, _>::new(io, pooled.clone());
+                    if !h1_writev {
+                        conn.set_write_strategy_flatten();
+                    }
                     let dispatch = proto::dispatch::Dispatcher::new(proto::dispatch::Client::new(rx), conn);
                     executor.execute(dispatch.map_err(|e| debug!("client connection error: {}", e)))?;
                     Ok(pooled)
@@ -256,6 +262,7 @@ impl<C: Clone, B> Clone for Client<C, B> {
         Client {
             connector: self.connector.clone(),
             executor: self.executor.clone(),
+            h1_writev: self.h1_writev,
             pool: self.pool.clone(),
         }
     }
@@ -307,9 +314,9 @@ pub struct Config<C, B> {
     connector: C,
     keep_alive: bool,
     keep_alive_timeout: Option<Duration>,
+    h1_writev: bool,
     //TODO: make use of max_idle config
     max_idle: usize,
-    no_proto: bool,
 }
 
 /// Phantom type used to signal that `Config` should create a `HttpConnector`.
@@ -324,8 +331,8 @@ impl Default for Config<UseDefaultConnector, proto::Body> {
             connector: UseDefaultConnector(()),
             keep_alive: true,
             keep_alive_timeout: Some(Duration::from_secs(90)),
+            h1_writev: true,
             max_idle: 5,
-            no_proto: false,
         }
     }
 }
@@ -348,8 +355,8 @@ impl<C, B> Config<C, B> {
             connector: self.connector,
             keep_alive: self.keep_alive,
             keep_alive_timeout: self.keep_alive_timeout,
+            h1_writev: self.h1_writev,
             max_idle: self.max_idle,
-            no_proto: self.no_proto,
         }
     }
 
@@ -362,8 +369,8 @@ impl<C, B> Config<C, B> {
             connector: val,
             keep_alive: self.keep_alive,
             keep_alive_timeout: self.keep_alive_timeout,
+            h1_writev: self.h1_writev,
             max_idle: self.max_idle,
-            no_proto: self.no_proto,
         }
     }
 
@@ -398,6 +405,20 @@ impl<C, B> Config<C, B> {
     }
     */
 
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Default is true.
+    #[inline]
+    pub fn http1_writev(mut self, val: bool) -> Config<C, B> {
+        self.h1_writev = val;
+        self
+    }
+
     #[doc(hidden)]
     #[deprecated(since="0.11.11", note="no_proto is always enabled")]
     pub fn no_proto(self) -> Config<C, B> {
@@ -444,6 +465,7 @@ impl<C, B> fmt::Debug for Config<C, B> {
         f.debug_struct("Config")
             .field("keep_alive", &self.keep_alive)
             .field("keep_alive_timeout", &self.keep_alive_timeout)
+            .field("http1_writev", &self.h1_writev)
             .field("max_idle", &self.max_idle)
             .finish()
     }

src/proto/h1/conn.rs

@@ -62,6 +62,10 @@ where I: AsyncRead + AsyncWrite,
         self.io.set_max_buf_size(max);
     }
 
+    pub fn set_write_strategy_flatten(&mut self) {
+        self.io.set_write_strategy_flatten();
+    }
+
     #[cfg(feature = "tokio-proto")]
     fn poll_incoming(&mut self) -> Poll<Option<Frame<MessageHead<T::Incoming>, Chunk, ::Error>>, io::Error> {
         trace!("Conn::poll_incoming()");

src/proto/h1/io.rs

@@ -65,6 +65,13 @@ where
         self.write_buf.max_buf_size = max;
     }
 
+    pub fn set_write_strategy_flatten(&mut self) {
+        // this should always be called only at construction time,
+        // so this assert is here to catch myself
+        debug_assert!(self.write_buf.buf.bufs.is_empty());
+        self.write_buf.set_strategy(Strategy::Flatten);
+    }
+
     pub fn read_buf(&self) -> &[u8] {
         self.read_buf.as_ref()
     }