Add `examples/service_struct_impl.rs`, which provides an up-to-date
example of implementing MakeService and Service on custom types.
The `Svc` struct has a Counter, which demonstrates how to instantiate
shared resources in the `MakeSvc` and pass the resource to the
services. Updates the `examples/README.md` and the doc in
`src/service/mod.rs`.
Closes#1691
Until this commit, servers have required that `Service` and their
`Future` to be `Send`, since the server needs to spawn some internal
tasks to an executor, and by default, that is `tokio::spawn`, which
could be spawning to a threadpool. This was true even if the user were
certain there was no threadpool involved, and was instead using a
different single-threaded runtime, like
`tokio::runtime::current_thread`.
This changes makes all the server pieces generic over an `E`, which is
essentially `Executor<PrivateTypes<Server::Future>>`. There's a new set
of internal traits, `H2Exec` and `NewSvcExec`, which allow for the type
signature to only show the generics that the user is providing. The
traits cannot be implemented explicitly, but there are blanket
implementations for `E: Executor<SpecificType>`. If the user provides
their own executor, it simply needs to have a generic `impl<F>
Executor<F> for MyExec`. That impl can have bounds deciding whether to
require `F: Send`. If the executor does require `Send`, and the
`Service` futures are `!Send`, there will be compiler errors.
To prevent a breaking change, all the types that gained the `E` generic
have a default type set, which is the original `tokio::spawn` executor.
- 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 #1563Closes#1395
