Signed-off-by: jimmycathy <[email protected]>

Running `cargo test` fails to compile because tests rely on types which
are behind a #[cfg(…)] which is disabled by default.

Add a #[cfg(…)] directive to tests which rely on types which are also
behind a #[cfg(…)] directive, so that these tests run only if the types
on which they depend exist.

this commit introduces some additional documentation to the
`HttpService` trait, and the `Service` trait.

notably, this commit introduces some intradoc links, so that rustdoc
will render links to types like `http::Request` and `http::Response`, or
to the `Body` trait.

additionally, mention of `hyper-util` is added to the `Service` trait,
to direct users to the glue implementations that they will likely need
to interact with e.g. `tower`.

Signed-off-by: katelyn martin <[email protected]>

`proto::h2::ping` has some documentation that won't be rendered
properly, because it is written as documentation of an item rather than
documenting the enclosing submodule.

this commit updates this comment, using `//!` notation.

Signed-off-by: katelyn martin <[email protected]>

this commit introduces a new inherent method to
`hyper::client::conn::TrySendError<T>`.

this error type includes a `TrySendError::take_message()` method today
that will return an owned instance of the inbound message, should the
underlying dispatch have been closed before serialization of the message
ever began.

this commit introduces a new method that allows callers to inspect the
message, e.g. to update metrics, without needing to take ownership of
the message.

Signed-off-by: katelyn martin <[email protected]>

this commit introduces a new inherent method to
`hyper::client::conn::TrySendError<T>`.

this error type includes a `TrySendError::into_error()` method today
that will consume the `TrySendError<T>`, returning the inner error. this
commit introduces a new method that allows callers to inspect the error,
e.g. to update metrics, without needing to consume the error.

this is akin to #3884, which added the `TrySendError::message()` method
that returns a reference to the `T`-typed message when applicable.

Signed-off-by: katelyn martin <[email protected]>

…equest (#3886)

Closes #3858

Make hyper usable for h1/h2 and client/server without this heavyweight
dependency. It's about 17k lines of code and takes up to 1.7 seconds to
compile on my machine, but hyper is only using a tiny fraction of it.
Larger applications probably still pull in futures-util by other means,
but it's no longer as unavoidable as in the early days of the ecosystem.

To remove futures-util without raising MSRV, I took these steps:

* When futures-util just re-exports something from its dependencies,
  use it directly from the source.
* Inline trivial helpers like `poll_unpin` that "only" communicate
  intent a little better but don't save any significant amount of code.
* Refactor the h2 client code to avoid `StreamFuture` for the "Client
  has been dropped" detection -- just poll the mpsc channel directly.
* Implement a couple of small helpers from scratch when they're
  straightforward and fit on one screen each. The majority of this is
  polyfills for standard library APIs that would require a higher MSRV.
* Use `AtomicWaker` from the `atomic-waker` crate, a separately
  published copy of the futures-util type of the same name. While the
  two crates are owned by different organizations (smol-rs vs.
  rust-lang), it's mostly the same people maintaining both copies.

The uses of future-util in hyper's tests/benches/examples and in the
`ffi` module seem much harder to remove entirely, so I did not touch
those modules at all.

`CachedDate` gets updated every second, but the current logic doesn't
take into account milliseconds - if the application starts at
`12:00:00.600`, hyper will report `date: ...T120000` up until
`12:00:01.599`, which is overzealous.

We can sidestep this by subtracing the nanoseconds part (which includes
milliseconds) from the time passed to `CachedDate::update()`.

…abilities (#3894)

Benchmarking tools often cause connections to be ungracefully shutdown.
This makes it possible to filter these errors out.

Closes #2745