src/client/mod.rs

//! HTTP Client
//!
//! There are two levels of APIs provided for construct HTTP clients:
//!
//! - The higher-level [`Client`](Client) type.
//! - The lower-level [`conn`](client::conn) module.
//!
//! # Client
//!
//! The [`Client`](Client) is the main way to send HTTP requests to a server.
//! The default `Client` provides these things on top of the lower-level API:
//!
//! - A default **connector**, able to resolve hostnames and connect to
//!   destinations over plain-text TCP.
//! - A **pool** of existing connections, allowing better performance when
//!   making multiple requests to the same hostname.
//! - Automatic setting of the `Host` header, based on the request `Uri`.
//! - Automatic request **retries** when a pooled connection is closed by the
//!   server before any bytes have been written.
//!
//! Many of these features can configured, by making use of
//! [`Client::builder`](Client::builder).
//!
//! ## Example
//!
//! For a small example program simply fetching a URL, take a look at the
//! [full client example](https://github.com/hyperium/hyper/blob/master/examples/client.rs).
//!
//! ```
//! use hyper::{Client, Uri};
//!
//! # #[cfg(feature = "runtime")]
//! # async fn fetch_httpbin() -> hyper::Result<()> {
//! let client = Client::new();
//!
//! // Make a GET /ip to 'http://httpbin.org'
//! let res = client.get(Uri::from_static("http://httpbin.org/ip")).await?;
//!
//! // And then, if the request gets a response...
//! println!("status: {}", res.status());
//!
//! // Concatenate the body stream into a single buffer...
//! let mut body = res.into_body();
//! let mut bytes = Vec::new();
//! while let Some(next) = body.next().await {
//!     let chunk = next?;
//!     bytes.extend(chunk);
//! }
//!
//! // And then, if reading the full body succeeds...
//! // The body is just bytes, but let's print a string...
//! let s = std::str::from_utf8(&bytes)
//!     .expect("httpbin sends utf-8 JSON");
//!
//! println!("body: {}", s);
//! # Ok(())
//! # }
//! # fn main () {}
//! ```

use std::fmt;
use std::mem;
use std::sync::Arc;
use std::time::Duration;

use futures_channel::oneshot;
use futures_util::future::{self, FutureExt as _, Either};
use futures_util::try_future::TryFutureExt as _;
use http::{Method, Request, Response, Uri, Version};
use http::header::{HeaderValue, HOST};
use http::uri::Scheme;

use crate::body::{Body, Payload};
use crate::common::{lazy as hyper_lazy, Lazy, Future, Pin, Poll, task};
use self::connect::{Alpn, Connect, Connected, Destination};
use self::pool::{Key as PoolKey, Pool, Poolable, Pooled, Reservation};

#[cfg(feature = "runtime")] pub use self::connect::HttpConnector;

pub mod conn;
pub mod connect;
pub(crate) mod dispatch;
mod pool;
pub mod service;
#[cfg(test)]
mod tests;

/// A Client to make outgoing HTTP requests.
pub struct Client<C, B = Body> {
    config: Config,
    conn_builder: conn::Builder,
    connector: Arc<C>,
    pool: Pool<PoolClient<B>>,
}

#[derive(Clone, Copy, Debug)]
struct Config {
    retry_canceled_requests: bool,
    set_host: bool,
    ver: Ver,
}

/// A `Future` that will resolve to an HTTP Response.
///
/// This is returned by `Client::request` (and `Client::get`).
#[must_use = "futures do nothing unless polled"]
pub struct ResponseFuture {
    inner: Pin<Box<dyn Future<Output=crate::Result<Response<Body>>> + Send>>,
}

// ===== impl Client =====

#[cfg(feature = "runtime")]
impl Client<HttpConnector, Body> {
    /// Create a new Client with the default [config](Builder).
    ///
    /// # Note
    ///
    /// The default connector does **not** handle TLS. Speaking to `https`
    /// destinations will require [configuring a connector that implements
    /// TLS](https://hyper.rs/guides/client/configuration).
    #[inline]
    pub fn new() -> Client<HttpConnector, Body> {
        Builder::default().build_http()
    }
}

#[cfg(feature = "runtime")]
impl Default for Client<HttpConnector, Body> {
    fn default() -> Client<HttpConnector, Body> {
        Client::new()
    }
}

impl Client<(), Body> {
    /// Create a builder to configure a new `Client`.
    ///
    /// # Example
    ///
    /// ```
    /// # #[cfg(feature  = "runtime")]
    /// # fn run () {
    /// use hyper::Client;
    ///
    /// let client = Client::builder()
    ///     .keep_alive(true)
    ///     .http2_only(true)
    ///     .build_http();
    /// # let infer: Client<_, hyper::Body> = client;
    /// # drop(infer);
    /// # }
    /// # fn main() {}
    /// ```
    #[inline]
    pub fn builder() -> Builder {
        Builder::default()
    }
}

impl<C, B> Client<C, B>
where C: Connect + Sync + 'static,
      C::Transport: 'static,
      C::Future: 'static,
      B: Payload + Unpin + Send + 'static,
      B::Data: Send + Unpin,
{
    /// Send a `GET` request to the supplied `Uri`.
    ///
    /// # Note
    ///
    /// This requires that the `Payload` type have a `Default` implementation.
    /// It *should* return an "empty" version of itself, such that
    /// `Payload::is_end_stream` is `true`.
    ///
    /// # Example
    ///
    /// ```
    /// # #[cfg(feature  = "runtime")]
    /// # fn run () {
    /// use hyper::{Client, Uri};
    ///
    /// let client = Client::new();
    ///
    /// let future = client.get(Uri::from_static("http://httpbin.org/ip"));
    /// # }
    /// # fn main() {}
    /// ```
    pub fn get(&self, uri: Uri) -> ResponseFuture
    where
        B: Default,
    {
        let body = B::default();
        if !body.is_end_stream() {
            warn!("default Payload used for get() does not return true for is_end_stream");
        }

        let mut req = Request::new(body);
        *req.uri_mut() = uri;
        self.request(req)
    }

    /// Send a constructed `Request` using this `Client`.
    ///
    /// # Example
    ///
    /// ```
    /// # #[cfg(feature  = "runtime")]
    /// # fn run () {
    /// use hyper::{Body, Client, Request};
    ///
    /// let client = Client::new();
    ///
    /// let req = Request::builder()
    ///     .method("POST")
    ///     .uri("http://httpin.org/post")
    ///     .body(Body::from("Hallo!"))
    ///     .expect("request builder");
    ///
    /// let future = client.request(req);
    /// # }
    /// # fn main() {}
    /// ```
    pub fn request(&self, mut req: Request<B>) -> ResponseFuture {
        let is_http_connect = req.method() == &Method::CONNECT;
        match req.version() {
            Version::HTTP_11 => (),
            Version::HTTP_10 => if is_http_connect {
                warn!("CONNECT is not allowed for HTTP/1.0");
                return ResponseFuture::new(Box::new(future::err(crate::Error::new_user_unsupported_request_method())));
            },
            other_h2 @ Version::HTTP_2 => if self.config.ver != Ver::Http2 {
                return ResponseFuture::error_version(other_h2);
            },
            // completely unsupported HTTP version (like HTTP/0.9)!
            other => return ResponseFuture::error_version(other),
        };

        let domain = match extract_domain(req.uri_mut(), is_http_connect) {
            Ok(s) => s,
            Err(err) => {
                return ResponseFuture::new(Box::new(future::err(err)));
            }
        };

        let pool_key = Arc::new(domain.to_string());
        ResponseFuture::new(Box::new(self.retryably_send_request(req, pool_key)))
    }

    fn retryably_send_request(&self, req: Request<B>, pool_key: PoolKey) -> impl Future<Output=crate::Result<Response<Body>>> {
        let client = self.clone();
        let uri = req.uri().clone();

        let mut send_fut = client.send_request(req, pool_key.clone());
        future::poll_fn(move |cx| loop {
            match ready!(Pin::new(&mut send_fut).poll(cx)) {
                Ok(resp) => return Poll::Ready(Ok(resp)),
                Err(ClientError::Normal(err)) => return Poll::Ready(Err(err)),
                Err(ClientError::Canceled {
                    connection_reused,
                    mut req,
                    reason,
                }) => {
                    if !client.config.retry_canceled_requests || !connection_reused {
                        // if client disabled, don't retry
                        // a fresh connection means we definitely can't retry
                        return Poll::Ready(Err(reason));
                    }

                    trace!("unstarted request canceled, trying again (reason={:?})", reason);
                    *req.uri_mut() = uri.clone();
                    send_fut = client.send_request(req, pool_key.clone());
                }
            }
        })
    }

    fn send_request(&self, mut req: Request<B>, pool_key: PoolKey) -> impl Future<Output=Result<Response<Body>, ClientError<B>>> + Unpin {
        let conn = self.connection_for(req.uri().clone(), pool_key);

        let set_host = self.config.set_host;
        let executor = self.conn_builder.exec.clone();
        conn.and_then(move |mut pooled| {
            if pooled.is_http1() {
                if set_host {
                    let uri = req.uri().clone();
                    req
                        .headers_mut()
                        .entry(HOST)
                        .expect("HOST is always valid header name")
                        .or_insert_with(|| {
                            let hostname = uri.host().expect("authority implies host");
                            if let Some(port) = uri.port_part() {
                                let s = format!("{}:{}", hostname, port);
                                HeaderValue::from_str(&s)
                            } else {
                                HeaderValue::from_str(hostname)
                            }.expect("uri host is valid header value")
                        });
                }

                // CONNECT always sends authority-form, so check it first...
                if req.method() == &Method::CONNECT {
                    authority_form(req.uri_mut());
                } else if pooled.conn_info.is_proxied {
                    absolute_form(req.uri_mut());
                } else {
                    origin_form(req.uri_mut());
                };
            } else if req.method() == &Method::CONNECT {
                debug!("client does not support CONNECT requests over HTTP2");
                return Either::Left(future::err(ClientError::Normal(crate::Error::new_user_unsupported_request_method())));
            }

            let fut = pooled.send_request_retryable(req)
                .map_err(ClientError::map_with_reused(pooled.is_reused()));

            // If the Connector included 'extra' info, add to Response...
            let extra_info = pooled.conn_info.extra.clone();
            let fut = fut.map_ok(move |mut res| {
                if let Some(extra) = extra_info {
                    extra.set(&mut res);
                }
                res
            });

            // As of futures@0.1.21, there is a race condition in the mpsc
            // channel, such that sending when the receiver is closing can
            // result in the message being stuck inside the queue. It won't
            // ever notify until the Sender side is dropped.
            //
            // To counteract this, we must check if our senders 'want' channel
            // has been closed after having tried to send. If so, error out...
            if pooled.is_closed() {
                return Either::Right(Either::Left(fut));
            }

            Either::Right(Either::Right(fut
                .map_ok(move |mut res| {
                    // If pooled is HTTP/2, we can toss this reference immediately.
                    //
                    // when pooled is dropped, it will try to insert back into the
                    // pool. To delay that, spawn a future that completes once the
                    // sender is ready again.
                    //
                    // This *should* only be once the related `Connection` has polled
                    // for a new request to start.
                    //
                    // It won't be ready if there is a body to stream.
                    if pooled.is_http2() || !pooled.is_pool_enabled() || pooled.is_ready() {
                        drop(pooled);
                    } else if !res.body().is_end_stream() {
                        let (delayed_tx, delayed_rx) = oneshot::channel();
                        res.body_mut().delayed_eof(delayed_rx);
                        let on_idle = future::poll_fn(move |cx| {
                            pooled.poll_ready(cx)
                        })
                            .map(move |_| {
                                // At this point, `pooled` is dropped, and had a chance
                                // to insert into the pool (if conn was idle)
                                drop(delayed_tx);
                            });

                        if let Err(err) = executor.execute(on_idle) {
                            // This task isn't critical, so just log and ignore.
                            warn!("error spawning task to insert idle connection: {}", err);
                        }
                    } else {
                        // There's no body to delay, but the connection isn't
                        // ready yet. Only re-insert when it's ready
                        let on_idle = future::poll_fn(move |cx| {
                            pooled.poll_ready(cx)
                        })
                            .map(|_| ());

                        if let Err(err) = executor.execute(on_idle) {
                            // This task isn't critical, so just log and ignore.
                            warn!("error spawning task to insert idle connection: {}", err);
                        }
                    }
                    res
                })))
        })
    }

    fn connection_for(&self, uri: Uri, pool_key: PoolKey)
        -> impl Future<Output=Result<Pooled<PoolClient<B>>, ClientError<B>>>
    {
        // This actually races 2 different futures to try to get a ready
        // connection the fastest, and to reduce connection churn.
        //
        // - If the pool has an idle connection waiting, that's used
        //   immediately.
        // - Otherwise, the Connector is asked to start connecting to
        //   the destination Uri.
        // - Meanwhile, the pool Checkout is watching to see if any other
        //   request finishes and tries to insert an idle connection.
        // - If a new connection is started, but the Checkout wins after
        //   (an idle connection becamse available first), the started
        //   connection future is spawned into the runtime to complete,
        //   and then be inserted into the pool as an idle connection.
        let checkout = self.pool.checkout(pool_key.clone());
        let connect = self.connect_to(uri, pool_key);

        let executor = self.conn_builder.exec.clone();
        // The order of the `select` is depended on below...
        future::select(checkout, connect)
            .then(move |either| match either {
                // Checkout won, connect future may have been started or not.
                //
                // If it has, let it finish and insert back into the pool,
                // so as to not waste the socket...
                Either::Left((Ok(checked_out), connecting)) => {
                    // This depends on the `select` above having the correct
                    // order, such that if the checkout future were ready
                    // immediately, the connect future will never have been
                    // started.
                    //
                    // If it *wasn't* ready yet, then the connect future will
                    // have been started...
                    if connecting.started() {
                        let bg = connecting
                            .map_err(|err| {
                                trace!("background connect error: {}", err);
                            })
                            .map(|_pooled| {
                                // dropping here should just place it in
                                // the Pool for us...
                            });
                        // An execute error here isn't important, we're just trying
                        // to prevent a waste of a socket...
                        let _ = executor.execute(bg);
                    }
                    Either::Left(future::ok(checked_out))
                },
                // Connect won, checkout can just be dropped.
                Either::Right((Ok(connected), _checkout)) => {
                    Either::Left(future::ok(connected))
                },
                // Either checkout or connect could get canceled:
                //
                // 1. Connect is canceled if this is HTTP/2 and there is
                //    an outstanding HTTP/2 connecting task.
                // 2. Checkout is canceled if the pool cannot deliver an
                //    idle connection reliably.
                //
                // In both cases, we should just wait for the other future.
                Either::Left((Err(err), connecting)) => Either::Right(Either::Left({
                    if err.is_canceled() {
                        Either::Left(connecting.map_err(ClientError::Normal))
                    } else {
                        Either::Right(future::err(ClientError::Normal(err)))
                    }
                })),
                Either::Right((Err(err), checkout)) => Either::Right(Either::Right({
                    if err.is_canceled() {
                        Either::Left(checkout.map_err(ClientError::Normal))
                    } else {
                        Either::Right(future::err(ClientError::Normal(err)))
                    }
                })),
            })
    }

    fn connect_to(&self, uri: Uri, pool_key: PoolKey)
        -> impl Lazy<Output=crate::Result<Pooled<PoolClient<B>>>> + Unpin
    {
        let executor = self.conn_builder.exec.clone();
        let pool = self.pool.clone();
        let mut conn_builder = self.conn_builder.clone();
        let ver = self.config.ver;
        let is_ver_h2 = ver == Ver::Http2;
        let connector = self.connector.clone();
        let dst = Destination {
            uri,
        };
        hyper_lazy(move || {
            // Try to take a "connecting lock".
            //
            // If the pool_key is for HTTP/2, and there is already a
            // connection being estabalished, then this can't take a
            // second lock. The "connect_to" future is Canceled.
            let connecting = match pool.connecting(&pool_key, ver) {
                Some(lock) => lock,
                None => {
                    let canceled = crate::Error::new_canceled().with("HTTP/2 connection in progress");
                    return Either::Right(future::err(canceled));
                }
            };
            Either::Left(connector.connect(dst)
                .map_err(crate::Error::new_connect)
                .and_then(move |(io, connected)| {
                    // If ALPN is h2 and we aren't http2_only already,
                    // then we need to convert our pool checkout into
                    // a single HTTP2 one.
                    let connecting = if connected.alpn == Alpn::H2 && !is_ver_h2 {
                        match connecting.alpn_h2(&pool) {
                            Some(lock) => {
                                trace!("ALPN negotiated h2, updating pool");
                                lock
                            },
                            None => {
                                // Another connection has already upgraded,
                                // the pool checkout should finish up for us.
                                let canceled = crate::Error::new_canceled().with("ALPN upgraded to HTTP/2");
                                return Either::Right(future::err(canceled));
                            }
                        }
                    } else {
                        connecting
                    };
                    let is_h2 = is_ver_h2 || connected.alpn == Alpn::H2;
                    Either::Left(Box::pin(conn_builder
                        .http2_only(is_h2)
                        .handshake(io)
                        .and_then(move |(tx, conn)| {
                            trace!("handshake complete, spawning background dispatcher task");
                            let bg = executor.execute(conn.map_err(|e| {
                                debug!("client connection error: {}", e)
                            }).map(|_| ()));

                            // This task is critical, so an execute error
                            // should be returned.
                            if let Err(err) = bg {
                                warn!("error spawning critical client task: {}", err);
                                return Either::Left(future::err(err));
                            }

                            // Wait for 'conn' to ready up before we
                            // declare this tx as usable
                            Either::Right(tx.when_ready())
                        })
                        .map_ok(move |tx| {
                            pool.pooled(connecting, PoolClient {
                                conn_info: connected,
                                tx: if is_h2 {
                                    PoolTx::Http2(tx.into_http2())
                                } else {
                                    PoolTx::Http1(tx)
                                },
                            })
                        })))
                }))
        })
    }
}

impl<C, B> Clone for Client<C, B> {
    fn clone(&self) -> Client<C, B> {
        Client {
            config: self.config.clone(),
            conn_builder: self.conn_builder.clone(),
            connector: self.connector.clone(),
            pool: self.pool.clone(),
        }
    }
}

impl<C, B> fmt::Debug for Client<C, B> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Client")
            .finish()
    }
}

// ===== impl ResponseFuture =====

impl ResponseFuture {
    fn new(fut: Box<dyn Future<Output=crate::Result<Response<Body>>> + Send>) -> Self {
        Self {
            inner: fut.into(),
        }
    }

    fn error_version(ver: Version) -> Self {
        warn!("Request has unsupported version \"{:?}\"", ver);
        ResponseFuture::new(Box::new(future::err(crate::Error::new_user_unsupported_version())))
    }
}

impl fmt::Debug for ResponseFuture {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.pad("Future<Response>")
    }
}

impl Future for ResponseFuture {
    type Output = crate::Result<Response<Body>>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
        Pin::new(&mut self.inner).poll(cx)
    }
}

// ===== impl PoolClient =====

// FIXME: allow() required due to `impl Trait` leaking types to this lint
#[allow(missing_debug_implementations)]
struct PoolClient<B> {
    conn_info: Connected,
    tx: PoolTx<B>,
}

enum PoolTx<B> {
    Http1(conn::SendRequest<B>),
    Http2(conn::Http2SendRequest<B>),
}

impl<B> PoolClient<B> {
    fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
        match self.tx {
            PoolTx::Http1(ref mut tx) => tx.poll_ready(cx),
            PoolTx::Http2(_) => Poll::Ready(Ok(())),
        }
    }

    fn is_http1(&self) -> bool {
        !self.is_http2()
    }

    fn is_http2(&self) -> bool {
        match self.tx {
            PoolTx::Http1(_) => false,
            PoolTx::Http2(_) => true,
        }
    }

    fn is_ready(&self) -> bool {
        match self.tx {
            PoolTx::Http1(ref tx) => tx.is_ready(),
            PoolTx::Http2(ref tx) => tx.is_ready(),
        }
    }

    fn is_closed(&self) -> bool {
        match self.tx {
            PoolTx::Http1(ref tx) => tx.is_closed(),
            PoolTx::Http2(ref tx) => tx.is_closed(),
        }
    }
}

impl<B: Payload + 'static> PoolClient<B> {
    fn send_request_retryable(&mut self, req: Request<B>) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>>
    where
        B: Send,
    {
        match self.tx {
            PoolTx::Http1(ref mut tx) => Either::Left(tx.send_request_retryable(req)),
            PoolTx::Http2(ref mut tx) => Either::Right(tx.send_request_retryable(req)),
        }
    }
}

impl<B> Poolable for PoolClient<B>
where
    B: Send + 'static,
{
    fn is_open(&self) -> bool {
        match self.tx {
            PoolTx::Http1(ref tx) => tx.is_ready(),
            PoolTx::Http2(ref tx) => tx.is_ready(),
        }
    }

    fn reserve(self) -> Reservation<Self> {
        match self.tx {
            PoolTx::Http1(tx) => {
                Reservation::Unique(PoolClient {
                    conn_info: self.conn_info,
                    tx: PoolTx::Http1(tx),
                })
            },
            PoolTx::Http2(tx) => {
                let b = PoolClient {
                    conn_info: self.conn_info.clone(),
                    tx: PoolTx::Http2(tx.clone()),
                };
                let a = PoolClient {
                    conn_info: self.conn_info,
                    tx: PoolTx::Http2(tx),
                };
                Reservation::Shared(a, b)
            }
        }
    }

    fn can_share(&self) -> bool {
        self.is_http2()
    }
}

// ===== impl ClientError =====

// FIXME: allow() required due to `impl Trait` leaking types to this lint
#[allow(missing_debug_implementations)]
enum ClientError<B> {
    Normal(crate::Error),
    Canceled {
        connection_reused: bool,
        req: Request<B>,
        reason: crate::Error,
    }
}

impl<B> ClientError<B> {
    fn map_with_reused(conn_reused: bool)
        -> impl Fn((crate::Error, Option<Request<B>>)) -> Self
    {
        move |(err, orig_req)| {
            if let Some(req) = orig_req {
                ClientError::Canceled {
                    connection_reused: conn_reused,
                    reason: err,
                    req,
                }
            } else {
                ClientError::Normal(err)
            }
        }
    }
}

/// A marker to identify what version a pooled connection is.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
enum Ver {
    Auto,
    Http2,
}

fn origin_form(uri: &mut Uri) {
    let path = match uri.path_and_query() {
        Some(path) if path.as_str() != "/" => {
            let mut parts = ::http::uri::Parts::default();
            parts.path_and_query = Some(path.clone());
            Uri::from_parts(parts).expect("path is valid uri")
        },
        _none_or_just_slash => {
            debug_assert!(Uri::default() == "/");
            Uri::default()
        }
    };
    *uri = path
}

fn absolute_form(uri: &mut Uri) {
    debug_assert!(uri.scheme_part().is_some(), "absolute_form needs a scheme");
    debug_assert!(uri.authority_part().is_some(), "absolute_form needs an authority");
    // If the URI is to HTTPS, and the connector claimed to be a proxy,
    // then it *should* have tunneled, and so we don't want to send
    // absolute-form in that case.
    if uri.scheme_part() == Some(&Scheme::HTTPS) {
        origin_form(uri);
    }
}

fn authority_form(uri: &mut Uri) {
    if log_enabled!(::log::Level::Warn) {
        if let Some(path) = uri.path_and_query() {
            // `https://hyper.rs` would parse with `/` path, don't
            // annoy people about that...
            if path != "/" {
                warn!(
                    "HTTP/1.1 CONNECT request stripping path: {:?}",
                    path
                );
            }
        }
    }
    *uri = match uri.authority_part() {
        Some(auth) => {
            let mut parts = ::http::uri::Parts::default();
            parts.authority = Some(auth.clone());
            Uri::from_parts(parts).expect("authority is valid")
        },
        None => {
            unreachable!("authority_form with relative uri");
        }
    };
}

fn extract_domain(uri: &mut Uri, is_http_connect: bool) -> crate::Result<String> {
    let uri_clone = uri.clone();
    match (uri_clone.scheme_part(), uri_clone.authority_part()) {
        (Some(scheme), Some(auth)) => {
            Ok(format!("{}://{}", scheme, auth))
        }
        (None, Some(auth)) if is_http_connect => {
            let port = auth.port_part();
            let scheme = match port.as_ref().map(|p| p.as_str()) {
                Some("443") => {
                    set_scheme(uri, Scheme::HTTPS);
                    "https"
                }
                _ => {
                    set_scheme(uri, Scheme::HTTP);
                    "http"
                },
            };
            Ok(format!("{}://{}", scheme, auth))
        },
        _ => {
            debug!("Client requires absolute-form URIs, received: {:?}", uri);
            Err(crate::Error::new_user_absolute_uri_required())
        }
    }
}

fn set_scheme(uri: &mut Uri, scheme: Scheme) {
    debug_assert!(uri.scheme_part().is_none(), "set_scheme expects no existing scheme");
    let old = mem::replace(uri, Uri::default());
    let mut parts: ::http::uri::Parts = old.into();
    parts.scheme = Some(scheme);
    parts.path_and_query = Some("/".parse().expect("slash is a valid path"));
    *uri = Uri::from_parts(parts).expect("scheme is valid");
}

/// A builder to configure a new [`Client`](Client).
///
/// # Example
///
/// ```
/// # #[cfg(feature  = "runtime")]
/// # fn run () {
/// use hyper::Client;
///
/// let client = Client::builder()
///     .keep_alive(true)
///     .http2_only(true)
///     .build_http();
/// # let infer: Client<_, hyper::Body> = client;
/// # drop(infer);
/// # }
/// # fn main() {}
/// ```
#[derive(Clone)]
pub struct Builder {
    client_config: Config,
    conn_builder: conn::Builder,
    pool_config: pool::Config,
}

impl Default for Builder {
    fn default() -> Self {
        Self {
            client_config: Config {
                retry_canceled_requests: true,
                set_host: true,
                ver: Ver::Auto,
            },
            conn_builder: conn::Builder::new(),
            pool_config: pool::Config {
                enabled: true,
                keep_alive_timeout: Some(Duration::from_secs(90)),
                max_idle_per_host: ::std::usize::MAX,
            },
        }
    }
}

impl Builder {
    /// Enable or disable keep-alive mechanics.
    ///
    /// Default is enabled.
    #[inline]
    pub fn keep_alive(&mut self, val: bool) -> &mut Self {
        self.pool_config.enabled = val;
        self
    }

    /// Set an optional timeout for idle sockets being kept-alive.
    ///
    /// Pass `None` to disable timeout.
    ///
    /// Default is 90 seconds.
    #[inline]
    pub fn keep_alive_timeout<D>(&mut self, val: D) -> &mut Self
    where
        D: Into<Option<Duration>>,
    {
        self.pool_config.keep_alive_timeout = val.into();
        self
    }

    /// 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) -> &mut Self {
        self.conn_builder.h1_writev(val);
        self
    }

    /// Sets the exact size of the read buffer to *always* use.
    ///
    /// Note that setting this option unsets the `http1_max_buf_size` option.
    ///
    /// Default is an adaptive read buffer.
    #[inline]
    pub fn http1_read_buf_exact_size(&mut self, sz: usize) -> &mut Self {
        self.conn_builder.h1_read_buf_exact_size(Some(sz));
        self
    }

    /// Set the maximum buffer size for the connection.
    ///
    /// Default is ~400kb.
    ///
    /// Note that setting this option unsets the `http1_read_exact_buf_size` option.
    ///
    /// # Panics
    ///
    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
    #[inline]
    pub fn http1_max_buf_size(&mut self, max: usize) -> &mut Self {
        self.conn_builder.h1_max_buf_size(max);
        self
    }

    /// Set whether HTTP/1 connections will write header names as title case at
    /// the socket level.
    ///
    /// Note that this setting does not affect HTTP/2.
    ///
    /// Default is false.
    pub fn http1_title_case_headers(&mut self, val: bool) -> &mut Self {
        self.conn_builder.h1_title_case_headers(val);
        self
    }

    /// Set whether the connection **must** use HTTP/2.
    ///
    /// The destination must either allow HTTP2 Prior Knowledge, or the
    /// `Connect` should be configured to do use ALPN to upgrade to `h2`
    /// as part of the connection process. This will not make the `Client`
    /// utilize ALPN by itself.
    ///
    /// Note that setting this to true prevents HTTP/1 from being allowed.
    ///
    /// Default is false.
    pub fn http2_only(&mut self, val: bool) -> &mut Self {
        self.client_config.ver = if val {
            Ver::Http2
        } else {
            Ver::Auto
        };
        self
    }

    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
    /// stream-level flow control.
    ///
    /// Default is 65,535
    ///
    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
    pub fn http2_initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
        self.conn_builder.http2_initial_stream_window_size(sz.into());
        self
    }

    /// Sets the max connection-level flow control for HTTP2
    ///
    /// Default is 65,535
    pub fn http2_initial_connection_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
        self.conn_builder.http2_initial_connection_window_size(sz.into());
        self
    }

    /// Sets the maximum idle connection per host allowed in the pool.
    ///
    /// Default is `usize::MAX` (no limit).
    pub fn max_idle_per_host(&mut self, max_idle: usize) -> &mut Self {
        self.pool_config.max_idle_per_host = max_idle;
        self
    }

    /// Set whether to retry requests that get disrupted before ever starting
    /// to write.
    ///
    /// This means a request that is queued, and gets given an idle, reused
    /// connection, and then encounters an error immediately as the idle
    /// connection was found to be unusable.
    ///
    /// When this is set to `false`, the related `ResponseFuture` would instead
    /// resolve to an `Error::Cancel`.
    ///
    /// Default is `true`.
    #[inline]
    pub fn retry_canceled_requests(&mut self, val: bool) -> &mut Self {
        self.client_config.retry_canceled_requests = val;
        self
    }

    /// Set whether to automatically add the `Host` header to requests.
    ///
    /// If true, and a request does not include a `Host` header, one will be
    /// added automatically, derived from the authority of the `Uri`.
    ///
    /// Default is `true`.
    #[inline]
    pub fn set_host(&mut self, val: bool) -> &mut Self {
        self.client_config.set_host = val;
        self
    }

    /// Provide an executor to execute background `Connection` tasks.
    pub fn executor<E>(&mut self, exec: E) -> &mut Self
    where
        for<'a> &'a E: tokio_executor::Executor,
        E: Send + Sync + 'static,
    {
        self.conn_builder.executor(exec);
        self
    }

    /// Builder a client with this configuration and the default `HttpConnector`.
    #[cfg(feature = "runtime")]
    pub fn build_http<B>(&self) -> Client<HttpConnector, B>
    where
        B: Payload + Send,
        B::Data: Send,
    {
        let mut connector = HttpConnector::new(4);
        if self.pool_config.enabled {
            connector.set_keepalive(self.pool_config.keep_alive_timeout);
        }
        self.build(connector)
    }

    /// Combine the configuration of this builder with a connector to create a `Client`.
    pub fn build<C, B>(&self, connector: C) -> Client<C, B>
    where
        C: Connect,
        C::Transport: 'static,
        C::Future: 'static,
        B: Payload + Send,
        B::Data: Send,
    {
        Client {
            config: self.client_config,
            conn_builder: self.conn_builder.clone(),
            connector: Arc::new(connector),
            pool: Pool::new(self.pool_config, &self.conn_builder.exec),
        }
    }
}

impl fmt::Debug for Builder {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Builder")
            .field("client_config", &self.client_config)
            .field("conn_builder", &self.conn_builder)
            .field("pool_config", &self.pool_config)
            .finish()
    }
}

#[cfg(test)]
mod unit_tests {
    use super::*;

    #[test]
    fn set_relative_uri_with_implicit_path() {
        let mut uri = "http://hyper.rs".parse().unwrap();
        origin_form(&mut uri);
        assert_eq!(uri.to_string(), "/");
    }

    #[test]
    fn test_origin_form() {
        let mut uri = "http://hyper.rs/guides".parse().unwrap();
        origin_form(&mut uri);
        assert_eq!(uri.to_string(), "/guides");

        let mut uri = "http://hyper.rs/guides?foo=bar".parse().unwrap();
        origin_form(&mut uri);
        assert_eq!(uri.to_string(), "/guides?foo=bar");
    }

    #[test]
    fn test_absolute_form() {
        let mut uri = "http://hyper.rs/guides".parse().unwrap();
        absolute_form(&mut uri);
        assert_eq!(uri.to_string(), "http://hyper.rs/guides");

        let mut uri = "https://hyper.rs/guides".parse().unwrap();
        absolute_form(&mut uri);
        assert_eq!(uri.to_string(), "/guides");
    }

    #[test]
    fn test_authority_form() {
        let _ = pretty_env_logger::try_init();

        let mut uri = "http://hyper.rs".parse().unwrap();
        authority_form(&mut uri);
        assert_eq!(uri.to_string(), "hyper.rs");

        let mut uri = "hyper.rs".parse().unwrap();
        authority_form(&mut uri);
        assert_eq!(uri.to_string(), "hyper.rs");
    }

    #[test]
    fn test_extract_domain_connect_no_port() {
        let mut uri = "hyper.rs".parse().unwrap();
        let domain = extract_domain(&mut uri, true).expect("extract domain");
        assert_eq!(domain, "http://hyper.rs");
    }
}