feat(http1): Add higher-level HTTP upgrade support to Client and Server (#1563)

- Adds `Body::on_upgrade()` that returns an `OnUpgrade` future.
- Adds `hyper::upgrade` module containing types for dealing with
  upgrades.
- Adds `server::conn::Connection::with_upgrades()` method to enable
  these upgrades when using lower-level API (because of a missing
  `Send` bound on the transport generic).
- Client connections are automatically enabled.
- Optimizes request parsing, to make up for extra work to look for
  upgrade requests.
  - Returns a smaller `DecodedLength` type instead of the fatter
    `Decoder`, which should also allow a couple fewer branches.
  - Removes the `Decode::Ignore` wrapper enum, and instead ignoring
    1xx responses is handled directly in the response parsing code.

Ref #1563 

Closes #1395

src/proto/h1/mod.rs

@@ -1,7 +1,7 @@
 use bytes::BytesMut;
 use http::{HeaderMap, Method};
 
-use proto::{MessageHead, BodyLength};
+use proto::{MessageHead, BodyLength, DecodedLength};
 
 pub(crate) use self::conn::Conn;
 pub(crate) use self::dispatch::Dispatcher;
@@ -19,12 +19,8 @@ mod io;
 mod role;
 
 
-pub(crate) type ServerTransaction = self::role::Server<self::role::YesUpgrades>;
-//pub type ServerTransaction = self::role::Server<self::role::NoUpgrades>;
-//pub type ServerUpgradeTransaction = self::role::Server<self::role::YesUpgrades>;
-
-pub(crate) type ClientTransaction = self::role::Client<self::role::NoUpgrades>;
-pub(crate) type ClientUpgradeTransaction = self::role::Client<self::role::YesUpgrades>;
+pub(crate) type ServerTransaction = role::Server;
+pub(crate) type ClientTransaction = role::Client;
 
 pub(crate) trait Http1Transaction {
     type Incoming;
@@ -40,14 +36,16 @@ pub(crate) trait Http1Transaction {
     fn update_date() {}
 }
 
+/// Result newtype for Http1Transaction::parse.
 pub(crate) type ParseResult<T> = Result<Option<ParsedMessage<T>>, ::error::Parse>;
 
 #[derive(Debug)]
 pub(crate) struct ParsedMessage<T> {
     head: MessageHead<T>,
-    decode: Decode,
+    decode: DecodedLength,
     expect_continue: bool,
     keep_alive: bool,
+    wants_upgrade: bool,
 }
 
 pub(crate) struct ParseContext<'a> {
@@ -64,12 +62,3 @@ pub(crate) struct Encode<'a, T: 'a> {
     title_case_headers: bool,
 }
 
-#[derive(Debug, PartialEq)]
-pub enum Decode {
-    /// Decode normally.
-    Normal(Decoder),
-    /// After this decoder is done, HTTP is done.
-    Final(Decoder),
-    /// A header block that should be ignored, like unknown 1xx responses.
-    Ignore,
-}